The SLL Lighting Handbook

The Society of Light and Lighting The Society of Light and Lighting The Society of Light and Lighting is part of the C...

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The Society of Light and Lighting


The Society of Light and Lighting is part of the Chartered Institution of Building Services Engineers

The SLL Lighting Handbook



Final Lighting book artwork 08

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222 Balham High Road, London SW12 9BS +44 (0)20 8675 5211 www.cibse.org


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This document is based on the best knowledge available at the time of publication. However, no responsibility of any kind for any injury, death, loss, damage or delay however caused resulting from the use of these recommendations can be accepted by the Chartered Institution of Building Services Engineers, The Society of Light and Lighting, the authors or others involved in its publication. In adopting these recommendations for use each adopter by doing so agrees to accept full responsibility for any personal injury, death, loss, damage or delay arising out of or in connection with their use by or on behalf of such adopter irrespective of the cause or reason therefore and agrees to defend, indemnify and hold harmless the Chartered Institution of Building Services Engineers, The Society of Light and Lighting, the authors and others involved in their publication from any and all liability arising out of or in connection with such use as aforesaid and irrespective of any negligence on the part of those indemnified. The rights of publication or translation are reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without the prior permission of the publisher. Note from the publisher This publication is primarily intended to give guidance. It is not intended to be exhaustive or definitive, and it will be necessary for users of the guidance given to exercise their own professional judgement when deciding whether to abide by or depart from it. © February 2009 The Society of Light and Lighting


The Society of Light and Lighting is part of the Chartered Institution of Building Services Engineers

The Society is part of CIBSE, which is a registered charity, number 278104. ISBN 978-1-906846-02-2 Project and Print management by entiveon Ltd. www.entiveon.com Design, linework and typsetting by Squarefox Design Ltd. www.squarefox.co.uk Printed in England on FSC certified Mixed Sources paper by Stones the Printers Ltd. www.stonestheprinters.co.uk

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FOREWORD 2009 is the centenary of the formation of the Illuminating Engineering Society, the progenitor of the Society of Light and Lighting. This handbook has been written to celebrate this anniversary and to fill a gap in the Society’s publications. The Society of Light and Lighting’s major publications are: The SLL Code for lighting, which offers recommendations on lighting for a wide range of applications The SLL Lighting Guides, which provide detailed guidance on specific lighting applications The SLL Lighting Handbook has been written to forge a link between them. It is designed to be complementary to the SLL Code for lighting but to go beyond it in terms of applications and background information without getting into the fine detail of the Lighting Guides. The SLL Lighting Handbook is intended to be the first-stop for anyone seeking information on lighting. It is aimed not just at lighting practitioners but also at lighting specifiers and students of lighting. For all three groups, we have tried to make it comprehensive, up-to-date and easily understandable. The contents summarise the fundamentals of light and vision, the technology of lighting and guidance on a wide range of applications, both interior and exterior. Authors Peter Boyce PhD, FSLL, FIESNA Peter Raynham BSc MSc CEng FSLL MCIBSE MILE Acknowledgements John Fitzpatrick Lou Bedocs (Thorn Lighting) Ted Glenny (Philips Lighting) Jennifer Brons for Figure 20.2 Kit Cuttle for Figures 13.1 and 13.2 Lighting Research Center for Figures 9.1, 10.3, 18.8, 18.9 and 20.3 McGraw Hill Inc, for Figures 2.4 and 2.9 Mick Stevens for Figures 20.3 and 22.1 The Illuminating Engineering Society of North America for Figures 1.5, 1.6, 1.7, 1.8, 2.8 and 2.13 Philips Lighting, iGuzzini Illuminazione, Havells Sylvania & Luxo Charlotte Wood Photography for Figures 14.1, 14.2 and 14.3 Editors Stuart Boreham (entiveon Ltd.) Peter Hadley (Squarefox Design Ltd.) SLL Secretary Liz Peck CIBSE Editorial Manager Ken Butcher CIBSE Director of Information Jacqueline Balian

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CONTENTS PART 1: FUNDAMENTALS Chapter 1: Light 1.1 The nature of light 1.2 The CIE standard observers 1.3 The measurement of light — photometry 1.3.1 Luminous flux 1.3.2 Luminous intensity 1.3.3 Illuminance 1.3.4 Luminance 1.3.5 Reflectance 1.3.6 Obsolete units 1.3.7 Typical values 1.4 The measurement of light — colourimetry 1.4.1 The CIE chromaticity diagrams 1.4.2 The CIE colour spaces 1.4.3 Correlated colour temperature 1.4.4 CIE colour rendering index 1.4.5 Colour gamut 1.4.6 Scotopic/photopic ratio 1.4.7 Colour order systems

1 1 3 3 3 4 4 4 6 6 7 7 10 11 12 13 14 14

Chapter 2: Vision 2.1 The structure of the visual system 2.1.1 The visual field 2.1.2 Eye movements 2.1.3 Optics of the eye 2.1.4 The structure of the retina 2.1.5 The functioning of the retina 2.1.6 The central visual pathways 2.1.7 Colour vision 2.2 Continuous adjustments of the visual system 2.2.1 Adaptation 2.2.2 Photopic, scotopic and mesopic vision 2.2.3 Accommodation 2.3 Capabilities of the visual system 2.3.1 Threshold measures 2.3.2 Factors determining visual threshold 2.3.3 Spatial thresholds 2.3.4 Temporal thresholds 2.3.5 Colour thresholds 2.3.6 Light spectrum and movement 2.4 Suprathreshold performance 2.5 Visual search 2.6 Visual discomfort 2.6.1 Insufficient light 2.6.2 Illuminance uniformity 2.6.3 Glare 2.6.4 Veiling reflections 2.6.5 Shadows 2.6.6 Flicker

16 16 16 17 19 22 23 23 24 24 25 26 26 26 28 28 30 31 32 32 34 37 37 37 38 39 40 41

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2.7 Perception through the visual system 2.7.1 The constancies 2.7.2 Attributes and modes of appearance 2.8 Anomolies of vision 2.8.1 Defective colour vision 2.8.2 Low vision

41 41 42 44 44 45

PART 2: TECHNOLOGY Chapter 3: Light sources 3.1 Production of radiation 3.1.1 Incandescence 3.1.2 Electric discharges 3.1.3 Electroluminescence 3.1.4 Luminescence 3.1.5 Radioluminescence 3.1.6 Cathodoluminescence 3.1.7 Chemiluminescence 3.1.8 Thermoluminescence 3.2 Daylight 3.2.1 Sunlight 3.2.2 Skylight 3.3 Electric light 3.3.1 Incandescent 3.3.2 Tungsten halogen 3.3.3 Fluorescent 3.3.4 High pressure mercury 3.3.5 Metal halide 3.3.6 Low pressure sodium 3.3.7 High pressure sodium 3.3.8 Induction 3.3.9 Light emitting diodes 3.3.10 Electroluminescent 3.4 Electric light source characteristics 3.4.1 Luminous flux 3.4.2 Power demand 3.4.3 Luminous efficacy 3.4.4 Lumen maintenance 3.4.5 Life 3.4.6 Colour properties 3.4.7 Run-up time 3.4.8 Restrike time 3.4.9 Other factors 3.4.10 Summary of lamp characteristics 3.5 Flames 3.5.1 Candle 3.5.2 Oil 3.5.3 Gas

vi

48 48 49 51 51 51 52 52 52 52 52 54 57 57 59 60 64 66 69 70 74 75 76 77 77 77 78 78 78 78 78 79 79 79 82 82 82 83


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Chapter 4: Luminaires 4.1 Basic requirements 4.1.1 Electrical 4.1.2 Mechanical 4.1.3 Optical control 4.1.4 Efficiency 4.1.5 Thermal 4.1.6 Acoustics 4.1.7 Environmental 4.2 Luminaire types 4.2.1 Interior lighting 4.2.2 Exterior lighting 4.3 Certification and classification 4.3.1 Certification 4.3.2 Classification

84 84 85 86 91 91 93 94 94 94 98 100 100 105

Chapter 5: Electrics 5.1 Control gear 5.1.1 Ballasts for discharge light sources 5.1.2 Transformers for low voltage light sources 5.1.3 Drivers for LEDs 5.2 Lighting controls 5.2.1 Options for control 5.2.2 Input devices 5.2.3 Control processes and systems

109 109 114 114 115 115 115 116

PART 3: APPLICATIONS Chapter 6: Lighting design 6.1 Objectives and constraints 6.2 A holistic strategy for lighting 6.2.1 Legal requirements 6.2.2 Visual function 6.2.3 Visual amenity 6.2.4 Lighting and architectural integration 6.2.5 Energy efficiency and sustainability 6.2.6 Maintenance 6.2.7 Lighting costs 6.2.8 Photopic or mesopic vision 6.2.9 Light trespass and skyglow 6.3 Basic design decisions 6.3.1 Use of daylight 6.3.2 Choice of electric lighting system 6.3.3 Integration 6.3.4 Equal and approved

117 117 118 118 119 120 120 121 121 121 122 124 124 124 125 128

Chapter 7: Daylighting 7.1 7.2 7.3 7.4

Benefits of daylight Daylight availability Daylight as a contribution to room brightness Daylight for task illumination

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7.5 Types of daylighting 7.5.1 Windows 7.5.2 Clerestories 7.5.3 Rooflights 7.5.4 Atria 7.5.5 Remote distribution 7.5.6 Borrowed light 7.6 Problems of daylighting 7.6.1 Visual problems 7.6.2 Thermal problems 7.6.3 Privacy problems 7.7 Maintenance

133 133 135 135 136 136 137 137 137 139 139 139

Chapter 8: Emergency lighting 8.1 Legislation and standards 8.2 Forms of emergency lighting 8.2.1 Escape route lighting 8.2.2 Signage 8.2.3 Open area lighting 8.2.4 High risk area 8.2.5 Standby lighting 8.3 Design approaches 8.4 Emergency lighting equipment 8.4.1 Power sources 8.4.2 Circuits 8.4.3 Luminaires 8.4.4 Luminaire classification 8.4.5 Light sources 8.4.6 Others 8.5 Scheme planning 8.5.1 Risk assessment 8.5.2 Recommended systems for specific places 8.5.3 Planning sequence 8.6 Installation, testing and maintenance 8.6.1 Installation 8.6.2 Maintenance and inspection 8.6.3 Documentation 8.6.4 Commissioning and certification 8.6.5 Completion certificate

140 141 141 142 142 144 144 144 145 145 146 147 148 148 149 149 149 150 153 153 153 153 154 154 155

Chapter 9: Office lighting 9.1 Functions of lighting in offices 9.2 Factors to be considered 9.2.1 Legislation and guidance 9.2.2 Type of work done 9.2.3 Screen type 9.2.4 Daylight availability 9.2.5 Ceiling height 9.2.6 Obstruction 9.2.7 Surface finishes

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156 156 156 157 157 158 158 159 159


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9.3 Lighting recommendations 9.3.1 Illuminances 9.3.2 Light distribution 9.3.3 Maximum luminances 9.3.4 Discomfort glare control 9.3.5 Light source colour properties 9.4 Approaches to office lighting 9.4.1 Direct lighting 9.4.2 Indirect lighting 9.4.3 Direct/indirect lighting 9.4.4 Localised lighting 9.4.5 Supplementary task lighting 9.4.6 Cove lighting 9.4.7 Luminous ceilings 9.4.8 Daylight

162 162 164 165 166 167 168 168 169 170 170 171 171 172 172

Chapter 10: Industrial lighting 10.1 Functions of lighting in industrial premises 10.2 Factors to be considered 10.2.1 Legislation and guidance 10.2.2 The environment 10.2.3 Daylight availability 10.2.4 Need for good colour vision 10.2.5 Obstruction 10.2.6 Directions of view 10.2.7 Access 10.2.8 Rotating machinery 10.2.9 Safety and emergency egress 10.3 Lighting recommendations 10.3.1 Control rooms 10.3.2 Storage 10.3.3 Ancillary areas 10.3.4 Speculative factory units 10.4 Approaches to industrial lighting 10.4.1 General lighting 10.4.2 Localised lighting 10.4.3 Local lighting 10.4.4 Visual inspection 10.4.5 Visual aids

173 173 173 174 174 175 175 176 177 177 177 177 178 180 181 182 182 182 183 183 183 184

Chapter 11: Lighting for educational premises 11.1 Functions of lighting for educational premises 11.2 Factors to be considered 11.2.1 Students’ capabilities 11.2.2 Daylight or electric light 11.2.3 Common lines of sight 11.2.4 Flat or raked floor 11.2.5 Presence of visual aids 11.2.6 Surface finishes

185 185 185 186 186 186 186 186

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11.3 Lighting recommendations 11.3.1 Illuminances 11.3.2 Illuminance uniformity 11.3.3 Glare control 11.3.4 Light source colour properties 11.3.5 Control systems 11.4 Approaches to lighting educational premises 11.4.1 Classrooms and lecture halls 11.4.2 IT room 11.4.3 Arts studio 11.4.4 Science laboratories 11.4.5 Seminar room 11.4.6 Library 11.4.7 Assembly hall 11.4.8 Music room 11.4.9 Drama studio

187 187 187 187 188 188 189 189 189 189 189 190 190 190 190 190

Chapter 12: Retail lighting 12.1 Functions of retail lighting 12.2 Factors to be considered 12.2.1 Shop profile 12.2.2 Daylight or electric light 12.2.3 Nature of merchandise 12.2.4 Obstruction 12.3 Lighting recommendations 12.3.1 Illuminances 12.3.2 Illuminance uniformity 12.3.3 Luminances 12.3.4 Light source colour properties 12.4 Approaches to retail lighting 12.4.1 General lighting 12.4.2 Accent lighting 12.4.3 Display lighting

191 191 191 192 192 192 192 192 193 193 193 194 194 194 195

Chapter 13: Lighting for museums and art galleries

x

13.1 Functions of lighting in museums and art galleries 13.2 Factors to be considered 13.2.1 Daylight or electric light 13.2.2 Conservation of exhibits 13.2.3 Light source colour rendering properties 13.2.4 Adaptation 13.2.5 Balance 13.2.6 Shadows and modelling 13.2.7 Glare 13.2.8 Veiling reflections and highlights 13.2.9 Out-of-hours activities 13.2.10 Security and emergency 13.2.11 Maintenance 13.2.12 Flexibility 13.3 Lighting approaches for museums and art galleries 13.3.1 Wall mounted displays 13.3.2 Three-dimensional displays 13.3.3 Showcase lighting

198 198 198 198 199 199 199 200 200 200 200 201 201 201 201 201 201 202


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Chapter 14: Lighting for hospitals 14.1 Functions of lighting in hospitals 14.2 Factors to be considered 14.2.1 Daylight 14.2.2 Lines of sight 14.2.3 Colour rendering requirements 14.2.4 Observation without disturbance to sleep 14.2.5 Emergency lighting 14.2.6 Luminaire safety 14.2.7 Cleanliness 14.2.8 Electro-magnetic compatibility (EMC) 14.3 Approaches for the lighting of different areas in hospitals 14.3.1 Entrance halls, waiting areas and lift halls 14.3.2 Reception and enquiry desks 14.3.3 Hospital streets and general corridors 14.3.4 Changing rooms, cubicles, toilets, bath, wash and shower rooms 14.3.5 Wards 14.3.6 Reading lighting 14.3.7 Night lighting 14.3.8 Night observation lighting (watch lighting) 14.3.9 Clinical areas and operating departments 14.3.10 Operating theatres

203 203 203 203 203 204 204 204 205 205 205 206 206 207 207 207 211 211 211 212 212

Chapter 15: Quasi-domestic lighting 15.1 Functions of quasi-domestic lighting 15.2 Factors to be considered 15.2.1 Occupants’ capabilities 15.2.2 Daylight 15.2.3 Light source colour properties 15.2.4 Energy efficiency 15.2.5 Safety 15.2.6 Security 15.3 Lighting recommendations 15.4 Approaches to lighting quasi-domestic buildings 15.4.1 Entrances 15.4.2 Corridors and stairs 15.4.3 Study bedrooms 15.4.4 Kitchens and utility rooms 15.4.5 Lounges 15.4.6 Dining halls 15.4.7 Games room

214 214 214 214 214 215 215 216 216 217 217 217 218 218 219 219 219

Chapter 16: Road lighting 16.1 Road classification 16.2 Lighting for traffic routes 16.2.1 Lighting recommendations for traffic routes 16.2.2 Lighting recommendations for areas adjacent to the carriageway 16.2.3 Lighting recommendations for conflict areas 16.2.4 Coordination 16.2.5 Traffic route lighting design

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16.3 Lighting for subsidiary roads 16.3.1 Lighting recommendations for subsidiary roads 16.3.2 Lighting design for subsidiary roads 16.4 Lighting for urban centres and public amenity areas 16.5 Tunnel lighting

230 230 232 232 233

Chapter 17: Exterior workplace lighting 17.1 Functions of lighting in exterior workplaces 17.2 Factors to be considered 17.2.1 Scale 17.2.2 Nature of work 17.2.3 Need for good colour vision 17.2.4 Obstruction 17.2.5 Interference with complementary activities 17.2.6 Hours of operation 17.2.7 Impact on the surrounding area 17.2.8 Atmospheric conditions 17.3 Lighting recommendations 17.3.1 Illuminance and illuminance uniformity 17.3.2 Glare control 17.3.3 Light source colour properties 17.3.4 Loading areas 17.3.5 Chemical and fuel industries 17.3.6 Sidings, marshalling yards and goods yards 17.4 Approaches to exterior workplace lighting 17.4.1 High mast floodlighting 17.4.2 Integrated lighting 17.4.3 Localised lighting

236 236 236 236 237 237 237 237 238 238 238 238 239 239 239 240 241 243 243 243 244

Chapter 18: Security lighting

xii

18.1 Functions of security lighting 18.2 Factors to be considered 18.2.1 Type of site 18.2.2 Site features 18.2.3 Ambient light levels 18.2.4 Crime risk 18.2.5 CCTV surveillance 18.2.6 Impact on the surrounding area 18.3 Lighting recommendations 18.3.1 Illuminance and illuminance uniformity 18.3.2 Glare control 18.3.3 Light source colour properties 18.4 Approaches to security lighting 18.4.1 Secure areas 18.4.2 Public spaces 18.4.3 Private areas 18.4.4 Multi-occupancy dwellings 18.5 Lighting Equipment 18.5.1 Light sources 18.5.2 Luminaires 18.5.3 Lighting columns 18.5.4 Lighting controls 18.5.5 Maintenance

245 245 245 246 247 247 247 247 247 247 249 249 249 249 252 253 254 254 254 255 255 256 256


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Chapter 19: Sports lighting 19.1 Functions of lighting for sports 19.2 Factors to be considered 19.2.1 Standard of play and viewing distance 19.2.2 Playing area 19.2.3 Luminaires 19.2.4 Television 19.2.5 Coping with power failures 19.2.6 Obtrusive light 19.3 Lighting recommendations 19.3.1 Athletics 19.3.2 Bowls 19.3.3 Cricket 19.3.4 Five-a-side football (indoor) 19.3.5 Fitness training 19.3.6 Football (Association, Gaelic and American) 19.3.7 Lawn tennis 19.3.8 Rugby (Union and League) 19.3.9 Swimming 19.4 Lighting in large facilities 19.4.1 Multi-use sports halls 19.4.2 Small sports stadia 19.4.3 Indoor arenas 19.4.4 Swimming pools

257 257 257 258 258 258 259 260 261 261 262 263 264 264 265 265 266 266 267 267 267 268 268

Chapter 20: Lighting performance verification 20.1 The need for performance verification 20.2 Relevant operating conditions 20.3. Instrumentation 20.3.1 Illuminance meters 20.3.2 Luminance meters 20.4 Methods of measurement 20.4.1 Average illuminance 20.4.2 Interior lighting 20.4.3 Exterior lighting 20.5 Measurement of illuminance variation 20.5.1 Illuminance diversity 20.5.2 Illuminance uniformity 20.6 Luminance measurements 20.7 Measurement of reflectance

270 270 271 271 271 272 272 272 274 275 275 276 276 276

Chapter 21: Lighting maintenance 21.1 The need for lighting maintenance 21.2 Lamp replacement 21.3 Cleaning luminaires 21.4 Room surface cleaning 21.5 Maintained illuminance 21.6 Designing for lighting maintenance 21.7 Determination of maintenance factor for interior lighting 21.7.1 Lamp lumen maintenance factor (LLMF) 21.7.2 Lamp survival factor (LSF) 21.7.3 Luminaire maintenance factor (LMF) 21.7.4 Room surface maintenance factor (RSMF)

278 278 278 280 280 280 280 281 281 282 284

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21.8 Determination of maintenance factor for exterior lighting 21.9 Disposal of lighting equipment

285 286

Chapter 22: On the horizon 22.1. Changes and challenges 22.2. The changes and challenges facing lighting practice 22.2.1 Costs 22.2.2 Technologies 22.2.3 New knowledge 22.2.4 External influences 22.3 The evolution of lighting practice

287 287 287 287 287 290 290

Chapter 23: Bibliography

xiv

23.1 Standards 23.2 Guidance 23.3 References

293 296 298

Index

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Chapter 1: Light 1.1 The nature of light Light is part of the electromagnetic spectrum that stretches from cosmic rays to radio waves (Figure 1.1). What distinguishes the wavelength region between 380–780 nanometers from the rest is the response of the human visual system. Photoreceptors in the human eye absorb energy in this wavelength range and thereby initiate the process of seeing.

Chapter One: Light

PART 1. FUNDAMENTALS

104

102

RADIO WAVES

100 780 nm 10–2

MICRO WAVES 700

10–4

INFRA RED 600

10–6

10–8

VISIBLE

ULTRA VIOLET 500

10–10

10–12

X RAYS 400 380 nm GAMMA RAYS

10–14

10–16

COSMIC RAYS

Wavelength (m)

Figure 1.1 A schematic diagram of the electromagnetic spectrum showing the location of the visible spectrum. The divisions between the different types of electromagnetic radiation are indicative only. 1.2 The CIE standard observers The sensitivity of the human visual system is not the same at all wavelengths in the range 380 nm to 780 nm. This makes it impossible to adopt the radiometric quantities conventionally used to measure the characteristics of the electromagnetic spectrum for quantifying light. Rather, a special set of quantities has to be derived from the radiometric quantities by weighting them by the spectral sensitivity of the human visual system. The result is the photometry system (see Section 1.3). The Commission Internationale de l’Eclairage (CIE) has established three standard observers to represent the sensitivity of the human visual system to light at different wavelengths, in different conditions. In 1924, the CIE adopted the Standard Photopic Observer to characterise the spectral sensitivity of the human visual system by day. 1


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Chapter One: Light

In 1990, in the interests of greater photometric accuracy, the CIE produced a Modified Photopic Observer, having greater sensitivity than the CIE Standard Photopic Observer at wavelengths below 460 nm. This CIE Modified Photopic Observer is considered to be a supplement to the CIE Standard Photopic Observer not a replacement for it. As a result, the CIE Standard Photopic Observer has continued to be widely used by the lighting industry. This is acceptable because the modified sensitivity at wavelengths below 460 nm has been shown to make little difference to the photometric properties of light sources that emit radiation over a wide range of wavelengths. It is only for light sources that emit significant amounts of radiation below 460 nm that changing from the CIE Standard Photopic Observer to the CIE Modified Photopic Observer makes a significant difference to photometric properties. Some narrow band light sources, such as blue light emitting diodes, fall into this category. In 1951, the CIE adopted the CIE Standard Scotopic Observer to characterise the spectral sensitivity of the human visual system by night. The Standard Scotopic Observer is used by the lighting industry to quantify the efficiency of a light source at stimulating the rod photoreceptors of the eye (see Section 2.1.4). The CIE Standard and Modified Photopic Observers and the CIE Standard Scotopic Observer are shown in Figure 1.2, the Standard and Modified Photopic Observers having maximum sensitivities at 555 nm and the Standard Scotopic Observer having a maximum sensitivity at 507 nm. These relative spectral sensitivity curves are formally known as the 1924 CIE Spectral Luminous Efficiency Function for Photopic Vision, the CIE 1988 Modified Two Degree Spectral Luminous Efficiency Function for Photopic Vision, and the 1951 CIE Spectral Luminous Efficiency Function for Scotopic Vision, respectively. More commonly, they are known as the CIE V (λ), CIE VM (λ), and the CIE V’ (λ) curves. These curves are the basis of the conversion from radiometric quantities to the photometric quantities used to characterise light. Relative luminous efficiency 1.0

0.8

= Standard photopic observer = Modified photopic observer = Standard scotopic observer = 10 degree field

0.6

0.4

0.2

0 300

400

500

600

700

800

Wavelength (nm)

Figure 1.2 The relative luminous efficiency functions for the CIE Standard Photopic Observer, the CIE Modified Photopic Observer, the CIE Standard Scotopic Observer, and the relative luminous efficiency function for a 10 degree field of view in photopic conditions 2


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1.3.1 Luminous flux The most fundamental measure of the electromagnetic radiation emitted by a source is its radiant flux. This is the rate of flow of energy emitted and is measured in watts. The most fundamental quantity used to measure light is luminous flux. Luminous flux is radiant flux multiplied, wavelength by wavelength, by the relative spectral sensitivity of the human visual system, over the wavelength range 380 nm to 780 nm (Figure 1.3). This process can be represented by the equation:

Chapter One: Light

1.3 The measurement of light — photometry

Φ = Km Σ Ψλ Vλ ∆λ where: Φ = luminous flux (lumens) Ψλ = radiant flux in a small wavelength interval ∆λ (watts) Vλ = the relative luminous efficiency function for the conditions Km= constant (lumens/watt) ∆λ = wavelength interval In System Internationale (SI) units, the radiant flux is measured in watts (W) and the luminous flux in lumens (lm). The values of Km are 683 lm/W for the CIE Standard and Modified Photopic Observers and 1699 lm/W for the CIE Standard Scotopic Observer. It is always important to identify which of the CIE Standard Observers is being used in any particular measurement or calculation. The CIE recommends that whenever the Standard Scotopic Observer is being used, the word scotopic should precede the measured quantity, i.e. scotopic luminous flux. Luminous flux is used to quantify the total light output of a light source in all directions. Energy output

V(λ)

Light output

350 400 450 500 550 600 650 700 750 800 350 400 450 500 550 600 650 700 750 800 350 400 450 500 550 600 650 700 750 800

Figure 1.3 The process for converting from radiometric to photometric quantities. The lefthand figure shows the spectral power distribution of a light source in radiometric quantities (watts/wavelength interval). The centre figure shows the CIE Standard Photopic Observer. Multiplying the spectral power at each wavelength by the luminous efficiency at the same wavelength given by the CIE Standard Photopic Observer, the right hand figure is produced. The right hand figure is the spectral luminous flux distribution in photometric quantities (lumens/wavelength interval). 1.3.2 Luminous intensity Luminous intensity is the luminous flux emitted/unit solid angle, in a specified direction. Solid angle is given by area divided by the square of the distance and is measured in steradians. An area of 1 square metre at a distance of 1 metre from the origin subtends one steradian. The unit of measurement of luminous intensity is the candela, which is equivalent to one lumen/steradian. Luminous intensity is used to quantify the distribution of light from a luminaire. 3


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Chapter One: Light

1.3.3 Illuminance Illuminance is the luminous flux falling on unit area of a surface. The unit of measurement of illuminance is the lumen/m2 or lux. The illuminance incident on a surface is the most widely used electric lighting design criterion. Figure 1.4 shows some typical illuminances on different surfaces under the noonday sun in temperate climates.

100 lux

2500 lux

5000 lux

10,000 lux

100,000 lux

Figure 1.4 Typical illuminances on different surfaces under the noonday sun in temperate climates 1.3.4 Luminance The luminance of a surface is the luminous intensity emitted per unit projected area of the surface in a given direction. The unit of measurement of luminance is the candela/m2. Luminance is widely used to define stimuli presented to the visual system. 1.3.5 Reflectance As might be expected, there is a relationship between the amount of light incident on a surface and the amount of light reflected from the same surface. The simplest form of the relationship is quantified by the luminance coefficient. The luminance coefficient is the ratio of the luminance of the surface to the illuminance incident on the surface and has units of candela/lumen. The luminance coefficient of a given surface is dependent on the nature of the surface and the geometry between the lighting, surface and observer. There are two other quantities commonly used to express the relationship between the luminance of a surface and the illuminance incident on it. For a perfectly diffusely-reflecting surface, the relationship is given by the equation:

luminance =

(illuminance × reflectance)

π

where luminance is expressed in candela/m2 and illuminance is expressed in lumens/m2. 4


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Chapter One: Light

For a diffusely-reflecting surface, reflectance is defined as the ratio of reflected luminous flux to incident luminous flux. For a non-diffusely-reflecting surface, i.e. a surface with some specularity, the same equation between luminance and illuminance applies but reflectance is replaced with luminance factor. Luminance factor is defined as the ratio of the luminance of the surface viewed from a specific position and lit in a specified way to the luminance of a diffusely-reflecting white surface viewed from the same direction and lit in the same way. It should be clear from this definition, that a non-diffusely-reflecting surface can have many different values of the luminance factor. Table 1.1 summarises these definitions. Table 1.1 The photometric quantities. Measure

Definition

Units

Luminous flux

That quantity of radiant flux which expresses its capacity to produce visual sensation

lumens (lm)

Luminous intensity

The luminous flux emitted in a very narrow cone containing the given direction divided by the solid angle of the cone, i.e. luminous flux/unit solid angle

candela (cd)

Illuminance

The luminous flux/unit area at a point on a surface

lumen/m2

Luminance

The luminous flux emitted in a given direction divided by the product of the projected area of the source element perpendicular to the direction and the solid angle containing that direction, i.e. luminous intensity/unit area

candela/m2

Luminance coefficient

The ratio of the luminance of a surface to the illuminance incident on it

candela/lumen

Reflectance

The ratio of the luminous flux reflected from a surface to the luminous flux incident on it

For a diffuse surface:

Luminance factor

For a non-diffuse surface, for a specific direction and lighting geometry:

luminance = (illuminance × reflectance ) / π

The ratio of the luminance of a reflecting surface viewed from a given direction to that of a perfect white uniform diffusing surface identically illuminated

luminance = (illuminance × luminance factor) / π 5


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Chapter One: Light

1.3.6 Obsolete units Photometry has a long history that has generated a number of different units of measurement for illuminance and luminance. Table 1.2 lists some of these obsolete units, together with the multiplying factors necessary to convert from the alternative unit to the SI units of lumens/m2 for illuminance and candela/m2 for luminance. Table 1.2 Some photometric units of measurement for illuminance and luminance and the multiplying factors necessary to change them to System Internationale (SI) units Quantity

Unit

Dimensions

Multiplying factor

Illuminance

lux metre candle phot footcandle

lumen/m2 lumen/m2 lumen/cm2 lumen/ft2

1.00 1.00 10,000 10.76

Luminance

nit stilb

candela/m2 candela/cm2 candela/in2 candela/ft2

1.00 10,000 1,550 10.76

Luminous exitance*

apostilb* blondel* lambert* footlambert*

lumen/m2 lumen/m2 lumen/cm2 lumen/ft2

0.32 0.32 3,183 3.43

* Luminous exitance is the product of the illuminance on the surface and the reflectance of the surface. It is only meaningful for completely diffusely reflecting surfaces. Luminous exitance has the dimensions of lumens/unit area. Luminous exitance is deprecated in the SI system. 1.3.7 Typical values Table 1.3 shows some illuminances and luminances typical of commonly occurring situations, all measured using the CIE Standard Photopic Observer. Table 1.3 Typical illuminance and luminance values.

6

Situation

Illuminance (lm/m2)

Typical surface

Luminance (cd/m2)

Clear sky in summer in temperate zones

100,000

Grass

1,910

Overcast sky in summer in temperate zones

16,000

Grass

300

Textile inspection

1,500

Light grey cloth

140

Office work

500

White paper

120

Heavy engineering

300

Steel

20

Good road lighting

20

Concrete road surface

2.0

Moonlight

0.5

Asphalt road surface

0.01


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Photometry does not take into account the wavelength combination of the light. Thus it is possible for two surfaces to have the same luminance but the reflected light to be made up of totally different combinations of wavelengths. In this situation, and provided there is enough light for colour vision to operate, the two surfaces will look different in colour. The CIE colourimetry system provides a means to quantify colour. 1.4.1 The CIE chromaticity diagrams The basis of the CIE colourimetry system is colour matching. The CIE Colour Matching Functions are the relative spectral sensitivity curves of the human observer with normal colour vision and can be considered as another form of standard observer. The CIE colour matching functions are mathematical constructs that reflect the relative spectral sensitivities required to ensure that all the wavelength combinations that are seen as the same colour have the same position in the CIE colourimetry system and that all wavelength combinations that are seen as different in colour occupy different positions. Figure 1.5 shows two sets of colour matching functions. The CIE 1931 Standard Observer is used for colours occupying visual fields up to 4° of angular subtense. The CIE 1964 Standard Observer is used for colours covering visual fields greater than 4° in angular subtense. The values of the colour matching functions at different wavelengths are known as the spectral tristimulus values.

Chapter One: Light

1.4 The measurement of light — colourimetry

2.5

2.0

z 1.5

1.0 y

x

0.5

0 400

450

500

550

600

650

700

Wavelength (nm)

Figure 1.5 Two sets of colour matching functions: The CIE 1931standard observer (2 degrees) (solid line) and the CIE 1964 standard observer (10 degrees) (dashed line). The colour of a light source can be represented mathematically by multiplying the spectral power distribution of the light source, wavelength by wavelength, by each of the three colour matching functions x(λ), y(λ) and z(λ), the outcome being the amounts of three imaginary primary colours X, Y, and Z required to match the light source colour. In the form of equations, X, Y and Z are given by: 7


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Chapter One: Light

X = h Σ S(λ) x(λ) λ Y = h Σ S(λ) y(λ) λ Z = h Σ S(λ) z(λ) λ where: S(λ) = spectral radiant flux of the light source (W/nm) x(λ), y(λ), z(λ) = spectral tristimulus values from the appropriate colour matching function λ = wavelength interval (nm) h = arbitrary constant If only relative values of the X, Y and Z are required, an appropriate value of h is one that makes Y = 100. If absolute values of the X, Y, and Z are required it is convenient to take h = 683 since then the value of Y is the luminous flux in lumens. If the colour being calculated is for light reflected from a surface or transmitted through a material, the spectral reflectance or spectral transmittance is included as a multiplier in the above equations. For a reflecting surface, an appropriate value of h is one that makes Y =100 for a perfect white reflecting surface because then the actual value of Y is the percentage reflectance of the surface. Having obtained the X, Y, and Z values, the next step is to express their individual values as proportions of their sum, i.e. x = X / (X+Y+Z) y = Y / (X+Y+Z) z = Z / (X+Y+Z) The values x, y and z are known as the CIE chromaticity coordinates. As x + y + z = 1, only two of the coordinates are required to define the chromaticity of a colour. By convention, the x and y coordinates are used. Given that a colour can be represented by two coordinates, then all colours can be represented on a two dimensional surface. Figure 1.6 shows the CIE 1931 chromaticity diagram. The outer curved boundary of the CIE 1931 chromaticity diagram is called the spectrum locus. All pure colours, i.e. those that consist of a single wavelength, lie on this curve. The straight line joining the ends of the spectrum locus is the purple boundary and is the locus of the most saturated purples obtainable. At the centre of the diagram is a point called the equal energy point, where a colourless surface will be located. Close to the equal energy point is a curve called the Planckian locus. This curve passes through the chromaticity coordinates of objects that operate as a black body, i.e. the spectral power distribution of the light source is determined solely by its temperature. The CIE 1931 chromaticity diagram can be considered as a map of the relative location of colours. The saturation of a colour increases as the chromaticity coordinates get closer to the spectrum locus and further from the equal energy point. The hue of the colour is determined by the direction in which the chromaticity coordinates move. The CIE 1931 chromaticity diagram is useful for indicating approximately how a colour will appear, a value recognised by the CIE in that it specifies chromaticity coordinate limits for signal lights and surfaces so that they will be recognised as red, green, yellow, and blue (CIE Publication 107:1994).

8


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Chapter One: Light

520 nanometers 530 0.8 540

510

0.7

550

560 0.6 570 500 0.5

580

Y 590 3500

2360

0.4

1900 1500

4800

510

6500 0.3

490

620 630 640

Equal energy

10,000

600

24,000

780

0.2

480 nanometers 0.1 470 460 450

0 0

0.1

380 0.2

0.3

0.4

0.5

0.6

0.7

0.8

X

Figure 1.6 The CIE 1931 Chromaticity Diagram showing the spectrum locus, the Planckian locus and the equal energy point) The CIE 1931 chromaticity diagram is perceptually non-uniform. Green colours cover a large area while red colours are compressed in the bottom right corner. This perceptual non-uniformity makes any attempt to quantify large colour differences using the CIE 1931 chromaticity diagram futile. In an attempt to improve this situation, the CIE first introduced the CIE 1960 Uniform Chromaticity Scale (UCS) diagram and then, in 1976, recommended the use of the CIE 1976 UCS diagram. Both diagrams are simply linear transformations of the CIE 1931 chromaticity diagram. The axes for the CIE 1976 UCS diagram are u' = 4x / (–2x +12y +3) v' = 9y / (–2x + 12y + 3) where x and y are the CIE 1931 chromaticity coordinates. Figure 1.7 shows the CIE 1976 UCS diagram.

9


Chapter One: Light

0.6

520

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560 580 600 620

500

640 770 nm

0.5

0.4

V' 0.3 480

0.2

470 0.1 460 450 440 420 0

0.1

0.2

400 nm 0.3

0.4

0.5

0.6

U'

Figure 1.7 The CIE 1976 Uniform Chromaticity Scale diagram (from the IESNA Lighting Handbook) 1.4.2 The CIE colour spaces All chromaticity diagrams are of limited value for quantifying colour differences because such diagrams are two-dimensional, considering only the hue and saturation of the colour. To completely describe a colour a third dimension is needed, that of brightness for a selfluminous object and lightness for a reflecting object. In 1964, the CIE introduced the U*, V*, W* colour space for use with surface colours, where U* = 13 W* (u – un) V* = 13 W* (v – vn) W* = 25 Y 0.33 – 17 (where Y has a range from 1 to 100) W* is called a lightness index and approximates the Munsell value of a surface colour (see Section 1.4.7). The coordinates u, v, refer to the chromaticity coordinates of the surface colour in the CIE 1960 UCS diagram while the chromaticity coordinates un, vn refer to a spectrally neutral colour lit by the source, that is placed at the origin of the U*, V* system. This U*, V*, W* system is little used now, about the only purpose for which it is routinely used is the calculation of the CIE colour rendering indices (see Section 1.4.4). For other purposes, the U*, V*, W* colour space has been superseded by two other colour spaces known by the initialisms CIELUV and CIELAB. 10


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L* = (116 (Y/Yn) 0.33 – 16) for Y/Yn > 0.008856 L* = 903.29 (Y/Yn) for Y/Yn ≤ 0.008856 u* = 13 L* (u' – u'n) v* = 13 L* (v' – v'n)

Chapter One: Light

The three coordinates of the CIELUV colour space are given by the expressions:

where u' and v' are the chromaticity coordinates from the CIE 1976 UCS diagram and u'n, v'n, Yn are values for a nominally achromatic colour, usually the surface with 100% reflectance (Y = 100) lit by the light source. The three coordinates of the CIELAB colour space are given by the expressions: L* = 116 f (Y/Yn) – 16 a* = 500 (f(X/Xn) – f(Y/Yn)) b* = 200(f(Y/Yn) – f(Z/Zn))

where f(q) = q 0.33 for q > 0.008856 and f(q) = 7.787 q + 0.1379 for q ≤ 0.008856 q = X/Xn or Y/Yn or Z/Zn Again, Xn, Yn, Zn are the values of the X, Y and Z for a nominally achromatic surface, usually that of the light source with Yn = 100. Each of these colour spaces have a colour difference formula associated with them. For the CIELUV colour space, the colour difference is given by E*uv = ((L*)2 + (u*)2 + (v*)2)0.5 For the CIELAB colour space, the colour difference is given by E*ab = ((L*)2 + (a*)2 + (b*)2)0.5 These two colour spaces are now widely used to set colour tolerances for manufacture in many industries. 1.4.3 Correlated colour temperature While the CIE colourimetry system is the most exact means of quantifying colour, it is complex. Therefore, the lighting industry has used the CIE colourimetry system to derive two single-number metrics to characterise the colour properties of light sources. The metric used to characterise the colour appearance of the light emitted by a light source is the correlated colour temperature. The basis of this measure is the fact that the spectral power distribution of a black body is defined by Planck's Radiation Law and hence is a function of its temperature only (see Section 3.1.1). 11


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Chapter One: Light

Figure 1.8 shows a section of the CIE 1931 chromaticity diagram with the Planckian locus shown. The locus is the curved line joining the chromaticity coordinates of black bodies at different temperatures. The lines running across the Planckian locus are iso-temperature lines. When the CIE 1931 chromaticity coordinates of a light source lie directly on the Planckian locus, the colour appearance of that light source is expressed by the colour temperature, i.e. the temperature of the black body that has the same chromaticity coordinates. For light sources that have chromaticity coordinates close to the Planckian locus but not on it, their colour appearance is quantified as the correlated colour temperature, i.e. the temperature of the isotemperature line that is closest to the actual chromaticity coordinates of the light source. The temperatures are usually given in kelvins (K). As a rough guide, nominally-white light sources have correlated colour temperatures ranging from 2,700 K to 7,500 K. A 2,700 K light source, such as an incandescent lamp, will have a yellowish colour appearance and be described as ‘warm’, while a 7,500 K lamp, such as some types of fluorescent lamp, will have a bluish appearance and be described as ‘cold’. It is important to appreciate that light sources that have chromaticity coordinates that lie beyond the range of the iso-temperature lines shown in Figure 1.8 should not be given a correlated colour temperature. The light from such light sources will appear greenish when the chromaticity coordinates lie above the Planckian locus or purplish if they lie below it.

5,000

1, 51 5

A 0.400

0 ,00 10

Y

2, 00 0

3,3 33

2,5 00

0.500

D65 C

0.300

0

0.200

0.200

0.300

0.400

0.500

0.600

X

Figure 1.8 The Planckian locus and lines of constant correlated colour temperature plotted on the CIE 1931 (x,y) chromaticity diagram. Also shown are the chromaticity coordinates of CIE Standard Illuminants, A, C, and D65 (from the IESNA Lighting Handbook). 1.4.4 CIE colour rendering index The CIE colour rendering index measures how well a given light source renders a set of standard test colours relative to their rendering under a reference light source of the same correlated colour temperature as the light source of interest. 12


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Chapter One: Light

The reference light source used is an incandescent light source for light sources with a correlated colour temperature below 5000 K and some form of daylight for light sources with correlated colour temperature above 5000 K. The actual calculation involves obtaining the positions of a surface colour in the CIE 1964, U*, V*, W*, colour space under the reference light source and under the light source of interest, correcting for any difference in white point under the two light sources and expressing the difference between the two positions on a scale that gives perfect agreement between the two positions a value of 100. The CIE has fourteen standard test colours. The first eight form a set of pastel colours arranged around the hue circle. Test colours nine to fourteen represent colours of special significance, such as skin tones and vegetation. The result of the calculation for any single colour is called the CIE special colour rendering index, for that colour. The average of the special colour rendering indices for the first eight test colours is called the CIE general colour rendering index (Ra). It is the CIE general colour rendering index that is usually presented in light source manufacturers’ catalogues. The CIE general colour rendering index varies widely across light sources (see Section 3.4.10). 1.4.5 Colour gamut The colour gamut of a light source is obtained by calculating the position of the first eight CIE standard test colours under the light source of interest and plotting them on the CIE 1976 UCS diagram. When the plotted positions are joined together, the colour gamut is formed. The colour gamut can be reduced to a single number by calculating the gamut area. Figure 1.9 shows the colour gamuts for a number of different light sources. A great deal can be learnt from the colour gamut. From a consideration of its shape and the spacing between the positions of the individual test colours, the extent to which the different parts of the hue circle can be discriminated is apparent. From its location on the CIE 1976 UCS diagram, the appearance of colours can be appreciated to some degree. By plotting different light sources on the same diagram it is easy to make comparisons between light sources. Further, by including the colour gamut of an ideal light source, such as daylight, it is possible to evaluate how close to the ideal light source is the light source of interest, as far as colour rendering is concerned. 0.58

0.56

*

0.54

*

+

* 0.52

*

+ V'

+

0.50

* *+

0.48

*

* 0.46

+

* 0.44

+

0.42

+

+ 0.14

0.16

0.18

0.20

+ 0.22

0.24

0.26

0.28

= = = = = = =

spectrum locus Planckian locus metal halide high pressure sodium fluorescent incandescent daylight

0.30

0.32

0.34

U'

Figure 1.9 The colour gamuts for high pressure sodium, incandescent, fluorescent and metal halide light sources, and for the CIE Standard Illuminant D65, simulating daylight, all plotted on the CIE 1976 uniform chromaticity scale diagram. The dotted curve is the Planckian locus. 13


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Chapter One: Light

1.4.6 Scotopic/photopic ratio One other measure of light source colour characteristics that has been gaining interest in recent years is the scotopic/photopic ratio (Berman, 1992). This is calculated by taking the relative spectral power distribution, in radiometric units, of the light source and weighting it by the CIE Standard Scotopic and Photopic Observers and expressing the resulting scotopic lumens and photopic lumens as a ratio. The value of scotopic/photopic ratios is that they express the relative effectiveness of different light sources in stimulating the rod and cone photoreceptors in the human visual system. A light source with a higher scotopic/photopic ratio will stimulate the rods more than a light source with a lower scotopic/photopic ratio when both produce the same photopic luminous flux. This information is useful when considering light sources for applications where the operation of both rod and cone photoreceptors is likely. Table 1.4 gives scotopic/photopic ratios for a number of commonly used light sources. Table 1.4 Scotopic/photopic ratios for a number of widely used electric light sources (from He et al., 1997) Light source

Photopic efficacy (lm/W)

Scotopic efficacy (lm/W)

Scotopic/photopic ratio

Incandescent

14.7

20.3

1.38

Fluorescent

84.9

115.9

1.36

Mercury vapour

52.3

66.8

1.28

Metal halide

107.4

181.7

1.69

High pressure sodium

126.9

80.5

0.63

Low pressure sodium

180.0

40.8

0.23

1.4.7 Colour order systems A colour ordering system is a physical, three-dimensional representation of colour space. There are several different colour ordering systems but one of the most widely used is the Munsell system. Figure 1.10 shows the organisation of the Munsell system. The azimuthal hue dimension consists of 100 steps arranged around a circle, with five principal hues (red, yellow, green, blue and purple) and five intermediate hues (yellow-red, green-yellow, bluegreen, purple-blue and red-purple). The vertical value scale contains ten steps from black to white. The horizontal chroma scale contains up to 20 steps from gray to highly saturated. The position of any colour in the Munsell system is identified by an alphanumeric reference made up of three terms, hue, value and chroma, e.g. a strong red is given the alphanumeric 7.5R/4/12. Achromatic surfaces, i.e. colours that lie along the vertical value axis and hence have no hue or chroma, are coded as Neutral 1, Neutral 2 etc. depending on their reflectance. To a first approximation, the percentage reflectance of a surface is given by the product of V and (V–1) of the surface, where V is the Munsell value of the surface. 14


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Chapter One: Light

White 10

Value scale

9 Hue scale

5PB 10B

5B

5P

10P 5RP

10BG

7

10RP

6

5BG 6

8

5

4

3

2

5R 1

1

2

3

4

5

6

Chroma scale

4

10G

10R 5G

5YR 10GY 5GY

10YR

10Y 2

5Y

1

Black

Figure 1.10 The organisation of the Munsell colour order system. The hue letters are B = blue, PB = purple/blue, P = purple, RP = red/purple, R = red, YR = yellow/red, Y = yellow, GY = green/yellow, G = green, BG = blue/green. The existence of several other colour ordering systems, such as the Natural Colour System, the DIN system and BS 5252 system, would seem to be a recipe for confusion. This is avoided by the fact that conversions are available between many of the colour ordering systems. For more detail on the Munsell system, other colour ordering systems and the relationships between them, see the SLL Lighting Guide 11: Surface reflectance and colour.

15


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Chapter Two: Vision

Chapter 2: Vision 2.1 The structure of the visual system The visual system consists of the eye and brain working together. Functionally, the visual system is an image-processing system that extracts specific aspects of the retinal image for interpretation by the brain. 2.1.1 The visual field Humans have two eyes, mounted frontally. Figure 2.1 shows the approximate extent of the visual field of the two eyes in humans, measured in degrees from the point of fixation. The enclosed white area can be seen with both eyes. The shaded area to the left is visible to the left eye only. The shaded area to the right is visible to the right eye only.

100

80 60

40

20

20 40

60

80 100

Figure 2.1 The binocular visual field expressed in degrees deviation from the point of fixation. The shaded areas are visible to only one eye (after Boff and Lincoln, 1988). Given this limited field of view for a fixed position, it is necessary for the two eyes to be able to move. There are two ways this can be done; by moving the head and by moving the eyes in the head. Humans have a limited range of head movements but a wide range of eye movements. 2.1.2 Eye movements The movement of the eye in its socket is controlled by six extra-ocular muscles arranged in opposing pairs. The pattern of eye movements used when examining a visual scene consists of a series of fixations and saccades. Fixations are attempts to keep the retinal image of the object of interest on the fovea. Figure 2.2 shows a pattern of fixation points for two people examining the seams on a pair of briefs. 16


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C

C

C E

Chapter Two: Vision

S

S

C

E

M

D

Figure 2.2 The pattern of fixations made by two inspectors examining men’s briefs held on a frame. S = start of scan path, C = end of scan of front and one side, rotation of frame and continuation of scan across back and sides, E = end of scan. Inspector M examines only the seams while Inspector D examines the fabric as well (after Megaw and Richardson, 1979). Movement between the fixation points is made by saccades. Saccades are very fast, velocities ranging up to 1000 degrees/second depending upon the distance moved. Saccadic eye movements have a latency of about 200 ms, which limits how frequently the line of sight can be moved to about five movements per second. Visual functions are substantially limited during saccadic movements. Fixations and saccades both occur in a single eye, but movements in the two eyes are not independent. Rather, they are coordinated so that the lines of sight of the two eyes are both pointed at the same target at the same time. Movements of the two eyes that keep the primary lines of sight converged on a target, or which may be used to switch fixation from a target at one distance to a new target in the same direction but at a different distance, are called vergence movements. These movements are very slow, up to 10 degrees/second, and can occur as a jump movement or can smoothly follow a target moving in a fore-and-aft direction. Both types of movement involve a change in the angle between the two eyes. 2.1.3 Optics of the eye Figure 2.3 shows a section through the eye, the upper and lower halves being adjusted for focus at near and far distances, respectively. The eye is basically spherical with a diameter of about 24 mm. The sphere is formed from three concentric layers. The outermost layer, called the sclera, protects the contents of the eye and maintains its shape under pressure. Over most of the eye’s surface, the sclera looks white but at the front of the eye the sclera bulges up and becomes transparent. It is through this area, called the cornea, that light enters the eye. The next layer is the vascular tunic, or choroid. This layer contains a dense network of small blood vessels that provide oxygen and nutrients to the next layer, the retina. As the choroid approaches the front of the eye it separates from the sclera and forms the ciliary body. This element produces the watery fluid that lies between the cornea and the lens, called the aqueous humor. The aqueous humor provides oxygen and nutrients to the cornea and the lens, and takes away their waste products. Elsewhere in the eye this is done by blood but on the optical pathway through the eye, a transparent medium is necessary. 17


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Chapter Two: Vision

As the ciliary body extends further away from the sclera, it becomes the iris. The iris forms a circular opening, called the pupil, that admits light into the eye. Pupil size varies with the amount of light reaching the retina but it is also influenced by the distance of the object from the eye, the age of the observer and by emotional factors such as fear, excitement and anger.

Near vision

Sclera Lens rounded

Cornea

Retina Fovea

Iris contracted

Blind spot Pupil

Cilary muscle Optic nerve

Iris opened

Distant vision Lens flattened

Figure 2.3 A section through the eye adjusted for near and distant vision After passing through the pupil, light reaches the lens. The lens is fixed in position, but varies its focal length by changing its shape. The change in shape is achieved by contracting or relaxing the ciliary muscles. For objects close to the eye, the lens is fattened. For objects far away, the lens is flattened. The space between the lens and the retina is filled with another transparent material, the jelly-like vitreous humor. After passing though the vitreous humor, light reaches the retina, the location where light is absorbed and converted to electrical signals. The retina is a complex structure, as can be seen from Figure 2.4. It can be considered as having three layers: a layer of photoreceptors, which can be divided into four types; a layer of collector cells which provide links between multiple photoreceptors, and a layer of ganglion cells. The axons of the ganglion cells form the optic nerve which produces the blind spot where it passes through the retina out of the eye. Light reaching the retina, passes through the ganglion and collector cell layers before reaching the photoreceptors, where it is absorbed. Any light that gets through the photoreceptor layer is absorbed by the pigment epithelium mounted on Bruch’s membrane. 18


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Chapter Two: Vision

Light

Vitreous Retinal ganglion cell axons

Retinal ganglion cells

Collector cells

Receptors

Pigment epithelium Bruch’s membrane Choroid

Figure 2.4 A section through the retina (after Sekular and Blake, 1994) 2.1.4 The structure of the retina The retina is an extension of the brain. The visual system has four photoreceptor types in the retina, each containing a different photopigment. These four types are conventionally grouped into two classes, rods and cones. All the rod photoreceptors are the same, containing the same photopigment and hence having the same spectral sensitivity. The relative spectral sensitivity of the rod photoreceptors is shown in Figure 2.5. The other three photoreceptor types are all cones, each with a different photopigment. Figure 2.6 shows the relative spectral sensitivity functions of the three cone photoreceptor types, called short (S), medium (M) and long (L) wavelength cones.

19


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Chapter Two: Vision

Log relative luminous efficiency 0

–0.5

–1.0

–1.5

–2.0

–2.5

–3.0

–3.5

–4.0

–4.5

–5.0 400

420

440

460

480

500

520

540

560

580

600

620

640

660

680

700

Wavelength (nm)

Figure 2.5 Log relative luminous efficiency of the rod photoreceptor Relative sensitivity 0.7 Long wavelength cones Medium wavelength cones

0.6

Short wavelength cones 0.5

0.4

0.3

0.2

0.1

0 350

400

450

500

550

600

650

700

750

Wavelength (nm)

Figure 2.6 The relative spectral sensitivities of long wavelength (L), medium wavelength (M) and short wavelength (S) cone photoreceptors (after Kaiser and Boynton, 1996) Rods and cones are distributed differently across the retina (Figure 2.7). Cones are concentrated in one small area that lies on the visual axis of the eye, called the fovea, although there is a low density of cones across the rest of the retina. 20


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Chapter Two: Vision

Density (thousands /mm2) 200

Cones Rods 150

100

50

0 100

80

60 nasal retina

40

20

0 fovea

20

40

60

80

temporal retina

Eccentricity (degrees)

Figure 2.7 The distribution of rod and cone photoreceptors across the retina. The 0 degree indicates the position of the fovea. The three cone types are also not distributed equally across the retina. The L- and M-cones are concentrated in the fovea, their density declining gradually with increasing eccentricity. The S-cones are largely absent from the fovea; reach a maximum concentration just outside the fovea and then decline gradually in density with increasing eccentricity. Over the whole retina there are approximately 120 million rods and 8 million cones. The fact that there are many more rod than cone photoreceptors should not be taken to indicate that human vision is dominated by the rods. It is the fovea that allows resolution of detail and other fine discriminations and the fovea is entirely inhabited by cones. There are three other anatomical features that emphasise the importance of the fovea. The first is the absence of blood vessels. The second is that the collector and ganglion layers of the retina are pulled away over the fovea. The third is the fact that the outer limb of the cone photoreceptor can act as a waveguide, making cones most sensitive to light rays passing through the centre of the lens. This last characteristic, known as the Stiles-Crawford effect, compensates to some extent for the poor quality of the eye’s optics by making the fovea less sensitive to light passing through the edge of the lens or scattered in the optic media. The fovea is populated only with cones. Rod photoreceptors, which dominate the population of the rest of the retina, do not show a StilesCrawford effect. 21


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2.1.5 The functioning of the retina The retina is where the processing of the retinal image begins. Recordings of electrical output from single ganglion cells have shown a number of important characteristics. The first is that the electrical discharge is a series of voltage spikes of equal amplitude. Variations in the amount of light falling on the photoreceptors supplying signals to the ganglion cell through the network of collector cells, produce changes in the frequency with which these voltage spikes occur but not in their amplitude. The second is that there is a level of electrical discharge present even when there is no light falling on the photoreceptors, called the spontaneous discharge. The third is that illuminating photoreceptors with a spot of light, can produce either an increase or a decrease in the frequency of electrical discharges, relative to the level of frequency of discharges present when light is absent. Further studies of the pattern of electrical discharges from a single ganglion cell have revealed two other important aspects of the operation of the retina. The first is the existence of receptive fields. A receptive field is the area of the retina that determines the output from a single ganglion cell. A receptive field always represents the activity of a number of photoreceptors, and often reflects input from different cone types as well as from rods. The sizes of receptive fields vary systematically with retinal location. Receptive fields around the fovea are very small. As eccentricity from the fovea increases, so does receptive field size. Within each receptive field there is a specific structure. Receptive fields consist of a central circular area and a surrounding annular area. These two areas have opposing effects on the ganglion cell’s electrical discharge. Either the central area increases and the annular surround decreases the rate of electrical discharge, or, in other receptive fields, the reverse occurs. These types of receptive fields are known as on-centre/off-surround and off-centre/on-surround fields, respectively. If either of these two types of retinal receptive fields is illuminated uniformly, the two types of effect on electrical discharge cancel each other, a process called lateral inhibition. However, if the illumination is not uniform across the two parts of the receptive field, a net effect on the ganglion cell discharge is evident. This pattern of response makes the retinal fields well suited to detect boundaries in the retinal image. While every retinal ganglion cell has a receptive field, not every ganglion cell is the same. In fact, there are two types of ganglion cell, called magnocellular (M) cells and parvocellular (P) cells. There are a number of important differences between the M-cells and P-cells. First, the axons of the M-cells are thicker than the axons of the P-cells, indicating that signals are transmitted more rapidly from the M-cells than from the P-cells. Second there are many more P-cells than M-cells and they are distributed differently across the retina. The P-cells dominate in the fovea and parafovea and the M-cells dominate in the periphery. Third, for a given eccentricity, the P-cells have smaller receptive fields than the M-cells. Fourth, the M-cells and P-cells are sensitive to different aspects of the retinal image. The M-cells are more sensitive to rapidly varying stimuli and to small differences in illumination but are insensitive to differences in colour. The P-cells are more sensitive to small areas of light and to colour. This brief description shows that the retina extracts information on boundaries in the retinal image and then extracts specific aspects of the stimulus within the boundaries, such as colour. These aspects are then transmitted up the optic nerve, formed from the axons of the retinal ganglion cells, along different channels.

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Lateral geniculate nucleus

Superior colliculus

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2.1.6 The central visual pathways Signals from the retina are transmitted to the visual cortex of the brain over the central visual pathways (Figure 2.8).

Visual cortex

Optic chiasm

Retina

Optic nerve

Optic tract

Cortical cells

Figure 2.8 A schematic diagram of the pathways from the eyes to the visual cortex (from the IESNA Lighting Handbook) The optic nerves leaving the two eyes are brought together at the optic chiasm where the nerves from each eye are split and parts from the same side of the two eyes are combined. This arrangement ensures that the signals from the same side of the two eyes are received together on the same side of the visual cortex. The pathways then proceed to the lateral geniculate nuclei. Somewhere between leaving the eyes and arriving at the lateral geniculate nuclei, some optic nerve fibers are diverted to the superior colliculus, responsible for controlling eye movements, and to the suprachiasmatic nucleus which is concerned with entraining circadian rhythms. After the lateral geniculate nuclei, the two optic nerves spread out to supply information to various parts of the visual cortex, the part of the brain where vision occurs. The visual cortex is located at the back of cerebral hemispheres. About 80% of the cortical cells are devoted to the central ten degrees of the visual field, the centre of which is the fovea, a phenomenon that again emphasises the importance of the fovea. 2.1.7 Colour vision Human colour vision is trichromatic. It is based on the L, M and S cone photoreceptors. Figure 2.9 shows how the outputs from the three cone photoreceptor types are believed to be arranged. The achromatic channel combines inputs from the M- and L-cones only. Its output is related to luminance. The other two channels are opponent channels in that they produce a difference signal. These opponent channels are responsible for the perception of colour. The red-green opponent channel produces the difference between the output of the M-cones and the sum of the outputs of the L- and S-cones. The blue-yellow opponent channel produces the difference between the S-cones and the sum of the M- and L-cones. 23


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S cones M cones L cones

Achromatic channel M+L

S cones M cones

Blue/yellow channel [(M+L) vs. S]

L cones

S cones M cones

Red/green channel [(L+S) vs. M]

L cones

Figure 2.9 The organisation of the human colour system showing how the three cone photoreceptor types are believed to feed into one achromatic, non-opponent channel and two chromatic, opponent channels (after Sekular and Blake, 1994) The ability to discriminate the wavelength content of incident light makes a dramatic difference to the information that can be extracted from a scene. Creatures with only one type of photopigment, i.e. creatures without colour vision, can only discriminate shades of grey, from black to white. Approximately 100 such discriminations can be made. Having three types of photopigment increases the number of discriminations to approximately 1,000,000. Thus, colour vision is a valuable part of the visual system, and not a luxury that adds little to utility.

2.2 Continuous adjustments of the visual system 2.2.1 Adaptation To cope with the wide range of luminances to which it might be exposed, from a very dark night (10–6 cd/m2) to a sunlit beach (106 cd/m2), the visual system changes its sensitivity through a process called adaptation. Adaptation is a continuous process involving three distinct changes. Change in pupil size: the iris constricts and dilates in response to increased and decreased levels of retinal illumination. The maximum change in retinal illumination that can occur through pupil changes is 16 to 1. As the visual system can operate over a range of about 1,000,000,000,000 to 1, this indicates that the pupil plays only a minor role in the adaptation of the visual system. Neural adaptation: this is a fast (less than 200 ms) change in sensitivity produced in the retina. Neural processes account for virtually all the transitory changes in sensitivity of the eye at luminance values commonly encountered in electrically lighted environments, i.e. below luminances of about 600 cd/m2. The facts that neural adaptation is fast, is operative at moderate light levels, and is effective over a luminance range with a maximum to minimum ratio of 1000:1 explain why it is possible to look around most lit interiors without being conscious of being misadapted. 24


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Photochemical adaptation: the sensitivity of the eye to light is largely a function of the percentage of unbleached pigment in each photoreceptor. Under conditions of steady retinal illumination, the concentration of photopigment produced by the competing processes of bleaching and regeneration is in equilibrium. When the retinal irradiance is changed, pigment is bleached and regenerated so as to re-establish equilibrium. Because the time required to accomplish the photochemical reactions is of the order of minutes, changes in the sensitivity can lag behind the irradiance changes. The cone photoreceptors adapt much more rapidly than do the rod photoreceptors. Exactly how long it takes to adapt to a change in retinal illumination depends on the magnitude of the change, the extent to which it involves different photoreceptors and the direction of the change. For changes in retinal illumination of about 2–3 log units, neural adaptation is sufficient so adaptation should be complete in less than a second. For larger changes photochemical adaptation is necessary. If the change in retinal illumination lies completely within the range of operation of the cone photoreceptors, a few minutes will be sufficient for adaptation to occur. If the change in retinal illumination covers from cone photoreceptor operation to rod photoreceptor operation, tens of minutes may be necessary for adaptation to be completed. As for the direction of change, once the photochemical processes are involved, changes to a higher retinal illuminance can be achieved much more rapidly than changes to a lower retinal illuminance. When the visual system is not completely adapted to the prevailing retinal illumination, its capabilities are limited. This state of changing adaptation is called transient adaptation. Transient adaptation is unlikely to be noticeable in interiors in normal conditions but can be significant where sudden changes from high to low retinal illumination occur, such as on entering a long road tunnel on a sunny day or in the event of a power failure in a windowless building. 2.2.2 Photopic, scotopic and mesopic vision This process of adaptation can change the spectral sensitivity of the visual system because at different retinal illuminances, different combinations of retinal photoreceptors are operating. The three states of sensitivity are conventionally identified as follows. Photopic vision: this occurs at luminances higher than approximately 3 cd/m2. For these luminances, the retinal response is dominated by the cone photoreceptors so both colour vision and fine resolution of detail are available. Scotopic vision: this occurs at luminances less than approximately 0.001 cd/m2. For these luminances only the rod photoreceptors respond to stimulation so colour is not perceived and the fovea of the retina is blind. Mesopic vision: this is intermediate between the photopic and scotopic states, i.e. between about 0.001 cd/m2 and 3 cd/m2. In the mesopic state both cones and rod photoreceptors are active. As luminance declines through the mesopic region, the fovea, which contains only cone photoreceptors, slowly declines in absolute sensitivity without significant change in spectral sensitivity, until vision fails altogether as the scotopic state is reached. In the periphery, the rod photoreceptors gradually come to dominate the cone photoreceptors, resulting in gradual deterioration in colour vision and resolution and a shift in spectral sensitivity to shorter wavelengths. The relevance of the different types of vision for lighting practice varies. Scotopic vision is largely irrelevant. Any lighting installation worthy of the name provides enough light to at least move the visual system into the mesopic state. Most interior lighting ensures the visual system is operating in the photopic state. Current practice in exterior lighting ensures the visual system is often operating in the mesopic state.

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All photometric quantities used by the lighting industry are based on the CIE Standard Photopic Observer, i.e. photopic vision. Therefore, it should not come as a surprise when light sources with different spectral content do not have the same effects when used to provide mesopic vision despite being matched photometrically. 2.2.3 Accommodation There are three optical components involved in the ability of the eye to focus an image on the retina, the thin film of tears on the cornea, the cornea itself, and the crystalline lens. The ciliary muscles have the ability to change the curvature of the lens and thereby adjust the power of the eye’s optical system in response to changing target distances; this change in optical power is called accommodation. Accommodation is a continuous process, even when fixating, and is always a response to an image of the target located on or near the fovea rather than in the periphery of the retina. Any condition that handicaps the fovea, such as a low light level, will adversely affect accommodative ability. As adaptation luminance decreases below 0.03 cd/m2, the range of accommodation narrows so that it becomes increasingly difficult to focus objects near and far from the observer. When there is no stimulus for accommodation, as in complete darkness or in a uniform luminance visual field such as occurs in a dense fog, the visual system typically accommodates to approximately 70 cm away.

2.3 Capabilities of the visual system The human visual system has a limited range of capabilities. These limits, conventionally called thresholds, are mainly of interest for determining what will not be seen rather than how well something will be seen. For the threshold measurements shown here the observers were all fully adapted, the target was presented on a field of uniform luminance and the observers’ accommodation was correct. 2.3.1 Threshold measures The threshold capabilities of the human visual system can conveniently be divided into spatial, temporal and colour classes. Spatial threshold measures Spatial threshold measures relate to the ability to detect a target against a background or to resolve detail within a target. Common spatial threshold measures are threshold luminance contrast and visual acuity. The luminance contrast of a target quantifies its visibility relative to its immediate background. The higher is the luminance contrast, the easier it is to detect the target. There are three different forms of luminance contrast. For uniform targets seen against a uniform background, luminance contrast is defined as

C=

Lt – Lb Lb

where: C = luminance contrast Lb = luminance of the background Lt = luminance of the target 26


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Another form of luminance contrast for a uniform targets seen against a uniform background is defined as C = Lt / Lb

Chapter Two: Vision

This formula gives luminance contrasts which range from 0 to 1 for targets which have details darker than the background and from 0 to infinity for targets which have details brighter than the background. It is widely used for the former, e.g. printed text on white paper.

where: C = luminance contrast Lb = luminance of the background Lt = luminance of the target This formula gives luminance contrasts that can vary from 0, when the target has zero luminance, to infinity, when the background has zero luminance. It is often used for selfluminous displays, e.g. computer monitors. For targets that have a periodic luminance pattern, e.g. a grating, the luminance contrast is given by C = (Lmax – Lmin) / (Lmax + Lmin) where: C = luminance contrast Lmax = maximum luminance Lmin = minimum luminance This formula gives luminance contrasts that range from 0 to 1, regardless of the relative luminances of the target and background. It is sometimes called the luminance modulation. Given the different forms of luminance contrast measure, it is always important to understand which is being used. Visual acuity is a measure of the ability to resolve detail for a target with a fixed luminance contrast. Visual acuity is most meaningfully quantified as the angle subtended at the eye by the detail that can be resolved on 50 percent of the occasions the target is presented. This angle is usually expressed in minutes of arc. Using this measure, the visual acuity corresponding to ‘normal’ vision is taken to be 1 min arc. Unfortunately for simplicity, there are several other measures used to quantify visual acuity. One is the reciprocal of the angle subtended at the eye by the detail that can be resolved on 50 percent of the occasions the target is presented. A relative measure is used by the medical profession. This is the distance at which a patient can read a given size of letter or symbol relative to the distance an average member of the population with normal vision could read the same letter or symbol. For example, if the patient is said to have 20/200 vision it means that the patient can only read a given letter at 20 feet that an average member of the population with normal vision can read from 200 feet. Again, given the different forms of visual acuity that are used by different professions, it is important to be sure which metric is being used.

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Temporal threshold measures Temporal threshold measures relate to the speed of the response of the human visual system and its ability to detect fluctuations in luminance. The ability of the human visual system to detect fluctuations in luminance can be measured as the frequency of the fluctuation, in hertz, and the amplitude of the fluctuation, for the stimulus that can be detected on 50 percent of the occasions it is presented. The amplitude is expressed as M = (Lmax – Lmin) / (Lmax + Lmin) where: M = modulation Lmax = maximum luminance Lmin = minimum luminance This formula gives modulations that range from 0 to 1. Sometimes, modulation is expressed as a percentage modulation, calculated by multiplying the modulation by 100. Colour threshold measures Colour threshold measures are based on the separation in colour space of two colours that can just be discriminated, usually measured on the CIE 1931 chromaticity diagram and the related uniform chromaticity scale diagrams. 2.3.2 Factors determining visual threshold There are three distinct groups of factors that influence the measured threshold; visual system factors, target characteristics and the background against which the target appears. Important visual system factors are the luminance to which the visual system is adapted, the position in the visual field where the target appears, and the extent to which the eye is correctly accommodated. As a general rule, the lower the luminance to which the visual system is adapted, the further the target is from the fovea, and the more mismatched the accommodation of the eye is to the viewing distance, the larger will be the threshold values. Important target characteristics are the size and luminance contrast of the target and the colour difference between the target and the immediate background. All three factors interact. For example, the visual acuity for a low luminance contrast, achromatic target will be much larger than for a high luminance contrast, achromatic target when expressed as minutes of arc but will be reduced if there is a colour difference between the target and the background. As for the effect of the background against which the target appears, the important factors are the area, luminance and colour of the background. As a general rule, the larger the area around the target that is of a similar luminance to the target and neutral in colour, the smaller will be the threshold measure. 2.3.3 Spatial thresholds One of the simplest visual tasks is the detection of a spot of light presented continuously against a uniform luminance background. For such a target the visual system demonstrates spatial summation, i.e. the product of target luminance and target area is a constant. This relationship between target luminance and target area is known as Ricco’s Law. It implies that the total amount of energy required to stimulate the visual system so that the target can be detected is the same, regardless of whether it is concentrated in a small spot or distributed over a larger area.

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Given that the size of the target is above the critical size, the detection of the presence of a spot of light is determined simply by the luminance contrast. For the luminance of the surround in the photopic range, there is a constant relationship between the luminance difference of the target and the background and the background luminance known as Weber’s Law. This relationship takes the form

Chapter Two: Vision

Spatial summation breaks down when the target is above about 6 min arc diameter for the fovea, above about 0.5 degree at 5 degrees from the fovea, and above about 2 degrees at 35 degrees from the fovea.

(Lt – Lb) / Lb = k where: Lt = luminance of the target Lb = luminance of the background k = constant A more general picture of the effect of adaptation luminance on threshold contrast for targets of different size is shown in Figure 2.10. The increase in threshold contrast as adaptation luminance decreases is obvious, as is the increase in threshold contrast with decreasing target size. These data were obtained using a disc of different sizes presented for 1 second in the fovea. Decreasing the presentation time and moving the target away from the fovea increases the threshold contrast, for all sizes, particularly at lower adaptation luminances.

Threshold contrast 1000

= 1 min arc = 2 min arc = 4 min arc

100

= 10 min arc = 60 min arc

10

1

0.1

0.01

0.001 0.001

0.01

0.1

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Figure 2.10 Threshold contrast plotted against background luminance for disc targets of various diameters, viewed foveally. The discs were presented for 1 second (after Blackwell, 1959). 29


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Threshold luminance contrast is relevant to the detection of targets on a background. Targets with a luminance contrast close to or below the threshold value are unlikely to be seen and targets with a luminance contrast more than twice the threshold value are likely to be seen every time. Figure 2.11 shows the variation in visual acuity with luminance for foveal viewing of the target. As luminance increases, visual acuity, measured as the reciprocal of the minimum gap size, improves, approaching an asymptote at very high luminances corresponding to about 0.45 min arc. Visual acuity deteriorates with increasing deviation from the fovea and improves as the area around the target that has the same luminance increases.

Reciprocal of gap size (min arc)–1 2.5

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Figure 2.11 Visual acuity, expressed as the reciprocal of the minimum gap size, for a Landolt ring, plotted against log background luminance (after Shlaer, 1937) 2.3.4 Temporal thresholds The simplest possible form of temporal visual task is the detection of a spot of light briefly presented against a uniform luminance background, i.e. a flash of light. For such a target the visual system demonstrates temporal summation, i.e. the product of target luminance and the duration of the flash is a constant. This relationship between target luminance and duration is known as Bloch’s Law. It implies that the total amount of energy required to stimulate the visual system so that the target can be detected is the same, regardless of the time for which the target is presented. Temporal summation breaks down above a fixed duration, ranging from 0.1 s for scotopic luminances to 0.03 s for photopic luminances. For presentation times longer than the critical duration, presentation time has no effect, the ability to detect the flash being determined by the difference in luminance between the flash and the background. 30


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An aspect of temporal thresholds relevant to lighting is the ability to detect flicker. Figure 2.12 shows the maximum frequency of a sinewave fluctuation at 100 percent modulation that is visible at different retinal illuminations, for visual fields of different sizes. Retinal illumination is measured in trolands which are the product of the luminance of the stimulus and the associated pupil area. For large field sizes, such as might occur when using indirect lighting, the maximum frequency increases linearly with retinal illumination in the scotopic state, shows little change in the mesopic state and increases linearly in the photopic state until saturation occurs.

Critical fusion frequency (Hz) 60 = 19˚ 50

= 16˚ = 0.3˚

40

30

20

10

0 –3

–2

–1

0

1

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4

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6

Log retinal illumination (trolands)

Figure 2.12 Critical fusion frequency plotted against log retinal illumination, for three different test field sizes (after Hecht and Smith, 1936) 2.3.5 Colour thresholds Figure 2.13 shows the MacAdam ellipses, ten times enlarged, plotted in the CIE chromaticity diagram. Each ellipse represents the standard deviation in the chromaticity coordinates for colour matches made between the two parts of a 2–degree bipartite field with the reference field having the chromaticity of the centre point of the ellipse. The lighting industry uses four-step MacAdam ellipses as its tolerance limits for quality control in lamp manufacture.

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530

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y

0.4 600 610 490

620 630

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Figure 2.13 The CIE 1931 chromaticity diagram with the MacAdam ellipses displayed, multiplied ten times (after MacAdam, 1942, from the IESNA Lighting Handbook) 2.3.6 Light spectrum and movement Adaptation luminance and position relative to the fovea are major factors in determining thresholds. Other factors, such as light spectrum and movement of the target are also important. Visual acuity is only slightly influenced by light spectrum, light sources with greater energy at short wavelengths enhance visual acuity. As for movement, as long as the movement is slow enough and smooth enough to allow the retinal image of the target to be kept on the fovea, visual acuity is only slightly worsened. However, smooth movements faster than 40 degrees per second or erratic movement at slower speeds will lead to a dramatic deterioration in visual acuity.

2.4 Suprathreshold performance Threshold measurements are used to define whether or not a target will be seen. When the target can be seen every time, it is said to be suprathreshold and the question of interest becomes how quickly and accurately the work of which the target is a part can be done. The answer to this question depends on the structure of the task. Most apparently visual tasks actually have three components; visual, cognitive and motor. The effect of lighting on task performance depends on the place of the visual component relative to the cognitive and motor components. Tasks in which the visual component is large or limiting will be more sensitive to changes in lighting conditions than tasks where the visual component is small or unimportant. 32


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The impact of lighting conditions on visual performance is determined by the size, luminance contrast and colour difference of the task and the amount, spectrum and distribution of the lighting. An analytical approach using a standard task measured over a wide range of conditions has served to demonstrate, qualitatively, the effects of increasing illuminance on visual performance (Figure 2.14). They are that increasing illuminance follows a law of diminishing returns, i.e. that equal increments in illuminance lead to smaller and smaller changes in visual performance until saturation occurs; that the point where saturation occurs is different for different sizes and contrasts of critical detail; that larger improvements in visual performance can be achieved by changing the task than by increasing the illuminance, at least over any illuminance range of practical interest; and, that it is not possible to make a visually difficult task reach the same level of performance as a visually easy task simply by increasing the illuminance over any reasonable range.

Chapter Two: Vision

It is important to distinguish between task performance and visual performance. Task performance is the performance of the whole task. Visual performance is the performance of the visual component of the task. Task performance is what is needed to measure productivity and estimate cost benefit ratios for lighting. Visual performance is all that lighting conditions can influence directly. Every task has a different relationship between visual performance and task performance depending on the structure of the task. This makes it impossible to generalise from measurements of visual performance to the performance of all tasks.

Mean performance score 0.6

0.5

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Figure 2.14 Mean performance scores for Landolt ring charts of different critical size and contrast, plotted against illuminance (after Weston, 1945) 33


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While this understanding is useful, it is not enough to make quantitative predictions of the effect of lighting conditions on visual performance for all tasks although it is possible for some. Specifically, the relative visual performance (RVP) model of visual performance (Rea and Ouellette, 1991) has been shown to make accurate predictions for tasks that are dominated by the visual component, that do not require the use of peripheral vision to any extent, that present stimuli to the visual system that can be completely characterised by their visual size, luminance contrast and background luminance only, and that are seen in photopic conditions e.g. reading and doing data-entry work. Figure 2.15 shows the form of relative visual performance produced by this model for a fixed size but variable luminance contrast target and a range of background luminances. This form has been described as the plateau and escarpment of visual performance, the point being that over a wide range of luminance contrasts and background luminances the change in relative visual performance is slight but at some point either contrast or luminance will be so low that performance will start to deteriorate rapidly. The objective of functional lighting is to keep performance on the plateau and well away from the escarpement.

Relative visual performance

1.0

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1 100

Luminance (cd⋅m–2)

Contrast 0.1 10

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Figure 2.15 The form of relative visual performance plotted against target luminance contrast and background luminance for a fixed target size (after Rea, 1986)

2.5 Visual search

34

One type of work that is outside the RVP model is visual search. Visual search proceeds via a series of fixations joined together by saccades (Figure 2.2). This implies that the target is most likely to be seen first, away from the fovea. For a uniform field, where any departure from uniformity is a target, the probability of off-axis detection can be related to the visibility of the defect. The concept used to model the effect of lighting conditions on search time is the visual detection lobe, i.e. a surface centred on the fovea that defines the probability of detecting the target at different deviations from the fovea within a single fixation pause (Figure 2.16).


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Probability of detection 1.0

0.8

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c

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Deviation from visual axis (degrees)

Figure 2.16 The probability of detection of targets of (a) contrast = 0.058, size = 19 min arc; (b) contrast = 0.08, size = 10 min arc; (c) contrast = 0.044, size = 10 min arc; within a single fixation pause, plotted against deviation from the visual axis. Each curve can be used to form a visual detection lobe for each target by assuming radial symmetry about the visual axis. The visual detection lobe has a maximum at the fovea; the probability of detecting the target decreasing as the target is located further off-axis. Different targets have different visual detection lobes. A large-area, high-contrast hole in some sheet material will have a large visual detection lobe while a small-size, low-contrast hole will have a small lobe. The size of the visual detection lobe matters because, provided the interfixation distance is related to it and the total search area is fixed, the total time taken to cover the search area is inversely proportional to the size of the visual detection lobe. Other important factors for determining visibility are the luminance contrast, and the colour of the target relative to the background. There is also the question of what happens when the area to be searched contains other items. For searching uniform, empty fields, it is the visibility of the target off-axis that determines the search time. Where there are other items present, the visibility of the target alone is not enough to predict the search time. The other factor that must be considered is the conspicuity of the target, i.e. how easy it is to distinguish the targets from the other items. For high conspicuity, the defects should differ from the other items in the field on as many dimensions as possible, e.g. size, contrast, shape, colour and movement. Many of the lighting techniques used for visual search are aimed at either increasing the visual size or luminance contrast of the defect, either by casting shadows (Figure 2.17) or by using specular reflections (Figure 2.18). Probably the most widely applicable aspect of lighting which aids visual search is to increase the illuminance on the search area. While illuminance is generally a useful method of reducing search times, it should not be used without thought. If the effect of increasing illuminance is to decrease the luminance contrast, or effective visual size of the targets or to produce confusing visual information in the search area, visual search performance will be worsened. 35


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Chapter Two: Vision Figure 2.17 A cut in textured material lit by directional lighting delivered at a glancing angle to the surface of the material. The cut is visible under the directional lighting because of the high luminance contrast. The high luminance contrast occurs because of the highlights on the sides of the cut and the deep shadow in the cut.

Figure 2.18 A specular aluminium surface with a cross scribed into it, lit by directional lighting from above and behind the camera. The scribed cross is easily seen because the scribed marks cut into the surface and thereby alter the reflection characteristics of the surface. The result is a high luminance reflection towards the camera for the cut and a high luminance reflection away from the camera for the undamaged surface. 36


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There are four situations in which lighting installations may cause visual discomfort. They are: visual task difficulty, in which the lighting makes the required information difficult to extract, under- or over-stimulation, in which the visual environment is such that it presents too little or too much information,

Chapter Two: Vision

2.6 Visual discomfort

distraction, in which the observer’s attention is drawn to objects that do not contain the information being sought, perceptual confusion, in which the pattern of illuminance can be confused with the pattern of reflectance in the visual environment. The occurrence of visual discomfort is made manifest by the occurrence of red, itchy eyes, headaches and aches and pains associated with poor posture. The most common aspects of lighting that cause visual discomfort are insufficient light, too much variation in illuminance between and across working surfaces, glare, veiling reflections, shadows and flicker. 2.6.1 Insufficient light There is insufficient light when the worker approaches the escarpment of the relative visual performance surface for the task (see Figure 2.15). Behavioural signs that there is insufficient light are attempts to move the work to get more light or movements by the worker to get closer to the task. Discomfort caused by insufficient light can be avoided by following the recommendations in the SLL Code for lighting and the guidance given in the application chapters of this Handbook. 2.6.2 Illuminance uniformity Lighting recommendations almost always include an illuminance uniformity criterion. These criteria can be direct or indirect. Direct criteria are ratios of illuminance, typically minimum/maximum or minimum/average measured on the relevant working plane. Indirect criteria are selected to produce a minimum illuminance uniformity ratio, e.g. spacing/mounting height ratio. Such criteria can be considered on different scales. For a whole room where tasks can be anywhere in the room, the minimum/average illuminance ratio on the working plane should not be less than 0.7. This criterion probably only applies where the lighting installation is perceived by the occupants to be intended to produce a uniform distribution of illuminance. In rooms with large windows, the illuminance on a desk close to the window will be much greater than on a desk well back from the window so the illuminance uniformity ratio will be much less than 0.7, but few complaints are heard. Similarly, studies in offices where the luminaires can be individually switched or dimmed have shown that wide variations in the illuminance on desks can be tolerated, without complaint. This suggests that illuminance uniformity limitations are more a design requirement adopted to ensure that no one has insufficient illuminance for their work rather than an intrinsic requirement of the visual system. On the scale of an individual work surface, there are two potential sources of discomfort. Distraction can occur where there are areas of high illuminance adjacent to the work area. 37


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Chapter Two: Vision

Perceptual confusion can occur when the illuminance pattern has a sharp edge so that it could be mistaken for a change in reflectance. The most preferred form of work surface lighting is one that provides a uniform illuminance over the area where the work is to be done (minimum/maximum illuminance ratio > 0.7) and lower illuminances outside that area. 2.6.3 Glare The presence of a luminance much above the average for the visual field will produce discomfort and is called glare. There are five forms of glare associated with lighting installations. Saturation glare This occurs when a large part of the visual field is at a very high luminance for a long time, e.g. sunlight on snow. Saturation glare is painful and the behavioural response is to shield the eyes in some way, e.g. by wearing low transmittance glasses. Adaptation glare This occurs when the visual system is exposed to a sudden, large increase in luminance of the whole visual field, e.g. on exiting a long road tunnel into bright sunlight. The perception of glare is due to the visual system being oversensitive. Adaptation glare is temporary in that visual adaptation will soon adjust the visual sensitivity to the new conditions. It can be avoided by providing a transition zone of intermediate luminance, the transition zone being large enough to allow the visual system time to adapt to the new conditions. Disability glare This occurs when high luminance is present in a low luminance scene. Light from the source is scattered in the eye thereby forming a luminous veil over the retinal image of parts of the scene adjacent to the source. This luminous veil reduces the luminance contrast and desaturates any colours in the retinal image of the adjacent parts of the scene. The magnitude of disability glare is quantified by the equivalent veiling luminance. For glare sources within an angular range of 0.1 to 30 degrees, this is given by the equation:

Lv = 10

∑

En Θ n2

where: Lv = equivalent veiling luminance (cd/m2) En = illuminance at the eye from the nth glare source (lx) Θn = angle of the nth glare source from the line of sight (degrees) The effect of the equivalent veiling luminance on the luminance contrast of an object can be estimated by adding it to the luminance of both the object and the immediate background. Disability glare can be associated with point sources and large area sources. The disability glare formulae can be applied directly to point sources but for large area sources, the area has to be broken into small elements and the overall effect integrated. Disability glare from point sources is experienced most frequently on the roads at night when facing an oncoming vehicle. Disability glare from an extended source can occur when looking at an object on a wall adjacent to a window. The sky seen through the window is the glare source.

38


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UGR = 8 log10

0.25 Lb

Ls ω p2 2

∑

where: UGR = Unified Glare Rating Lb = background luminance (cd/m2), excluding the contribution of the glare sources. This is numerically equal to the indirect illuminance on the plane of the observer’s eye, divided by π Ls = luminance of the luminaire (cd/m2) ω = solid angle subtended at the observer’s eye by the luminaire (steradians) p = Guth position index

Chapter Two: Vision

Discomfort glare This occurs when people complain about visual discomfort in the presence of bright light sources, luminaires or windows. Discomfort glare is quantified by the Unified Glare Rating (UGR), derived from the equation:

UGR values typically range from 13 to 30, the lower the value, the less the discomfort. Luminaire manufacturers publish UGR values for regular arrays of their luminaires in a number of standardised rooms. This enables comparisons to be made between different luminaire types. When making such a comparison the smallest meaningful difference is one whole unit in UGR. Where a luminous ceiling or uniform indirect lighting is used, discomfort glare is limited by setting a maximum average illuminance. Specifically, if a UGR value of 13 is desired then the average illuminance provided should not exceed 300 lx, for UGR = 16, the maximum average illuminance should not exceed 600 lx and for UGR = 19, the maximum average illuminance should not exceed 1,000 lx. Overhead glare A high luminance immediately overhead can also cause discomfort, even though it cannot be seen when looking directly ahead. The cause of the discomfort is distraction, caused by high luminance reflections from eyebrows, glasses and facial features. The UGR system can be applied to overhead glare to predict the magnitude of the discomfort. 2.6.4. Veiling reflections Veiling reflections are luminous reflections from specular surfaces that physically change the contrast of the visual task and therefore change the stimulus presented to the visual system (Figure 2.19). The two factors that determine the nature and magnitude of veiling reflections are the specularity of the surface being viewed and the geometry between the observer, the surface, and any sources of high luminance. If the surface is a perfectly diffuse reflector, no veiling reflections can occur. If the surface has a specular reflection component, veiling reflections can occur. Veiling reflections occur at positions where the geometry between the observer, the surface and any sources of high luminance is such that the angle of incidence between the surface and the source of high luminance equals the angle of reflection between the surface and the observer. The effect of veiling reflections on the luminance contrast of a specific target may be quantified by adding the luminance of the veiling reflection to the appropriate components of the luminance contrast formulae. What the appropriate components are depends on the reflection properties of the material being viewed. For glossy ink writing on matte paper, the luminance of the veiling reflections should only be added to the luminance of the ink. 39


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Chapter Two: Vision

For a glossy magazine page or a VDT screen veiling reflections occur over the whole surface. In this case the luminance of the veiling reflections should be added to all terms in the luminance contrast formula.

Figure 2.19 A glossy book, with and without veiling reflections Although veiling reflections are usually considered a negative outcome of lighting that can cause discomfort, they can be used positively, but when they are, they are conventionally called highlights. Physically, veiling reflections and highlights are the same thing. Display lighting of specularly reflecting objects is all about producing highlights to reveal the specular nature of the surface. 2.6.5 Shadows Shadows are cast when light coming from a particular direction is intercepted by an opaque object. If the object is big enough, the effect is to reduce the illuminance over a large area. This is typically the problem in industrial lighting where large pieces of machinery cast shadows in adjacent areas. The effect of these shadows can be overcome either by increasing the proportion of inter-reflected light by using high reflectance surfaces or by providing local lighting in the shadowed area. If the object is smaller, the shadow can be cast over a meaningful area which in turn can cause perceptual confusion, particularly if the shadow moves. An example of this is the shadow of a hand cast on a blueprint. This problem can also be reduced by increasing the inter-reflected light in the space or by providing local lighting which can be adjusted in position. 40


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The number and nature of shadows produced by a lighting installation depends on the size and number of light sources and the extent to which light is inter-reflected around the space. The strongest shadow is produced from a single point source in a black room. Weak shadows are produced when the light sources are large in area and the degree of inter-reflection is high.

Chapter Two: Vision

Although shadows can cause visual discomfort, it should be noted that they are also an essential element in revealing the form of three-dimensional objects. Techniques of display lighting are based around the idea of creating highlights and shadows to change the perceived form of the object being displayed. Many lighting designers insist that the distribution of shadows is as important as the distribution of light in achieving an attractive and meaningful visual environment.

2.6.6 Flicker Virtually all electric light sources that operate from an alternating-current supply produce regular fluctuations in the amount of light emitted. When these fluctuations become visible they are called flicker. The probability that a lighting installation will be seen to flicker can be minimised by ensuring a stable supply voltage and by the use of high-frequency electronic control gear for discharge lamps. Incandescent light sources do not require control gear but they are particularly sensitive to fluctuations in supply voltage. Where the local electricity network has equipment attached to it that can impose sudden large loads, e.g. the motors of a steel rolling mill, local fluctuations in supply voltage are likely and, in consequence, so are fluctuations in light output of incandescent light sources. These can be minimised by using a voltage regulator between the electricity supply and the light source. Discharge lamps are less sensitive to supply voltage fluctuations than incandescent lamps because the electricity supply is filtered through the control gear. Electromagnetic control gear typically produces an output at the same frequency as the electricity supply. Electronic control gear for fluorescent lamps typically produces an output at much higher frequencies. Given the time constants of the light producing processes in most discharge lamps, this increase in supply frequency not only produces a higher frequency but also a smaller percentage modulation in light output. Another approach used to reduce the probability of flicker is to combine light from lamps powered from different phases of the electricity supply on the working plane. This results in an increased frequency and a reduced percentage modulation and hence a decrease in the probability of flicker being seen when looking at the working plane. Obviously, it does nothing for the probability of flicker being seen when looking directly at an individual light source. Although flicker occurring over a large area is almost always disturbing, localised flicker does have its uses. Localised flicker is a potent means of attracting attention because peripheral vision is sensitive to changes in the retinal illumination pattern, either in space or time. Localised flicker can also create a stroboscopic effect (see Section 10.2.8).

2.7 Perception through the visual system 2.7.1 The constancies When considering how we perceive the world, the overwhelming impression is one of stability in the face of continuous variation. This invariance of perception is called perceptual constancy. 41


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Chapter Two: Vision

There are four fundamental attributes of an object that are maintained constant over a wide range of lighting conditions. Lightness: lightness is the perceptual attribute related to reflectance. In most lighting situations, it is possible to distinguish between the illuminance on a surface and its reflectance, i.e. to perceive the difference between a low-reflectance surface receiving a high illuminance and a highreflectance surface receiving a low illuminance, even when both surfaces have the same luminance. It is this ability perceptually to separate the luminance of the retinal image into its components of illuminance and reflectance that makes the use of luminance as the basis of lighting design criteria problematical. Colour: physically, the stimulus a surface presents to the visual system depends on the spectral content of the light illuminating the surface and the spectral reflectance of the surface. However, quite large changes in the spectral content of the illuminant can be made without causing any changes in the perceived colour of the surface, i.e. colour constancy occurs. Colour constancy is similar in many ways to lightness constancy. There are two factors that need to be separated; the spectral distribution of the incident light and the spectral reflectance of the surface. As long as the spectral content of the incident light can be identified the spectral reflectance of the surface, and hence its colour, will be stable. Size: as an object gets further away, the size of its retinal image gets smaller but the object itself is not seen as getting smaller. This is because by using clues such as texture and masking, it is usually possible to estimate the distance and then to compensate unconsciously for the increase in distance. Shape: as an object changes its orientation in space, its retinal image changes. Nonetheless, in most lighting conditions the distribution of light and shade across the object makes it possible to determine its orientation in space. This means that in most lighting conditions a circular plate that is tilted will continue to be seen as a tilted circular plate even though its retinal image is elliptical. These constancies represent the application of everyday experience and the integration of all the information about the lighting available in the whole retinal image to the interpretation of a part of the retinal image that bears several alternative interpretations. Constancy is likely to break down whenever there is insufficient or misleading information available from the surrounding parts of the visual field. The constancies are most likely to be maintained when there is enough light for the observer to see the object and the surfaces around it clearly, the light being provided by an obvious but not necessarily visible light source, there are a variety of surface colours, including some small white surfaces and there are no large glossy areas. Lighting conditions used in display lighting sometimes set out to break the constancies, particularly lightness constancy, in order to give the display some drama. 2.7.2 Attributes and modes of appearance While lighting has an important role in preserving or eliminating constancy, it also has a role in determining the perceived visual attributes of objects. Objects can have five different attributes: brightness, lightness, hue, saturation, transparency and glossiness, depending on their nature and the way they are lit. These attributes are defined as follows. Brightness: an attribute based on the extent to which an object is judged to be emitting more or less light.

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Hue: an attribute based on the classification of a colour as reddish, yellowish, greenish, bluish or their intermediaries or as having no colour. Saturation: an attribute based on the extent to which a colour is different from no colour of the same brightness or lightness.

Chapter Two: Vision

Lightness: an attribute based on the extent to which an object is judged to be reflecting a greater or lesser fraction of the incident light.

Transparency: an attribute based on the extent to which colours are seen behind or within an object. Glossiness: an attribute based on the extent to which a surface is different from a matte surface with the same lightness, hue, saturation and transparency. Not all these attributes occur in every situation. Rather, different combinations of attributes occur in different modes of appearance. The four modes of appearance are as follows. Aperture mode: this occurs when an object or surface has no definite location in space, as occurs when a surface is viewed through an aperture. Illuminant mode: this occurs when an object or surface is seen to be emitting light. Object mode (volume): this occurs when a three-dimensional object has a definite location in space with defined boundaries. Object mode (surface): this occurs when a two-dimensional surface has a definite location in space with defined boundaries. Table 2.1 shows which of the attributes can be associated with each mode of appearance. Of particular interest to the perception of lighting is the shift between the attributes of brightness and lightness in different modes of appearance. An object which appears in the self-luminous mode, such as a VDT screen or a light source, is perceived to have a brightness but not a lightness. In this mode of appearance, the concept of reflectance is perceptually meaningless. However, an object that appears in the volume mode, such as a VDT screen or a light source that is turned off, does not have an attribute of brightness but does have a lightness in that its reflectance can be estimated. Table 2.1 The visual attributes that can occur with each mode of appearance Attribute

Aperture

Illuminant

Brightness

*

*

Lightness

Volume

Surface

*

*

Hue

*

*

*

*

Saturation

*

*

*

*

*

*

*

Transparency Glossiness

* 43


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Chapter Two: Vision

A similar transformation occurs between the volume or surface modes of appearance and the aperture mode. Even non-self-luminous objects seen in the aperture mode are perceived as having a brightness but not a lightness. When seen in the object mode they have a lightness but not a brightness. This is important because lighting can be used to change the mode of appearance. For example, a painting hung on a wall has a lightness attribute when lighted so that both it and the wall appear in the object mode (surface). However, if the painting is illuminated solely with a carefully aimed framing spot so that the edge of the beam coincides with the edges of the painting, the painting is seen in the aperture mode and takes on a selfluminous quality with a brightness attribute. Adjusting the modes of appearance is an important technique in display lighting, both indoors and outdoors.

2.8 Anomolies of vision All the capabilities of human vision discussed above assume normal vision. However, there are a number of forms of defective vision that occur due to either genetics or ageing. 2.8.1 Defective colour vision About 8 percent of males and 0.4 percent of females have some form of defective colour vision. People with defective colour vision are classified into three categories: monochromats, dichromats, and anomalous trichromats, according to the number of photoreceptors present and the nature of the photopigments present in the photoreceptors. Monochromats, although very rare, occur in two forms: rod monochromats, where there are no cone photoreceptors, only rod photoreceptors; and cone monochromats, where there are rod photoreceptors and only one type of cone photoreceptor, usually the short-wavelength cone. Rod monochromats are truly colour-blind and see only differences in brightness. Cone monochromats have a very limited form of colour vision in the luminance range where both rod and short-wavelength cones are operating. Dichromats have two cone photoreceptors. They see a more limited range of colours than people with normal colour vision and have a different spectral sensitivity, depending on which cone photoreceptor is missing. Dichromats with the long-wavelength cone missing are called protanopes. Dichromats with the medium-wavelength cone missing are called deuteranopes, while dichromats with short-wavelength cones missing are called tritanopes. Anomalous trichromats have all three cone photopigments present, but one of the cones contains a photopigment that does not have the usual spectral sensitivity. Anomalous trichromats who have a defective long-wavelength photopigment are called protonamalous. Anomalous trichromats who have a defective medium-wavelength photopigment are called deteuranomalous, while anomalous trichromats who have a defective short-wavelength photopigment are called tritanomalous. The colour vision of anomalous trichromats can vary widely from almost as bad as a dichromat to little different from someone with normal colour vision. People with defective colour vision have trouble with some everyday tasks (see Table 2.2) and are prohibited from some occupations. Defective colour vision is usually inherited, although it can also be acquired through age, disease, injury or exposure to some chemicals.

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Activity

Dichromats

Anomalous trichromats

Normal

Selecting clothes, cosmetics etc.

86

66

0

Distinguishing the colours of wires, paints etc.

68

23

0

Identifying plants and flowers

57

18

0

Determining when fruits and vegetables are ripe, by colour

41

22

0

Determining when meat is cooked, by colour

35

17

0

Difficulties in participating or watching sports, because of colour

32

18

0

Adjusting the colour balance of a television satisfactorily

27

18

2

Recognising skin conditions such as a rash or sunburn

27

11

0

Taking the wrong medication because of difficulties with colour

0

3

0

Chapter Two: Vision

Table 2.2 Percentage of people with different types of colour vision reporting difficulties with everyday tasks (from Steward and Cole, 1989)

2.8.2 Low vision As the visual system ages, the ability to focus close up is diminished, the amount of light reaching the retina is reduced, more of the light reaching the retina is scattered, the spectrum of the light reaching the retina is changed and more straylight is generated inside the eye. These changes start in early adulthood and continue at a steady rate with increasing age. The consequences of these changes with age for the capabilities of the visual system are many and varied. At the threshold level, old age is characterised by reduced absolute sensitivity to light, reduced visual acuity, increased contrast threshold, reduced colour discrimination and greater sensitivity to glare. In practice, the elderly have difficulty seeing in dim light, moving from bright to dark conditions suddenly, reading small print and distinguishing dark colours. With increasing age comes a greater likelihood of pathological changes leading to low vision and eventual blindness. The World Health organisation (WHO) defines classes of vision based on visual acuity and visual field size (Table 2.3).

45


Chapter Two: Vision

Table 2.3

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The WHO classification of vision (after Tielsch et al, 1990) Grade

Criteria

Normal vision

0

20/25 or better

Near normal vision

0

20/30 to 20/60

Moderate visual impairment

1

20/70 to 20/160

Severe visual impairment

2

20/200 to 20/400

Profound visual impairment

3

20/500 to 20/1000 or a visual field less than 10°

Near-total visual impairment

4

Worse than 20/1000 or a visual field less than 5°

5

No light perception

Category

Low vision

Blindness

Total visual impairment

The prevalence of low vision and blindness increases dramatically after 70 years of age (Table 2.4) The four most common causes of low vision in developed countries are cataract, macular degeneration, glaucoma and diabetic retinopathy. Table 2.4 Percentage prevalence of blindness and low vision for different age groups and races. In this case, blindness is defined as a visual acuity of 20/200 or worse, and low vision is defined as a visual acuity of from 20/40 to 20/200 (after Tielsch et al, 1990) Age range (years)

Blindness (Caucasian)

Blindness (Afro-American)

Low vision (Caucasian)

Low vision (Afro-American)

40–49

0.6

0.6

0.2

0.6

50–59

0.5

0.7

0.7

1.3

60–69

0.2

1.6

1.1

3.4

70–79

0.6

2.9

5.2

8.1

80+

7.3

8.0

14.6

18.0

Cataract is an opacity developing in the lens. The effect of cataract is to absorb and scatter more light on passage through the lens. This results in reduced visual acuity and increased contrast thresholds over the entire visual field, as well as greater sensitivity to glare. Macular degeneration occurs when the macular, which covers the fovea, becomes opaque. An opacity immediately in front of the fovea implies a serious reduction in foveal vision so seeing detail becomes difficult if not impossible. However, peripheral vision is unaffected so the ability to orient oneself in space and to find ones way around is little changed. 46


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Diabetic retinopathy is a consequence of chronic diabetes mellitus and effectively destroys parts of the retina. The effect this has on visual capabilities depends on where on the retina the damage occurs and the rate at which it progresses.

Chapter Two: Vision

Glaucoma is shown by a progressive narrowing of the visual field. Glaucoma is due to an increase in intraocular pressure which damages the blood vessels supplying the retina. Glaucoma will continue until complete blindness occurs unless the intraocular pressure is reduced.

These changes with age can be compensated, to some extent. The limited range of focus of the elderly can be overcome by the use of lenses. The tasks they have difficulty with can be redesigned to make them visually easier, usually by increasing the luminance contrast of the task details, making the task details bigger and using more saturated colours. Lighting can also be used to compensate for aging vision. The elderly benefit more from higher illuminances than do the young, but simply providing more light may not be enough. The light has to be provided in such a way that both disability and discomfort glare are carefully controlled and veiling reflections are avoided. Where elderly people are likely to be moving from a well-lit area to a dark area a transition zone with a gradually reducing illuminance is desirable. People with low vision may or may not benefit from such changes in lighting depending on the specific cause of the low vision. However, there is one approach that is generally useful. This approach is to simplify the visual environment and to make its salient details more visible by attaching high luminance contrast to those details, and only to those details. Figure 2.20 shows an interior where this principle has been applied. Figure 2.20 Contrast in the visual environment

47


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Chapter Three: Light sources

PART 2. TECHNOLOGY Chapter 3: Light sources 3.1 Production of radiation 3.1.1 Incandescence When an object is heated to a high temperature, the atoms within the material become excited by the many interactions between them and energy is radiated in a continuous spectrum. The exact nature of the radiation produced by an idealised radiator, known as a black body, was studied by Max Planck at the end of the 19th century and he developed the following formula to predict the radiation produced c1 th = M eλ λ5 [exp(c2 / λT) –1] where:

M eλth is the spectral radiant exitance, c1 and c2 are constants, with values

of 3.742 × 10–16 W/m2 and 1.439 × 10–2 m⋅K respectively. λ is the wavelength in metres T the temperature in kelvins.

The values of the spectral radiant exitance are plotted for different temperatures in Figure 3.1.

4500 20 × 106

15 × 106 T (K) 4000

10 × 106

th

Spectral radiant excitance M eλ (W⋅m–2 per µm waveband)

Wien’s Displacement Law

λmax 5 × 106 3500

20 × 106 3000

2500 2000 500

1000

1500

Wavelength (nm)

48

Figure 3.1 Spectral power distribution of radiation according to Planck’s Law


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λmax =

c3 T

c3 has a value of 2.90 × 10–3 mK. The result of the application of this formula is that if an object is heated to a high enough temperature (in excess of 2,000 ˚C) a reasonable amount of light is produced; this provides the basic operating principle of the incandescent lamp.


The wavelength for maximum power (λmax) is inversely proportional to the temperature (T). The following formula was developed by Planck’s co-worker at the University of Berlin and is known as Wien’s Displacement Law.

In practice many materials when heated radiate energy at slightly different rates to that predicted by Planck. This property can be exploited by light source makers. For example tungsten emits about a third more energy as light than would be predicted by Planck’s formula. 3.1.2 Electric discharges An electric discharge is an electric current that flows through a gas. These discharges generally take a high voltage to initiate but once started they can carry considerable currents with very little voltage drop. A good example of such a discharge is the natural phenomenon of lightning. In an electric discharge the electric current is carried by electrons that have been removed from the gas atoms and ions that are gas atoms with one or more electrons removed. This is shown in Figure 3.2.

Electron

+ Cathode

+

+

+ Positive Ion

Current direction

Anode

Figure 3.2 Electric discharge through an ionised gas The negatively charged electrons tend to drift towards the anode whilst the positively charged ions drift towards the cathode. As the ions are several thousand times heavier than the electrons they tend to be less mobile. When an electron collides with an atom, one of three things may happen: (a) The electron rebounds with only a small change in energy – elastic collision (b) The impact excites the atom and the electron loses energy – excitation (c) The impact removes an electron from the atom – ionisation Elastic collisions just heat the gas. Excitation raises the energy state of the atom so that it may radiate light. Ionisation generates more free electrons so that the discharge is maintained. 49


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Page 64

Radiation Ion

10.43

Green 546.1

Energy (electron volts)


Ionisation

25/3/09

Blue 435.8

Violet 404.7

nm

7.73

Excited states 5.46 4.89 4.67

Ultraviolet resonance radiation 253.7 nm

Ground state

Figure 3.3 Simplified energy level and transition diagram for mercury The result of any collision between an electron and an atom is largely dependent on the energy of the electron. If the energy of the electron is less than that necessary to raise the atom to the first excited state then the collision will be elastic. The most common transition is between the ground state of the atom and the first excited state. Radiation from the atom returning to ground state tends to dominate the output of the discharge; this radiation is known as resonance radiation. In low pressure discharges, such as low pressure sodium, the light output tends to be at a series of discrete wavelengths, each corresponding to a particular energy transition in the atoms of the gas. In high pressure discharges the atoms of the gas interact with one another and this coupled with the higher electric and magnetic fields in the discharge cause the individual wavelengths found in the low pressure discharge to broaden into wider bands of radiation output. In developing lamps the selection of atoms or molecules that have energy transitions that correspond to radiation in the visible and ultra-violet is important (Figure 3.3). Starting a discharge can be difficult because if there are no ions and free electrons present, the gas will not conduct a current. Most lamps use either a high voltage pulse or heated electrodes covered in special powders to get started. The electrical properties of the discharge are unusual and in general discharges do not obey Ohm’s Law. This is because the current in a discharge is carried by electrons and ions and their number is generally a function of the current, thus at higher currents it is easier for the charge to pass through the discharge and the voltage drops. In order to maintain a steady current through a lamp most discharge lamps require control gear. 50


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Pure semi-conductors have intrinsically a very high resistivity and it is only when they are doped with other materials that it is possible to pass electricity through them. Some materials induce conduction by negatively charged carriers (n-type) and some by positively charged carriers (p-type). When charged carriers of different types recombine the energy released may be emitted as light. See section 3.3.9 for more information on light emitting diodes. Some phosphors can be excited by electrical fields (usually an alternating field) to produce light. The most common material used is zinc sulphide generally doped with another metal such as copper. The process by which the radiation is created is not fully understood. However this has not stopped the process being used to make self luminous signs. For more information on electroluminescent light sources see section 3.3.10.


3.1.3 Electroluminescence Some materials will convert electricity into light directly. Two major physical processes account for the majority of the various electroluminescence phenomena. They are the recombination of current carriers in certain semi-conductors and via the excitation of luminescent centres in certain phosphors.

3.1.4 Luminescence The term luminescence is sometimes also known as fluorescence, or photoluminescence. The process involves a material absorbing radiation and then re-emitting light. The energy may be re-radiated almost immediately or it may take several hours. There are a number of ways that the material can hold the energy and this impacts on length of the time the energy is stored and the amount of energy that is re-radiated.

a

b

c

Figure 3.4 Simplified representations of energy level schemes in luminescence In Figure 3.4 image (a) represents simple luminescence where the material absorbs the energy and the next transition is to re-radiate the energy. In (b) the some of energy in the material is lost via another process before re-radiation takes place. In (c) some of the energy is dissipated and the material falls into a state where it can not re-radiate until it is restored to the higher energy level. This process can lock energy into materials and is the basis of some ‘glow in the dark’ materials. 3.1.5 Radioluminescence This occurs in a similar manner to luminescence but the primary source of the activation energy is particles or gamma rays emitted by a decaying nucleus of a radioactive atom. 51


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3.1.6 Cathodoluminescence In cathodoluminescence the energy driving the phosphor is an electron that has been accelerated away from a cathode. This process is the means by which light is generated in a cathode ray tube. 3.1.7 Chemiluminescence Some chemical reactions can produce light directly, not via the heat the reaction creates. The process is used by some living organisms to generate light; the best known example being the glow worm. 3.1.8 Thermoluminescence This is exhibited by some materials when they are heated. The materials give out much more light than would be expected due to black body radiation. The best known practical use of the method of light production is the mantle used in some types of gas lamps.

3.2 Daylight The sun is a large cloud of high temperature hydrogen gas. It is held together by its own gravitational force. As the atoms of hydrogen are held together at such pressure and high temperature it is possible for nuclear fusion to take place and the hydrogen is converted into heavier elements, mainly helium. This process releases a lot of energy which keeps the sun hot; because the sun is so hot it radiates energy by incandescence. The sun is the biggest source of light on earth. Light from the sun not only gives us light so that we can see, it also powers the whole ecosystem on earth. Light from the sun can reach the earth in two ways: directly as sunlight, and, after it has been modified and redistributed by the atmosphere, as skylight. 3.2.1 Sunlight The key to the understanding of sunlight is knowing where the sun will be in the sky at any given time or date relative to the site in question. On any given day the sun will rise in the east. In the northern hemisphere the sun then rises through the southern sky; reaching its highest altitude at due south at solar noon and passes through the southern sky before setting in the west.

W

S

Figure 3.5 The daily sun path 52

N

E


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Summer solstice

Equinox Winter solstice


At different times of the year the sun follows different paths in the sky (Figure 3.6). The angle of inclination of the path of the sun from the perpendicular is equal to the latitude of the site.

W

S

N

E

Figure 3.6 Annual variations in the sun path To understand the reasons behind these sun paths and to be able to predict the position of the sun at any time it is necessary to consider the relative motions of the sun and the earth. The earth rotates on its axis in approximately 23 hours and 56 minutes and it orbits the sun once per year. The reason that days last approximately 24 hours is that due to its motion around the sun, the earth has to turn a little bit more than one rotation before the same point on its surface is facing the sun again. The orbit of the of the earth around the sun is shown in Figure 3.7.

23˚ 27’ March

Sun June

December

September

Figure 3.7 Orbit of the earth around the sun 53


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The tilt of the earth’s axis away from the normal to the plane of the orbit is what causes the seasonal variation in the sun path. The angle that the sun makes to the earth normal to the equator is known as the angle of declination. To be able to predict the sun’s position in the sky it is first necessary to define a system of angular co-ordinates by which the sun’s position may be described.

W

a

S

N

g

E

Figure 3.8 Angular co-ordinates used to describe the sun’s position There are formulae available to calculate the position of the sun at any time and any date, however care needs to be used in the calculations as they rely on inverse trigonometric functions and it is quite easy to confuse the results as most of the functions may take the same value for more than one angle. 3.2.2 Skylight Whilst equations mentioned in the previous section can predict the position of the sun in the sky, they tell us very little about the distribution of light throughout the sky. This is because the light from the sun is scattered by the atmosphere, and the distribution and amount of light received at ground level is dependent on atmospheric conditions. To calculate the distribution of luminance under various atmospheric conditions the standard BS EN 15469: 2004: Spatial distribution of daylight — CIE standard general sky may be used. This lists a series of 15 sky distributions and gives a formula that may be used for calculating the relative luminance distribution of the sky.

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Type Number

Description of luminance distribution

1

CIE Standard Overcast Sky, steep luminance gradation towards zenith, azimuthal uniformity

2

Overcast, with steep luminance gradation and slight brightening towards the sun

3

Overcast, moderately graded with azimuthal uniformity

4

Overcast, moderately graded and slight brightening towards the sun

5

Sky of uniform luminance

6

Partly cloudy sky, no gradation towards zenith, slight brightening towards the sun

7

Partly cloudy sky, no gradation towards zenith, brighter circumsolar region

8

Partly cloudy sky, no gradation towards zenith, distinct solar corona

9

Partly cloudy, with the obscured sun

10

Partly cloudy, with brighter circumsolar region

11

White-blue sky with distinct solar corona

12

CIE Standard Clear Sky, low luminance turbidity

13

CIE Standard Clear Sky, polluted atmosphere

14

Cloudless turbid sky with broad solar corona

15

White-blue turbid sky with broad solar corona


Table 3.1 CIE standard sky types

The standard helps with the distribution of daylight but it gives no information on the actual amount of daylight available at any particular time. There are a number of stations that record the global and diffuse (not including light direct from the sun) horizontal plane illuminance values on an unobstructed site and these data can be used to predict daylight availability. Whilst data are logged every five minutes or so at most measuring stations it is usually presented as a chart showing monthly averages of hourly values. Figure 3.9 shows a typical chart giving data on daylight availability.

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24 1 klx = 1000 lux

5 klx 18

10 klx

20 klx

12 35 klx

Time of day (GMT)

6

Time of year

0 Winter

Spring

Summer

Autumn

Winter

Figure 3.9 A typical daylight availability chart The colour of the light from the sun and sky depends not only on the colour of the light from the sun but also on the way that light is absorbed and scattered by the atmosphere.

300

350

400

450

500

550

600

650

700

750

800

850

Wavelength (nm)

Figure 3.10 The spectrum of daylight with a colour temperature of 6500 K (from CIE Publication 15.2) Figure 3.10 shows the standardised spectrum of daylight from the CIE Publication 15.2 which gives formulae for the calculation of daylight spectra of different colour temperatures. In practice the sky condition is constantly changing so it is difficult to give exact values of the colour of the sky, however, Table 3.2 lists approximate values of correlated colour temperature for various sky conditions. 56


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Table 3.2 Correlated colour temperatures of the sky Sky condition

CCT (K)

Bright midday sun

5,200

Lightly overcast sky

6,000

Heavily overcast sky

6,500

Hazy sky

8,000

Deep blue clear sky

20,000

3.3 Electric light 3.3.1 Incandescent The incandescent lamp is operated by heating a filament in the lamp to a high temperature, so that it emits light. The basic principle of the lamp may be simple but the technology required to maintain a filament at a high enough temperature to give significant amount of light whilst ensuring the lamp has a reasonable life is highly complex. The basic and most popular form of the lamp is the General Lighting Service (GLS) lamp.

Glass bulb

Tungsten filament

Lead wire

Molybdenum filament supports

Dumet wire

Glass pinch

Balotini filled fuse sleeve

Exhaust tube

Fuse

Cement

Lead wire

Cap

Figure 3.11 The construction of a GLS incandescent lamp

Contacts

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The filament design is critical in setting up the operating characteristics of the lamp. The length of the filament wire is largely determined by the supply voltage, whilst the thickness of the wire is determined by the operating current of the lamp. The filament is coiled to reduce heat convection to the filling gas. There are various forms of filament coiling with the coiled coil being one of the most common (see Figure 3.12).

Figure 3.12 A coiled coil filament The filament must be robust enough to withstand the shocks and vibration that the lamp receives during its life and at the same time be rigid enough so that it does not droop. Support wires can help prevent the filament from drooping but they conduct heat away from the filament and thus reduce the efficiency of the lamp. Therefore normal service lamps are made with hard brittle filaments that only need a few support wires. Lamps for rough service are made with a softer more malleable filament but have several support wires. The bulb is generally made of a soft soda glass and its size is set so that it does not get too hot and the tungsten that evaporates from the filament during the life of the lamp does not blacken the bulb too much. The gas filling of the lamp is present to reduce the rate at which the tungsten evaporates and thus make the lamp last longer. To minimise the heat losses from the filament noble gasses are used as the primary fill gases. Most lamps have argon based filling but some high performance lamps use krypton. In addition to the noble gas filling most mains voltage lamps have a small percentage of nitrogen added to the filling to help suppress arcing at the end of life. There are many variations on this basic lamp type. They are designed to run on voltages between 1.5 and 415 volts at wattages between 1 and 1,000 watts. There is also a wide variety of bulb shapes including lamps with built in reflectors.

Figure 3.13 Forms of incandescent lamp 58


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Lamp wall temperature 250 ˚C minimum


3.3.2 Tungsten halogen The applications of conventional incandescent lamps are limited by their physical size and luminous efficiency. Raising the filament temperature to increase the luminous output has the effect of increasing the rate of blackening of the glass envelope, blackening which is a result of the evaporation of tungsten from the filament. By adding a halogen to the gas fill a chemical transport cycle involving the reaction of tungsten reduces the amount of blackening of the envelope. It is then possible to reduce the size of lamp, increase the pressure of the filling gas and thereby limit the loss of the tungsten from the filament.

Ceramic

Fil seal 350 ˚C maximum

Filament support

Zone 1

Zone 2

Zone 3

Tungsten filament

Figure 3.14 A representation of the tungsten halogen cycle The chemistry of the tungsten halogen cycle is highly complex. However the key stages are: the halogen combining with the tungsten on the wall of the lamp (zone 3) the tungsten halide vapour mixing with the fill gas of the lamp (zone 2) the tungsten halide dissociating close to the filament of the lamp, leaving the halogen free to migrate though the fill gas to the lamp wall again and the tungsten being deposited on the filament (zone 1). To enable an efficient cycle it is necessary for the wall of the lamp to run at a temperature above 250 ˚C; this means that the bulb has to be made from quartz or hard glass. 59


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Chapter Three: Light sources Figure 3.15 Forms of tungsten halogen lamps Tungsten halogen lamps are more efficient and have longer lives compared with standard tungsten lamps. Also they are more compact than standard lamps. However they are more expensive as it is hard to make the quartz outer bulb and it is harder to introduce the gas fill into the lamp due to the high filling pressure. 3.3.3 Fluorescent Fluorescent lamps are the most commonly used form of discharge lamp. They come in a variety of shapes and sizes and are available in a wide range of colours. The original form of the lamp was a long straight tube. New forms of the lamp known as compact fluorescent lamps have been developed where the lamp tube is bent or folded to produce a smaller light source. Fluorescent lamps work by generating ultraviolet radiation in a discharge in low pressure mercury vapour. This is then converted into visible light by a phosphor coating on the inside of the tube. The electric current supplied to the discharge has to be limited by control gear to maintain stable operation of the lamp. Traditionally this is done with magnetic chokes but most circuits now use high frequency electronic control gear. Electronic control gear has a number of advantages: first, driving the lamp at high frequency maintains the ions in the gas and thus makes the lamp run more efficiently. Secondly, it reduces the amount of flicker in the lamp and, finally, electronic gear consumes less power than a magnetic choke.

Ultraviolet radiation

Visible radiation

Fluorescent powder

Mercury atom

Figure 3.16 Working principle of a fluorescent lamp 60

Electrons

Electrode


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The tube: this is made from a glass with a high iron content so that any short wave UV radiation that gets through the phosphor coating is absorbed by the glass The phosphor coating: there are a wide variety of phosphors available. Each produces a different spectrum of light and by careful blending of the various phosphors lamp makers can tailor a wide range of lamp colours. The lumen output of the lamp also depends on the choice of phosphor mix. It is also important to control the particle size of the phosphor powders and the thickness of the coating. There are three main types of phosphor mixes currently used in fluorescent lamps:


The lamps are made from the following main components.

Halophosphates: this range of phosphors tend to emit light in a relatively wide band and it is normal to use only one phosphor of this type at any one time. Halophosphates are only reasonably efficient as phosphors and generally have poor colour rendering. Tri-phosphors: are mixes of three narrow band phosphors. They generally achieve CIE general colour rendering indices greater than 80 and have a high efficacy and good lumen maintenance. Multi-phosphors: are mixes of a number, usually five, phosphors. These mixes usually give a CIE general colour rending index higher than 90, however the efficacy is normally lower than a tri-phosphor mix. The electrodes: generally coils of tungsten wire that are coated in a material that when heated will give off electrons readily. To start the lamp a current is passed through the coil to heat the emissive coating. However, once the lamp is running the ionised gas atoms hitting the electrode provide enough energy to keep the cathode hot. The electrodes are generally surrounded by a shield as some of the material used to coat the electrode evaporates during the life of the lamp. If the shield was not there the material would be deposited on the wall of the lamp causing a black ring and reducing the light output. The gas fill: the lamp fill is made up of two components; a noble gas mixture and the mercury vapour. The noble gas in the lamp has three main functions. First, it reduces the mobility of the free electrons in the lamp and by careful control of the pressure; it optimises the number of electrons with the right amount of energy to excite the mercury atoms. Secondly, the gas reduces the rate at which the coatings on the electrodes evaporate and thus prolongs the life of the lamp. Finally it lowers the breakdown voltage of the lamp and thus makes starting easier. Most lamps use either a mixture of argon and krypton or neon and argon. The use of the heaver krypton gas makes the lamps slightly more efficient but it is significantly more expensive. The vapour pressure of mercury in the lamp is significantly lower than the pressure of the noble gas mixture and it is controlled by the temperature of the coolest part of the lamp. At the cold spot of the lamp the mercury condenses to form liquid mercury. At this point the liquid and gaseous mercury are in equilibrium and the vapour pressure is determined by the temperature. As the vapour pressure of mercury is critical to the operation of the lamp, the light output of the lamp varies with temperature. Most lamps are optimised to run in an environment with an ambient temperature of 25 ˚C. 61


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100

Relative luminous flux (%)


However, some of the new types of lamp are set up to run in an ambient temperature of 35 ˚C. In some lamp types the mercury dose is mixed with other metals such as bismuth or indium. These metals form an amalgam with the mercury and this reduces the vapour pressure of the mercury at any given temperature. This enables the lamp to operate at higher temperatures but has the drawback that the lamp takes a long time to reach full output.

90

Amalgam lamps

80 Standard lamps

70

60

50 10

20

30

40

50

60

70

80

Ambient temperature (˚C )

Figure 3.17 Luminous flux as a function of temperature for standard and amalgam fluorescent lamps. 100 percent corresponds to the maximum luminous flux. There are two main types of fluorescent lamps; the traditional linear lamps and the compact fluorescent lamps. Linear lamps come in variety of diameters and lengths. The main diameters of lamp are the T12 lamps which are 38 mm in diameter, T8 lamps which are 25 mm and the T5 types which are 16 mm. All of these families of lamps come in a variety of lengths and wattages. Linear fluorescent lamps are generally efficient light sources with some of the lamps approaching 100 lumens per watt. They also come in a wide variety of colours with a range of colour rendering properties. Table 3.3 gives a summary of the main lamp colours.

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Colour appearance

Triphosphor colour rendering group 1b

Multi-phosphor colour rendering group 1a

Northlight (6000–6500 K)

Colour 865 Lumilux Plus ECO 860 Luxline Plus ECO 860 Polylux XLR 860

Colour 965

Daylight (5000–5500 K)

Colour 950 Lumilux De Luxe 950 Colour 840 Lumilux Plus ECO 840 Luxline Plus ECO 840 Polylux XLR 840

Cool White (4000 K) Intermediate (3500 K) White


Warm White (3000 K)


Very Warm (2700 K)


Colour 940 Lumilux De Luxe 940 Polylux Deluxe 940


Table 3.3 Colours of fluorescent lamps

Colour 930 Lumilux De Luxe 930 Polylux Deluxe 930

There is a large variety of compact fluorescent lamp types. Figure 3.18 below illustrates the range.

Quad-lamp

Twin-tube

Triple-twin

Circline

F-lamp

Oct lamp

2-D

Helical

Figure 3.18 Types of compact fluorescent lamp 63


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In general compact fluorescent lamps are less efficient than linear lamps, but because of their small size, they are suited to many applications where a smaller lamp is needed. Some of the lamps have the control gear built into them and can be retro-fitted into GLS lamp sockets. 3.3.4 High pressure mercury In this type of lamp a discharge takes place in a quartz discharge tube containing mercury vapour at high pressure (2 to 10 atmospheres). Some of the radiation from the discharge occurs in the visible spectrum but part of the radiation is emitted in the ultraviolet. The outer bulb of the lamp is coated internally with a phosphor that converts this UV radiation into light. The general construction of the lamp is shown in Fgure 3.19 below.

Support for discharge tube

Discharge tube

Outer bulb

Main electrode

Auxiliary electrode

Resistor

Lamp cap

Figure 3.19 Construction of a high pressure mercury lamp 64


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First ignition; when power is first applied to the lamp the voltage is not high enough to strike an arc between the two main electrodes. Ignition is achieved using an auxiliary electrode placed close to one of the main electrodes. The auxiliary electrode is connected via a resistor (typically 25,000 ohms). This limits the size of the current in the arc formed by the auxiliary electrode so the voltage across the starting arc is reduced as the current increases. This means that the ions in the arc are drawn towards the main electrode at the other end of the lamp and these ions allow the main arc to start. The next stage is the run-up. Once the arc has started between the main electrodes very little light is given out because the mercury pressure is too low as the tube is cool. The arc in the gas slowly warms up the tube and so the mercury vapour pressure rises and the light output increases. Typically it takes about 4 minutes for the lamp to achieve 80% of the final light output.


The operation of the lamp is quite complex and needs to be considered in three phases: ignition, run-up and stable running.

When the lamp reaches stable running and normal operating pressure all the mercury in the lamp is in the vapour phase. This means that the vapour pressure of the mercury is controlled by the amount of mercury put into the lamp rather than the temperature of the lamp. High pressure mercury lamps are made from the following main components. The discharge tube is generally made of quartz and has the main electrodes and the starting electrode sealed into it. The main electrodes are usually made of tungsten rods which have coil of tungsten wire wrapped round them. This coil is usually impregnated with emitter material similar to that used in fluorescent lamps. The auxiliary electrode is generally wire made out of molybdenum or tungsten. The fill gas in the discharge tube is commonly argon and a very carefully controlled dose of mercury is also added. The discharge tube is fitted into a support frame and the whole assembly is sealed into the outer bulb. The gas fill in the outer bulb is usually nitrogen or argon or a mixture of the two. The pressure of this fill gas is controlled to ensure that the arc tube operating temperature is correct. The outer bulb is made out of a soft soda lime glass for low wattage lamps (up to 125 W). High power lamps use a borosilicate glass outer. There are two common shapes for the outer bulb the ovoid or isothermal bulb, and the reflector bulb. Figure 3.20 show these two shapes.

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Chapter Three: Light sources Figure 3.20 Forms of high pressure mercury lamps The performance of these lamps is not considered to be very good nowadays. Their efficiency is around 40 lumens per watt. Their CIE general colour rendering index is between 40 and 50 and they have a very long life but, because of poor lumen maintenance, it is generally recommended that the lamps are changed after 8,000 to 10,000 hours of use. Because of their poor performance and the fact that better lamp types are available for almost all of the applications these lamps are being phased out. 3.3.5 Metal halide Metal halide lamps were developed as a way of improving the performance of high pressure mercury lamps in terms of their colour appearance and light output. They work by introducing the salts of other metals into the arc tube. As each element has its own characteristic spectral line, by adding a mixture of different elements into the discharge it is possible to create a light source with good colour rendering in a variety of colours. There are a lot of problems with introducing new elements into a discharge. First, the element must be volatile and secondly it should not chemically attack the arc tube. To avoid these problems it has become common practice to introduce metals into the lamp as metal halides. Metal halides are generally more volatile than the metals themselves and the metal halides do not attack the arc tube. The metal halide compound breaks up into the metal and halogen ions at the high temperatures in the centre of the discharge and reforms at the lower temperatures near the wall of the tube. Many different combinations of elements have been used to make metal halide lamps, Figure 3.21 lists some of the more common combinations of elements together with the spectral output they create. 66


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Li ln

400

500

600

Tl

Relative spectral power


ln

300

Dy, (Tm, Ho, Tl) T = 5600 K Ra = 86

ln, Ti, Na T = 4500 K Ra = 61

Na

Tl

Dy

300

700

400

500

600

Three colour (indium, thallium, sodium) metal halide lamp. The lithium line is due to impurities in quartz of the tube wall.

Dysprosium lamp with thulium, holmium and thallium additives.

Na

Sc Hg Sc Sc Sc

400

500

Tm, (Dy, Ho, Tl, Na) T = 4300 K Ra = 87



Sc, Na T = 3800 K Ra = 56

300

700

Wavelength (nm)

Wavelength (nm)

Sc Hg


Figure 3.21 Relative spectral power distributions of metal halide lamps

Na Tl

Dy Li

Li

600

700

Wavelength (nm)

300

400

500

600

700

Wavelength (nm)

Scandium lamp with sodium additive.

Thulium lamp with a range of additives.


SnI2/SnCl2(Na) T = 3000 K Ra = 74

Na Hg

300

400

500

Li

600

700

Wavelength (nm)

Tin halide lamp with sodium additive. 67


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Because of the differing lamp chemistry there is a wide range of lamps that vary in terms of their efficacy, colour and electrical properties. One of the main problems with metal halide lamps that use quartz discharge tubes is colour stability. As the colour of the light output is a function of the ions present in the discharge tube, any changes to the gas composition due to some metals being absorbed by the quartz tube or changes in temperature in the tube can cause significant colour shifts. These colour shifts are particularly a problem for the lower wattage lamps. This problem has largely been solved by the introduction of a new material for the discharge tube. Ceramic or sintered alumina tubes are much more resistant to chemical attack than quartz tubes and can operate at higher temperatures. Lamps with these tubes are now very popular for low wattage (up to 150 W) metal halide lamps. The construction of a metal halide lamp is similar to that of a high pressure mercury lamp. The key differences are that it is unusual to use an auxiliary electrode in the lamp, lamp ignition being achieved using a high voltage pulse from the control gear. Also, there is no phosphor coating on the outer bulb. There are a wide variety of shapes of lamp. Figure 3.22 shows some of them.

Figure 3.22 Forms of metal halide lamps 68


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There are many points to watch for when selecting metal halide lamps as there are problems associated with some lamp types shattering at the end of life or giving off UV radiation. It is important with these lamps to ensure that the luminaire in which they are used is suitable. 3.3.6 Low pressure sodium Low pressure sodium lamps are similar in many ways to fluorescent lamps as they are both low pressure discharge lamps. All the differences in characteristics stem from the use of sodium in the discharge tube rather than mercury. The key differences are the need to run the lamp hotter to maintain the vapour pressure of sodium, the need to contain the very reactive sodium metal; and the fact that sodium emits its light in the visible rather than the UV frequency range, so there is no need for a phosphor layer.


There is a vast range of metal halide lamps ranging in power between 20 W to over 2 kW. The lamps have a CIE general colour rendering index between 60 and 93 and they have high luminous efficacies, in the range 60 to 98 lumens per watt. For these reasons, this lamp type has many applications where a compact light source with good colour rendering is needed.

There used to be a range of designs for sodium lamps but currently the U-tube lamp is by far the most common type. A typical lamp of this design is shown in Figure 3.23.

Bend Isolation

Discharge tube

Figure 3.23 The construction of a low pressure sodium lamp

Dimple filled with sodium

Outer bulb

Electrode

Getter

Lamp cap

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The main components of a low pressure sodium lamp are as follows. The arc tube; this is made of normal soda lime glass with a coating on the inside of a special sodium resistant aluminoborate glass. Making this ‘ply-glass’ tube is technically difficult as great care is needed to ensure that there are no thermal stresses in the final tube that might lead to cracking during the life of the lamp. Some lamp types have dimples in the side of them to act as reservoirs of sodium. The gas fill of the tube is neon with about 1% of argon at a pressure of approximately 1000 Pa. This mixture is used as it has a much lower breakdown voltage than neon on its own and thus makes starting the lamp much easier. Sodium metal is also put into the tube. The sodium vapour pressure in the tube when it is at its operating temperature of 260 ˚C is about 0.7 Pa. The outer bulb is of soda lime glass, the inside is coated with a layer of indium oxide. This layer reflects the bulk of the infrared radiation from the arc tube and thus keeps it warm. Between the outer bulb and the arc tube the gas pressure is very low, below 0.01 Pa. To maintain the vacuum a barium getter is used. A relatively high voltage is needed to start an arc in the neon fill gas. The arc then slowly warms up the lamp and the discharge tube and the vapour pressure of the sodium starts to rise until the lamp reaches thermal stability after about 15 minutes. One of the curious properties of the sodium atom is the predominance of the energy transitions associated with the two spectral lines at 589 nm and 589.6 nm. This means that virtually all the visible radiation from the lamp is given off in this very narrow band. However, sodium atoms will also re-absorb and re-emit the radiation very readily; this means that nearly all the light emerging from a low pressure sodium lamp has come from close to the arc tube wall. The light from a low pressure sodium lamp is a wavelength close to the peak of the photopic sensitivity curve, and as the lamp is relatively efficient at converting electricity into visible radiation, the lamp is one of the most efficient light sources in terms of lumens per watt. The best of the range can achieve in excess of 180 lumens per watt. The problems with the lamp are large size, long run-up time and monochromatic light that does not render colours. The lamp has been mainly used for street lighting but recently the importance of some colour rendering on roads has been recognised and the lamp is rarely used in new installations. 3.3.7 High pressure sodium The high pressure sodium lamp generates light in a discharge through sodium vapour at high pressure. As the vapour pressure of sodium in a lamp rises the spectrum at first broadens and then it splits in two with a gap appearing at about 586 nm. Figure 3.24 shows the spectra from sodium lamps with different vapour pressures.

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400

500

600

T = 2000 K Ra = 23



T = 1700 K

700

400

Wavelength (nm)

600

700

T = 2500 K Ra = 80



T = 2150 K Ra = 40

500

600

Standard high pressure sodium lamp; sodium vapour pressure 10 kPa

Low pressure sodium lamp; sodium vapour pressure 0.7 Pa

400

500

Wavelength (nm)


Figure 3.24 The spectra of sodium lamps with different vapour pressures of sodium

700

400

Wavelength (nm)

500

600

700

Wavelength (nm)

Colour improved high pressure sodium lamp; sodium vapour pressure 40 kPa

White high pressure sodium lamp; sodium vapour pressure 95 kPa

As the vapour pressure rises the colour rendering of the lamp increases. However, this is at the expense of efficacy in terms of lumens per watt. Figure 3.25 shows the construction of a high pressure sodium lamp.

Top support

Discharge tube of sintered alumina Hellical support wire

Outer bulb

Figure 3.25 The construction of a high pressure sodium lamp

Electrode Flexible connection to allow for thermal expansion Getter

71


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The main components used in the construction of the lamp are as follows. The arc tube is made of polycrystalline alumina (PCA). This material is ceramic rather than a glass, this makes it very hard to work as it is not possible to soften it and it is hard to cut. PCA is used because it is resistant to chemical attack by hot sodium, it is stable at high temperatures and it is transparent. Because it is not possible to work the PCA the tube is cut to length and fitted with end caps, Figure 3.26 shows some of the designs used for closing the ends of the discharge tube.

Monolithic arc tube

Alumina disc

Niobium support wire

Seal glass

Alumina disc Seal glass

Niobium tube

Niobium wire

b

a

Metallic braze

Titanium braze

Alumina bushing

Seal glass

Niobium tube

Niobium cap

c

Niobium exhaust tube

d

Figure 3.26 Types of arc tube seal in high pressure sodium lamps The use of niobium metal as part of the end cap assembly is common as it expands with temperature at the same rate as the PCA tube and thus does not cause stresses in the lamp as it heats up. The electrodes in the lamp are made from tungsten rods with tungsten wire wound around them, with emitter material made from oxides of metals such as barium, calcium and yttrium. 72


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The fill gas in the tube is usually xenon at a cold pressure of 3 kPa, which corresponds to an operating pressure of about 20 kPa. A higher xenon pressure would improve lamp efficacy but make starting harder as it needs a high voltage to break down. Some types of lamp use high pressure xenon and use an ignition wire held close to the tube to help starting. There are also some lamps that use argon as a fill gas; they are much easier to start but are less efficient in term of lumens per watt. A dose of sodium mercury amalgam is used in most high pressure sodium lamps. Mercury is used because its vapour acts as a buffer gas and helps improve the efficiency of the lamp. However, the mercury contributes very little to the output spectrum of the lamp. Some lamps are now made without mercury in them. The absence of mercury makes the disposal of the lamp at the end of life easier as there are no environmentally damaging substances in the lamp. The metal dose in the lamp is never fully vapourised and so the pressure of the sodium and mercury vapours in the lamp is dependent on the temperature of the coolest part of the discharge tube. This makes the output of the lamp temperature dependent and can also give problems associated with the voltage across the tube rising if the lamp gets too hot. The cold spot on most discharge tubes is in the area behind the electrode. As this area of the tube is blackened through the life of the lamp, the cold spot temperature tends to rise through life. This can give rise to problems in old lamps where the pressure in the discharge tube rises to the point where it is no longer possible for the voltage available from the supply to sustain an arc in the lamp. The discharge tube is mounted into a support frame and sealed into an outer bulb. The outer bulb is generally made of a borosilicate glass and may be in a number of different shapes, Figure 3.27 shows some of the more common shapes.

Tubular outer bulb

Linear double ended in a quartz outer bulb

Ellipsoidal or isothermal coated outer bulb

Reflector bulb

Figure 3.27 Outer bulb shapes for high pressure sodium lamps 73


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The high pressure sodium lamp is an efficient source of light (efficacies up to 142 lumens per watt), it has a long life with reasonable lumen maintenance and whilst the colour rendering on the standard lamp is poor it is acceptable for a number of applications. The white high pressure sodium lamp has a spectrum with minimal output in the yellow. This has the property of making a large number of colours appear more vivid and so this lamp has a number of applications in retail lighting. 3.3.8 Induction Induction lamps are essentially gas discharge lamps that do not have electrodes. Instead the electric field in the lamp is induced by an induction coil that is operating at high frequency. The only types of induction lamps that are currently in production are based on fluorescent lamp technology. Figure 3.28 shows the layout of a cavity type lamp. Phosphor coating Electron/ion plasma

Figure 3.28 Construction of a cavity type induction lamp

Plastic housing Induction coil

Electronics

The lamp consists of a glass bottle with a cavity in it into which the induction coil is placed. The glass vessel has a gas filling similar to a conventional fluorescent lamp and the phosphor coating on the inside of the lamp is also similar. The induction coil in the centre of the lamp is fed from a high frequency generator. An alternative architecture for this type of lamp is to have the induction coil wrapped around a toroidal lamp. Figure 3.29 shows a lamp of this type.

Figure 3.29 An external coil induction lamp

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3.3.9 Light emitting diodes The basic operating principle behind light emitting diodes (LEDs) is covered in section 3.1.3. LEDs are available in a wide variety of sizes, colours and power ratings and development is proceeding at a rapid rate (see the Lighting Industry Federation LED Guide 2005 and the EBV Electronik and Philipslumileds web sites). Whilst LEDs come in a variety of styles, Figure 3.30 illustrates two common forms.


Induction lamps have many of the same properties as fluorescent lamps. They are, however, slightly less efficient. The big advantage with this type of lamp is long life. This is because there are no electrodes to fail and the inside of lamp does not get coated with material that has been vapourised away from the electrodes. A number of lamps of this type have rated lives of 100,000 hours. These lamps are more expensive than conventional fluorescent lamps so they tend to be used in places where it is difficult to change lamps and thus long life is an important requirement.

The main components of a LED are as follows. The chip of semiconductor material in the centre of the lamp may be made of a wide variety of materials. Differing materials result in a different colour of light being produced Table 3.4 lists some of the more commonly used materials. Table 3.4 Materials used in LEDs and the radiation produced Materials

Radiation

Aluminum gallium arsenide (AlGaAs)

Red and infrared

Aluminum gallium phosphide (AlGaP)

Green

Aluminum gallium indium phosphide (AlGaInP)

Orange-red, orange, yellow, and green

Gallium arsenide phosphide (GaAsP)

Red, orange-red, orange, and yellow

Gallium phosphide (GaP)

Red, yellow and green

Gallium nitride (GaN)

Green, pure green (or emerald green), and blue

Indium gallium nitride (InGaN)

Near ultraviolet, green, bluish-green and blue

Zinc selenide (ZnSe)

Blue

Aluminum nitride (AlN), Aluminum gallium nitride (AlGaN)

Near to far ultraviolet

Diamond (C)

Ultraviolet

The chip is mounted onto one of the lead in wires. In high power LEDs the mounting is designed in such a way as to conduct heat away from the chip. The other lead wire is bonded to the chip generally connecting to a very small area close to the actual semi conductor junction. The whole device is then potted in a plastic resin, usually epoxy. 75


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Light emitted forward

Light emitted forward

LED Chip Epoxy housing

Plastic lens Reflector Silicon encapsulation PC board

Cathode lead

InGan LED chip Cathode lead

Anode lead

Solder connection

Gold wire Heat slug

Reflector cup

Figure 3.30 The construction of low power (left) and high power (right) LEDs LEDs generally have a long life and may last up to 100,000 hours. LEDs generally emit light in a relatively narrow band so that most LEDs produce light that is a saturated colour. It is possible to make white LEDs by using a blue or ultraviolet chip and putting a phosphor coat round it. White can also be achieved by combining a mixture of red, green and blue chips. LEDs have a lot of applications associated with signals and signage. The use of saturated colours in these applications is a real bonus. This coupled with the ease of producing light in a number of small units means that LEDs are replacing a number of other light sources in these areas. It is also possible to make lamps that are a cluster of LEDs of different colours. By controlling the outputs of the different colours it is possible to make a lamp that can produce light in a wide variety of colours. At the time of writing, white LEDs are making fast technical progress but have not proved to have that many applications in the area of general lighting as the lumen packages tend to be small and their efficacy does not compare favourably with other sources such as fluorescent lamps. 3.3.10 Electroluminescent The basic principles of electroluminescent (EL) light sources are discussed in section 3.1.3. Generally the light sources are made up as panels with a construction similar to that shown in Figure 3.31.

Transparent medium Conducting layer S

Phosphor plus phosphor embedding layer Conductive material

Figure 3.31 A section through an electroluminescent panel

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The lower conductor carries one side of the electrical supply into the light source. In older types of panel this conductor may have been a sheet of metal, but in the newer flexible panels it is generally some type of foil. The phosphor layer contains the phosphor used to generate the light together with a medium, usually some form of plastic resin, used to keep the grains of phosphor apart from one another. The top conductor is a made of a transparent material that conducts electricity to the top surface of the phosphor layer. The top layer of the device is a transparent medium. In older devices this layer is usually made of glass, but in more modern units it is likely to be a flexible transparent film.


The EL panel is made up of the following components.

EL panels are not a particularly efficient light source. Typically they have efficacies of a few lumens per watt. The light output of an EL panel is not that great, typically less than 300 lumens per square metre. There are many applications for EL panels as it is relatively easy to cut them to shape and size so they can be used for signage and to backlight displays in electronic equipment.

3.4 Electric light source characteristics There are a number of key properties of lamps that need to be considered when choosing which lamp is right for a particular application. The following sections list these properties. 3.4.1 Luminous flux In any lighting application the amount of light that is needed is a key decision that has to be made. From this it is then possible to work out how many lamps of given rating are needed. There are lamps with lumen outputs less than 1 lumen through to lamps with outputs in excess of 200,000 lumens. In most applications, it is the average maintained illuminance that is important so it is important to consider the lumen maintenance through life at the same time as the initial luminous flux. 3.4.2 Power demand It is important in any lighting scheme to know what the total power demand is going to be so that the electrical infrastructure can be correctly designed. The power consumed by the lamp is important. However with many lamp types it is important also to consider the impact of the control gear as well. In most cases it will be the total circuit watts that is important rather than the lamp wattage. One further complication with some lamp types is that the voltage and current waveforms are not exactly in phase with one another. Thus the volts multiplied by the amps in the circuit may be higher than the watts. The power factor of the circuit is defined by the following equation:

power factor

=

watts volts × amps

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Most high wattage lamp circuits are designed to have a power factor greater than 0.85. The other factor that may affect the sizing of the cables that supply a lighting installation is the current required during the run-up of the lamps. With some types of lamp this can be over double the nominal running current. When using lighting controls the power demand is more difficult to predict as the power consumed may be reduced at times when full output is not required from the lamp. 3.4.3 Luminous efficacy Luminous efficacy is usually expressed in terms of lumens per watt. Many lamp manufacturers produce lumens per watt figures for their lamps. However, for discharge lamps and other lamps requiring some form of control gear, these figures may be misleading as they refer to the power consumed in the lamp only and do not consider the power lost in the control gear. All the values quoted in this chapter for efficacy are based on total circuit watts. Efficacy is a primary concern when selecting a lamp. In general, if a range of lamps suitable for a particular installation then it is the most efficient that should be used. 3.4.4 Lumen maintenance The light output of most lamps decreases as the lamps get older. With some relatively short life lamps this is not a problem as they fail before the light output has fallen significantly. See Section 21.7.1 for further details of the lamp lumen maintenance factor (LLMF). 3.4.5 Life It is normal when considering the life of a lamp to talk about the percentage of lamps that will survive after a certain number of hours of operation. This value is known as the lamp survival factor (LSF). See Section 21.7.2 for further details. Other factors in a particular installation may affect the life of the lamp used. These factors include the switching frequency, the supply voltage, the ambient temperature and presence of vibration. It is often the case that the combined effect of the number of lamp failures coupled with the reduced lumen output of the lamps makes it necessary to replace the lamps in an installation. Sometimes lamp makers quote an economic service life for lamps, this generally is the point where the LSF multiplied by the LLMF falls below 0.7. 3.4.6 Colour properties The colour of the light produced by a lamp is generally described by two parameters; the correlated colour temperature and the CIE general colour rendering index. These two terms are described in Sections 1.4.3 and 1.4.4 respectively For most applications there is a minimum requirement for the colour rendering properties of the lamps used and the correlated colour temperature of the source is generally chosen for the atmosphere that the lighting is designed to produce. 3.4.7 Run-up time When a lamp is switched on it takes a certain amount of time to reach full light output. The usual measure used to assess run-up time is the time that it takes for a lamp to reach 80% of its full output.

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3.4.8 Restrike time When some gas discharge lamps go out due to an interruption in the mains supply it is not possible to restart them until the lamp has cooled down. This may take several minutes. The use of lamps with a long restrike time may cause problems in some installations due to the possibility of a small power outage causing a long blackout. 3.4.9 Other factors There are also many other factors that impact upon the use of lamps in a particular application. These factors include the following.


For a GLS lamp this might be a fraction of a second, while for low pressure sodium this could be as much as 20 minutes. For some applications such as road lighting the run-up time is not important. However, for occasionally used rooms in a home it is very important.

Lamp size: some lamps are too large for certain applications, whilst some small lamps may produce too high a luminance for others. Burning position: not all lamps may be used in all orientations, for some discharge lamps, lamp manufacturers produce diagrams similar to Figure 3.32 to show which burning positions are permitted. The figure shows that the lamp in question must only be used in the horizontal position ± 20˚.

Figure 3.32 A typical restricted burning position symbol Dimming: it is not possible to dim all lamp types and some types may be only dimmed down to given percentage of their output. Dimming for some lamps may require the use of special control gear. Ambient temperature: not all lamps will run at a given temperature. For example some compact fluorescent lamps are not suitable for outdoor use as they will not start if they are too cold. Disposal of lamps: lamps may contain hazardous substances such as lead, sodium and mercury. This may mean with particular lamps particular procedures have to be followed when disposing of the lamps. Under the WEEE Directive of the European Commission it is the responsibility of the lamp manufacturer to provide the means of recycling used lamps. See http://www.recolite.co.uk for more information about the recycling of lamps in the UK 3.4.10 Summary of lamp characteristics Table 3.5 gives a summary of the key characteristics of the main lamp families. 79

80

40–50,000

TH

650–6200

120–8850

T8

T5

100–1500

CFLi (Integral control gear)

2000–58,500

5,200–200,000

1,600–26,000

Quartz tube

Ceramic Tube

Metal halide lamps

MBF/HPL

High pressure mercury

250–9000

CFLni (Non integral control gear)

20–250

85–2050

60–1040

5–30

8–120

6–120

65–97

60–98

33–57

20–50

Yes

Yes

Yes

No

Yes

Yes

20–93 (6)

30–70

Yes

3000–4400

3000–6000

3200–3900

2700

2700–6500

2700–17000

2700–17000

3000–6500

2700–3200

No (2)

Yes

2500–2700

Colour temp (K)

No

Control gear

50–96

50–80

15–25

8–14

Efficacy (lm/W)

(3)

78–93

60–90

2 min

1–8 min

4 min

60 sec

> 80 40–50

15–90 sec

30 sec

30 sec

30 sec

Instant

Instant

Run-up time

85–90

82–95

50–98

50 – 90

100

100

Colour rendering (Ra)

Limited

No

No

(7)

Some types to 20%

Some types to 5%

Easy to 2%

Easy to 2%

Limited to 25%

Easy to 0%

Easy to 0%

Dimming

(5)

(5)

6,000–10,000

2,000 – 7000

8,000–10,000

5,000–15,000

Up to 15,000 (5)

8,000–19,000

8,000–17,000

8,000–12,000

1,500–5,000

1,000

Life (h) (1)

The lamp range is increasing rapidly

There are some higher power lamps available for special applications such as cold stores

Large variety of shapes and sizes of lamp

Comments

10:04

13–70

25–140

4–2000

1–1000

Power range (W)

25/3/09

Compact (CFL)

1000–10,500

T12 (4)

Fluorescent

5–12,000

Output range (lm)

GLS

Incandescent

Lamp name

Chapter Three: Light sources Table 3.5 Summary of lamp characteristics

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Output range (lm)

1,800–32,000

1,800–5,000

White SON

1–5

30–100

47–80

40–44

75–86

Yes

Yes

Yes

Yes

Yes

Yes

Control gear

2,685–6500

2,550–4,000

2,500

2,150

1,900–2,100

N/A

Colour temp (K)

40–85

80

83

65

19–25

N/A

Colour rendering (Ra)

Instant

Easy to 0%

15,000–60,000(9)

60,000+

6,000–9,000

No

2 min

No

10,000–14,000

Limited to 25%

5 min

1 min

10,000–20,000

15,000–20,000

Life (h) (1)

Limited to 25%

No

Dimming

3-7 min

10-20 min

Run-up time

The range of LEDs is increasing rapidly

Good lumen maintenance, but power consumption goes up through life

Comments

1 2 3 4 5 6


Economic lamp life may be limited by lumen depreciation. A lot of TH types are designed to run on low voltages and thus need a transformer or other device to supply the necessary voltage. Some lamps with dichroic reflectors have part of the red end of the spectrum missing and thus do not have a colour rendering index of 100, information from lamp makers on this topic is hard to find. T12 lamps are not generally used in new installations as T5 and T8 types are more efficient. Lamps also available with exceedingly long lamp lives of e.g. 30,000 hours and 60,000 hours. Most T5 lamps are optimised to give maximum light output at 35˚C. The figures in this table are based upon their output at 25˚C. As in most luminaires the lamp runs close to 35˚C then the apparent light output ratio (LOR) of the luminaire appears to be higher than normal. 7 Most manufacturers are working on dimming control gear for this sort of lamp, but most products released onto the market so far have had major problems. 8 The LEDS can be integrated within the LED lamp, LED module or LED luminaire. The values represent the values of the LED alone of current technology Jan 09 and two points should be noted: – thermal, driver and optical losses (potentially 50%), will reduce these lumen output and efficiency values, when built into a luminaire. – the lumen output and efficiency development curves are much steeper than existing other lamp technologies. 9 For lamp life both electrical failures and lumen maintenance should be considered to measurement standards e.g. B10/L70 (10% electrical failures and 70% lumen depreciation at lamp life).

20–220

55–165

45–115

165–430

53–142

70–180

Efficacy (lm/W)

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LEDs(8)

2,600–12,000

12,500–37,000

Delux SON

85–1040

26–200

Power range (W)

25/3/09

Induction

4,300–130,000

Std SON


SOX SOX-E

Low pressure sodium

Lamp name

Table 3.5 Summary of lamp characteristics cont...

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3.5 Flames Historically flames were the first form of artificial lighting. They are occasionally still used to create a particular atmosphere, but they are not considered as major sources of artificial light. 3.5.1 Candle It is said that the ancient Egyptians invented the candle. They made candles by soaking reeds in molten tallow (animal fat). However this was not the candle as we know it today as it had no wick as such. It appears that the Romans made the first true candle with a wick, but it still used tallow. The problem with tallow candles is that they produce a lot of smoke and acrid smells. In the Middle Ages beeswax was introduced for making candles. It overcame the problems of tallow candles, but due to its cost only rich people could afford them. The last advance in candle making was in the 19th century when whale oil wax and paraffin wax were introduced. The actual processes involved in a candle burning are very complex; in 1861 Michael Faraday was able to fill a series of six lectures just discussing them. The key points of the process are that the heat of the candle flame melts the wax, which is absorbed in the wick, which transports it to the flame where it is burnt. In the burning process some particles of carbon are produced. These particles glow as they are hot. 3.5.2 Oil The oil lamp has been around for a very long time. Some of the earliest examples are hollowed out stones that were filled with oil and these may be 70,000 years old. There are examples of earthenware lamps made by all the ancient civilisations. In Europe the most common oils used in these lamps were olive and colza. The wick was generally made out of bark, moss or plant fibres. The first major development in modern history was the use of a flat wick in the lamp that started in 1773 and the tubular wick in 1784. This coupled with the glass chimney made the lamps significantly more efficient. Figure 3.32 shows such a lamp.

Figure 3.32 An oil lamp with a tubular wick and a glass chimney

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3.5.3 Gas Gas lighting only became possible during the industrial revolution. During the 1780s several inventors had been working with the flammable gas that is produced when coal is made into coke and they realised that it could be used for lighting. The problem was that it became necessary to set up a whole infrastructure of pipes to supply the gas to where it was needed. In 1813 a company was set up in London to supply gas and by 1815 there were 26 miles of gas pipe installed. The first gas light burners were little more than small openings at the end of a gas pipe. Over a period of time the shape of the burners evolved so that each unit would produce more light. However, a major improvement in performance was achieved in 1887 with the invention of the gas mantle. The gas mantle is a cube of fabric, impregnated with thorium and cerium oxides. When the lamp is lit the fabric burns away leaving a brittle mesh of oxides. The cerium oxide is a thermo-luminescent material, see Section 3.1.8.


In the 1860s with the introduction of paraffin the oil lamp became very popular and was one of the leading sources of artificial light until it was overtaken by gas and electric lighting.

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Chapter Four: Luminaires

Chapter 4: Luminaires 4.1 Basic requirements A luminaire is the apparatus containing the light source. A luminaire is designed to: connect the light source to the electricity supply protect the light source from mechanical damage control the distribution of light be efficient withstand the expected conditions of use be safe when used in the recommended manner. To meet these design objectives it is necessary to consider the electrical, mechanical, optical, thermal and acoustic aspects of luminaires. 4.1.1 Electrical Electrical wiring The internal wiring of a luminaire has to be capable of handling the electrical current and the thermal conditions in the luminaire. The cross sectional area of the wire will determine the maximum allowable current. IEC 598 specifies a minimum cross section of 0.5 mm2 although this may be reduced to 0.4 mm2 where space is severely restricted. The wire itself can be solid or stranded. Solid wire is easier to hold in position and to strip, making it simpler to install in a luminaire. However, solid wire is not suitable for luminaires that are subject to vibration or for luminaires that may be frequently adjusted. For such luminaires, stranded wire is better. Both types of wire are covered with insulating material. The choice of insulation material is largely determined by its heat resistance. The wiring of a luminaire has to be capable of withstanding not only the air temperatures inside the luminaire but also the surface temperatures of components that the wiring may contact, such as lamps, control gear and lamp holders. PVC insulation that is heat resistant up to 90 ˚C, 105 ˚C and 115 ˚C is available. Where higher temperatures may be experienced, silicon rubber (170 to 200 ˚C) and PTFE (250 ˚C) insulation may be used. Additional thermal insulation can be achieved by covering the electrical insulation with a glass fibre sleeve. Connection to the electricity supply There are three approaches commonly used to connect a luminaire to the electricity supply; the connection block, automatic connection and through wiring. The most common method is via a connection block within the luminaire. To prevent the connection being accidentally broken, the supply wire should pass through a cable clamp before reaching the connection block.

84

Luminaires mounted on trunking systems are often designed so that connection to the electricity supply occurs when the luminaire is mounted on the trunking. For this to occur the electrical socket carrying the electricity supply is part of the trunking and the plug is contained within the luminaire.


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Through wiring is a system for connecting a series of luminaires in parallel across a supply cable. This reduces the amount of cabling required and speeds up installation. The supply cable should have a cross section of 2.5 mm2 as a minimum, but the wiring from the connection block in each luminaire may have a smaller cross section, typically 0.5 or 0.75 mm2. Earthing Metal parts of Class 1 luminaires (see Section 4.3.2, Table 4.11) that are accessible when the luminaire is installed or open for maintenance or that may become live if the insulation fails should be permanently connected to an earth terminal. The wire used for earthing should be at least 2.5 mm2 in cross section.


The earth pin of the plug is longer than the live and neutral pins so that when the luminaire is offered up to the track, the earth connection is made before the live and neutral, and when removing the luminaire, the live and neutral connections are broken before the earth.

4.1.2 Mechanical The mechanical integrity of a luminaire depends on the materials used and the quality of its construction. Materials Steel Many interior lighting luminaires are made from ready-painted sheet steel, white being the usual paint colour. Where corrosion is a problem, galvanised sheet steel is used. Where a very durable paint finish is required, enamelling is used. Stainless steel Stainless steel is rarely used for luminaire bodies but it is widely used for many small, unpainted luminaire components that have to remain free from corrosion. Aluminium sheet Aluminium sheet is mainly used for reflectors in luminaires. It can have good reflection properties and the physical strength to form stable reflectors of the desired form. Cast aluminium Cast aluminium is widely used for floodlight housings. Such housings are light in weight and can be used in damp or corrosive atmospheres without any further treatment provided that the correct grade of aluminium has been used. Plastics There are many different forms of plastic used in luminaires, either for complete housings or components. These plastics differ in their transparency, strength, toughness, sensitivity to UV radiation and heat resistance. Glass Three types of glass are used in luminaires; soda lime glass, borosilicate glass, and very high resistance glass. Soda lime glass is used where there are no special heat resistance demands. Where high heat resistance, chemical stability and resistance to heat shock are required, borosilicate glass is used. High resistance glass has the advantage that it can deliver high heat resistance, high thermal shock resistance and great physical strength even in thin sheets. 85


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Ceramics Some components of luminaires that produce very high temperatures are made of ceramics. Construction All luminaires should be designed to withstand the rigours of transport to the site, installation and prolonged use. Generally, exterior luminaires need to be more substantial than those designed for interior use. Some luminaires are designed to resist the ingress of foreign objects, dust and moisture. Such luminaires have a transparent front cover and all points of access to the luminaire have a seal. Front covers are usually made of glass or plastic. Where there is a risk of physical impact, as in a sports hall, glass or acrylic front covers need to be covered with a wire screen. If a polycarbonate front cover is used, no such screen is necessary. As for the seals, these come in various forms from a simple felt seal to convoluted notched rubber seals. The effectiveness of these seals is quantified by the IP classification system (see Section 4.3.2 Table 4.10). 4.1.3 Optical control Optical control of the light output from a light source is achieved by some combination of reflectors, refractors, diffusers, baffles or filters. Reflectors Three types of reflector are used in luminaires; specular, spread and diffuse. Specular reflectors are used when a precise light distribution is required. The shape of the reflector and its position relative to the light source determine the light distribution. The most common shapes for reflectors are circular, parabolic and elliptical. A circular reflector with a point light source at its focus will produce a light distribution of the type shown in Figure 4.1, reflections from some parts of the reflector being almost parallel while those from parts of the reflector away from the axis are divergent. This type of circular reflector is used in cylindrical form for picture lighting using tubular incandescent and fluorescent light sources.

Figure 4.1 The light distribution from a circular reflector with a point light source at its focus 86


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A circular reflector with a point light source at its centre of curvature produces a light distribution of the type shown in Figure 4.2. This type of reflector is widely used in projection systems and spotlights to increase the amount of light delivered to the associated lens system.

Figure 4.2 The light distribution from a circular reflector with a point light source at its centre of curvature A parabolic reflector with a point light source at its focus produces a parallel beam of reflected light (Figure 4.3). Moving the light source in front or behind the point of focus will cause the beam to converge or diverge. The parabolic reflector is widely used in spotlight design either exactly, when the reflector is smooth, or approximately, when the reflector is facetted.

a F b

A

B

Figure 4.3 The light distribution from a parabolic reflector with a point light source at its focus. The beam intensity will be greater at the centre than at the edge — compare cones aFb and AFB. 87


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An elliptical reflector with a point light source at one focus will ensure that the reflected rays all pass through the second focus (Figure 4.4) Elliptical reflectors in trough form are widely used for tubular fluorescent luminaires.

F F

Figure 4.4 Elliptical reflectors showing the change in light distribution as the point light source is moved relative to the first focus (F) Spread reflectors are deliberately distorted specular reflectors. They can be circular, parabolic or elliptical in cross section and spherical or cylindrical in form. The distortion takes the form of modulating the specular surface of the reflector by hammering (peening) to produce a regular array of dimples, or by etching or brushing the surface. The advantage of this distortion is that it smears out variations in light distribution caused by inaccuracies in the manufacture of the reflector and the size of the light source. Spread reflectors are used where a well-defined but even light distribution is required. Diffuse reflectors are the opposite of specular reflectors. Unlike a specular reflector, the shape of a diffuse reflector has only a small effect on the light distribution. Diffuse reflectors are used where there is a need to redirect light with a very wide beam. Many different materials are used in reflectors. Typical values of reflectance for these materials are given in Table 4.1. Refractors Refractors control light distribution by turning the incident light ray through a desired angle following Snell’s Law. This can be done using either prisms or lenses. For luminaires using large area light sources, such as a fluorescent lamp, multiple prisms are moulded in a transparent material, usually acrylic or polycarbonate plastic. The number, location, angle of incidence and shape of the different types of prism determine the light distribution. For luminaires using a point light source a lens can be used. The position and shape of the lens determines the light distribution.

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Reflector type

Material

Reflectance

Specular

Commercial grade aluminium

0.70

Specular

Aluminium with super purity coating

0.80

Specular

Aluminium with silver coating

0.90

Specular

Glass or plastic with aluminium coating

0.85–0.88

Spread

Peened aluminium

0.70–0.80

Spread

Etched aluminium

0.70–0.85

Spread

Brushed aluminium

0.55–0.58

Spread

Satin chromium

0.50–0.55

Spread

Aluminium painted steel

0.60–0.70

Diffuse

White paint on steel

Up to 0.84

Diffuse

Glossy white plastic

Up to 0.90


Table 4.1 Typical reflectance values for materials used in reflectors

Diffusers Diffusers are transparent materials that scatter light in all directions. They provide no control of light distribution but do serve to reduce the brightness of the luminaire. Diffusers are commonly made of materials that maximise light scatter and minimise absorption, such as opal glass or plastic. Baffles Baffles can have three functions; to hide the light source from common viewing angles, to reduce the amount of spill light, and to control the light distribution. The extent to which the light source is hidden from view is quantified by two angles, the shielding angle and its complementary, the cut-off angle. The shielding angle is the angle between the horizontal and the direction at which the light source ceases to be visible. Figure 4.5 shows the shielding angle for a simple fluorescent luminaire.

Luminaire using an internal baffle to improve screening

Shielding angle. Beyond this angle the lamp is not visible to the user

Figure 4.5 The shielding angle for a simple fluorescent luminaire 89


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A common example of a baffle being used to hide the light source is the diffusely reflecting louvre. This louvre can take a wide variety of forms, lamellae, eggcrate, concentric rings and honeycomb depending on the shape and size of the luminaire and is usually made of a white diffusely reflecting material. If the purpose is primarily to reduce spill light, the material used for the louvre will be of low reflectance, i.e. black. In addition to louvres, spill light can be controlled by the use of low reflectance baffles, called barn doors, mounted on the luminaire (Figure 4.6).

Figure 4.6 Barn door baffles mounted on a spotlight

If the purpose is to hide the light source and also to control light distribution, the louvre is made from a specularly reflecting material and shaped so as to direct light downwards and hence increase the shielding angle (Figure 4.7). As a general rule, the finer the louvre and hence the more the light source is hidden, the lower will be the light output ratio of the luminaire (see Section 4.1.4).

Shielding angle ca. 45˚

Figure 4.7 A section through and an example of a louvre designed to hide the light source and control the light distribution Filters For display and decorative lighting it is sometimes required to change the colour of light emitted by a luminaire. This can be done by the use of filters, either absorption or interference. 90


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4.1.4 Efficiency The efficiency of a luminaire is quantified by its light output ratio (LOR). This is the ratio of the total light output of a luminaire to the total light output of the light sources used in the luminaire when operating outside the luminaire. LOR is sometimes split into upward and downward components. LOR measures the efficiency of the luminaire in the sense that it quantifies how much of the light emitted by the light source escapes from the luminaire. LOR does not measure the efficiency of a lighting installation. However, LOR is an element in determining a lighting installation’s compliance with Part L of the Building Regulations. Light output ratio is defined as the ratio of luminous flux emitted by the luminaire divided by the flux emitted by the bare lamps in free air. This means that for temperature sensitive lamps the LOR is a function of the increase in temperature of a lamp within the luminaire as well as the optical efficiency of the luminaire.


Absorption filters are usually made of plastic or glass. They absorb the unwanted wavelengths and thereby raise their temperature. Plastic absorption filters are likely to change their properties if they get too hot. The transmittance of absorption filters is limited. Typical transmittances for different colour filters are blue = 5 percent, red = 20 percent, green = 15 percent, and yellow = 40 percent. Another type of filter is the interference filter. Interference filters are more expensive and more exact than absorption filters and do not absorb the unwanted wavelengths. Rather, they split the light into two beams, one transmitted and one reflected, of two different colours (hence the name dichroic filters).

4.1.5 Thermal All luminaires increase in temperature when in operation. The internal temperature of the luminaire can affect the efficiency of some light sources and the associated control gear. These changes in efficiency contribute to the light output ratio of the luminaire. The external surface temperature of a luminaire may also pose a fire hazard if mounted on a flammable surface (see Section 4.3.2). Of course, the external temperature of the luminaire will increase more when it is surrounded by thermal insulation so care should be taken when considering recessing luminaires into confined or insulated spaces. Air handling luminaires are used to deliver conditioned air to the occupied space or to extract heat from the occupied space and the luminaire. There are three types of air handling system using luminaires; plenum exhaust, single ducted and double ducted. In a plenum exhaust system conditioned air is supplied through air diffusers, while stale air is extracted through slots in the luminaires into the plenum that acts as a return duct (Figure 4.8a). The plenum exhaust system is only used where the maximum number of air changes per hour is less than six. In a single ducted system, conditioned air is delivered along the plenum and then through air diffusers, and stale air is extracted through the luminaires into a duct (Figure 4.8b). The single ducted system is used for spaces with low ceiling heights. In a double ducted system conditioned air is delivered through air diffusers supplied by a duct, and stale air is extracted through the luminaires and an attached duct (Figure 4.8c). These three systems differ in cost and efficiency. The double ducted system is the most expensive and most efficient.

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Chapter Four: Luminaires (a)

(b)

(c)

Figure 4.8 Sections through and drawings of (a) the plenum exhaust, (b) the single ducted and (c) the double ducted air handling systems 92


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4.1.6 Acoustics Luminaires may amplify the sound produced by components in the luminaire, e.g. the control gear, or produced elsewhere but transmitted to the luminaire through the building structure. Either way, the result is noise. Some spaces, such as concert halls have strict criteria about background noise, usually expressed as a noise rating (NR). A noise rating consists of numbered curve showing the maximum sound pressure level allowed in each frequency band (Figure 4.9). Table 4.2 gives recommended NR values for different applications. Where noise is likely to be a problem, care should be taken to use well constructed luminaires and to mount them so they are free from vibration. It is also desirable to use high frequency control gear but if this is not possible, remote positioning of control gear may be necessary.


The design of air conditioning incorporating luminaires is complex and requires knowledge of heat load, air change rates, pressure drop and supply air temperatures. Failure to consider these factors carefully could cause the luminaires to fail to fulfil their function.

70 NR 70 60 60

50 40 40 30 30

Noise rating (NR)

Sound pressure level (dB)

50

20 20 10 10 0

0

–10 62.5

125

250

500

1000 2000 4000

Frequency (Hz)

Figure 4.9 A set of noise rating curves, plotted as sound pressure level at different frequencies Application

Noise rating

Studios

10

Concert halls

20

Conference rooms

25

Lecture rooms

25

Auditoria

25

Hospitals

30

Private offices

30

Table 4.2 Recommended noise rating values for different applications

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4.1.7 Environmental Luminaires may contain a variety of materials and some of these could be hazardous to the environment when the luminaire is disposed of at the end of life. To stop environmental pollution there are two sets of European regulations, WEEE and RoSH. WEEE or more fully the Waste Electrical and Electronic Equipment Directive requires that all luminaires are recycled at the end of life and are not just thrown away. To ensure that this occurs, luminaire suppliers are required to make provision for the collection and recycling of old luminaires; see http://www.lumicom.co.uk for more information. RoHS, the Restriction of Hazardous Substances Directive, controls the use of certain materials used in luminaires. These materials such as lead, mercury, cadmium and polybrominated biphenyls are all toxic and their use in luminaires is limited.

4.2 Luminaire types The lighting industry produces many thousands of different luminaires. Given below are brief outlines of the main types of luminaire used in interior and exterior lighting. Details of any specific luminaire are best obtained from the manufacturers. 4.2.1 Interior lighting Direct luminaires Direct luminaires are luminaires in which the light distribution is predominantly downward (see Table 4.7). Such luminaires are typically recessed into or surface mounted on the ceiling. They are widely used in offices where the ceiling height is restricted. The usual light source is a fluorescent lamp, either linear or folded. Many different forms of optical control are available, from diffusers through prismatic refractors to parabolic reflectors and louvres. Consequently, direct luminaires are available with a wide range of luminous intensity distributions. Direct luminaires are available for operation in dirty, corrosive or hazardous conditions. Direct luminaires are available with dimming or switching facilities linked to manual, occupancy sensor and photocell control. The most common problems with lighting installations using direct luminaires is the creation of a dark ceiling and poor illuminance uniformity in obstructed spaces. This problem can be overcome by choosing direct luminaires with a little upward light output or by having high reflection factors in the space. Figure 4.10 shows a direct luminaire.

Figure 4.10 An example of a direct luminaire 94


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Indirect luminaires Indirect luminaires are luminaires in which the light distribution is predominantly upward (see Table 4.7). Such luminaires can be suspended below the ceiling, wall mounted or free standing. They require a clean, white ceiling for efficient operation. Indirect luminaires are most practical where the ceiling height is over 2.75 m. The usual light source in suspended indirect luminaires is a linear fluorescent lamp. Wall mounted and free-standing indirect luminaires tend to use a high intensity discharge lamp. Optical control is confined to ensuring that the light output from the luminaire is widely spread across the ceiling so that no hot spots of high luminance are apparent. While indirect luminaires have a high light output ratio, lighting installations using indirect luminaires are usually less energy efficient than those using direct luminaires because of the losses caused by having to use the ceiling as a secondary reflector. This is compensated by the bright appearance of the space, the high level of illuminance uniformity and the absence of discomfort glare. Figure 4.11 shows a selection of indirect luminaires.

Figure 4.11 Examples of indirect luminaires Direct/indirect luminaires Direct/indirect luminaires are luminaires in which the light distribution is evenly divided between the upward and downward directions. In many ways, direct/indirect luminaires provide the best of both worlds. The energy efficiency of a lighting installation using direct/ indirect luminaires will be higher than that of one using indirect luminaires but the problems of dark ceilings and poor illuminance uniformity are reduced by the indirect component. Direct /indirect luminaires are suspended below the ceiling. They are difficult to use where the ceiling height is below about 2.75 m. The usual light source in direct/indirect luminaires is a linear fluorescent lamp. Optical control is different for the two directions of light output, being much tighter for the downward component than the upward. Direct/indirect luminaires are available with individual dimming of the direct component. Figure 4.12 shows a selection of direct/indirect luminaires.

Figure 4.12 Examples of direct/indirect luminaires 95


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Downlights Downlights are a form of direct luminaire characterised by a small light emitting aperture. Downlights are usually recessed into the ceiling so they direct all of their light output downward. They are widely used in shops, hotels and other places where a lighting installation with a discreet appearance is desired. Many different light sources can be used in downlights, the most common being incandescent, tungsten halogen, compact fluorescent and metal halide. Through the use of reflectors, louvres, lenses and refractors many different beam spreads and beam sizes are possible (see Section 4.3.2). Some downlights allow for adjustable aiming which is useful when the intention is accent lighting. A number of downlights are fitted with decorative elements directly beneath the downlight aperture to give an impression of brightness to the luminaire. The most common problems with lighting installations using an array of downlights to create uniform illumination are poor illuminance uniformity caused by overspacing and dark ceilings. Care is necessary to avoid a fire hazard when recessing downlights into an insulated ceiling. Figure 4.13 shows a selection of downlights.

Figure 4.13 Examples of downlights Spotlights Spotlights are narrow beam luminaires with beam spreads in the range 5 to 30 degrees. They are usually mounted on either a base plate or lighting track. When track mounted, spotlights can be obtained for operation at mains voltage, low voltage or extra low voltage, the latter requiring the installation of a step-down transformer. Spotlights are widely used in shops, hotels and museums for accent lighting. Spotlights are available that use incandescent, tungsten halogen, metal halide and extra high pressure sodium light sources of small physical size. Some incandescent and tungsten halogen light sources can be used as spotlights themselves because they have reflectors giving the desired beam spread built in. Other light sources have to use reflectors to attain optical control. Filters mounted in front of the spotlight can be used to change the light colour. Irises and baffles mounted in front of the spotlight can be used to modify the beam shape. Care is necessary when using spotlights to avoid glare to passers by. Figure 4.14 shows a selection of spotlights.

Figure 4.14 Examples of spotlights 96


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Wall washers Wall washers are asymmetric luminaires with beam spreads up to 130 degrees. They are usually mounted on either a base plate or lighting track. As their name implies, wall washers are used where it is required to wash a large area with light, evenly. Point and extended light sources can be used in wall washers, typically tungsten halogen and fluorescents. Wall washers require careful aiming to achieve their best effect. Figure 4.15 shows an example of a wall washer.

Figure 4.15 Example of a wall washer Task lights Task lights are a necessary part of a task/ambient lighting system. They provide local lighting of a specific area by bringing the light source closer to the task. The value of task lights is that they enable the user to have some control of the amount and distribution of light on the task by switching or dimming the light source and by changing the position of the luminaire relative to the task. Typically, the light sources used in task lights are incandescent, tungsten halogen or compact fluorescent. The degree of adjustment available can vary widely as can the amount of desk space taken. When selecting task lights attention should be given to the coverage area for common positions and the likelihood of glare to the user. Figure 4.16 shows a selection of task lights.

Figure 4.16 Examples of task lights 97


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4.2.2 Exterior lighting Road lighting luminaires Road lighting luminaires used for lighting traffic routes are designed to deliver light to a road so that the surface is seen to be of uniform luminance and objects on the road can be seen in silhouette. The light distribution is therefore dependent on the position of the luminaire relative to the road. Most road lighting luminaires are mounted on columns placed at regular intervals at the side of the road or between crash barriers in the median. A few installations use a catenary system in which the luminaires are suspended over the median in a continuous series. For conflict areas and subsidiary roads (see Chapter 16) the luminaires are designed with a wide light distribution so as to give a uniform illuminance across the road. The light sources used in road lighting luminaires are typically low pressure sodium, high pressure sodium or metal halide. Road lighting luminaires are often provided with adjustable lamp holders and/or reflectors so as to allow the light distribution to be optimised for the light source and road layout. Two broad classes of road lighting luminaire are semi-cutoff and full cutoff (see Section 4.3.2, Table 4.9) these classes reflecting a different balance between luminaire efficiency and the control of glare. Road lighting luminaires need protection against dust and moisture and so are classified according to the IP system (see Section 4.3.2, Table 4.10). They are almost always fitted with a photoelectric control package. Figure 4.17 shows a selection of road lighting luminaires.

Figure 4.17 Examples of road lighting luminaires Post tops Post top luminaires are a form of road lighting luminaire but unlike the road lighting luminaires described above, which are intended for the lighting of high speed traffic routes, post top luminaires are intended for urban areas, where pedestrians are considered as important as drivers and the decorative aspect of the luminaire is as important as the functional. Post top luminaires are available with either rotationally symmetric or road lighting light distributions, so that the same luminaire can be used to light both roads and open pedestrian areas in a city. Post top luminaires take many different forms, some mimicking traditional styles for historic areas, while others represent the latest design trends. Because of their use in urban areas, low pressure sodium light sources are not used in post top luminaires, the most common light sources being high pressure sodium, metal halide, compact fluorescent and induction lamps. Post top luminaires need protection against dust and moisture and so are classified according to the IP system (see Section 4.3.2, Table 4.10). Because of their relatively low mounting heights, post top lanterns are often constructed of materials that resist attacks by vandals. They are almost always fitted with a photoelectric control package. The most common problem with post top luminaires is glare. This problem can be avoided if there is no direct view of the light source. Figure 4.18 shows a selection of post top luminaires. 98


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Figure 4.18 Examples of post tops Secondary reflectors Secondary reflector luminaires are designed for use in pedestrianised places such as city squares and parks. In this luminaire, light is directed up from the light source in or on the column and then distributed from a large surface at the top of the column. By changing the area and tilt of the reflecting surface, the light distribution can be altered. Secondary reflector luminaires are inevitably inefficient compared to post top luminaires, but they do not cause glare, are not easily damaged by vandals and can provide a pleasing ambience. Figure 4.19 shows two secondary reflector luminaires.

Figure 4.19 Examples of secondary reflector luminaires Floodlights Floodlights can be used to wash a large surface with light or to pick out a specific feature of a building. Floodlights vary enormously in their size, power and light distribution. The smallest floodlights consist of little more than a 150 W linear tungsten halogen lamp with a spread reflector. The largest consist of a high intensity discharge lamp with power in the kilowatt range and a carefully shaped reflector. The light distribution of a floodlight can be rotationally symmetric, symmetrical about one axis or asymmetrical about one axis. This distribution is usually classified as narrow, medium or wide beam (see Section 4.3.2, Table 4.8). The light sources used in floodlights include incandescent, tungsten halogen, high pressure sodium and metal halide. Floodlights need protection against dust and moisture and so are classified according to the IP system (see Section 4.3.2, Table 4.10) and are often soundly constructed of materials that resist attacks by vandals. Filters mounted in front of the floodlight can be used to change the light colour. Barn door baffles mounted on the floodlight can be used to modify the beam shape. Care is necessary when using floodlights to avoid glare to passers by. Figure 4.20 shows a selection of floodlights. 99


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Figure 4.20 Examples of floodlights Wallpacks As their name suggests, wall packs are designed to be mounted on walls so as to provide a low level of illumination in the nearby area. They are widely used for security and amenity lighting. The light distribution is usually wide and is achieved by a combination of reflecting and refracting elements. The light sources used in wall packs are usually low wattage low pressure sodium, high pressure sodium and compact fluorescent. Wallpacks need protection against dust and moisture and so are classified according to the IP system (see Section 4.3.2, Table 4.10). Because of their relatively low mounting heights, wallpacks should be solidly constructed of materials that resist attacks by vandals. The most common problem experienced with wallpacks is glare. This problem is much reduced if there is no direct view of the light source. Figure 4.21 shows a selection of wallpacks.

Figure 4.21 Three examples of wallpacks

4.3 Certification and classification 4.3.1 Certification The principal EU Directives for electrical products are the Electro-Magnetic Compatibility (EMC) Directive and the Low Voltage (LV) Directive, summarised for lighting products in Table 4.3. The LV Directive and the EMC Directive both require products put on the EU market to be safe: Compatibility being designated by the CE mark. Products complying with specified Euronorm (EN) safety standards are presumed to comply. EN standards are based upon existing international standards, e.g. an IEC standard. For a list of current EN standards relevant to lighting products see Tables 4.4 and 4.5 (EMC and Safety), and Table 4.6 (Performance). In most instances, there is an equivalent British Standard (BS), known as a BS EN. (For established products a compatible BS may still be used, but preference should be given to the EN.) Electrical EN standards are issued by the EU sponsored organisation, CENELEC. They are type tests, and manufacturers are required to associate them with controls for conformity of production. 100


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Table 4.3 EU Directives and lighting products EMC Directive

LV Directive

From 1 January 1996

From 1 January 1997

Applies to: (see Table 4.4)

Applies to: Luminaires Lighting components Lamps

EN standards Table 4.4

EN safety standards Table 4.5


Responsibility for compliance of a product with the Directives and with the specified EN standards rests on the person putting the product on the EU market, usually the manufacturer.

UK enforcing authorities Trading Standards Officers HM Revenue and Customs

The EMC and LV Directives, in conjunction with the CE Marking Directive, require complying products to be accompanied by the CE-mark. CE represents Conformity European. The CE-mark should preferably be on both product and packaging. Responsibility for marking rests on the person putting the product on the EU market. It is important to note that CE-marks on components do not imply that a luminaire complies. The luminaire as a whole must comply and carry the CE-mark. Further, if a luminaire is modified for use in the EU (e.g. with emergency lighting) the modifier takes over responsibility and must make a new CE mark. A lighting product outside the LV Directive (e.g. an ELV product) comes under the General Products Safety Directive. The ENEC mark indicates independent confirmation that the product complies with all relevant EN safety standards and, where available, EN performance standards. (Note: the ENEC mark is not applicable to lamps or emergency luminaires). The ENEC mark is not obligatory. Testing and approval are carried out by national Certification Bodies, e.g. in the UK by BSI. The XX in the diagram is replaced by a number from 01 to 17, e.g. 12 for the UK. The ENEC mark of each of the Certification Bodies is valid throughout the EU. Again, it is important to note that ENEC marks on components do not imply that a luminaire has an ENEC mark. Further, if a luminaire is modified the modifier must remove the ENEC mark.

XX

101


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Table 4.4 EN standards and lighting products (CE-mark and EMC Directive) Product

EN

BS EN

Disturbance in supply system

EN 60555-2 EN 61000-3-2

BS EN 61000-3-2 M M M

Luminaires with control gear Control gear Lamps with integral control gear

Radio frequency interference (up to 30 MHz)

EN 55015

BS EN 55016

M M M

Luminaires with control gear Control gear Lamps with integral control gear

Immunity

EN 50081 & 2 EN 61547

Luminaires with electronic control gear Control gear with electronics Lamps with integral electronics (electro-magnetic control gear deemed to comply)

Notes for Tables 4.4, 4.5 and 4.6 M = CE-mark obligatory (LV Directive) S = ENEC mark optional (safety standard only available) SP = ENEC mark optional (to safety standard and performance standard) V = Older standard, still valid n/a = Not applicable Associated standards: BS EN 40 Lighting columns; BS EN 60730–2–3 Thermal protectors for ballasts. The EN standards are based on IEC standards, and their numbers are the IEC numbers plus 60,000; for example EN 60570 = IEC 570. BS EN standards have the EN number. BS EN 60598–2 is linked to BS EN 60598–1

102

CE-mark

M M M


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Product

EN

BS EN

Compatible BS

CE ENEC mark mark

Luminaires EN 60570

BS EN 60570

–

M

S

Street lighting

Track systems

EN 60598–2–3

BS EN 60598–2–3

–

M

S

Emergency

EN 60598–2–22

–

BS 4533–102–22

M

n/a

–

M

S

BS EN 60920

–

M

SP

Others (see X)

EN 60598–2–X BS EN 60598–2–X

Ballasts For fluorescent – Safety

EN 60920

For discharge – Safety

EN 60922

BS EN 60922

–

M

SP

DC electronic – Safety

EN 60924

BE EN 60924

–

M

SP

AC electronic – Safety

EN 60928

BS EN 60928

–

M

SP


Table 4.5 EN Safety standards for lighting products (CE mark and LV Directive)

Transformers EN 61046

BS EN 61046

–

M

SP

Isolating

EN 60742

BS EN 60742

–

M

S

Neon

EN 61050

–

–

M

S

EN 60926

BS EN 60926

–

M

SP

EN 60155

–

BS 3772

M

S

EN 61048

BS EN 61048

–

M

SP

Electronic stepdown – Safety

Starters/Ignitors Electronic starters – Safety Glow starters Capacitors For lamp circuits – Safety Lampholders Edison screw

EN 60238

BS EN 60238

–

M

S

Fluorescent lamp & starter holders

EN 60400

BS EN 60400

–

M

S

Bayonet

EN 61184

BS EN 61184

–

M

S

Lamp caps and holders

EN 60838

BS EN 60838

–

M

S

Lamp caps and holders (V)

EN 60061

BS EN 60061

–

M

S

Lamps GLS

EN 60432–1

BS EN 60432–1

–

M

n/a

Tungsten halogen – Domestic

EN 60432–2

BS EN 60432–2

–

M

n/a

Double capped fluorescent

EN 61195

BS EN 61195

–

M

n/a

Single capped fluorescent

EN 61199

BS EN 61199

–

M

n/a

CFL Integral – Safety

EN 60968

–

BS 7173

M

n/a


EN 60662

BS EN 60662

–

M

n/a

Low pressure sodium

EN 60192

BS EN 60192

–

M

n/a

High pressure mercury

EN 60188

–

BS 3677

M

n/a

Metal halide

EN 61167

BS EN 61167

–

M

n/a

Double capped fluorescent (V)

EN 60081

BS EN 60081

–

M

n/a

Single-capped fluorescent (V)

EN 60901

BS EN 60901

–

M

n/a

Note: ‘X’ identifies luminaire types as follows: 1 General purpose, 2 Recessed, 4 Portable, 5 Floodlights, 6 With transformer, 7 Portable – garden, 8 Handlamps, 9 Photo – amateur, 17 Stage and studio, 18 Swimming pools, 19 Air-handling and 20 Lighting chains

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Table 4.6 EN Performance standards and lighting products Product

EN

BS EN

Compat. BS

EN EC mark

For fluorescent – Performance

EN 60921

BS EN 60921

–

SP

For discharge – Performance

EN 60923

BS EN 60923

–

SP

DC electronic fluorescent – Performance

EN 60925

BS EN 60925

–

SP

AC electronic fluorescent – Performance

EN 60929

BS EN 60929

–

SP

EN 61047

BS EN 61047

–

SP

EN 60927

BS EN 60927

–

SP

EN 61049

BS EN 61049

–

SP

GLS

EN 60064

BS EN 60064

BS 161

n/a

Tungsten halogen (non-vehicle) (V)

EN 60357

BS EN 60357

BS 1075

n/a

CFL integral – Performance

EN 60969

BS EN 60969

–

n/a

Luminaires No performance standard at present Photometry – see EN 13032–1 Ballasts

Transformers Electronic stepdown – Performance Starters/ignitors Electronic starters – Performance Capacitors For lamp circuits – Performance Lamps

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Table 4.7 CIE classification of general indoor luminaires Luminaire class

Percentage of total luminous flux emitted above the horizontal

Percentage of total luminous flux emitted below the horizontal

Direct

0–10

90–100

Semi-direct

10–40

60–90

General (diffuse)

40–60

40–60

Semi-indirect

60–90

10–40

Indirect

90–100

0–10


4.3.2 Classification General lighting for interiors — luminous flux distribution Luminaires for general indoor lighting are classified by the CIE according to the percentage of the total luminous flux emitted above and below a horizontal plane through the luminaire (Table 4.7).

Spotlights — luminous intensity distribution Spotlights are characterised by their tight beam control. Most have a rotationally symmetric luminous intensity distribution. The most common way of classifying spotlights is by their beam spread. The beam spread of a spotlight is the angle over which the luminous intensity is 50 percent or more of the maximum luminous intensity in the beam. It is important to note that beam spread, expressed in this way, is not a good indication of the appearance of the beam. A better classification of the appearance of the beam is the beam size. The beam size is derived from the distribution of illuminance across a uniformly reflecting surface at a given distance from the spotlight. This distribution is differentiated to obtain the illuminance gradient. The locations of the peaks in the illuminance gradient distribution define the edges of the beam. The beam size is given as the angle subtended at the spotlight by the distance between the two edges and is expressed in degrees. The magnitude of the peaks in the illuminance gradient profile indicate the sharpness of the edge of the beam; the higher the peaks, the sharper is the edge of the beam. Floodlights — luminous intensity distribution Floodlights are classified according to their beam spread. The beam spread is the angle over which the luminous intensity drops to a stated percentage of the maximum, usually 50 percent or 10 percent. For a floodlight having a rotationally symmetric luminous intensity distribution, only one figure is necessary to specify the beam spread. For a floodlight with an asymmetrical luminous intensity distribution, as is usual with rectangular floodlights, two beam spreads are needed, one for the vertical plane and one for the horizontal plane. If the luminous intensity distribution in either of these planes is itself asymmetrical relative to the beam axis, two angles are given for that plane and one for the other plane. A simple classification of beam spreads is sometimes used (Table 4.8). Luminaire classification

Beam spread at 50 percent of maximum luminous intensity

Narrow beam

< 20°

Medium beam

20° to 40°

Wide beam

> 40°

Table 4.8 Floodlight beam spread classification

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Road lighting luminaires — luminous intensity distribution Road lighting luminaires have traditionally been classified as full cutoff or semi-cutoff, according to their luminous intensity distribution. BS EN 13201: Part 2: 2003 has introduced a finer classification designed to give better control of disability glare and obtrusive light. This classification uses the maximum luminous intensity per 1000 lamp lumens at different angles from the downward vertical in any direction as a criterion. Table 4.9 shows the limits for each of the six classes (G levels) and their relationship to the traditional semi-cutoff and full cutoff terms. Table 4.9 BS EN 13201: Part 2: 2003 road lighting luminaire classification G level Cutoff classification

Semi-cutoff

Full cutoff

Maximum luminous intensity/1000 lamp lumens, at 70° from downward vertical



Other requirements

G1

-

200

50

None

G2

-

150

30

None

G3

-

100

20

None

G4

500

100

10

0 at greater than 95°

G5

350

100

10


G6

350

100

0


Operating conditions The International Protection (IP) system classifies luminaires according to the degree of protection provided against the ingress of foreign bodies, dust and moisture. The degree of protection is indicated by the letters IP followed by two numbers. The first number indicates the degree of protection against the ingress of foreign bodies and dust. The second indicates the protection against the ingress of moisture. Table 4.10 shows the degree of protection indicated by each number. Using Table 4.10 it can be seen that a luminaire classified as IP55 is dust protected and able to withstand water jets.

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First number

Degree of protection

Second number

Degree of protection

0

Not protected

0

Not protected

1

Protected against solid objects greater than 50 mm

1

Protected against dripping water

2

Protected against solid objects greater than 12 mm

2

Protected against dripping water when tilted up to 15 degrees

3

Protected against solid objects greater than 2.5 mm

3

Protected against spraying water

4

Protected against solid objects greater than 1.0 mm

4

Protected against splashing

5

Dust-protected

5

Protected against water jets

6

Dust-tight

6

Protected against heavy seas

7

Protected against the effects of immersion

8

Protected against submersion to a specified depth


Table 4.10 IP classification of luminaires according to the degree of protection against foreign bodies, dust and moisture

Electrical protection Luminaires are also classified according to the protection they provide against electric shock. Table 4.11 shows the luminaire classes in the IEC classification.

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Table 4.11 The classification of luminaires according to the degree of electrical protection Luminaire class

Degree of electrical protection

0

A luminaire having functional insulation, but no double insulation or reinforced insulation throughout, and without provision for earthing. This type of luminaire is not permitted in the UK.

1

A luminaire having at least functional insulation throughout and provided with an earthing terminal or earthing contact, and, for luminaires designed for connection by means of a flexible cable or cord, provided with either an appliance inlet with earthing contact, or a non-detachable flexible cable or cord with earthing contact and a plug with earthing contact

2

A luminaire with double insulation and/or reinforced insulation throughout and without provision for earthing

3

A luminaire designed for connection to extra-low voltage circuits and which has no circuits, either internal or external which operate at a voltage greater than extra-low safety voltage

Flammability The temperature of a luminaire may limit the surfaces on which it can be mounted. If the surface is non-combustible, then any luminaire may be mounted on it. But when the surface is either normally flammable or readily flammable, restrictions may apply. A normally flammable surface is one having an ignition temperature of at least 200 ˚C and that will not deform or weaken at this temperature. A readily flammable surface is one that cannot be classified as normally flammable or non-combustible. Readily flammable materials are not suitable for direct mounting of luminaires. The IEC recommends a two part classification system. For luminaires suitable for direct mounting only on non-combustible surfaces, a warning notice may be required. For luminaires suitable for direct mounting on normally flammable surfaces a symbol consisting of a letter F inside an inverted triangle is required.

F 108


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5.1 Control gear A wide range of lamps require control gear of some kind to ensure correct running and, in some cases, starting of the lamp. With discharge lamps it is the job of the control gear to limit the current through the lamp whereas with some incandescent lamps the gear is there to reduce the voltage. Some low voltage tungsten lamps need units to supply them with the correct voltage and LEDs need electronics to limit the current going through them.

Chapter Five: Electrics

Chapter 5: Electrics

5.1.1 Ballasts for discharge light sources General principles Control gear for discharge lamps has to perform a number of functions: limit and stabilises lamp current: due to the negative resistance characteristic of gas discharge lamps (see Section 3.1.2) it is necessary to control the current in the lamp circuit ensure that the lamp continues to operate despite the mains voltage falling to zero at the end of each half cycle provide the correct condition for the ignition of the lamp: this generally requires the gear to provide a high voltage and in the case of fluorescent lamps requires a heating current to be passed through the electrodes. As well as these basic functions control gear may also have the following requirements placed on it: ensure a high power factor limit the harmonic distortion in the mains current limit any electromagnetic interference (EMI) produced by the lamp and ballast limit the short-circuit and run up currents to protect the lamp electrodes and to help the supply wiring system keep the lamp current and voltage within the specified limits for the lamp during mains voltage fluctuations. With electromagnetic control gear several separate control components may be needed — these may include ballasts, starters, igniters, capacitors and filter-coils. When electronic control gear is used it is common to integrate all the components into one package. The details of the various circuits used are discussed in the following sections. Electromagnetic control gear for fluorescent light sources Choke coils used to be the most common type of current limiting device used with linear and compact fluorescent lamps. The most common circuit is the switch start, see Figure 5.1.

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B

La

La = Lamp B = Ballast S = Switch

S

0

Figure 5.1 Schematic diagram of a fluorescent lamp operated using a choke ballast and a switch start The choke ballast is made from a large number of windings of copper on a laminated iron core. It works on the self-inductance principle and is designed so that impedance of the choke limits the current through the circuit to the correct value for a given lamp and supply voltages. A range of ballasts is available for different lamps and different voltages. Also the ballast design has to be changed if it is to operate at a different mains supply frequency. To start the lamp it is common to use a glow starter. The glow starter switch consists of one or two bi-metallic strips enclosed in a glass tube containing a noble gas. The glow starter is connected across the lamp so it is possible for a current to pass through the ballast, through the electrode at one end of the lamp, through the electrode at the other end of the lamp and back to neutral. When the mains voltage is first applied to the lamp circuit, the total mains voltage appears across the electrodes of the starter and this initiates a glow discharge. This discharge heats the bi-metallic elements within the starter and as the electrodes heat up they bend towards each other until eventually they touch. While the electrodes are touching the current passing through the lamp electrodes pre-heats them. While the electrodes in the starter are touching there is no glow discharge and so the electrodes cool and separate. At the moment that the electrodes come apart the current through the ballast is interrupted causing a voltage peak across the lamp. Note: the glow starter does not always create the conditions for the lamp to start and sometimes the starting cycle has to be repeated a number of times. Figures 5.2 to 5.4 illustrate the starting process. Figure 5.2 The heat from the discharge in the starter causes the bi-metallic electrodes to bend together

Figure 5.3 The bi-metallic electrodes touch and a current flows through the circuit preheating the electrodes of the lamp

Figure 5.4 The electrodes cool and separate, causing a voltage peak which ignites the lamp

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Electromagnetic control gear for HID light sources There are a number of different types of circuits used for high intensity discharge (HID) lamps; they vary according to the type of lamp and its requirements for starting. The most common type of ballast used is a choke or inductive ballast in series with the lamp. The choke, which is a coil of copper wire wound on a laminated iron core, limits the current through the lamp. Figure 5.5 shows a typical circuit using a choke.

+

B

–

+


In addition to the ballast and the starter most fluorescent lamps circuits have a capacitor connected across the supply terminals to ensure a high power factor for the circuit.

– La

+ La = Lamp B = Ballast

0

–

Figure 5.5 Schematic diagram of a HID lamp circuit using a choke This type of circuit is used for all high intensity discharge lamps apart from the low pressure sodium lamp. The low pressure sodium lamp has a long run-up during which time the voltage across the lamp needs to be greater than normal mains voltage; this has given rise to a number of circuits for running the lamp that provide the necessary voltage. The most common of these circuits is the autoleak transformer (Figure 5.6). La = Lamp B = Ballast C = Capacitor

L

B

La

C

N

Figure 5.6 Schematic diagram of a low pressure sodium lamp circuit using an autoleak transformer 111


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The autoleak transformer works like an autotransformer increasing the supply voltage, but by careful design of the secondary winding it can also act as a choke to control the current through the lamp. Most high pressure sodium lamps and metal halide lamps require a high voltage pulse to start the arc in the lamp. This is usually provided by an electronic ignitor. There are several types of ignitor circuits, the two most common are the semi-parallel and the superimposed pulse type (Figures 5.7 and 5.8). B

B L

L

La

La

C

N

N La = Lamp B = Ballast C = Capacitor

Figure 5.7 A semi-parallel ignition system

La = Lamp B = Ballast

Figure 5.8 A superimposed ignition system

The semi-parallel ignitor relies on the tapped ballast coil to generate the ignition pulse whereas the superimposed type ignitor has its own coil to generate the pulse. The semi-parallel has many advantages in that it consumes no power when the lamp is running, it is cheaper and lighter but, as it relies on the ballast, it may only be used with the ballast for which it has been specifically designed. Ignitors sometimes have other features built in such as self-stopping ignitors that will not continually try to restrike a lamp that has come to the end of its life. There are also some that are designed to produce extra high voltages that can restrike hot lamps. Electronic control gear for fluorescent light sources Operating fluorescent lamps at high frequency has a number of advantages (see Section 3.3.3) and most modern control gear is now of this type. Most electronic ballasts for fluorescent lamps are integrated into a single package that performs a number of functions. These functions are: a low pass filter: this limits the amount of harmonic distortion caused by the ballast, controls the amount of radio frequency interference, protects the ballast against high voltage mains peaks and limits the inrush current the rectifier: this converts the AC power from the mains supply into DC a buffer capacitor: this stores the charge from each mains cycle thus providing a steady voltage to the circuits that provide the power to the lamps 112


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the output of the power oscillator is fed through a small HF coil that acts as a stabilisation coil to the lamp. Figure 5.9 shows the main components in typical HF fluorescent lamp ballast


the HF power oscillator takes the steady DC voltage from the buffer capacitor and using semi conductor switches controlled by the ballast controller creates a high frequency square wave

C S1 L L Control 1 electronics

2 L

N + –

S2

C low pass filter

rectifier

buffer capacitor

HF power oscillator

Lamp stabilisation

Figure 5.9 A circuit diagram of an electronic ballast for two fluorescent lamps In some ballasts the electronics that control the power oscillator can vary the frequency at which the power oscillator runs; as the frequency increases the current passing through the coils decreases and thus it is possible to dim the lamps. Some types of ballast have a 0 to 10 volt input that is used to regulate the output while some have digital interfaces. See Section 5.2 for further information on controls. Electronic gear for HID light sources Making electronic control gear for HID light sources is a complex process. There are many different lamp types each with different electrical requirements and a limited range of frequencies in which they can be operated. Also many lamp types do not show a significant gain in efficiency when operated on high frequencies. For these reasons electronic control gear has been developed more slowly for HID lamps than for fluorescent lamps. However, it is possible to gain a number of benefits from electronic gear for HID lamps. These include: increased lamp life elimination of visible flicker better system efficacy less sensitivity to mains voltage or temperature fluctuations the possibility of dimming with some lamp types. 113


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Not all these benefits are possible for all lamp types and all control gear combinations. However, the availability and quality of electronic gear available for HID lamps is rapidly increasing. 5.1.2 Transformers for low voltage light sources Many tungsten halogen lamps are designed to run on low voltages the most common of which is 12 volts. Thus they need a device to reduce the supply voltage. The traditional way to do this was by using a transformer. Figure 5.10 shows the various currents and voltages in a transformer and gives the approximate relationship between the voltages, currents and the number of turns in the primary and secondary coils. Ip

Vp

Np : Ns

Is

Ep

Es

Vp Vs

=

Is Ip

=

Vs

Np Ns

Figure 5.10 A circuit diagram for a transformer As well as reducing the voltage the transformer also isolates the lamp supply from the mains. This means that even under a fault condition the voltage in the secondary circuit will not rise significantly above the nominal output voltage and so it will always be safe to touch the conductors on the low voltage side. Most modern transformers for halogen lamps involve electronics. They usually contain high frequency oscillators to permit the use of smaller transformers that have smaller power losses. With the introduction of electronics it is possible to introduce additional features such as constant voltage output and soft starting of the lamps. 5.1.3 Drivers for LEDs LEDs need to be run at a controlled current to ensure proper operation. To provide this drivers are used. Most drivers take mains power and provide a constant current output.However, it is possible to control some drivers so that output current is varied so that the LED may be dimmed. In more complex systems it is possible to dim three separate channels separately, so that when red, green and blue LEDs are used together it is possible to make colour changes. Most LED drivers can maintain their constant current output over a range of voltages so it is often possible to connect a number of LEDs in series on one driver. 114


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5.2.1 Options for control There are a number of factors that need to be considered in any control system; these are the inputs to system, how the system controls the lighting equipment and what is the control process that decides how a particular set of inputs will impact on the lighting. Thus for a control system to work it must have: input devices: such as switches, presence detectors, timers and photocells


5.2 Lighting controls

control processes: these may consist of a simple wiring network through to a computer based control system controlled luminaires: the system may control luminaires in a number of ways, from simply switching them on and off to dimming the lamp and in more complex systems causing movement and colour changes. 5.2.2 Input devices Manual inputs These vary from simple switches used to turn the lights on though dimmer switches and remote control units that interface to a control system to lighting control desks that are used in theatres. The point of these units is to allow people to control the lighting and care is always needed in the application of such devices to ensure that users of the system can readily understand the function of any such control. Presence detectors Most presence detectors are based on passive infrared (PIR) detectors, however some devices are based on microwave or ultrasonic technology. PIR devices monitor changes in the amount of infrared radiation that they are receiving. The movement of people in a space will be detected by them and this can be signalled to a control system. Thus, if a device detects the presence of a person this can be used to signal the control system to switch the lights on, but if the device has not detected anybody for some time this can be used to signal that there is nobody there and that the lights can be turned off. Timers Most computerised control systems have timers built in so that they can turn the lighting on or off at particular times. However, there are also a large number of time switches available that can turn lamps on an off at given times. There are also timers used in street lighting that change the time that they switch at throughout the year so that the lamps are switched at dawn and dusk. Photocells There are many different types of photocell used to control lighting. The simplest to use are those which switch on at one illuminance value and switch off at another; these are commonly used to turn exterior lights on at dusk and off at dawn. Some photocells communicate the illuminance value to the central control system, which uses the information to adjust the lighting in some way. Some photocells are mounted on ceilings with shields around them so that they only receive light reflected from the working plane, this makes them act like luminance meters and provided the reflectance of the working plane remains constant they can be set up to follow the illuminance of that plane. 115


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5.2.3 Control processes and systems In the case of simple control systems these are generally configured as some form of automated switching in the power supply to a luminaire or group of luminaires. However, more complex systems are generally configured as a network of devices including luminaires, sensors and control inputs. In most systems the devices are physically connected using some form of cabled network but, in principle, devices can be controlled using wireless or infrared communication. There are several systems in common use for lighting systems and care needs to be taken to specify the correct type for each component in the system. Two of the most common systems available are DALI and DMX 512. The basic specification for DALI systems is contained in BS EN 60929: 2006: AC-supplied electronic ballasts for tubular fluorescent lamps — Performance requirements. The DALI system is largely used for lighting systems in buildings but has been extended so that it can be used more widely. It controls luminaires via the ballast used to control the lamps. The system is designed to run up to 64 luminaires on one circuit but there are devices that can control a series of different DALI clusters thus making it possible to control all the lights in a large building. DMX 512 was designed to control lights and other equipment in the entertainment industry. The system provides 512 channels of control to a series of devices. In a typical spotlight that has its aiming controlled, three channels may be used, one to dim the luminaire and one for each axis of rotation. The system has traditionally been used in theatres but is increasingly being used in architectural feature lighting where the lighting equipment is more complex. The basic operating properties of the system are described in ANSI E1.11: USITT DMX512-A: Asynchronous serial digital data transmission standard for controlling lighting equipment and accessories.

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6.1 Objectives and constraints Lighting design can have many different objectives. Ideally, these objectives are determined by the client and the designer in collaboration and cover both outcomes and costs (Figure 6.1). The most common objective for a lighting installation is to allow the users of a space to carry out their work quickly and accurately, without discomfort. However, this is a rather limited view of what a lighting installation can achieve. For traffic routes, the objective of lighting is to facilitate the safe and rapid movement of vehicles after dark. For urban areas where people and traffic may come into conflict, safety is the primary concern although the appearance of people and buildings is also important. In areas where crime is rampant, lighting can be used to enhance security. Sport facilities are lit at night to encourage their use. Businesses use lighting to promote their brand and attract customers. Most lighting installations have to serve multiple functions. When designing lighting it is always desirable to identify all the functions that the lighting is expected to fulfill.

Chapter Six: Lighting design

PART 3: APPLICATIONS Chapter 6: Lighting design

As for constraints, an important aspect of lighting design is the need to minimise the amount of electricity consumed, for both financial and environmental reasons. It is also necessary to consider the sustainability of the lighting equipment. This means using materials that can be easily replaced and considering to what extent the equipment can be recycled at the end of its life. The financial costs, particularly the capital cost, are always an important constraint. No one wants to pay more for something than is absolutely necessary so the designer needs to be able to justify the proposal in terms of value for money. Architectural integration

Visual amenity

Visual function

Lighting design

Costs (capital and operating)

Energy efficiency

Installation maintenance

Figure 6.1 Objectives, outcomes and costs

6.2 A holistic strategy for lighting A holistic strategy for lighting design is necessary because without it important benefits will be lost and money and human resources will be wasted. The starting point is an in-depth conversation with the client and other members of the design team to formulate a design brief. At such a discussion, it will be necessary to address such fundamental questions as what do you want to see and what do you not want to see, what is the function of the space, what is the proposed architectural style and what is the budget?

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More formally, nine distinct aspects of lighting need to be considered. They are: legal requirements

maintenance

visual function

costs

visual amenity

photopic or mesopic vision

architectural integration

light trespass and sky glow.

energy efficiency and sustainability All these aspects will contribute to the success of a design, but they may not all carry equal weight depending on the particular application and situation. Also there is no particular order in which they should be considered. The important issue is that all the elements are considered, perhaps more than once, for a satisfactory solution to emerge. 6.2.1 Legal requirements There are a number of legal requirements that apply to all lighting installations. Some are general, e.g. the Construction (Design and Management) Regulations. Some are specific about the type and form the lighting that should be provided, e.g. emergency lighting in buildings (see Chapter 8). Others influence lighting design by the limits they place on the type or amount of equipment that can be used, e.g. Building Regulations. Details of the requirements of the Construction (Design and Management) Regulations can be obtained from the Health and Safety Executive publications. Details of the significance of Part L of the Building Regulations can be found in SLL Factfile 9: Lighting and the 2006 Building Regulations. It is essential that the designer and the client are aware of the relevant legal requirements. 6.2.2 Visual function This aspect is related to the lighting required for doing tasks without discomfort. Chapter 2 has shown how the illuminance incident on the task will affect the level of visual performance achievable. Recommended illuminances for different tasks are given in the SLL Code for lighting, various SLL Lighting Guides as well as in Part 3 of this Handbook. These values apply to the task area and do not necessarily need to apply to the whole working plane. The traditional way of lighting an interior work place has been a regular array of luminaires. For this approach, a minimum task illuminance uniformity (minimum/average task illuminance ≥ 0.7) is recommended. This approach has the benefit that the tasks can be carried out on the horizontal plane anywhere in the work place. In some cases the task will have a colour recognition element. In such cases it will be necessary to use lamps with a high general colour rendering index (CRI). For such tasks it will be appropriate to use lamps with a CRI ≥ 80 but for tasks with a requirement for very good colour discrimination, lamps with a CRI ≥ 90 will be necessary. The human visual system can adapt to a wide range of luminances but it can only cope with a limited luminance range at any single adaptation state. When this range is exceeded, glare will occur. If a field of view contains bright elements that cause glare it is likely that they will affect performance or at least cause stress and fatigue which in turn will cause problems.

118

To avoid this will mean using luminaires and windows that have limited luminances within the normal fields of view relative to the adaptation level. Glare limits for different tasks are given in the SLL Code for lighting, various SLL Lighting Guides as well as in Part 3 of this Handbook.


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Leisure

Figure 6.2 Map showing the possible locations of three application areas on a schematic diagram linking subjective impressions of visual interest and visual lightness

Commercial

Industrial

Low

Visual interest (Degree of light non-uniformity)

High


6.2.3 Visual amenity There is no doubt that lighting can add visual amenity to a space which can give pleasure to the occupants but whether this provides a more tangible performance benefit is uncertain (Boyce, 2003). Studies have shown that people respond to the lit appearance of a room on two independent dimensions: visual lightness and visual interest (Hawkes et al, 1979, Loe et al, 1994, 2000). Visual lightness describes the overall lightness of the space, which is related to the average luminance of vertical surfaces. Visual interest refers to the non-uniformity of the illumination pattern or the degree of ‘light and shade’. People prefer some modulation in the light pattern rather than an even pattern of illumination, the magnitude of the modulation depending on the application. There is some evidence that visual lightness and visual interest are inversely correlated (Figure 6.2).

Low

High

Visual lightness (brightness)

Although variation in the light pattern is desirable, it has to be seen as meaningful in terms of the application and the architecture. To provide random patches of light in an uncoordinated way for no reason other than to provide light variation would be a poor design solution. Acceptable examples could be highlighting displays within a retail outlet, or a floral display in a hotel lobby. There are two further areas of visual amenity that need to be considered and these are in the colour rendering and colour appearance of the lighting. The required colour rendering will depend on the functions the lighting is designed to fulfill. Where fine colour discrimination is required, light sources with a CIE general colour rendering index of at least 80 should be used. Where a natural appearance is required for people and objects, light sources with a CIE general colour rendering index of at least 60 and preferably higher should be used. Where such functions are not important poorer colour rendering light sources can be used. As for colour appearance, a light source with a correlated colour temperature (CCT) ≤ 3000 K will appear warm and if it has a CCT ≥ 5300 K it will appear cool (see Section 1.4.3). Where on this scale from warm to cool the colour appearance should be will depend on the nature of the space. In quasi-domestic situations, such as hotels, a warm colour appearance will be required but in commercial interiors a CCT of around 4000 K is appropriate as it blends reasonably well with daylight. The designer should be wary of the names applied to light sources as these can be misleading and differ between manufacturers. The best way to choose colour appearance is through practical trials. 119


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There is still much to learn about design for visual amenity but it would be negligent to ignore it. The best way to develop an understanding of visual amenity is through personal observations and trial installations. 6.2.4 Lighting and architectural integration All elements of a lighting installation contribute to the architecture or the interior design of a building. Understanding the space will be important when deciding what sort of lighting is to be employed. The dimensions, finishes, texture and colour of the materials forming the space and the appearance of the luminaires, lit and unlit, should be considered if the desired atmosphere is to be achieved. A good place to start is with the daylighting since the windows and roof lights are a fundamental element of the fabric of the building. This means considering the amount and pattern of daylight required for the particular application, and hence the size and positions of windows and roof lights. But windows cannot be designed on the basis of the daylighting alone and other visual, thermal, acoustic and privacy issues need to be addressed. Only a few lighting designers get involved with daylighting design. This is a pity because only a few architects have the skills to design an effective and efficient window system, which means that many opportunities are lost. More information on daylighting design can be obtained from the SLL Lighting Guide 10: Daylighting and window design and Chapter 7 of this Handbook. Once the daylighting has been determined then the electric lighting can be planned. To integrate electric lighting with the architecture means considering not only its operation with respect to the daylighting, but the appearance of the luminaires and controls and the way they are incorporated into the fabric of the building, as well as the lighting effect produced. Just as the light pattern needs to be meaningful with respect to the building use, the lighting scheme needs to be meaningful with respect to the architecture. 6.2.5 Energy efficiency and sustainability It is the responsibility of the lighting profession to use energy as efficiently as possible but at the same time to provide lit environments that enable people to operate effectively and comfortably. The current estimate for the UK is that approximately 19% of the electricity generated is consumed by lighting. This amounts to around 64 TW⋅h/annum. Energy use involves two components: the power demand of the equipment and its hours of use. The lighting industry has worked hard to develop equipment that has reduced the demand for electricity for lighting by producing more efficient light sources and their related control circuits, as well as more efficient luminaires. Then there are design options to be considered, such as the use of task/ambient lighting rather than a blanket provision of light by a regular array of ceiling mounted luminaires. The savings for the task/ambient approach have been estimated to be up to 50% (Loe, 2003). Good energy efficient lighting design is not just about equipment; it is also about the use of lighting. There are many examples where lighting is left on when it is not required. This may be because there is inadequate lighting through daylighting or because people are not present and therefore the lighting is unnecessary. This aspect of lighting design needs a dramatic change in attitude to improve the energy efficiency of all lighting installations. This requires changes to how the lighting is controlled both manually and automatically as well as how lighting is provided in terms of the distribution of light, particularly with respect to the daylighting. It is also necessary for the lighting industry and its customers to use equipment that is sustainable.

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6.2.6 Maintenance It must be recognised that both daylight and electric light within a building will depreciate with time. To minimise the effect of this a maintenance programme will need to be designed and implemented. The maintenance programme will also affect the lighting design and the designer will need to state the maintenance programme on which the design has been based, otherwise there could be problems when a client is comparing different design proposals. It will also be important for the client to be provided with a maintenance schedule so that they know what will need to be done. Chapter 21 discusses the various factors that need to be considered when developing a maintenance program.


This means that the materials used are wherever possible from renewable sources and that at the end of life the redundant equipment can be disposed of safely with most of the base materials being recycled.

6.2.7 Lighting costs Costs are always a major concern for any project and it is important to consider these before any work is undertaken. Both the capital cost and the running, or operational, costs must be considered at the outset. If the two cost elements are not considered together in terms of life cycle costing, then a solution which has a low capital cost but a high operational cost could be more costly overall than an installation with a more expensive capital cost but a low operating cost. A conflict of interests may arise if the two cost elements are paid for from different budgets or organisations. This can happen with local authority projects. Here the designer needs to present a balanced view of the options to enable the clients to decide on the best approach. The capital costs include the cost of the design process, the equipment and the installation process, both physical and electrical. It also includes the commissioning and testing of the installation. Allowance must also be made for any builders’ work that forms part of the lighting installation. Any other costs that are particular to the lighting design need to be included. It is important that the capital cost is agreed at an early stage if a lot of time is not to be wasted. The capital cost should be challenged if the client’s expectations seem to be unrealistic. The operational costs include the cost of the electricity consumed, which comprises items such as standing charges, maximum demand charges and electricity unit costs. They will also include the cost of maintenance, which includes cleaning and relamping throughout the life of the installation. In some cases charges may have to be budgeted for the disposal of redundant equipment although this may be borne by the supplier. 6.2.8 Photopic or mesopic vision The photometric quantities used to characterise lighting are all based on photopic vision (see Section 1.2). This makes sense for interior lighting where the luminances are usually high enough to ensure the visual system is operating in the photopic state but there may be problems for exterior lighting. This is because for adaptation luminances below about 3 cd/m2 peripheral vision is operating in the mesopic state (see Section 2.2.2) and exterior lighting often produces luminances below this level. This is a problem because the spectral sensitivity of the peripheral retina changes continually during mesopic vision depending on the adaptation luminance, the peak sensitivity moving from the 555 nm to 507 nm as the adaptation luminance decreases to the scotopic state. There is no CIE mesopic observer so no system of mesopic photometry. In this situation, the simplest approach to ensuring good mesopic vision in exterior lighting is to use a light source with a scotopic/photopic (S/P) ratio greater than 1.5. Such light sources provide stimulation to both the cone and rod photoreceptors of the retina. 121


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6.2.9 Light trespass and skyglow Light can be considered a form of pollution. This is implied by the inclusion of light as a statutory nuisance in the Clean Neighbourhoods and Environment Act: 2005. Exterior lighting is the major source of light pollution. Complaints about light pollution from exterior lighting can be divided into two categories, light trespass and skyglow. Light trespass is local in that it is associated with complaints from individuals in a specific location. The classic case of light trespass is a complaint about light from a road lighting luminaire entering a bedroom window and keeping the occupant awake. Light trespass can be avoided by the careful selection, positioning, aiming and shielding of luminaires and by operating a curfew system where lighting is only available during specified times. The Institution of Lighting Engineers (ILE) has produced general guidance on the vertical illuminance that should be allowed to fall on windows, the maximum luminous intensity of any obtrusive light source and a maximum building luminance for floodlighting. These limits are different for different environmental zones. The idea behind environmental zones is that some locations are more sensitive to light pollution than others. Table 6.1 shows the four environmental zones identified by the CIE. The limits recommended by the ILE for limiting light trespass are given in Table 6.2. Table 6.1 The environmental zoning system of the CIE Environmental zone

Zone description and examples of sub-zones

E1

Areas with intrinsically dark landscapes: National Parks, areas of outstanding natural beauty (where roads are usually unlit)

E2

Areas of ‘low district brightness’: outer urban and rural residential areas (where roads are lit to residential road standard) Areas of ‘middle district brightness’: generally urban residential areas (where roads are lit to traffic route standard)

E3

Areas of ‘high district brightness’: generally, urban areas having mixed recreational and commercial land use with high night-time activity

E4

Table 6.2 Maximum vertical illuminance on windows, maximum luminous intensity for obtrusive luminaires and maximum building luminance produced by floodlighting, for four environmental zones Environmental zones

122

Maximum vertical illuminance on windows (lx)

Maximum luminous intensity (cd)

Maximum building luminance (cd/m2)

Before curfew

After curfew

Before curfew

After curfew

E1

2

1

0

0

0

E2

5

1

50

0.5

5

E3

10

5

100

1.0

10

E4

25

10

100

2.5

25


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Sky glow is more diffuse than light trespass in that it can affect people over great distances. Sky glow is caused by the multiple scattering of light in the atmosphere, resulting in a diffuse distribution of luminance. The problem this causes is that it reduces the luminance contrast of all the features of the night sky thereby reducing the number of stars and other astronomical phenomena that can be seen. Sky glow has two components, one natural and one due to human activity. Natural sky glow is light from the moon, planets and stars that is scattered by interplanetary dust, and by air molecules, dust particles, water vapour and aerosols in the Earth’s atmosphere, and light produced by a chemical reaction of the upper atmosphere with ultra-violet radiation from the sun. The luminance of the natural sky glow at zenith is of the order of 0.0002 cd/m2. The contribution of human activity is produced by light traversing the atmosphere and being scattered by dust and aerosols in the atmosphere. The magnitude of the contribution of city lights to sky glow at a specific remote location can be crudely estimated by Walker’s Law. This can be stated as


The values in Table 6.2 are for general guidance only and may need to be adjusted for specific circumstances. For example, the criteria given under zone E1 would not preclude the installation of lighting to meet health and safety requirements. As for the maximum building luminance, this is given to avoid overlighting but should be adjusted according to the general district brightness. An alternative approach based on limiting light crossing a property’s boundary is the outdoor site-lighting performance (OSP) method (Brons et al, 2008). This method has the advantage that it deals with the site the designer is responsible for and does not require detailed knowledge of areas outside the site.

I = 0.01 P d–2.5 where: I = the proportional increase in sky luminance relative to the natural sky luminance, for viewing 45° above the horizon in the direction of the city (e.g. I = 0.1 = 10 percent increase) P = the population of the city d = distance to the city (km) This empirical formula assumes a certain use of light per head of population. Experience suggests the predictions are reasonable for cities where the number of lumens per person is between 500 and 1000 lumens. Sky glow can be reduced by limiting the amount of light used for exterior lighting, by using full-cutoff luminaires that have no upward component (see Table 4.9) and by adopting a curfew in which the exterior lighting is either extinguished or reduced to a lower level when there are few people using it. For each environmental zone the maximum installed upward light output ratio of the luminaires used should be limited as shown in Table 6.3. Again, this is general guidance only and may need to be overturned in specific circumstances. The OSP method (Brons et al, 2008) again provides an alternative and more comprehensive approach in that it takes the whole installation and covers reflected light as well as direct upward light.

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Table 6.3 Maximum installed upward light output ratio; luminous flux emitted above the horizontal plane as a percentage of the total luminous flux emitted by the luminaire Environmental zone

Maximum upward light output ratio (%)

E1

0

E2

5

E3

15

E4

25

6.3 Basic design decisions 6.3.1 Use of daylight One of the first decisions to be made when approaching lighting design for interiors is what role will daylight play. The role will depend on the building use but the decision should be recorded early on and be part of the brief. The roles may be any one or any combination of the following: to provide a view out to provide enough light to work by to save energy to provide lighting for particular tasks requiring very good colour rendering to enhance the appearance of the space by providing meaningful variation in the lighting. Depending on the primary role or roles of daylight and hence the amount and distribution of daylight in the space, the electric lighting will need to be designed as a stand-alone system or as an integrated system. 6.3.2 Choice of electric lighting system The selection of the luminaire, light source and control system to be used is an important one if electricity is not to be wasted and an efficient lighting installation achieved. The first choice to be made will be to determine the technique to be employed. For interiors, the techniques, in order of decreasing energy consumption, can be simply categorised as: a general system: providing a uniform illuminance over the whole working plane area a localised system: using luminaires located adjacent to the workstation to provide the task illuminance, whilst the overall ambient lighting is provided by the spill light from the luminaires

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For exteriors, a general system is the usual choice where work is carried out but much greater degrees of non-uniformity are acceptable where the function of the lighting is essentially decorative. The second decision to be made will be the choice of light source and luminaire. The characteristics of available light sources and luminaire types are set out in Chapters 3 and 4 respectively. It is important to appreciate that light sources differ in their luminous efficacy, life, colour properties, run-up and restrike times and in their ability to be dimmed. Luminaires differ in the distribution of light and the efficiency with which they emit the light produced by the light source.


a local lighting system, sometimes called task/ambient: this uses two separate systems that are inter-dependant; a general lighting installation to provide an ambient lighting condition and a desk or partition mounted task light under the control of the occupant and topping up the ambient lighting illuminance to achieve the required task illuminance.

The third choice to be made is the type of control system. Switching luminaires used to be the only viable approach to take, but now, with high frequency electronic dimmable ballasts dramatically reducing in price, dimming is a realistic option. For interiors, dimming can be used to save energy even when daylight is absent. This is due to the fact that all lighting is designed for average maintained illuminance, which provides more light to start with than is required. When daylight is present, dimming can be used to balance the electric lighting to the daylight. For exteriors, switching and dimming can be used to match the lighting to the patterns of use, e.g. a supermarket car park does not need to be completely lit at 3 a.m. Any users at that hour will park near the doors. There are basically two forms of lighting control systems: analogue and digital (see Section 5.2). Analogue systems typically use a 1–10 volt protocol providing continuously variable dimming. The digital systems most widely used are DALI and DMX512 (see Section 5.2.3). Both also provide continuously variable dimming. The advantages of digital over analogue control are many, one of the most important being the facility to monitor an installation through a two-way communication capability. This transfer of information makes preventative maintenance and energy monitoring possible. Control systems can provide the facility for individual or group addressing, zoning and scene setting. The recording of energy consumption is also highly desirable if the installation is to provide the information for building monitoring required by Part L of the Building Regulations. Some control systems allow remote monitoring via the internet. This can be of great benefit to companies with large building estates, such as the NHS, education authorities, banks, national retail chains etc. By monitoring centrally in a region or area, preventative maintenance can be undertaken such as the anticipation of bulk lamp replacement from the hours-run data. 6.3.3 Integration Integration of a lighting installation takes four forms: integration within the space, architecture, interior design integration with other services integration with daylight integration with the surroundings. 125


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Integration within the space A lighting installation can be visible and express the interior design or it can disappear into the background with only its effect being seen. Both approaches rely heavily on attention to detail, Specifically, attention to the appearance of the luminaire, lit and unlit, is necessary for a design that is intended to express the interior design, while attention to the builder’s work details is required if the intention is to hide the luminaires. The other aspects of the space that can interact with the lighting are the reflectances and colours of the interior décor. Large areas of low reflectance reduce the amount of inter-reflected light. If inter-reflected light is planned to make a significant contribution to the amount of light delivered, large areas of high reflectance surfaces are needed. As for surface colour, the extent to which they interact with the lighting depends on the saturation of the colour and the area it covers. Large areas of saturated colour can distort the colour of the light delivered. However, spaces without colour can be very uninteresting. The use of saturated colours over small areas provides some interest without distorting the lighting. Integration with other services Most services like sprinklers, loudspeakers, fire detectors and supply and extract grilles/diffusers have an optimum spacing to cover the area under consideration and lighting to some extent is the same. Creating a ceiling plane that is restful and harmonious to the eye requires compromise. Integration with air conditioning systems needs particular care. Luminaires on the ceiling can short circuit or deflect airflows thereby creating overheating or draughts. Also, the light output of fluorescent lamps is affected by the ambient temperature. This means extracting hot air through luminaires and integrating luminaires into chilled beams needs careful consideration. Integration with daylight To integrate electric lighting with daylight requires zoning of the electric lighting according to the distribution of daylight and a choice between switching and dimming control. For buildings with perimeter glazing a rough guide to zoning is to divide the floor plate into 3 m wide strips starting at the perimeter. For buildings with a regular array of rooflights, zoning may not be necessary. As for switching or dimming, field studies of switching behaviour have shown that, with manual switching, electric lighting is usually either all on or all off. Switching is almost entirely confined to the beginning and end of a period of occupation; people may switch lighting on when entering a room but seldom turn it off until they all leave. The year-round probability that an occupant will switch lights on when entering a room depends on the time of day, orientation of the windows and the minimum orientation-weighted daylight factor on the working area (see Chapter 7). Figure 6.3 can be used to estimate the likely energy consumption of an electric lighting installation when manual switching is used to adjust it to daylight. If the minimum orientationweighted daylight factor in the room is 1 percent and work starts at 0800 hours, Figure 6.3 shows a 60 percent probability of switching on on entering. If the room is continually occupied, we may conclude that 60 percent is the probability that the lighting will be on at any moment during the working day. Thus for a lighting installation with a load of 3 kW, and a working year consisting of 260 days, each of 8 hours, the total annual energy consumption would be 260 × (8 × 0.60) × 3 = 3744 kW⋅h

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Probability of switch on (%)

90 80 70 0.5 percent

60

1 percent 50 2 percent 40

5 percent

30 20 10


100

0 4

6

8

10

12

14

16

18

20

22

Time

Figure 6.3 The probability of electric lighting being switched on at different times of day for locations with different orientation-weighted daylight factors (from Crisp and Henderson, 1982) If luminaires are logically zoned with respect to daylight with convenient pull-cord switches for the occupants to use, each zone can be treated as a separate room. The probability of switching will differ from zone to zone, depending on the minimum orientation-weighted daylight factor in each zone. Figure 6.3 will still be applicable but the minimum orientation-weighted daylight factor, and consequent energy savings, must be estimated separately for each zone. If switching is to be relatively unnoticeable to the occupants, the proportion of the electric lighting switched should not be more than 20 percent of the total task illuminance. Automatic photo-electric controls can be used to switch electric lighting in response to daylight. Figure 6.4 shows the percentage of a normal working year during which the luminaires would be off, as a function of the orientation-weighted daylight factor and of the illuminance at which the luminaires are switched; the ‘design’ illuminance. These curves assume that ‘on’ and ‘off ’ switching will occur at the same illuminance. Where this is not the case, where the luminaires are switched off at an illuminance appreciably greater than that at which they are switched on, the mean of the two illuminances should be taken as the ‘design’ illuminance.

100 90

Percentage off

100 lx 80

300 lx

70

500 lx 1000 lx

60 50 40 30 20 10 0 0

1

2

3

4

5

Figure 6.4 The percentage of the working year that electric lighting will be switched off plotted against orientationweighted daylight factor for different ‘design’ illuminances, assuming an on/off photoelectric switching system (from Hunt, 1979)

6

Orientation weighted daylight factor

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Automatic photoelectric controls can also be used to dim the electric lighting in response to daylight. Figure 6.5 shows the percentage of a normal working year during which the luminaires would have to be switched off in order to ensure the energy saving obtainable by continuous photo-electric dimming are achieved. It applies to dimmer systems that can control down to 10 percent light output or less. Recommendations for daylighting and supplementary electric lighting are given in BS 8206: Part 2. Integration with the surroundings For exterior lighting, the lighting of the surrounding area has an impact on the perception of the brightness of the installation. The same installation in rural and urban settings will look very bright in the former and dim in the latter. This means that the maintained illuminance selected needs to be matched to the illuminances of the surroundings if the expected appearance is to be achieved. 100 90 100 lx

Percentage off

80

300 lx 500 lx

70

1000 lx 60 50 40 30 20 10 0 0

1

2

3

4

5

6

Orientation weighted daylight factor

Figure 6.5 The percentage of the working year that electric lighting will be switched off plotted against orientation-weighted daylight factor for different ‘design’ illuminances, assuming a top-up photoelectric dimming system (from Hunt, 1979) 6.3.4 Equal and approved One problem that frequently afflicts lighting designers is the substitution of a cheaper luminaire for the one specified in the original design. Such substitutions are usually made in an effort to save money. Sometimes, substitutions are justified, sometimes they are not. The key to determining if a substitution is justified is a review carried out by the original designer to determine if the substitute luminaire is the equal of the originally specified luminaire and approved to the relevant standards, i.e. if it is equal and approved. The factors to be considered in the review are the photometric characteristics, the construction and the aesthetics of the substitute luminaire. In addition, attention should be paid to the electrical characteristics, conformity to the relevant standards and the impact on maintenance. Further details of these elements of the review can be found in the joint statement issued by the Society of Light and Lighting, the Electrical Contractors Association, the Institution of Lighting Engineers and the Lighting Industry Federation in 2004 (Joint statement, 2004). 128


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7.1 Benefits of daylight In the face of increasing energy costs and concern about global warming, there is considerable interest in using daylight as the major light source in buildings. Unfortunately, there is little point in doing this if daylighting causes problems to the occupants of buildings. The possibility of daylight causing problems to occupants may seem unlikely given the well established desire of people to have natural light wherever possible, whenever available. However, a short walk around any city will reveal numerous well-glazed office buildings where the blinds on many windows are permanently closed (Figure 7.1). Such behaviour demonstrates the existence of a failed daylighting design for at least some people within the building. Nonetheless, unless there is a good reason why there should be no daylight in the building, daylighting should always be encouraged.

Chapter Seven: Daylighting

Chapter 7: Daylighting

Figure 7.1 A modern office building with extensive glazing and extensive use of blinds To make the best use of daylight it is first necessary to recognise that daylight can have both positive and negative effects on people. The conclusions of an extensive literature review on daylight (Boyce et al, 2003a) can be summarised as follows: Physically, daylight is just another source of electromagnetic radiation in the visible range. Physiologically, daylight is an effective stimulant to the human visual system and the human circadian system. Psychologically, daylight and a view out are much desired and, in consequence, may have benefits for human well-being. The performance of tasks limited by visibility is determined by the stimuli the task presents to the visual system and the operating state of that system. Daylight is not inherently better than electric light in determining either of these factors. However, daylighting does have a greater probability of maximising visual performance than most forms of electric lighting because it tends to be delivered in large amounts with a spectrum that ensures excellent colour rendering. There can be no guarantee that daylighting will always be successful in maximising visual performance. Daylight can cause visual discomfort through glare and distraction, and it can diminish the stimuli the task presents to the visual system by producing veiling reflections or by shadows. The effectiveness of daylighting for visual performance will depend on how it is delivered. 129


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People will take action to reduce or eliminate daylight if it causes discomfort or increases task difficulty. The performance of both visual and non-visual tasks will be affected by disruption of the human circadian system. To avoid such disruption, the exposure to bright light during the day and little light at night is necessary. Daylighting is a convenient means to deliver bright light during the day to people who have little opportunity to go outside. Different lighting conditions can change the mood of occupants of a building. However, there is no simple recipe for what lighting conditions produce the most positive mood. Windows are strongly favoured in work places for the daylight they deliver and the view out they provide, as long as they do not cause visual or thermal discomfort, or a loss of privacy. Therefore, the presence of well-designed windows is expected to enhance positive mood and their absence to increase negative mood, although whether it is the view out or the admission of daylight that provides the benefit is unclear. Exposure to daylight can have both positive and negative effects on health. The strongest effects occur outdoors. Exposure to daylight outdoors can cause tissue damage, which is bad, and generate vitamin D, which is good. Daylight and sunlight delivered through glass will have less ultra-violet radiation than the same radiation outdoors, but can still have adverse effects on people who are sensitive to ultra-violet radiation. Daylighting that makes what needs to be seen difficult to see can cause eyestrain. Conversely, daylighting that makes what needs to be seen easy to see can reduce eyestrain. Windows that provide a view out as well as daylight can reduce stress. These conclusions imply that good daylighting design is not simple. Thought needs to be given to the amount of daylight available, the view out, the control of glare, the light distribution in the space, solar heat gain and integration with electric lighting. When done well, daylighting can make a very effective and attractive space (Loe and Mansfield, 1998; Philips, 2004) but when done without thought or with thought limited to the external appearance of the building, daylighting can cause discomfort to occupants and add to the energy consumption of the building.

Figure 7.2 An attractive daylighting design 130


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Daylight varies in both amount and spectrum with sun altitude and atmospheric transmission. This means that the availability of daylight will vary with the season of the year and the nature of cloud cover. Figure 7.3 shows how the illuminance on a horizontal plane provided by daylight varies with the time of year and the time of day. Details on the availability of daylight can be found in SLL Lighting Guide 10 and Littlefair and Aizlewood (1999) 24 1 klx = 1000 lux


7.2 Daylight availability

5 klx 18

10 klx

20 klx

12

35 klx

Time of day (GMT)

6

Time of year

0 Winter

Spring

Summer

Autumn

Winter

Figure 7.3 The illuminance on a horizontal plane provided by daylight varies with the time of year and the time of day Of course, these illuminances are measured on an unobstructed horizontal plane. In a building, the amount of daylight available will depend on the position and size of the windows or rooflights. The contribution of daylight inside a room is given by the daylight factor in conjunction with the daylight availability. This can indicate a minimum, a range or an average. The daylight factor is defined as the ratio of the illuminance at a point within a building to the illuminance on an unobstructed horizontal surface at the same position. Daylight factor is usually expressed as a percentage. For determining the minimum contribution of daylight to an interior, it is usual in temperate climates like that of the UK to assume the luminance distribution of the sky follows the CIE Standard Overcast Sky. (Figure 7.4) This assumption eliminates sunlight from consideration. For the Standard Overcast Sky, daylight factor is the sum of three components; the sky component, the internally reflected component and the externally reflected component (Figure 7.5). The sky component is the light that reaches the measurement point directly from the sky. The internally reflected component is daylight that arrives at the measurement point after reflection inside the room. The externally reflected component is daylight that arrives at the measurement point after reflection outside the room. 131


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60˚

45˚

1.0

0.8

0.6

0.4

Relative luminance


90˚ Zenith

10:08

30˚

0.2

Horizon

0

0˚

Figure 7.4 The luminance distribution of the sky follows the CIE Standard Overcast Sky

SC = sky component ERC = externally reflected component IRC = internally reflected component

IRC SC

ERC

Measurement point

Figure 7.5 The components of the daylight factor

132

Daylight factor can be given either as a value at a specific point or as an average over a defined area like a room (Littlefair, 1991; Littlefair, 1995, Littlefair and Aizlewood, 1999). Computer software for estimating point daylight factors which can then be presented as contours or average is available.


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Daylight requirements for buildings are covered in BS 8206: Part 2 and the SLL Lighting Guide 10: Daylighting and window design. Unless the designer has some guidance about the amount of daylight preferred or required, the window area may be reduced on the basis of the building’s overall thermal performance.


It is important to appreciate that while daylight factor is useful for identifying the minimum contribution daylight will make to the illuminance, it is not relevant for determining if visual discomfort is likely to occur. Visual discomfort is most likely to occur when either the sun or a high luminance part of the sky is visible. Even when examining the minimum contribution that daylight can make to the illuminance, it is important to appreciate that, in practice, the daylight factor will vary with orientation of the window, e.g. in the UK, windows facing south will have higher values than those facing north. Corrections for window orientation can be applied by multiplying the daylight factor by a weighting factor to give the orientation-weighted daylight factor. The weighting factors for north, east, south and west-facing windows are 0.77, 1.04, 1.20 and 1.00 respectively.

7.3 Daylight as a contribution to room brightness In most buildings, users prefer rooms to have a daylit appearance during daytime hours, even when there is significant use of electric light. This appearance can be achieved by ensuring that the changing brightness of daylight is clearly noticeable on walls and other interior surfaces. For a daylit appearance without any electric lighting, the average daylight factor should not be less than 5 percent. For a daylit appearance with the use of electric lighting, the average daylight factor should be not less than 2 percent. For this condition, daylight will be sufficient for part of the year but for others additional electric lighting will be required. In both cases, the surface reflectances and the positions of windows should be high so that inter-reflected lighting in the space is strong and even. In a room where the average daylight factor is less than 2 percent, the general appearance will be of an electrically lit interior. Daylight will be noticeable only on room surfaces immediately adjacent to windows, although the windows may still provide adequate views out for occupants throughout the room.

7.4 Daylight for task illumination Where daylight alone is required to provide the illumination for a visual task, the illuminance should not fall below the recommended maintained value during daytime. The illuminance uniformity within the immediate task area should be similar to that recommended for electric lighting although the illuminance diversity may be greater. This can be determined from the daylight factors and the daylight availability.

7.5 Types of daylighting Daylight can be delivered into a building through conventional windows, clerestory windows or rooflights as well as a number of remote distribution systems, such as light pipes. 7.5.1 Windows Windows have the advantage of providing both daylight to the interior and a view out. Their disadvantage is that the amount of daylight delivered to the office decreases dramatically as the distance from the window increases, although the view out is preserved over a larger distance as long as there are no major internal obstructions.

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As a rule of thumb, daylight will penetrate to a depth of twice the height of the window head above the window sill, assuming no external obstruction of the sky. Where there is an external obstruction the extent of daylight penetration is given by the no-sky line. This is the line on the working plane beyond which no direct light from the sky will penetrate (Figure 7.6).

No-sky line Working Plane

Figure 7.6 The extent of direct daylight penetration is given by the no-sky line The important aspects of windows as far as people are concerned are their size, shape, spectral transmittance and solar shielding. Desired size and shape are determined by the nature of the view out. Glazed areas of 15 percent or less of the window-wall area and window shapes and layouts that break up the view are disliked (Keighly, 1973 a and b). Larger windows are liked depending on the nature of the view. As for spectral transmittance, there are two aspects that need to be considered, the total transmittance of light and the colour appearance of the light transmitted. Transmittances above about 40 percent are highly acceptable but as the percentage transmittance decreases, percentage acceptance also decreases (Boyce et al, 1995). There are also limits on the colours of the glass that are acceptable (Cuttle, 1979). Figure 7.7 shows the dissatisfaction contours for glass to be used in windows for daylighting. It is clear that glass types with chromaticities that depart from the central part of the black body locus risk being considered unsatisfactory. 0.6

565 nm Spectral Locus

570 nm

0.4

3.5 kK

3 kK

2.5 kK

4 kK 5 kK

30 %

50 %

y

70 %

90 %

0.5

di ss at di isf ss ac at di tio isf ss at n a ct isf io ac n tio n

di ss at isf ac tio n

575 nm

6 kK Planckian Locus

8 kK 0.3 10 kK 20 kK inf 0.2

0.1 0.15

134

0.2

0.3

0.4

x

0.5

Figure 7.7 Percent dissatisfaction contours for the chromaticity of glazing plotted on the CIE 1931 chromaticity diagram (after Cuttle, 1979)


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Even when sunlight is excluded from working areas, windows can still be a source of discomfort if bright clouds or sunlight falling on blinds cause high luminance reflections in computer screens.


Windows also need to be considered in terms of their solar shading because solar shading can have an impact on both the visual and thermal environment through the admission of sunlight. The impact on the thermal environment is through the heat gain and heat loss of the whole building and, locally, on the likelihood of thermal discomfort caused by overheating due to excessive thermal radiation (sunlight) or overcooling, due to radiant heat loss to a cold window or the generation of draughts. Visual and thermal discomfort is unlikely if direct sunlight is excluded from working areas, although there is a desire for sunlight to be visible in nonworking areas. Solar shading can be achieved through fixed features of the building such as light shelves and adjustable features such as blinds (Littlefair, 1999).

Guidance on the design of windows is given in the SLL Lighting Guide 10: Daylighting and window design. 7.5.2 Clerestories Clerestory windows are strictly a narrow strip of windows high up on the wall (Figure 7.8). They may be vertical or sloping. Because of their position, clerestory windows provide deeper penetration of daylight into the space but little by way of a view out. Clerestory windows provide a direct view of the upper parts of the sky so care is necessary to avoid glare.

Figure 7.8 Clerestory windows and a rooflight

One way to increase the penetration of daylight even further into the space is to fit prismatic refractors in clerestory windows instead of conventional glass. The effect of these refractors is to bend the light from the upper sky up onto the ceiling, from where it will be diffusely reflected. Good quality refractors are required if bright spots on the ceiling are to be avoided. Guidance on the design of clerestory windows is given in the SLL Lighting Guide 10: Daylighting and window design. 7.5.3 Rooflights Rooflights are a glazed opening in the roof of a building. Rooflights can be vertical or sloping (Figures 7.8 and 7.9). Rooflights can be oriented to minimise sun penetration as in the traditional north-facing monitor roof. 135


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The daylight penetration from rooflights can vary widely depending on the design of the rooflight and the presence of internal devices to limit sun penetration. Rooflights are a very effective way to provide daylight over a large area, single story building.

Figure 7.9 Sloping roof lights providing daylight in a factory

Guidance on the design of rooflights is given in the SLL Lighting Guide 10: Daylighting and window design. 7.5.4 Atria Atria have become an increasingly popular feature of buildings. Atria are often used to light a central circulation or social area by daylight admitted through a glass roof or wall (Figure 7.10). Atria will provide some daylight to adjacent working areas, but the amount is often small and does not penetrate very far. The main function of an atrium is to provide a pleasing visual experience and a degree of contact with the outside for people in the working areas.

Figure 7.10 An atrium providing plentiful daylight into a circulation/relaxation area of an office but limited daylight into the working areas

7.5.5 Remote distribution It is possible to provide some daylight into spaces that have no possibility of windows or rooflights through remote distribution devices such as light pipes. Such systems take various forms but all collect daylight and sunlight in some way and transmit in through a shaft or pipe by reflection to a distribution point in the space (Figure 7.11). 136


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Figure 7.11 Internal and external views of two light pipe installations


Remote daylight distribution systems are inherently inefficient and the further they have to transmit the daylight and the more convoluted the path, the greater is the inefficiency (Littlefair, 1990; Littlefair et al., 1994). The efficiency of many remote distribution systems can also vary dramatically from clear to overcast skies. Nonetheless, where there is no other possibility of providing daylight to a space, remote distribution systems can be appreciated.

7.5.6 Borrowed light Borrowed light is a term used to describe the lighting of an enclosed internal space through a window that connects to an adjacent daylit space. Borrowed light rarely brings much daylight into the internal space but it does provide a connection with the outside and can be useful when the amount of light required in the internal space is less than in the daylit space, e.g. in a corridor.

7.6 Problems of daylighting Daylighting can cause both visual, thermal and privacy problems. 7.6.1 Visual problems The visual problems of daylighting are glare and veiling reflections. Glare is caused by a direct view of either the sun or the bright sky. Glare is usually experienced when facing a window in a façade receiving direct sunlight. Veiling reflections are most commonly experienced when sitting with ones back to a window, when the high brightness impinging on a computer screen reduces the contrast of the display. The first step in overcoming glare is to ensure that the differences in luminance between the window or rooflight and the immediate surroundings are minimised. This can be done either by decreasing the luminance of the sky or by increasing the luminance of the window surround or both. The luminance of the sky can be reduced by fitting tinted, reflective or fritted glass. This can be effective for a bright sky but not for direct sunlight. The downside of such glazing is that it permanently reduces the availability of daylight. As a consequence, the view out can seem dull, particularly with an overcast sky. As for increasing the luminance of the window surrounds, this means that the glazing bars should be of high reflectance, the edges of the window or rooflight aperture should be splayed back and the wall or ceiling in which the window or rooflight is installed should be of high reflectance and well illuminated (Figure 7.12). If this is not enough then the solution to both these problems is the provision of some form of shading device or screening (Littlefair, 1999; Dubois, 2003).

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Figure 7.12 Splayed surround to a skylight

Shading devices can be either passive or active. Passive shading devices restrict daylight at all times, active shading devices do not. Passive shading devices consist of light shelves, overhangs and louvres. Light shelves are formed by a light reflective surface mounted either internally or externally, part way down a window. They are designed to shade the area near the window and reflect daylight and sunlight up onto the ceiling. This action changes the appearance of the space and balances the daylight distribution better. Light shelves do not generally increase the amount of daylight in the depth of a space by any significant amount. Light shelves need regular cleaning if they are to be effective. To ensure that parts of the ceiling near the window do not exceed the recommended maximum luminance (1,500 cd/m2) and that sunlight does not penetrate directly into the building through the window above the light shelf, it is essential to examine the geometry of the light shelf in relation to the yearly sun paths. Structural overhangs shield the windows from areas of high brightness sky and are useful for limiting building heat gain. However, they will not shield the occupants from the low winter sun. To minimise glare, the underside of overhangs should have as high a reflectance as possible. For maximum effect, louvres are best located on the exterior of a building (Figure 7.13) where they are more effective at controlling solar heat gain. The size and shape of the louvres will be influenced by orientation of the building and its latitude. South-facing facades are best protected with horizontal elements whilst east and west facades are better protected by using vertical elements angled slightly to the north. Roof lights can be protected by shaped cells where the dimensions will be decided by whether all sunlight is to be excluded at all times (Lynes and Cuttle, 1988). Grills are an alternative to louvres for shading a window wall.

Figure 7.13 External louvres

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Others, such as venetian and vertical blinds allow the user to adjust blind coverage and the angle of the blades to preserve a limited view out while restricting the admission of sunlight. Yet others, such as roller blinds allow the view of the sky to be restricted while preserving a view of the ground outside. While such adjustments are possible in principle, in practice human inertia usually means that blinds are adjusted rarely with the consequence that the amount of daylight in the interior is less than expected by the designer (see Figure 7.1). Such inertia can be overcome by using motorised rather than manual blinds linked to sunlight on the façade but this is expensive and is another maintenance issue. All blinds should have a reflectance of at least 0.5. Where they are likely to be subject to direct sunlight, blinds should have a transmittance of less than 0.1.


Active shading devices, such as louvres and awnings, are located on the exterior of a building. Motorised louvres can be effective at maximising the amount of daylight available, whilst reducing the penetration of the sunlight. Movement of louvres can be distracting. They also impose a maintenance requirement. The same concerns apply to motorised awnings but in addition, there is a need to sense wind speed so that the awnings can be retracted if necessary. Screening is usually provided by some sort of blind fitted to the window. Blinds can be used to reduce glare and direct radiation but in so doing they may also restrict daylight and view out. Some blind materials, such as perforated fabric, allow a degraded view out to be retained while limiting daylight admission.

7.6.2 Thermal problems Daylight admitted to a building represents a heat load. In winter this may be useful but in summer it can represent an additional cooling load. Therefore, when considering the energy balance of the whole building, it is essential to consider the contribution of daylighting. On a local scale, sunlight directly incident on people near a window can cause thermal discomfort. This is a good reason for not positioning workplaces close to a window but rather to use this space for circulation. When selecting shading devices, consideration should be given to these effects. 7.6.3 Privacy problems Extensively glazed buildings can present privacy problems, particularly on the ground floor. Concerns about privacy can lead to blinds being closed at all times with a consequent lack of daylight and view out. There is little that can be done about the admittance of daylight but a degraded view out can be preserved without sacrificing privacy by using blinds made from perforated fabric, particularly when the outside face of the blind is of high reflectance and the inside face is of low reflectance. An alternative solution is to move workplaces away from the windows and to use this space for circulation. Recommendations for daylighting and supplementary electric lighting are given in BS 8206: Part 2.

7.7 Maintenance Dirt will build up on the exterior and interior surfaces of windows and rooflights. This will reduce the transmittance of the glass and therefore the amount of daylight entering the building. The degree to which this will occur will depend largely on the inclination of the glass and the air quality of the local environment. A busy urban environment will produce more dirt than a rural one. To minimise the problem a regular window cleaning programme is needed, which will require easy and safe access to the windows. Without this, window cleaning will be expensive and is likely that it will not be carried out as often as necessary. 139


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Chapter Eight: Emergency lighting

Chapter 8: Emergency lighting 8.1 Legislation and standards Emergency lighting is a legal requirement in almost all premises. Details of emergency lighting systems can be found in SLL Lighting Guide 12: Emergency lighting design guide. When the normal mains lighting fails in areas without natural light it is necessary to evacuate the premises, to move people to a place of safety or to allow essential processes to continue or be shut down. During this period, emergency lighting should be provided from a source independent of that supplying the normal lighting. A number of European Union Directives have implications for emergency lighting. They are: The Construction Products Directive (89/106/EEC) The Workplace Directive (89/654/EEC) The Signs Directive (92/58/EEC). These Directives have been implemented into UK law. For emergency lighting, this has been achieved through the Building Regulations: Approved Document B in England and Wales, the Building Standards (Scotland) Regulations and associated Technical Standards for Scotland and the Building Regulations (Northern Ireland) 2000 and Technical Booklet E for Northern Ireland, the Fire Precautions (Workplace) Regulations and the Health and Safety (Safety Signs and Signals) Regulations. In addition, the responsibility for ensuring safety in fire has now been shifted by the introduction of the Regulatory Reform (Fire Safety) Order 2005, from the fire authorities to any person who exercises some level of control over premises. This person is required to take reasonable steps to reduce the risk of fire and to ensure that occupants can safely escape if a fire does occur. To meet these obligations, it is necessary to carry out a risk assessment, create and implement a plan to deal with an emergency and to document the findings. Guidance is available from BS 5266-10: 2008. As well as these legal requirements for emergency lighting, standards govern both equipment design and performance and the design of emergency lighting systems. BS EN 60598 is the standard covering all types of luminaires. Part 2.22 covers emergency lighting luminaires. BS 5499 covers the colours, design and layout of emergency signs and is based on the international standards ISO 3864 and 6309. There are numerous product standards covering lamps and individual components of luminaires. BS 5266 covers design of emergency lighting systems as well as some specific equipment. It consists of the following Parts: BS 5266-1: Code of practice for the emergency lighting of premises BS 5266-2: Code of practice for electrical low mounted way guidance systems for emergency use BS 5266-3: Specification for small power relays (electromagnetic) for emergency lighting applications up to and including 32 A BS 5266-4: Code of practice for design, installation, maintenance and use of optical fibre systems BS 5266-5: Specification for component parts of optical fibre systems

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BS EN 1838, BS 5266-7: Lighting applications. Emergency lighting BS 5266-8: Emergency escape lighting systems layout (2004) (dual numbered BS EN 50172). Various standards covering design of lighting schemes make reference to emergency lighting, including BS EN 12464: Lighting of workplaces, BS EN 12193: Sports lighting and BS EN 50172: Emergency escape lighting systems.

8.2 Forms of emergency lighting Emergency lighting can take several different forms depending on its purpose. Figure 8.1 shows a classification of emergency lighting. The first division is between escape lighting and standby lighting. Escape lighting is designed to ensure the safe evacuation of the space. Standby lighting is designed to enable continued operation of space. Escape lighting is subdivided into the lighting of the escape route, the lighting of open areas where there is no defined escape route and high risk areas where a hazardous activity takes place and needs to be made safe before evacuation.


BS 5266-6: Code of practice for non-electrical low mounted way guidance systems for emergency use. Photoluminescent systems

Emergency lighting

Escape lighting

Escape route

Open area

Standby lighting

High risk area

Low mounted way guidance system

Figure 8.1 Classification of emergency lighting 8.2.1 Escape route lighting An escape route is a clearly defined, permanently unobstructed route equal to or more than 20 m long and up to 2 m wide. The lighting of such routes, or the 2 m strips of wider routes, is specified in terms of minimum illuminances on the floor, illuminance diversity, glare limits, response times, duration and light source colour rendering. The specific criteria are as follows: Minimum illuminance on the centre line: 0.2 lx, but preferably 1 lx. Minimum illuminance on the centre band of the route, consisting of at least 50% of the route width: 0.1 lx, but preferably 0.5 lx. Illuminance diversity: maximum/minimum illuminance on the centre line < 40.

Maximum luminaire luminous intensity for level routes: see values in Table 8.1. These apply in all directions for angles between 60 and 90 degrees from the downward vertical. Maximum luminaire luminous intensity for non-level routes: see values in Table 8.1. These apply for all directions within the lower hemisphere.

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Maximum response time: minimum illuminance within 5 s of supply failing (15 s if occupants familiar with place). Minimum duration: 1 hour. Minimum light source general colour rendering index: 40. 8.2.2 Signage The style and details of the safety signs for escape routes are defined in BS 5499 (Figure 8.2). ISO 3864 gives the internationally agreed formats of exit signs and safe condition signs (Figure 8.3). The designs consist of a rectangular or square shaped frame with a white pictogram on a green background. The green area must be more than 50% of the total area of the sign and the colour must conform to ISO 3864-1. As the pictograms can differ in style and content, it is important to consult the enforcing authority for a particular project on its interpretation prior to choosing the signs.

Exit

Figure 8.2 Safety signs for escape routes

Figure 8.3 Exit signs and safe condition signs

In addition to the design of the sign, there are photometric, geometric, response time and duration requirements for safety signs. These are as follows: Colour: conform to ISO 3864-1 chromaticity co-ordinates. Minimum luminance of safety colour: 2 cd/m2.

Luminance diversity: maximum/minimum luminance of colour < 10.

Luminance contrast range: luminance ratio of white to colour > 5 but < 15. Maximum viewing distance (externally illuminated sign): 100 × mounting height.

Maximum viewing distance (internally illuminated sign): 200 × mounting height. Minimum mounting height: 2 m above floor. Minimum response time: 50% of design luminance in 5 s, 100% of design luminance in 60 s. Minimum duration: 1 hour.

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8.2.3 Open area lighting An open area is defined as an area of at least 60 m2 which people have to move through before reaching an escape route. Open areas are divided into two types: those which are unfurnished or in which the furnishings can be easily reconfigured and those in which the seating is fixed. Examples of the former are open plan offices and covered car parks. Examples of the latter are concert halls and lecture halls. Signage defining access to escape routes should be visible from all points in both types of open area.


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Minimum illuminance on the empty floor, excluding a 0.5 m wide perimeter band: 0.5 lx. Illuminance diversity: Maximum/minimum illuminance on the empty floor < 40. Maximum luminaire luminous intensity: see values in Table 8.1. These values apply in the zone 60 to 90 degrees from downward vertical. Maximum response time: 50% of minimum illuminance within 5 s of supply failing and 100% within 60 s. Minimum duration: 1 hour. Minimum light source general colour rendering index: 40.


The lighting requirements for the open areas which are empty or where the furniture can be easily reconfigured are as follows:

Table 8.1 Maximum luminaire luminous intensity for escape route, open area, fixed seating area and high risk area emergency lighting for different luminaire mounting heights

Mounting height above floor (m) h < 2.5

2.5 ≤ h < 3.0

3.0 ≤ h < 3.5 3.5 ≤ h < 4.0 4.0 ≤ h < 4.5 h ≥ 4.5

Maximum luminaire luminous intensity for escape route, open area and fixed seating area lighting (cd)

Maximum luminaire luminous intensity for high risk area lighting (cd)

500

1,000

900

1,800

1,600

3,200

2,500

5,000

3,500

7,000

5,000

10,000

The lighting requirements for fixed seating open areas, which may be raked, are as follows: Minimum illuminance on a plane 1 m above the floor of the seated area: 0.1 lx. Illuminance diversity: maximum/minimum illuminance on the plane 1 m above the floor of the seated area < 40. Maximum luminaire luminous intensity: see values in Table 8.1. These values apply in the zone 60 to 90 degrees from downward vertical.

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Maximum response time: 100% of minimum illuminance within 5 s of supply failing. Minimum duration: 1 hour. Minimum light source general colour rendering index: 40. 8.2.4 High risk area A high risk area is defined as one where a hazardous activity occurs that has to be made safe or terminated before leaving or where people passing by may be exposed to the hazard, e.g. moving machinery. The presence of a high risk area should be revealed by the risk assessment required by the Fire Precautions (Workplace) Regulations 1997. The lighting requirements for high risk areas are as follows: Minimum illuminance on the task: 10% of the maintained illuminance on the reference plane of the task (see SLL Code for lighting) but at least 15 lx. Minimum/average illuminance uniformity on the reference plane for the task > 0.1.

Maximum luminaire luminous intensity: see values in Table 8.1. These values apply in the zone 60 to 90 degrees from downward vertical. Maximum response time: 100% of minimum illuminance within 0.5 s of supply failing. Minimum duration: period for which the risk exists to people. Minimum light source general colour rendering index: 40. 8.2.5 Standby lighting In areas or places where a continuous operation is required during the failure of the supply to the normal lighting, standby lighting should be installed. An example of such a location would be an operating theatre in a hospital. This system should provide adequate illumination for the visual tasks as recommended in the Schedule of the SLL Code for lighting. If standby lighting is used for escape lighting, then the escape lighting part should be segregated from the rest of the system and should conform to the rules applied to emergency lighting systems.

8.3 Design approaches Emergency lighting should be considered as an integrated part of the building lighting. Unless this is done, there is a risk that the normal lighting and the emergency lighting will clash in appearance to the detriment of the whole scheme. Emergency lighting can be provided using either self-contained units or a centrally powered system using either batteries or a motor-generator set. A self-contained unit contains its own power source and can be a stand-alone luminaire or an emergency version of the normal lighting luminaires. Central systems provide power to the emergency light source via separate, protected wiring to slave luminaires.

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For small buildings, the most economic solution is nearly always self-contained units. In large buildings, such as office blocks, factories and shopping centres, the most economic solution is nearly always central battery systems unless a generator is required for other purposes. The balance of costs between the options is related to the equipment cost and the wiring cost. Central systems use cheaper luminaires without batteries but have a costly central battery and charger/inverter or generator and fuel tanks, both requiring segregated protected wiring.


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8.4 Emergency lighting equipment 8.4.1 Power sources Self contained luminaires Self-contained luminaires have a secondary sealed battery, a charger (control unit), circuitry (which monitors the mains supply) and a lamp. In the mains-healthy condition, the battery is charged. In the event of a failure of the mains supply, the battery is connected to the lamp either directly or via an inverter module. The battery is usually a sealed rechargeable nickel-cadmium, lead acid or nickel-metal hydride type. These batteries are small, with limited storage capacity and life, and are very temperature sensitive. They should conform to IEC 60285, IEC 60896-2 or IEC 61056-1 and should provide four years service life. Care will be necessary in their disposal (see Section 21.9).


The running costs of central systems are usually lower than those of a system using selfcontained luminaires, as only the central unit needs to be monitored whereas self-contained units need regular servicing and replacement of the battery packs.

Central battery systems Central battery systems consist of a remotely located power source connected by protected wiring to slave luminaires. The batteries consist of either vented or sealed lead-acid or nickel cadmium alkaline cells. They have high storage capacity, long life and a wide operating voltage range. These batteries should conform with BS EN 50171. In addition to the battery, the system includes subcircuit monitoring of the supply to normal lighting, and an automatic change-over device to connect the slave luminaires to the power supply when the mains supply fails. There are three main types of systems. AC/DC battery powered systems supply direct current from the battery to the emergency slave luminaires, normally at 24, 50 or 110 V. If a maintained system is required, this is normally achieved by using floating batteries or by using a transformer to provide the appropriate output voltage in the supply healthy condition. Special or modified luminaires have to be used to be compatible with the range of output voltages and the effects of supply-cable voltage drop. These luminaires normally provide higher light outputs than are available from self-contained luminaires. AC/AC battery powered systems modify the output from the battery by using an inverter to create 230/240 V AC. These systems can operate any suitable normal luminaires, which do not need to be modified, and so they can provide full light output in the emergency condition. The power unit has to be matched to the emergency load and be capable of supplying both the total wattage and VA rating of the load and also providing the full starting surge of the luminaires. Static inverters designed for the application should be compatible with the luminaire characteristics but caution should be exercised if a system using a general purpose uninterruptible power supply unit (see below) is being designed. BS EN 50171 sets out some important points that need to be checked. Uninterruptible power supplies (UPS) are a form of AC inverter which continue to provide their output without a break during a supply failure enabling them to be used with discharge lamps that otherwise would have unacceptably long re-strike times. Because these inverters are normally used for computer back-up care must be taken to ensure they are correctly engineered for emergency lighting use. The UPS must comply with the requirements of BS EN 50091 as well as BS EN 50171. 145


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The charger must be capable of recharging the battery to 80% of capacity within 12 hours. The battery must be designed for 10 years design life (lower life batteries exhibit a sudden failure mode, which will not be picked up by the emergency lighting testing procedures). The output must be capable in the emergency condition of clearing all distribution protection devices and fuses (normally a UPS unit drops down to zero voltage when sensing a distribution short circuit). It is important to clear the protection device and re-supply those parts of the building that do not have a fault. The inverter must be capable of starting the load from the battery in an emergency. The system monitors, as defined in BS EN 50171, should be supplied. Generators The main components of a generator system are a prime mover driving an alternator, fuel tanks, operating controls and starter batteries. The generator has to be able to start automatically and to provide the power for the load within 5 s (or in some cases within 15 s) as detailed in BS 5266-1. As with all central systems, the distribution wiring must be fire protected and also the last normal lighting circuits must be monitored and the emergency luminaires automatically activated if the local circuit fails. As compliance with the safety requirements for the whole generator system may be arduous, it may be preferable to provide one-hour duration battery-powered luminaires in addition to the generator set. Testing of generators should be in accordance with the manufacturer’s instructions and Home Office guidance. 8.4.2 Circuits Cabling For self contained systems, all the wiring is internal to the luminaire. The luminaire should conform to BS EN 60598 and be CE-marked. For central systems, the integrity of the system is the paramount design consideration as the failure of a single part could render the entire emergency lighting installation ineffective. Where possible, the power supply should incorporate some redundancy, for example more than one battery room and multiple distribution circuits can be provided. To enhance integrity further, the distribution circuits should be divided and segregated such that the risk of a total loss of emergency lighting in any one area is minimised. Precautions should include the use of fire survival cables such as mineral-insulated copper conductor (MICC) cables, armoured power cables to BS 7846 or low-smoke-and-fume (LSF) cables in protected routes. Examples of methods of protection include metal trunking and conduit. Cables run in ceiling voids that do not form part of a fire-rated zone should not be run in open trays unless they are of the MICC type, armoured cable to BS 7846 or conform to cable performance standards BS 6387 or IEC 60364-5-52. Particular attention should be paid to the most vulnerable parts of the distribution system, for example where cabling enters and leaves enclosures and luminaires. Suitable glands should be provided which maintain the same level of integrity as the cabling being used. Where slave luminaires are spurred off a main circuit, the final cabling should be to the same standard as the rest of the system. Cabling provided solely for emergency lighting purposes should be clearly identified as such and labelled accordingly. It is desirable to include some form of sensing to prove the integrity of the emergency lighting circuits. Electromagnetic compatibility (EMC) It is also important that the overall design of a centrally supplied emergency lighting system is EMC compliant, as many of the components used in these systems, although individually suitable, may interact in such a way as to generate electrical interference. Verification should be sought from the equipment manufacturers and systems integrators that EMC issues have been considered properly This is particularly important when attempting to convert conventional luminaires to emergency lighting luminaires with an ‘emergency pack.’

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Surge-protection devices should be self-resetting and not render the emergency lighting inoperative. Interactions Where a building management system (BMS) is employed, it is essential that any failure of this does not adversely affect the emergency lighting, for example by incorrectly switching maintained luminaires. A BMS failure should not be seen by the emergency lighting system hold-off relays as a general lighting power supply failure. Lighting controls may be in use on circuits that include emergency lights. The permanent line feed to hold-off relays should be taken from a point that is independent of the control-system power supply. Where dimming systems are linked to fire alarms (e.g. in restaurants and night clubs), note that lighting provided by the dimming system under alarm conditions is additional to and separate from the emergency lighting.


Protection Cabling, changeover relays and luminaires should be resistant to interference from transient over-voltages caused by supply surges and by switching (changeover). Protection should be provided which ensures safe operation of the emergency lighting under transient conditions, as well as protecting the equipment itself from damage.

Special circuits In addition to these general considerations, there are some special circuits required for maintenance work or testing. For details, see SLL Lighting Guide 12: Emergency lighting design guide. 8.4.3 Luminaires There are two basic types of emergency lighting luminaires: self-contained and slave. These should both conform to BS EN 60598-2-22. Self contained luminaires Self-contained emergency luminaires contain a battery to provide power and may be of three types: maintained, non-maintained or combined. A maintained luminaire is one in which all the emergency lighting lamps are operating when the normal lighting is on and when there is a failure of the mains electricity supply. A non-maintained luminaire is one in which all the emergency lighting lamps are in operation only when the electricity supply to the normal lighting fails. A combined (or sustained) luminaire is one containing at least two lamps, one of which is energised from the normal lighting supply and the other from the emergency lighting supply. Self-contained luminaires may be dedicated or may be converted from normal luminaires by adding an emergency conversion unit. If the work is not carried out by the original equipment manufacturer, the person who does it must have relevant training and experience. More detailed guidance can be found in ICEL Publication 1004. The product must be retested for compliance with CE-mark requirements and conform to BS EN 60598-2-22. Slave luminaires Slave luminaires are normal luminaires that have mains-voltage operating components or have components intended only for emergency use, and have a power feed from a central emergency power source. Special care must be taken over the loop-in and loop-out of supply wiring using joint glands so that fire will not damage the feed cables in the luminaire. 147


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Alternatively, the luminaires may be fed by means of a spur off a protected ring. Slave luminaires may be designed to operate from either AC or DC power supplies. For an AC supply, the luminaire is normally AC, but may be DC with internal rectifiers. Supply voltage in emergency mode may not be the same as that in mains mode — if the luminaires are maintained, a changeover relay will be needed. For a DC supply, the luminaires may be DC or fitted with an inverter to operate on AC. Again, if they are maintained, a changeover relay will be required. In both cases, the designer must be clear as to the lumen output available from the luminaires in emergency mode. 8.4.4 Luminaire classification Table 8.2 shows an emergency lighting luminaire classification system. The resulting code identifies the type of system, mode of operation, facilities, and for self-contained luminaires, the rated duration. The classification of a specific emergency lighting luminaire is shown by the label attached. Table 8.2 Emergency lighting luminaire classification Type

Mode of operation

Facilities

Duration for self-contained luminaires

X = Self-contained

0 = Non-maintained

A = Includes test device

10 = 10 minutes

Z = Central system

1 = Maintained

B = Includes remote test module

60 = 1 hour

2 = Combined non-maintained

C = Includes inhibiting mode

120 = 2 hours

3 = Combined maintained

D = High-risk task luminaire

180 = 3 hours

4 = Compound non-maintained 5 = Compound maintained 6 = Slave

8.4.5 Light sources To be suitable for use in emergency lighting luminaires, light sources need to have fast run-up and restrike times, and preferably a long life. Tungsten and tungsten halogen lamps are infrequently used because of their low efficiency and short life, except in low-temperature applications because in such conditions their light output is not affected. The fluorescent lamp with hot cathodes, in either linear or compact form, is the lamp used for most emergency lighting applications because its high efficiency and long life are an ideal combination. However, cold-cathode lamps, despite lower efficiency, can be useful because of their even longer lamp life. Lamps with internal starters should not be used. Also, care must be taken when using amalgam versions of fluorescent lamps because these have slow run-up characteristics. 148


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Light emitting diodes can be used, particularly for safety signs where long lamp life is a priority. They are also very efficient at low temperatures. An important consideration in selection of lamps for use in emergency lighting is the likelihood of lamp failure, as any dark spot in an emergency lighting installation can be dangerous. Information on the likelihood of lamp failure is given in the lamp survival factor (LSF). Table 21.3 gives typical LSFs for a range of common lamps. For accurate results, the lamp manufacturer’s data should be used for all actual designs of emergency lighting. The data are based on lamps running on conventional control gear and thus give values of survival factor that may be expected for maintained emergency lighting installations. LSF in non-maintained installations is harder to predict. Although the number of hours that lamps are running in nonmaintained installations is low, it is common for the control gear to heat the cathodes of fluorescent lamps continuously by passing a current through them; regular inspection is therefore necessary to ensure all units are working.


High-pressure discharge lamps are not normally suitable for emergency lighting because of their extended run-up and restrike times.

8.4.6 Others There are two forms of safety sign that do not require any power to be delivered. One uses radioactive tritium as a light source. Tritium powered signs give a low light output but can be useful in locations where flammable or explosive atmosphere is present. A risk assessment should be undertaken to ensure that their output is adequate at the location where they are intended to be used. Special care must be taken during disposal of these devices as they are radioactive; there are legal obligations for safe handling and storing. The other uses the phenomenon of photoluminescence to provide light (see Section 3.1.4). For this to work, the sign has to be well illuminated prior to the emergency. In the event of mains failure, a chemical reaction, created by the previous illumination, causes the sign to emit light at a low level, considerably less than the signage requirements of BS 5266-7/BS EN 1838; however, they are useful to provide additional information and are required for emergency lighting on ships. Low-mounted way guidance systems may be used in addition to the required emergency lighting. Such systems should conform to BS 5266-6.

8.5 Scheme planning 8.5.1 Risk assessment The first step in planning an emergency lighting installation is to carry out a fire risk assessment. In work places where five or more people are employed, such an assessment is a legal requirement. A fire risk assessment requires working through the following steps: Identify potential fire hazards in the workplace: sources of ignition, fuels, work processes. Identify the location of people at significant risk in case of fire: who might be in danger (employees, visitors) and why? Evaluate the risks: are safety measures adequate or does more need to be done (fire detection, warning, means of fighting fire, means of escape, fire safety training of employees, maintenance and testing of fire precautions?)

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Carry out improvements. Record findings and actions taken: prepare emergency plans, inform, instruct and train employees. Keep assessment under review: revise it when situation changes. 8.5.2 Recommended systems for specific places The schedule in Table 8.3 is intended for guidance only. The recommendations assume that the risk assessment has been completed and that the space has no windows or has windows but the space is in use after daylight hours, or that the daylight does not penetrate into the space. It is also assumed that the occupants/visitors have adequate familiarity with the layout of the emergency routes and facilities of the building, that occupants of small rooms are able to vacate their rooms without emergency lighting but that corridors, stairs and escape routes are provided with emergency lighting. It is essential that routes and exit doors are kept clear and unobstructed so that they are fit for use at all times. It is also important to avoid placing emergency lighting luminaires on escape routes or close to exit doors in such a position that they cause disability glare to those evacuating the building. Most premises requiring emergency lighting can be associated with areas in the ‘general building areas’ section of Table 8.3. Other applications are included only if there is a change to the ‘general building area’ recommendations. Note that some of the recommended durations and modes of operation are subject to statutory requirements and should be determined during consultation with the appropriate enforcing authorities.

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System

Locations of luminaires

Notes

Entrance lobby/reception

NM/1

Wall or ceiling mounted

Consider security

Corridors

NM/1

Wall mounted at changes of direction or level, at fire alarm call points and at firefighting equipment

Consider identification of exits

Staircase

NM/1

Wall or ceiling mounted at each landing

Consider identification of exits

Staff restaurants

NM/1

Wall or ceiling

Consider additional requirements if used for entertainment purposes

Telecommunication/ control rooms

NM/3

Wall or ceiling to illuminate switchboard, control desk etc

Consider additional illuminance, e.g. 5 lx

Plant room/boiler room/lift motor room

NM/3

Wall or ceiling to illuminate panels, plant switchgear etc

Consider additional illuminance, e.g. 5 lx

Lift

NM/1

Ceiling

Refer to BS 5655-1

Toilet

NM/1

Wall or ceiling

Only required for toilets greater than 8 m2 floor area (see BS 5266)

Offices (cellular)

Not required

Exit signs on wall or ceiling

Consider emergency lighting where an office gives access to other areas or where large areas of open plan are proposed

Offices (open plan)

NM/1

Ceiling

Department store

NM/1

Wall or ceiling

People may be unfamiliar with layout

Covered shopping complex

NM/1

Wall or ceiling (shatter proof)


Hotels/boarding houses

NM/3

Ceiling or wall (see general building areas) Special care required in identifying means of escape with directional and exit signs


Hospitals

NM/3

Ceiling or wall

Escape lighting required for the movement of patients and staff to safe location. Longer durations may be necessary. Standby lighting may be needed for the continued treatment of patients

Application (area)

General building areas


Table 8.3 Recommended systems for different building types. In this table, M = maintained emergency lighting, NM = non-maintained emergency lighting, and the number following is the minimum duration in hours.

Non-domestic residential

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Application (area)

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System

Locations of luminaires

Notes

M/3

Ceiling or wall. Special care required in identifying means of escape with directional and exit signs

Lower illuminance of 0.02 lx is generally maintained during public use

Public places Cinemas (auditoria)

As above but illuminance raised to 0.2 lx when normal supply fails

Theatres (auditoria)

Places of assembly

M/3

Ceiling or wall. Special care required in identifying means of escape with directional and exit signs

Other systems may be acceptable depending on size and location

Covered car parks

NM/1

Ceiling. Shatter-proof luminaires should be considered. Special care required in identifying means of escape with directional and exit signs

In some cases, exit signs may be adequate

Computer rooms

NM/1

Ceiling or wall to illuminate working areas and walkways

Where standby or no-break supply is available emergency lighting may be connected to this supply

Conference facilities

NM/1

Ceiling or wall and exit signs

Consider unfamiliar persons using facilities. Consider alternative applications of facilities

Industrial factories

NM/1

Locate to define gangways, corridors and safe areas. Proof luminaires may be required in some areas (IP54)

Consider additional luminaires to highlight specific hazards

Schools, colleges

NM/1

Ceiling or wall

Consider additional luminaires for entertainment use out of normal hours. Consider alternative applications of area

Sports

NM/1

Wall or ceiling, shatterproof. Special consideration of location

Consider alternative applications of area and the mechanical protection of equipment

Pedestrian walkways, where forming part of the escape route

NM/1

Wall. Shatterproof luminaires should be considered

Consider waterproof luminaires if walkways are exposed or external

Museums and art galleries

NM/1 or NM/3 on larger sites

Wall or ceiling. Special care required in identifying means of escape with directional and exit signs

Consider security aspects

Educational and recreational

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8.6 Installation, testing and maintenance The success of an emergency lighting system depends not only on the design, planning and selection of the right equipment but also on the satisfactory installation and maintenance of the equipment throughout its service life. 8.6.1 Installation The emergency lighting system should be installed as instructed by the designer of the scheme and in accordance with the equipment manufacturer’s instructions. The designer usually provides a schedule of installation, including scheme plans and wiring/piping drawings in which the location of equipment, placing of protection devices and the choice and routing of wiring/piping are set out. The schedule or drawings may also give the sequence of fixing and connections, particularly of complex systems. All such schedules and drawings should be added to the logbook on completion of the installation. These should be updated with information of all scheme modifications made during the life of the installation.


8.5.3 Planning sequence Given that the risk assessment reveals a need for emergency lighting, it is then necessary to identify the lighting requirements that have to be met, the type of system to be used and its mode of operation. Once these decisions have been made, the next step is to adapt the generic design to the specific location. Advice on how to do this can be found in SLL Lighting Guide 12: Emergency lighting design guide.

8.6.2 Maintenance and inspection Maintenance and inspection of the installation should be done regularly. The designer should provide a maintenance schedule that should list and give details of replacement components such as lamp type, battery, fuses, cleaning and topping-up fluids. Caution should be exercised while carrying out maintenance as un-energised circuits may suddenly become energised automatically. Prime movers and generators will almost always be started without warning in an emergency or automatic test since a sensor remote from the plant enclosure initiates the sequence of operations. Batteries should be maintained in accordance with the manufacturer’s recommendations. Sealed batteries used in self contained luminaires require no maintenance. Self-contained nickel–cadmium (Ni–Cd) batteries have an operational life of four years. After this period the batteries must be replaced with a type specified by the manufacturer. Sealed batteries, used in central systems, will not require maintenance but it is advisable to check, clean and grease the terminals at regular intervals. Luminaires and safety signs should be cleaned at regular intervals that may coincide with the time of inspection. Any defects noted should be recorded in a logbook and rectified as soon as possible. The cleaning interval is dependent on the environment around the installation. Serviceable components should be replaced at the end of the recommended component service life by an approved part. Inspection and testing of various aspects of emergency lighting should be carried out daily, monthly and yearly. The charging supply to central battery systems should be checked daily as should progress on rectifying any faults entered in the logbook. 153


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A short-duration test should be performed monthly, by simulating a failure of the normal lighting power supply, to verify that all emergency luminaires are operating. This applies for both self-contained and central systems. The duration of the function test should be as brief as possible, so as not to discharge batteries unduly or damage the lamps. Generators should be checked for automatic starting and to ensure that they energise the emergency lighting system correctly. A full duration test of all systems should be performed yearly, to verify that the emergency lighting provides its design output for the full design duration. The duration test should be arranged to occur when the time needed to recharge batteries has the least impact on the occupation of the building. Records should be kept of all the tests made and of the results obtained. Where self-testing or remote testing features are being used, those responsible for emergency lighting systems should verify that the tests have been conducted on schedule and have given satisfactory results. Details of routine testing are given in BS EN 50172: 2004. An increasing trend is for emergency lighting to incorporate some form of self-testing facility, or for the luminaires to incorporate a remote monitoring feature. The electrical test should verify that any self-testing system performs as intended, without impairing the integrity of the lighting design. Where self-testing or remote monitoring systems are used as the basis of compliance with BS 5266-1: Section 12, visual inspection of the installed equipment should be carried out at least annually to verify that it is in good mechanical condition. BS EN 62034: 2006 gives details of automatic test systems for battery powered emergency escape lighting. 8.6.3 Documentation Given the extensive regulatory framework associated with emergency lighting, good documentation of the installation is essential. The documentation should include the completion certificate, an initial inspection certificate based on the model in BS 5266-1, a maintenance schedule and a logbook. 8.6.4 Commissioning and certification Electrical testing A full electrical test in accordance with BS 7671 is required when commissioning an emergency lighting installation. For self-contained systems, an electrical test should be carried out to ascertain that all luminaires are working in the correct manner, i.e. maintained, non-maintained and, where appropriate, combined. It should be verified that the battery-charging supply is present and indicated, and that the luminaires operate in emergency mode on simulation of a general supply failure. After initial commissioning, and allowing for a full charge of all batteries, it is good practice to perform a duration test to confirm that the system will perform for the designed duration. It should be confirmed that all luminaires reset to normal or standby mode as appropriate after the restoration of the normal supply. Where additional controls such as switched–maintained, inhibiting or rest mode are fitted, it shall be verified that these operate in the correct manner. For central battery or generator systems, the system should be tested in normal and emergency modes to determine the correct changeover of luminaires and full functionality in emergency mode. With central systems, it is essential that a duration test is carried out.

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Where self-testing and remote testing systems are included, the system should be set up and tested for functioning in accordance with the suppliers’ instructions. A copy of these instructions should be placed with the logbook. Photometric testing Photometric measurements to confirm that the system meets the lighting requirements are also desirable. When photometric measurements are being made, it is necessary to ensure that the correct power-supply voltages are present. On-site performance testing of emergency lighting installations can be very difficult. The testing requires good instrumentation and well laid out plans for the measurement conditions. Any illuminance meter used should have a photocell with good cosine incident light correction. An illuminated-dial or digital-display type meter should be used so that readings may be visible at low illuminances. The light meter should have an operating range of 0.001 to 10.0 lx with a sensitivity of 0.001 lx for escape routes and areas, and a range of 10.0 to 1000.0 lx with a sensitivity of 1.0 lx for high risk areas. The accuracy of the instrument should conform to BS 667 Type F. The photocell should preferably be on a remote lead to avoid shadowing.


It should be confirmed that all luminaires and off-line battery units reset to normal or standby mode, as appropriate, after the restoration of the normal supply.

The illuminance measurements should be made on a horizontal plane on the escape route area or task area. In most cases it is advisable to select a number of specific areas or points for test that represent the worst conditions. See SLL Lighting Guide 12: Emergency lighting design guide for suggested measurement locations. The results of these illuminance measurements can be checked against design data. Measurements should be taken during the hours of darkness. If there is steady extraneous light from street lighting or moonlight the contribution of the emergency lighting can be estimated by taking the difference between measurements of the same point, with and without emergency lighting. The illuminances provided by the emergency lighting system will vary with time, so the tests should be completed as quickly as is possible within the rated duration. This will minimise the charge losses from the batteries. This is particularly relevant in an occupied building because, with fully discharged batteries, the building may have reduced emergency lighting cover for up to 24 hours. It is valuable to have data that relate the lumen output of the luminaire at any time to the lamp/battery life cycle. 8.6.5 Completion certificate On completion of design, installation and commissioning of the emergency lighting system, a completion certificate should be prepared and supplied to the occupier/owner of the premises as part of the handover. An example of a completion certificate is given in SLL Lighting Guide 12: Emergency lighting design guide. All sections of the completion certificate should be signed by the specified competent persons.

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Chapter Nine: Office lighting

Chapter 9: Office lighting 9.1 Functions of lighting in offices As the UK has moved from a manufacturing economy to a service economy, the number of people working in offices has increased. The purpose of office work is the collection, recording and distribution of information, together with the making of decisions based on that information and the direction of effort to carry out the decisions made. What has changed in offices over the last twenty years has been immense growth in the ability to collect, record and distribute information rapidly, over vast distances, electronically. This process began with the introduction of the personal computer, gained strength with the development of local networks and reached its full flowering with the arrival of e-mail and the World Wide Web. The function of lighting in offices is primarily to make the information handled visible, without discomfort. Consequently, the change from paper-based work to screen-based work has important implications for lighting. In the paper-based office, the primary surface to be viewed is horizontal and increasing the amount of light makes any information on that surface more visible. In the computer-based office, the primary surface to be viewed is vertical and increasing the amount of light in the office makes the information displayed on the self-luminous screen less visible. But this distinction is more theoretical than actual, a survey of offices today would reveal very few that were completely screen-based or completely paper-based. The vast majority of offices use a combination of paper and screen. This means that any lighting installation designed for an office today has to be satisfactory for materials that are self-luminous, i.e. computer screens, and seen by reflected light, i.e. paper, and for lines of sight that can be both across the office and down at the desk.

9.2 Factors to be considered Offices come in many different forms. They can be private or multi-occupied. If multioccupied they can be open-plan or furnished with cubicles. They can have varying amounts of daylight available. They can fill complete buildings or be part of other buildings. Despite the variability faced by the designer of office lighting, the objectives are the same everywhere. They are: to facilitate quick and accurate work to contribute to the safety of those doing the work to create a comfortable visual environment. To meet these objectives it is necessary to consider many aspects of the situation. 9.2.1 Legislation and guidance There are several different pieces of legislation relevant to office lighting, ranging from statements of general principle to specific requirements. Under the Health and Safety at Work Act 1974 the employer must, as far as reasonably practicable, provide and maintain a safe working environment with adequate lighting.

156

In Section 8 of the Offices, Shops and Railway Premises Act 1963, reference is made to suitable and sufficient lighting, either natural or artificial.


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Health and Safety (Signs and Signals) Regulations 1996, (plus BS 5266, EN 1838) Building Regulations, Part L: Conservation of fuel and power Building Regulations, Part B: Fire safety Fire Precautions (Workplace) Regulations 1997 Visual Display Screens Act 1992


Most associated Regulations and Acts call for adequate lighting and installation maintenance, some of these are listed below:

Electricity at Work Regulations 1989. Extensive guidance on office lighting is given in the SLL Lighting Guide 7: Office lighting. 9.2.2 Type of work done The stereotypical office consists of a room filled with workstations or desks where individuals handle information presented either on paper or on a screen. While this is undoubtedly part of the work done in an office, frequently office work requires verbal communication between individuals. This can be done by telephone, via a video link or face to face. That this is so is evident from the existence of meeting rooms, conference rooms, boardrooms and training rooms in many offices. The lighting of such spaces should be designed to facilitate non-verbal communication as well as the visibility of paper and screen-based materials. Offices also contain circulation and reception areas, such areas frequently representing the public face of the business. The lighting of such areas should be designed to send the required message to the visitor. 9.2.3 Screen type An important consideration for office lighting is the optical and geometric properties of the computer screens in the office. The relevant optical properties are diffuse reflectance, specular reflectance, display polarity and display background luminance. The relevant geometric properties are screen tilt and curvature. The optical properties of the screen matter because they determine the visibility of reflections from the screen relative to the visibility of the display itself. The higher the diffuse reflectance, the greater will be the reduction in contrast of the display. The higher the specular reflectance; the sharper will be the reflected image in the screen and the greater the probability that it will be distracting. A positive polarity screen (bright characters on a dark background) will make reflected images more visible than a negative polarity (dark characters on a bright background) screen. The higher the background luminance of the display, the less visible will be the reflected image in the screen. What all this means is that a computer screen with anti-reflection treatment and a negative contrast display with a high background luminance, has a low probability of disturbing screen reflections. Conversely, a screen without anti-reflection treatment, using a positive contrast display with a low background luminance will be very sensitive to the lighting conditions.

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Given that the optical properties of the screen are such that reflections are likely to be seen, then the geometry of the screen becomes important because it determines the probability that high luminances, such as those produced by luminaires, will be in a position to cause disturbing reflections in the screen. Office lighting installations are almost always installed in or on the ceiling, so the further the screen is tilted from the vertical the more likely it is that disturbing reflections will occur. As for screen curvature, the more curved the screen, the larger the area of the office that is reflected in the screen. Wherever possible, it is desirable to know the optical and geometric properties of the screens that will be used in the office because different properties place different constraints on the design of the office lighting (see Section 9.3.3 Maximum luminances). 9.2.4 Daylight availability Most offices have access to daylight through windows. Depending on the time of day and season of the year, the weather conditions, the size and shape of the windows, the orientation of the windows and the presence of external obstructions, the amount of daylight available in the office can vary over a wide range. It will always be necessary to install electric lighting for use after dark but whether or not to invest in a control system that automatically adjusts the electric lighting to supplement the available daylight will depend on the amount of daylight available. As a crude guide, in offices where the minimum daylight factor is less then 2 percent there is little to be gained from modifying the electric lighting. Where the minimum daylight factor is more than 5 percent, controlling the electric lighting to blend with daylight should always be considered. Of course, daylight will only be available if the window is unobstructed and a short walk around any business district will show how frequently windows are obstructed. Windows may be obstructed for a number of reasons. Among them are visual discomfort caused by a direct view of the sun or bright sky; visual discomfort caused by the presence of high luminance patches of sunlight on the workstation; visual discomfort caused by reflected images of the windows in computer screens; and thermal discomfort caused by excessive radiant heating or cooling. Visual discomfort can be minimised by careful attention to external shading of the windows or the use of different types of glazing or internal screening (see SLL Lighting Guide 7: Office lighting). The problem of reflections from computer screens can be solved by orienting the screens so that they are perpendicular to the plane of the windows. As for thermal problems, these have to be dealt with through the heating and ventilating system. 9.2.5 Ceiling height Ceiling height is important for office lighting design because it determines whether indirect lighting is an option. Floor, furniture and wall mounted indirect lighting luminaires rely on height to shield the occupants of the office from a direct view of the lamp. This is the reason why the vast majority of floor mounted luminaires are at least 1.8 m high and why wall and furniture mounted indirect luminaires should have their top surface at least 1.8 m above the floor. This minimum height above the floor for luminaires sets a minimum ceiling height that can be used for indirect lighting. As a rule of thumb, floor furniture and wall mounted indirect lighting luminaires are best used with ceiling heights in the range 2.5 m to 3.5 m. Below 2.5 m there is a risk of high luminance ‘hot spots’ being produced on the ceiling. Above 3.5 m the additional energy consumption required for floor mounted indirect lighting becomes difficult to justify.

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9.2.6 Obstruction Obstructions in offices are created by the use of partitions between individual workstations and/or the use of full height partitions to subdivide the office. The degree of obstruction created by the use of partitions between individual workstations will depend on the height of the partitions; the higher the partition, the greater the obstruction. 1.2 m high partitions provide visual privacy for anyone sitting at the workstation but not when standing. 2 m high partitions provide visual privacy for both sitting and standing occupants. An office equipped with 2 m high partitions is effectively a collection of very small offices. This has both advantages and disadvantages for lighting. The advantage is that luminaires and windows are very unlikely to be seen reflected in the computer screen. The disadvantage is that the amount of light on the workstation will be reduced unless allowance is made for the additional light absorption in the design of the electric lighting. As for daylight, the presence of partitions between workstations limits the role of windows in providing a view out, the amount of daylight reaching the workstation being negligible.


Where indirect luminaires are suspended from the ceiling, the luminaires need to be well above normal head height. A minimum height of 2.3 m to the underside of the luminaire is recommended. As for the separation from the ceiling, this is a matter of luminaire design. Manufacturers usually specify a minimum separation from the ceiling. This minimum should not be ignored.

Figure 9.1 A view of partitioned office

Most office buildings constructed for lease show the office floor as one large open space but require the lighting to be designed so as to allow full height partitions to be installed to subdivide the space into offices of different sizes. The effect of these partitions will depend on the size of the offices created and the reflectance of the partitions. The smaller the office and the lower the reflectance of the partitions, the greater is the reduction in illuminance. Ideally the designer needs to know the size of the smallest office in order to determine the most suitable type and layout of lighting. Thought will also have to be given to the control system for the lighting. 9.2.7 Surface finishes The colour and reflectance of all the surfaces in an office influence the distribution of light. Figure 9.2 gives recommended ranges of average cavity reflectances for floor and ceiling and the average wall reflectance. 159


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Figure 9.2 Recommended ranges of floor and ceiling cavity reflectance, wall reflectance and relative surface illuminance in offices

Ceiling cavity reflectance 0.6 minimum Relative ceiling illuminance 0.3 to 0.9

Effective wall reflectance 0.3 to 0.7

Relative wall illuminance 0.5 to 0.6 Task illuminance 1.0

Effective floor cavity reflectance - 0.2 to 0.4

Window wall reflectance - 0.6 minimum

When estimating the average surface or cavity reflectance it is necessary to take into account all the reflectances forming the surface or cavity. For example, if a painted wall is lined with filing cabinets, the average wall reflectance is made up of the reflectances of the painted surface and the filing cabinets weighted by the area of each. Table 9.1 gives the reflectances of some common materials found in buildings and some paint colours. Details of the reflectance of other materials can often be obtained from the manufacturers or by the methods described in SLL Lighting Guide 11: Surface reflectance and colour. For direct lighting, where the luminaires are recessed into the ceiling, light reaching the ceiling and upper part of the walls is first reflected from the floor and work stations. To avoid a gloomy appearance caused by dark walls and ceiling it is necessary to have a floor cavity reflectance towards the top end of the range given in Figure 9.2. Unfortunately, it is difficult to achieve this without using a light floor finish, something that is not practical in heavily trafficked offices. The solution to this problem is a supplementary lighting installation designed to light the ceiling directly. There are also limitations on the colour of the floor finish. Where direct lighting with luminaires recessed into the ceiling is used, the ceiling is illuminated primarily by light reflected from the floor. Consequently, a strongly coloured floor will result in a strongly coloured ceiling.

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Materials

Reflectance

Paint colours and BS 4800 code

Reflectance

White paper

0.8

White 00E55

0.85

Stainless steel

0.4

Pale cream 10C31

0.81

Cement screed

0.4

Light grey 00A01

0.68

Light carpet

0.3

Strong yellow 10E53

0.64

Light oak veneer

0.4

Mid grey 00A05

0.45

Teak veneer

0.2

Strong green 14E53

0.22

Dark oak veneer

0.1

Strong red 04E53

0.18

Quarry tiles

0.1

Strong blue 18E53

0.15

Window glass

0.1

Dark grey 10A11

0.14

Dark carpet

0.1

Dark brown 08C39

0.10

Dark red-purple 02C39

0.10

Black 00E53

0.05


Table 9.1 Reflectances of common materials found in buildings and some paint colours

There is much to be said for the use of high reflectance surface finishes of neutral or low chroma colour, particularly in small offices. Surface finishes of this type increase the inter-reflected component of the illumination thereby diminishing shadows and reducing the probability that the occupants will experience discomfort glare or be annoyed by veiling reflections. For indirect lighting (see Section 9.4), it is important to provide a high ceiling cavity reflectance free from colour. Failure to do this will result in an inefficient installation producing coloured light. It is also desirable to use large areas of high reflectance on the walls to enhance the interreflected component of the illumination, with small areas of colour to offset the blandness of indirect lighting. For direct/indirect lighting (see Section 9.4), a high ceiling cavity reflectance free from colour is again desirable to ensure the efficiency of the indirect lighting. However, there is no need to have a high floor cavity reflectance as the ceiling is illuminated by the indirect lighting. For general guidance, Table 9.2 recommends the range of reflectances for the most common surfaces in an office. Surface

Reflectance

Ceiling

> 0.7

Walls

0.5–0.7

Partitions

0.4–0.7

Floor

0.1–0.3

Furniture

0.2–0.5

Window blinds

0.4–0.6

Table 9.2 Recommended reflectance ranges for common office surfaces

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9.3 Lighting recommendations 9.3.1 Illuminances Offices contain rooms with different functions. Tables 9.3 to 9.5 give the recommended maintained illuminances for the most common spaces in an office building. The recommended maintained illuminance is the minimum average illuminance that should be provided in the given space throughout the life of the installation. Unless specified otherwise, the recommended maintained illuminance is measured on a horizontal working plane at desk height. Table 9.3 gives the recommended maintained illuminances for the primary office spaces. A primary office space is a space where most of the work is done and where most of the staff spend most of their time. Table 9.3 Recommended maintained illuminances on a horizontal working plane in primary office spaces. Space Recommended maintained illuminance Open plan office – mainly screen based work

300 lx

Open plan office – mainly paper based work

500 lx

Deep plan core area (more than 6m from window)

500 lx

Cellular office – mainly screen based work

300 lx

Cellular office – mainly paper based work

500 lx

Graphics work stations

300 lx

Dealing rooms

300–500 lx

Executive offices

300–500 lx

These maintained illuminances are adequate for task performance but are insufficient to ensure comfortable visual conditions, particularly for deep offices with windows and large open plan offices. For deep offices with windows, there is a risk that the parts of the office away from the windows will look dull compared with the parts adjacent to the windows. This perception can be overcome by taking care to light the walls of the office as well as the horizontal plane. For large open plan offices, lighting the walls is still useful but will not be effective in the centre of the office where there are no walls. In such areas, an additional illuminance criterion should be applied. This is the ratio of cylindrical illuminance to horizontal illuminance at a height of 1.2 m above the floor. Table 9.4 gives the minimum values of this ratio recommended for different floor reflectances. Table 9.4 The minimum cylindrical/horizontal illuminance ratios recommended for different floor reflectances

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Floor reflectance

Minimum cylindrical/horizontal illuminance ratio

0.1

0.48

0.2

0.37

0.3

0.26


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Offices frequently contain a number of secondary spaces that are used intermittently for a wide variety of purposes. Table 9.5 gives the recommended maintained horizontal illuminances for these secondary spaces. Where face to face interaction is important it will also be necessary to provide adequate vertical illuminance. These spaces can contain specialised equipment or furnishings that require lighting to different illuminances than the general lighting (see SLL Lighting Guide 7 for advice). Table 9.5 Recommended maintained illuminances for secondary office spaces Space

Recommended maintained illuminance

Recommended maintained illuminance for special situations

Meeting or break-out rooms

300 lx (for normal meetings)

500 lx (if more intense reading and writing is done)

Training rooms



Conference rooms



Board rooms



Reprographics rooms

300 lx (vertical on reprographic equipment)

300 lx (on collating, binding and dispatch tables)

Libraries/information centres

300 lx (general)

200 lx (vertically on bookcases); 500 lx (on reading desks and counters)

Archives/document stores

300 lx (general)

200 lx (vertically on fronts of shelving)

Break rooms

200 lx (general)

300 lx (on serving and preparation areas)

Medical rooms

300 lx (general)

500 lx (on medical examination area)

Canteens/restaurants

200 lx (general)

300 lx (serveries); 500 lx (kitchens)


For a regular array of luminaires, the cylindrical/horizontal illuminance ratio should be calculated or measured at two positions, one directly beneath a luminaire and the other at the midpoint between luminaires. The minimum cylindrical/horizontal illuminance ratio should be exceeded at both positions.

All offices have circulation areas and service areas. Table 9.6 gives the recommended maintained illuminances for these areas, some of which will contain special equipment that requires lighting to different illuminances than the general lighting in the space.

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Table 9.6 Recommended maintained illuminance for circulation and service areas Space

Recommended maintained illuminance

Recommended maintained illuminance for special situations

Entrance halls/reception

200 lx (general)

300 lx over reception desks and seating areas

Stairs/escalators

150 lx (on treads)

Lift lobbies

200 lx (on floor)

Corridors

100 lx (on floor)

Security/control rooms

200 lx (general around CCTV monitors)

Cleaner’s cupboards

200 lx (general)

Plant room

200 lx (general)

200 lx vertically on control panels, valve sets and instruments etc

Workshops

300 lx (general)

300 lx vertically on machines, 500 lx on workbenches

Lift motor rooms

200 lx (general)

200 lx vertically on sides of winding machine and front of control panel

Generator/UPS rooms

200 lx (general)

200 lx vertically on sides of generator, front of control panel and instruments etc

Storeroom for bulk items

200 lx (general)

Storeroom for small items

300 lx (general)

300 lx where there is use of written materials

200 lx vertically on front of shelving

9.3.2 Light distribution The illuminances given above are averages. To avoid complaints about non-uniform lighting, it is necessary to have limits on how much the illuminance on any single work surface is allowed to drop below the average. For any individual work surface, e.g. a desk, the illuminance uniformity (the ratio of the minimum illuminance/average illuminance) should not be less than 0.7. Most offices are furnished with many desks or workstations. To ensure different desks or workstations are perceived to be treated equally, the illuminance uniformity (minimum average illuminance on the desks/overall average illuminance) should not be less than 0.7. This illuminance diversity criterion applies to electric lighting designed to produce a uniform illuminance across the whole working plane. Where there is daylighting from side windows, or where individual control of the light output from luminaires is used, the illuminance uniformity criterion should be ignored. 164


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9.3.3 Maximum luminances One of the concerns of people working in offices is the reflection of high luminance objects in computer screens. Such reflections can be disturbing because they mask the display or distract attention from it. This used to be a major problem when screens used bright characters on a dark background and were highly reflective but the development of better quality, higher luminance screens that allow dark characters on a bright background, and the wider use of screen treatments to reduce both diffuse and specular reflections made it less of a problem. Nonetheless, there are still many of the older type of screens in use and some of the new screens designed to provide a crisp image are very specular so it is necessary to recognise that lighting needs to be designed with care if problems are to be avoided.


The appearance of the office will also be affected by the illuminance of the walls and ceiling as well as the working plane. Figure 9.2 shows desirable ranges of illuminance on the walls and ceiling as a percentage of the average working plane illuminance. What illuminances are actually achieved on the walls and ceilings will depend on the type of office lighting used. For direct lighting, the ceiling illuminance will be at the bottom end of the specified range. If this cannot be achieved, some form of supplementary lighting to brighten up the ceiling is required. For indirect lighting, it will not be possible to achieve a ceiling illuminance within the range specified, unless the illuminance on the working plane is increased through supplementary lighting. For direct/indirect lighting it should always be possible to achieve wall and ceiling illuminance percentages within the ranges specified.

The obvious solution to reflections from screens is to obtain a better quality screen. However, if it is necessary to solve a screen reflection problem by doing something about the lighting then the answer is not to exceed the maximum luminance limits set for luminaires. Table 9.7 gives the maximum luminances of any part of a luminaire that can be seen in a screen, for different screen types. The luminance limit is normally applied at and above a 65° angle of elevation where the screens are not tilted back more than 15°. Where screens are unusually sensitive to reflections, it may be necessary to use a 55° luminaire luminance limit angle.

Ceiling

Luminaire

Limit of area seen reflected in screen

Windows

Curvature of top of screen

Tilt of screen

Figure 9.3 Defining what can be seen reflected in a display screen

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Table 9.7 Maximum luminaire luminance limit for different types of computer screen Screen type

Maximum luminaire luminance (cd/m2) where some negative polarity displays are used

Maximum luminaire luminance (cd/m2) where only positive polarity displays are used

Type 1: Good or moderate screen treatment

1000

1500

Type 2: No screen treatment

200

500

Limiting luminaire luminance is important to solving a problem of screen reflections because luminaires are often the highest luminance object in the office, but not always. Sometimes, the view out of the window will have a higher luminance and, with indirect and direct/indirect lighting, the ceiling may have the highest luminance. For indirect lighting, it is recommended that the average luminance of the major surface reflecting light, which is usually the ceiling, should be less than 500 cd/m2 and the maximum luminance at any point should be less than 1,500 cd/m2. Further, the luminance variation across the surface should change gradually and not suddenly. The same criteria can be applied to windows, which will usually mean fitting some form of blind. 9.3.4 Discomfort glare control Discomfort glare is controlled by ensuring that the unified glare rating (UGR) of the lighting installation does not exceed the maximum recommended value. Table 9.8 gives the maximum UGR values for different parts of an office. It is important to appreciate that differences in UGR of less than one unit are not meaningful. Discomfort can also be caused by a view of the sun or bright sky through a window. This source of discomfort can be limited either by the use of light shelves and similar elements of the building structure or by blinds. The best blinds are those that shield the occupants from the excessive brightness while preserving some of the view out.

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Category of space

Type of office

Maximum UGR

Primary office space

Open plan offices

19

Deep plan areas

19

Cellular offices

19

Graphics work stations

19

Dealing rooms

19

Executive offices

19

Meeting rooms

19

Training rooms

19

Conference rooms

19

Board rooms

19

Reprographics rooms

22

Libraries/information centres

19

Archives/document stores

25

Tea points/rest rooms

22

Sick bays/medical rooms

19 (16 toward practitioner for medical examination)

Canteens/restaurants

22

Entrance halls/reception

22

Atria

-

Stairs escalators

25

Lift lobbies

22

Corridors

25

Security/building control rooms

22

Cleaner’s cupboards

25

Plant rooms

25

Workshops

22 or 19 depending on task

Lift motor rooms

25

Generator/UPS rooms

25

Storerooms

25

Secondary office space

Circulation areas

Service areas


Table 9.8 Maximum UGR values for different parts of an office

9.3.5 Light source colour properties Light sources with a CIE general colour rendering index (CRI) of at least 80 should be used in all parts of the office, except the service areas. For service areas, light sources with a CRI of at least 60 are acceptable. As for colour appearance, the correlated colour temperatures (CCT) of light sources commonly used in offices varies from 3,000 K to 5,000 K and sometimes as high as 6,500 K. The choice between these different CCTs is a matter of individual preference. CCTs at the lower end of this range will give a warm appearance to the interior but do not blend well with daylight. Higher CCTs will blend better with daylight but give a cool colour appearance to the space. 167


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Very high CCTs will also produce a perception of greater brightness for the same luminance and enhance visual acuity. Whatever light source CCT is chosen should be used throughout the office.

9.4 Approaches to office lighting 9.4.1 Direct lighting Direct lighting uses luminaires that are designed to emit the vast majority of their light output directly down onto the nominal horizontal working plane. Any upward light emitted plays an insignificant part in lighting the task. Direct lighting luminaires can be surface mounted, recessed into the ceiling or suspended (Figure 9.4).

Figure 9.4 Direct lighting in an office

The main potential problem with direct lighting is the fact that the ceiling and the upper parts of the walls tend to be underlit resulting in a gloomy, cave-like appearance. This problem can be alleviated in a number of ways. One is by using high reflectance finishes to the floor, furnishing, walls and ceilings. If this is not practical, then supplementary wall mounted uplighting can be used or a direct lighting luminaire can be chosen that diverts a small amount of light onto the ceiling (Figure 9.5). This will have the effect of making the office appear brighter and more interesting although care has to be taken to avoid high luminance patches appearing on the walls or ceiling as these may be seen as high luminance reflections in computer screens.

Figure 9.5 Reflectors suspended below a direct luminaire to reflect some light onto the ceiling

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For comparable illuminance distributions on a horizontal working plane, direct lighting will almost always be more energy efficient than either indirect or direct/indirect lighting. However, the effectiveness of direct lighting may be compromised where there is a lot of obstruction from partitions in the space. It is also important to appreciate that surface mounted or suspended luminaires may interfere with air distribution in the office, thereby causing thermal discomfort. Coordination of luminaire layout and air distribution pattern is very desirable.


Undesirable high luminance reflections of the luminaires can be eliminated by choosing luminaires within the luminance limits specified in Table 9.7. The same luminance limits will minimise discomfort glare to occupants looking across the office. To eliminate overhead glare it is necessary to shield any direct view of high luminance light sources such as T5 fluorescents, or clear envelope metal halides. In addition, it is better not to use highly specular reflectors with such high luminance light sources as these reflectors can provide an image of the light source with almost the same luminance as the light source itself.

9.4.2 Indirect lighting Indirect lighting uses luminaires where all, or almost all, of the light produced by the luminaire is reflected off some surface, usually the ceiling, before reaching the working plane. In the interests of energy efficiency it is important to ensure that the surface from which the light is reflected has a high diffuse reflectance, at least 0.7 and preferably 0.8 and higher. In the interests of colour rendering, it is important that the reflecting surface is spectrally neutral in colour. The lighting effect produced by indirect lighting is typically diffuse, without strong modelling or shadows. Therefore, it is important to use the office décor to provide some visual interest and variety. This can take the form of small areas of strong colour associated with architectural features or gentle spotlighting of interesting features such as artwork or notice boards.

Figure 9.6 Indirect lighting in an office

Indirect lighting can be highly effective in a heavily obstructed office. Further, provided the maximum surface luminances given in Section 9.3.3 are not exceeded, there should be no problem with either discomfort glare to the occupants or high luminance reflection from screens. Indirect lighting is most suitable for ceiling heights within the range 2.5 to 3.5 m. Indirect luminaires can only be used at ceiling heights in the range 2.3 to 2.5 m if careful attention is paid to light distribution to avoid high luminance spots occurring immediately above the luminaire. Ceiling heights greater than 3.5 m can be used but at extra cost in terms of installed power. Indirect lighting luminaires will usually be seen against the ceiling. To avoid excessive contrast, the outer surfaces of indirect luminaires should be light in colour. 169


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Occasionally, ceiling recessed luminaires in which the vast majority of the light from the light source is reflected from the interior of the luminaire before exiting the luminaire are described as indirect luminaires. This is misleading. Such luminaires should be treated as direct lighting luminaires. 9.4.3 Direct/indirect lighting Direct/indirect lighting uses a luminaire or a combination of luminaires that provides some lighting on the working plane directly and some after reflection from a surface, usually the ceiling. Direct/indirect lighting can be very effective because the two components are complementary. By using direct/indirect lighting the office will have not only well-lit walls and ceiling but also some modelling (Figure 9.7). The exact proportion of direct and indirect lighting is not critical in most circumstances although the appearance of the office will change with a change in proportions. As a rule of thumb, if the lighting is to be considered direct/indirect lighting, the minimum percentage for either component is 20 percent. The recommendations and limitations given above for direct lighting and indirect lighting should be applied to each component separately. Direct/indirect lighting luminaires come in several different forms. One form uses the same light source or sources to provide the two components. Another uses different light sources for the two components. In this case, an option is often available to switch or dim the two components independently. This option may be used to allow occupants to adjust the direct lighting in their local area to match their own preferences but the extent of interaction between adjacent areas needs to be considered. Some direct/indirect lighting luminaires come with a canopy attached to provide a close-up reflector for the indirect component. This is useful in spaces with very high ceilings. Yet another form of direct/indirect lighting uses two entirely different luminaires for the two components, usually direct lighting luminaires and free standing or wall mounted uplighters.

Figure 9.7 Direct/indirect lighting in an office

9.4.4 Localised lighting Unlike direct lighting, indirect lighting and direct/indirect lighting, which are most frequently used to provide a uniform illuminance across the whole working plane, localised lighting deliberately sets out to provide non-uniform lighting, with a higher illuminance around the workstations and a lower illuminance elsewhere. Workstations typically occupy about 25 to 30 percent of office floor area so this approach offers the potential for energy savings but with reduced flexibility unless care is taken to ensure easy movement and reconnection when workstations are relocated. 170


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Luminaires recessed into or surface mounted on the ceiling are usually part of a re-locatable ceiling tile system. Suspended luminaires can be connected to a ceiling mounted track system. The direct component of free standing direct/indirect lighting adjacent to the work station should ideally be positioned to throw light from either left or right side of the work surface and should cover the task area with a uniformity ratio of 0.8 or better. Lighting placed in front of the task area is likely to produce veiling reflections.


Localised lighting can take various forms such as luminaires in or suspended from the ceiling above each work station, or free standing direct/indirect lighting adjacent to a work station, or indirect lighting located in the centre of a cluster of workstations (Figure 9.8).

Figure 9.8 Localised lighting

9.4.5 Supplementary task lighting Supplementary task lighting consists of a task light attached to each desk or workstation. Supplementary task lighting is usually designed so that the ratio of task area illuminance to the ambient illuminance is 2:1 as this gives a reasonable balance between visual comfort and energy savings. Supplementary task lighting luminaires should allow the occupant some degree of control, both of light output and position. Control of light output can be provided either by switching or dimming. The position of the luminaire should be limited so as to ensure that it cannot become a source of discomfort to others. To avoid discomfort to those sitting at the desk, the supplementary task lighting should not be above sitting eye height. Further, the luminaire should not be positioned so low that deep shadows are cast across the work area. As a rule of thumb, the minimum height for the luminaire above the task area should not be less than 0.5 of the width of the task area. Task lighting luminaires need to be mechanically and electrically safe and not too hot to touch or work close to. 9.4.6 Cove lighting Cove lighting aims to produce indirect lighting by throwing light across the ceiling from a ledge or recess high up on a wall. This approach has three limitations. First, great care has to be taken to avoid the wall immediately above the cove and the adjacent ceiling having a luminance higher than the maximum luminance limits given in Table 9.7. Second, depending on the cove’s distance below the ceiling it may be difficult to light the ceiling more than 2 to 3 m from the wall. Third, the energy efficiency is low. Apart from in corridors, this method is rarely used in offices today. 171


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9.4.7 Luminous ceilings Luminous ceilings usually consist of an array of light sources contained above a translucent diffusing ceiling. The surfaces of the cavity above the ceiling are finished in a high diffuse reflectance. The cavity itself has to be high enough for the individual light sources not to be detectable through the diffusing material. Although luminous ceilings are not a form of indirect lighting, they produce a very similar light distribution. Luminous ceilings vary widely in energy efficiency depending on the transmittance of the diffusing material and the light source used. However, they almost always pose problems for access and maintenance so are rarely used in offices today. 9.4.8 Daylight Regulation 8(2) of the Workplace Regulations states that ‘The lighting in (every workplace) shall, as far as is reasonable practicable, be by natural light.’ This means that the provision and control of daylight should be considered for every office. Of course, most building footprints and the fact that daylight predictably fails every night means that reliance can rarely be placed on daylight alone. What is required is a useful combination of daylight and electric light. For a comprehensive guide see SLL Lighting Guide 10: Daylighting and window design. For details of various approaches to combining electric lighting and daylighting in offices see SLL Lighting Guide 7: Office lighting. For guidance on some of the factors to consider about daylighting, see Chapter 7 of this Handbook.


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10.1 Functions of lighting in industrial premises The basic problem of lighting for industry is the wide variability in the amount and nature of visual information required to undertake work in different industries. Some industrial work requires the extraction of a lot of visual information, typically the detection and identification of detail, shape and surface finish. Other types of industrial work require accurate eye-hand coordination and the judgment of colour. Yet other types of industrial work can be done with very little visual information at all. The materials from which visual information has to be extracted can be matte or specular in reflection or some combination of the two, and the information can occur on many different planes, implying many different directions of view. Further, the material from which the information has to be extracted can be stationary or moving. This variability means that the design of industrial lighting is inevitably a matter of tailoring the lighting to the situation. There is no ‘one size fits all’ solution to industrial lighting.

Chapter Ten: Industrial lighting

Chapter 10: Industrial lighting

However, there is a limit to how closely the lighting can be tailored. This limit is set by the fact that many different tasks are likely to occur on the same industrial site, within the same building, on the same production line and, certainly, within the area lit by one general lighting installation. The usual solution to this problem is to provide general lighting of the whole area appropriate for the average level of task difficulty; localised lighting where work is concentrated, e.g. on an assembly line and local lighting where fine detail needs to be seen, e.g. on a lathe in a machine shop, or where obstruction reduces the visibility of the task, e.g. on the work piece of a hydraulic press, or where there is an obvious hazard, e.g. on the feed to a circular saw. The only place where this general/localised/local lighting approach is impossible is where the scale of the equipment is so large that both the people and the lighting work within the equipment, e.g. a chemical plant. For such applications, lighting equipment is integrated into the plant.

10.2 Factors to be considered Despite the variability faced by the designer of industrial lighting, the objectives are the same everywhere. They are: to facilitate quick and accurate work to contribute to the safety of those doing the work to create a comfortable visual environment. To meet these objectives it is necessary to consider many aspects of the situation. 10.2.1 Legislation and guidance There are several different pieces of legislation relevant to industrial lighting, ranging from statements of general principle to specific requirements. Under the Health and Safety at Work Act 1974 the employer must, as far as reasonably practicable, provide and maintain a safe working environment with adequate lighting. Under the Factories Act 1961, Section 4, reference is made for the effective provision for sufficient and suitable lighting in every part of the factory in which persons are working or passing through.

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In Section 8 of the Offices, Shops and Railway Premises Act 1963, reference is made to suitable and efficient lighting, either natural or artificial. Again the need for maintenance is highlighted. Most associated Regulations and Acts call for adequate lighting and installation maintenance. Some are listed below: Health and Safety (Signs and Signals) Regulations 1996, (plus BS 5266, EN 1838) Building Regulations, Part L: Conservation of fuel and power Building Regulations, Part B: Fire safety Fire Precautions (Workplace) Regulations 1997 Visual Display Screens Act 1992 Electricity at Work Regulations 1989. Guidance on lighting for specific industries is given in the SLL Lighting Guide 1: Industrial lighting. 10.2.2 The environment Industrial lighting may be required to operate in extremes of temperature and humidity, may be exposed to atmospheres that are corrosive, explosive or dirty, and may need to be capable of withstanding water jets and vibration. Some light sources are temperature sensitive. For example, fluorescent lamps only produce their full light output at a specific ambient temperature, higher or lower temperatures causing a significant reduction in light output. LEDs produce less light output and have shorter lives as the ambient temperature increases. Where ambient temperatures are low, for example in a cold store, care is necessary to avoid starting problems with discharge lamps. Control gear has a maximum operating temperature above which life will be reduced. Electronic control gear is more sensitive than electromagnetic control gear in this respect. Therefore, care should be taken in selecting and locating control gear when lighting industries where the ambient temperature near the luminaires is high, such as in a foundry. Luminaires designed to cope with damp, corrosive, explosive, flammable or dirty atmospheres are available, at a price. Luminaires capable of operating in damp and dirty conditions are classified using the International Protection (IP) system (see Table 4.10). Some industrial activities produce considerable vibration, for example movement of an overhead crane. Light sources where a hot filament is used are sensitive to vibration. 10.2.3 Daylight availability Many industrial premises have the potential to use daylight. For new buildings, this can be done through a special roof construction, such as a north light (Figure 10.1). For existing roofs, it is sometimes possible to replace existing roof panels with simple translucent panels. The lighting objective for any daylighting system should be to provide diffuse daylight without direct sunlight. Direct sunlight can cause glare and strong shadows on the workplace and should be avoided.

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Figure 10.1 Daylight provided by a north light roof

10.2.4 Need for good colour vision Where colour is used to convey information, lighting with good colour rendering properties is required. Examples of applications where colour is used in this way are electrical assembly, where components are colour coded; food processing, where colour is used to judge freshness and suitability for consumption; and printing and painting, where consistency of colour is important. For such applications, a light source with a CIE general colour rendering index of at least 80 is recommended. For some tasks where very fine colour discrimination is required, e.g. grading diamonds, special lighting which enhances the relevant colour differences is used. Where colours are used to identify the contents of pipes and conduits, it is essential that the lighting should make it easy to identify these colours correctly. 10.2.5 Obstruction Many industrial premises contain obstructions. Obstructions tend to produce shadows. Shadows are cast when light coming from a particular direction is intercepted by an opaque object. Shadows can be minimised by: using a larger number of smaller wattage light sources rather than a smaller number of larger wattage light sources so that light is incident from many directions using luminaires with a widespread light distribution having high-reflectance surfaces in the space providing local lighting of the shadowed area. Figure 10.2 shows a small workshop where shadows have been minimised by using a large number of fixtures and high reflectance surfaces.

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Figure 10.2 A small workshop with high reflectance walls and lit by a regular array of luminaires with a wide luminous intensity distribution. The result is a shadow-free environment.

At the very least, a proportion of the light emitted by luminaires should be emitted upward to be reflected from a high-reflectance ceiling or roof. Although shadows can be a problem, it should be noted that they are also an essential element in revealing the form of three-dimensional objects. 10.2.6 Directions of view Directions of view in industry can vary widely, from vertically downward into a case where components are being assembled, through horizontal for work on a press, to upward for a fork lift truck driver picking a pallet off the top of a rack (Figure 10.3). This wide variety of directions of view means that care has to be taken to avoid both disability and discomfort glare. This can be done by: using smaller wattage light sources so that the source luminance is lower using luminaires which do not allow a direct view of the light source using large area luminaires with an upward light component having high-reflectance surfaces in the space.

Figure 10.3 Directions of view for a fork lift truck driver

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10.2.8 Rotating machinery Where rotating or reciprocating machinery is present a stroboscopic effect is possible. A stroboscopic effect is evident when oscillations in the illumination of a moving object cause that object to appear to move at a different speed from the speed it is actually moving or even to appear to be stationary. All light sources operating from an alternating current electrical supply produce oscillations in light output. Whether these oscillations are enough to produce a stroboscopic effect will depend on the frequency and amplitude of the oscillation. The closer the fundamental frequency of light oscillation is to the frequency of rotation and the larger the amplitude of light oscillation, the more likely a stroboscopic effect is to occur. The probability of a stroboscopic effect occurring can be reduced by:


10.2.7 Access All lighting installations require maintenance. For this to occur, access is necessary. When designing an industrial lighting installation, it is essential to consider how access is to be achieved without disrupting operations.

using high-frequency electronic control gear for discharge lamps mixing light from light sources operating from different phases of the electricity supply before it reaches the relevant machinery supplementing the general lighting of machinery with task lighting using a light source with inherently small oscillation in light output, such as an incandescent lamp. 10.2.9 Safety and emergency egress Some consideration of the impact of lighting on safety is appropriate in all lighting applications but it is particularly important in industrial situations. This is because of the complex layout of many plants, the hazards associated with some manufacturing processes and the dangers from moving equipment. Minimum illuminances are recommended for safety whenever the space is occupied, ranging from 10 lx where there is little hazard and a low level of activity to 50 lx where there are definite hazards and a high level of activity. But illuminance alone is not enough. Hazardous situations can arise whenever seeing is made difficult by disability glare, strong shadows and sudden changes in illuminance. Emergency lighting is required in all industrial premises (see Chapter 8): When designing emergency lighting, it is essential to understand the hazards associated with different operations so that the appropriate form of emergency lighting can be determined, i.e. which areas can be evacuated immediately, which areas contain operations that need to be shut down before leaving, and which areas contain operations that need to be maintained.

10.3 Lighting recommendations There are many different industrial operations but there are also some areas common to many industrial premises. These will be discussed here. Details on lighting for a range of specific industries are given in SLL Lighting Guide 1: Industrial lighting.

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10.3.1 Control rooms Control rooms are often crucial for the production and safe operation of a wide range of processes. Staff monitor and act upon incoming status information (plant, fuel, and product etc.) which is normally displayed on visual display terminals or mimic diagrams (Figure 10.4). The work is often multi-functional and the lighting scheme must enable a wide range of visual tasks to be performed whilst revealing incoming status information with absolute clarity. The lighting should be as flexible as possible to meet the different visual tasks with general dimming or alternative switching arrangements and/or local lighting. The luminaires should blend with the room as far as practical to avoid being sources of distraction. Low glare or shielded, flickerfree high frequency lighting, is preferred where possible.

Figure 10.4 Lighting of a control room

The lighting designer will need to establish precisely how and where the information will be displayed so that the layout geometry and light distribution of the luminaires can be coordinated. Often incoming information will be displayed in a vertical or near vertical plane and the display screen(s) or dial(s) will often be fronted by glass or clear plastic. It is essential to avoid veiling reflections in these displays. There are three ways to do this: position downlighter luminaires to avoid the critical luminaire/screen/eye geometry select downlighter luminaires with low luminance at the critical luminaire/screen/eye geometry (see Table 10.1) treat the ceiling/upper walls as a low luminance source by uniform uplighting with uplighter luminaires. Table10.1 Downlighter luminance limits in display screen areas

178

Screen treatment

Maximum luminance (cd/m2) where some negative polarity software is used

Good or moderate treatment (Type 1)

1000

None (Type 2)

200


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Where positive polarity software only is being used on Type 2 screens the luminance limit can be increased to 500 cd/m2. The above limits should be applied to the downlighter elevation angle, which impinges on the screen at the relevant luminaire/screen/eye geometry. Typically this will be in the range 55 to 85 degrees. For uplighting, the maximum average ceiling luminance is 500 cd/m2 and the maximum point luminance is 1500 cd/m2. Horizontal display screens These will reflect large areas of ceiling and it will often be extremely difficult to plan a satisfactory downlighter scheme, which avoids veiling reflections, leaving uniform low luminance uplighting or local lighting as the only viable solutions.


Where positive polarity software only is being used on Type 1 screens the luminance limit can be increased to 1500 cd/m2.

When uplighting it is important that the ceiling and upper walls have matte finishes to provide a diffuse reflection. High reflection factors are essential for high efficiency lighting. Uniform ceiling luminance is the key objective and it is preferable to use more low output uplighters than fewer with a high output. Ceiling ventilation grills or other obstructions should be painted a matching finish to the ceiling to avoid luminance imbalances reflected in screens. Mimic diagrams These need to be evenly illuminated and the level of illuminance will depend on the detail, the viewing distance, and if the display is self-luminous (where overlighting will wash out the luminous detail). Dimming is advisable and asymmetric ‘wall washer’ luminaires are available which can be surface or recessed mounted. Room surface luminances Surface luminances need to be controlled to ensure no excessive contrasts between the screen and other objects within the same field of view, or other items, which are regularly looked at. In general, light coloured matte finishes are preferable for all room surfaces and furnishings. Windowed control rooms These often provide operatives with an essential view of the processes under control. As with display screen lighting it will be necessary to avoid veiling luminaire reflections in the glass and the same principles will apply. Reflections of room surfaces must also be controlled, especially if the average luminance outside the control room is significantly lower than within. Dimming controls will often be necessary to provide the requisite balances. Emergency lighting This deserves careful consideration in control rooms, since high-risk processes may need to be continued or shut down in the event of an emergency. This may require lighting levels in excess of the normal escape route levels, even up to 100% of the normal lighting levels. In these circumstances it is often necessary to consider uninterruptible power supplies to the lighting rather than self contained battery operated luminaires which only deliver a relatively low light output.

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Table 10.2 Lighting recommendations for direct lighting in control rooms Activity

Average illuminance (lx)

Minimum colour rendering index

Maximum unified glare rating

Display screen tasks, selfluminous mimic diagrams

300

80

19

Paperwork tasks, general display boards

500

80

19

Low contrast mimic diagrams

1000

80

19

10.3.2 Storage Many industrial premises contain areas where raw materials or finished product are stored. In such areas, many visual tasks are performed on vertical surfaces at different heights (Figure 10.5). The lighting designer will require a lot of information regarding the movement of goods and proposed stocking arrangements if all the lighting needs are to be met. In particular, the location of fixed items such as racking is critical, as luminaire layouts must be planned according to the layout of the aisles.

Figure 10.5 Lighting of a storage area

Luminaires are available with optics tailored to the requirements of high rack lighting (> 5 m). These luminaires have a high downward luminous intensity to maximise penetration into the aisles. A sharp cut-off in transverse plane ensures minimal light waste on the tops of racks and a broad axial light distribution maximises luminaire spacing along the aisles. In ‘concertina’ storage mechanisms (bins or racks which push together to reveal access aisles) continuous fluorescent trough reflectors are mounted above the bins and at 90 deg to the aisle openings. Consideration should be given to localising the lighting according to occupation of the access aisles, e.g. pull cord switching or presence detection controls. This will avoid wasted energy due to all the luminaires being needlessly switched on. With random bulk storage it is best to use wide distribution luminaires in a closely spaced array. This will help to minimise the effects of shadows due to stacking and maximise vertical illuminance. 180


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Automated picking warehouses need only sufficient lighting for safe access. However, any maintenance work will need additional portable lighting. Direct glare from luminaires can be particularly problematic, especially for forklift truck drivers. The selection of a greater number of low luminance luminaires is preferable to a smaller number of high luminance luminaires. Fitting louvres or diffusers can help but may compromise the light distribution. Uplighting onto a reflective ceiling background will reduce the brightness contrast between the source and background to lessen direct glare. This may be achieved by selecting downlighter luminaires with an upward light component, or by secondary uplighting. Reflected glare from floors etc. can also be problematic and matte should always be used in preference to glossy finishes.


Cold stores should be illuminated with luminaires which are reliable and efficient at the temperatures concerned. Advice from manufacturers should be sought before luminaires are specified.

Table 10.3 Lighting recommendations for storage areas Activity

Minimum Minimum colour Maximum unified maintained rendering index glare rating illuminance (lx)

Automated aisles

20

40

30

Manned aisles

150

60

25

Continuously occupied areas with little perception of detail required

200

80

25

Continuously occupied areas with perception of detail required

300

80

22

10.3.3 Ancillary areas Circulation When lighting circulation areas such as corridors or stairs, visual guidance is as important as illuminance. Care should be taken to ensure sufficient light is directed onto the walls thereby preventing the corridor appearing oppressive. Luminaires should be positioned in stairways so as to provide sufficient contrast between the treads and the risers. Provision should be made for emergency lighting in all areas, particularly those defined as escape routes. The reader should consult SLL Lighting Guide 12: Emergency lighting design guide. Canteens and mess rooms Many ancillary areas can be illuminated with a regular array of luminaires. However, some areas such a receptions, canteens and rest rooms benefit from a more imaginative approach, thereby creating a better visual impression. In these situations the recommended illuminances should only be treated as a guide — the ‘feel’ of the lighting is far more important than the illumination level achieved.

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Table 10.4 Lighting recommendations for ancillary areas Area

Minimum Minimum colour Maximum unified maintained rendering index glare rating illuminance (lx)

Lifts, corridors and stairs, toilets

100

80

22

Mess rooms

100–300

80

22

Canteens

300

80

22

Plant rooms, store rooms

100

60

25

10.3.4 Speculative factory units Speculative factory units are typically simple shed-type buildings. Often these are built before a tenant is found, and therefore there is no knowledge of what the building will be used for. Typically the lighting is provided by a combination of daylight and electric light. Roof lights usually provide the daylight, supplemented by general lighting from a regular array of luminaires. The purpose of the electric lighting is to illuminate the space uniformly, using conventional equipment. Extreme conditions such as high temperature, high dust levels etc. are not catered for. Table 10.5 Lighting recommendations for speculative factory units Activity

Minimum maintained illuminance (lx)



Workshop units

300

60

22

10.4 Approaches to industrial lighting Industrial lighting usually consists of some combination of general lighting, localised lighting and local lighting. For some visual inspection tasks, special lighting arrangements are needed to reveal what is being sought. 10.4.1 General lighting General lighting is designed to produce a uniform illuminance on the working plane throughout the area involved. A minimum illuminance uniformity of 0.8 is recommended. General lighting is usually provided by a regular array of luminaires. This approach offers considerable freedom in the location of workbenches and machinery. The choice of light source to be used for general lighting is influenced by the level of colour rendering required and the mounting height. Some examples of the level of colour rendering required are given in Section 10.3. The influence of available mounting heights is shown in the Table 10.6. The lower the mounting height, the greater the care that needs to be taken to control glare. Where common viewing directions are upward towards the lighting installation, large area, low luminance luminaires should be used. Where linear fluorescent luminaires are used, orienting the luminaires to run parallel to the direction of view and at right angles to rows of workbenches or machines is usually the best layout. 182


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Mounting height (m)

Usual light source

2.5 to 3.0

Fluorescent

3.0 to 6.0

Fluorescent or low wattage, high pressure discharge

Above 6.0

High wattage high pressure discharge

10.4.2 Localised lighting Localised lighting is characterised by higher illuminances in one part of a workshop and lower illuminances in another. Localised lighting is appropriate where the arrangement of work positions is permanent and the visual demands of the work are different in different areas, where there is large scale obstruction to general lighting or where the visual demands of the work call for additional illumination or a different light distribution.


Table 10.6 The usual light sources used for general lighting at different mounting heights

10.4.3 Local lighting Local lighting is designed to illuminate the task and its immediate surround. Local lighting should be regarded as a supplement to general lighting or localised lighting, not a substitute. Local lighting can be fixed or adjustable by the worker. 10.4.4 Visual inspection Rapid visual inspection calls for off-axis detection of defects. How well this can be done will depend on the visibility of the defect and, if there are other objects in the area to be searched, the conspicuity of the defect. There are many different methods of lighting for visual inspection. All depend on the use of lighting to make the defect more visible and more conspicuous. Figure 10.6 shows some arrangements for revealing different features of products.

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Figure 10.6 Examples of lighting for visual inspection

(a)

(b)

(c)

(f)

(d)

(e)

(g)

(h)

(a) To prevent veiling reflections, light must not coincide with angle of view. (b) The observation of specular detail on a diffuse background is aided if reflected light does coincide with angle of view. (c) Low-angle lighting used to emphasise surface irregularities. (d) Reflected light from a source having a large surface area facilitates detection of blemishes in a polished surface. (e) Diffuse lighting from an extended source aids typesetting. (f) Irregularities in transparent materials are revealed using a transmitted light from a diffuse source. (g) Silhouette is an effective means of checking contour. (h) Directional lighting is needed to reveal form and texture.

10.4.5 Visual aids There are some features of products that can be much more easily seen with the use of visual aids. Such aids include magnifiers, stroboscopes and ultraviolet lamps. Magnifiers can be head mounted or hand held. Magnifiers are useful for inspecting very fine detail but there is a trade-off to be made against field size. The greater the magnification, the smaller is the field size. The lowest magnification necessary to see the required detail should be used. It is sometimes necessary to examine machined parts while they are in motion. A stroboscope will help with this by apparently stopping the motion. To do this is it is necessary for the frequency of the stroboscope to be adjustable so that it can be matched to the frequency of motion. Seals can be tested by placing a fluorescent dye in the sealed container and searching for leaks using an ultraviolet lamp. 184


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11.1 Functions of lighting for educational premises Educational premises contain spaces with many different functions. For schools, these can range from the ubiquitous classrooms through the assembly hall to specialist locations such as art rooms and sports halls. For universities, there are lecture halls with raked seating, research laboratories and seminar rooms. The lighting of educational premises should be both functional and inspirational. Functionally, the lighting should allow the students to see the teacher and the teacher to see the students. For inspiration, the lighting should be consistent with the psychological and emotional needs of the students. Guidance on the lighting of some parts of educational premises is given elsewhere in this Handbook, e.g. for the lighting of sports halls and swimming pools see Chapter 19, for emergency lighting see Chapter 8. More guidance on the lighting of educational premises is published by the Department for Children, Schools and Families in the form of Building Bulletins and is given in the SLL Lighting Guide 5: Lecture, teaching and conference rooms. The lighting that will be considered here is that of the functional parts of educational premises, such as classrooms and lecture halls.

11.2 Factors to be considered

Chapter Eleven: Lighting for educational premises

Chapter 11: Lighting for educational premises

11.2.1 Students’ capabilities The policy today is to educate many students with disabilities in conventional schools. This means that a classroom may contain students with seeing and hearing difficulties or who are autistic and therefore sensitive to sudden changes in the environment. For students who have difficulty hearing, it is important that the movements of the teacher’s lips are clearly visible. For students who are partially sighted, it is important to control glare from luminaires and windows, to minimise veiling reflections and to use the décor to give high contrast to salient details of the environment, such as the position of the door (Figure 11.1). For autistic children, it is necessary to avoid sudden and dramatic changes in the environment. This implies that slow dimming control is better than simple switching and that control of any changes should reside in the classroom so students can be warned about any changes. More advice is given in Department for Education and Science Building Bulletin 77.

Figure 11.1 A classroom with good luminance and colour contrast on salient detail

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11.2.2 Daylight or electric light Most school premises make extensive use of daylight yet electric lighting is always installed for use after dark and to supplement daylight in some parts of the space. Daylight should be used whenever it is available provided it is available without causing visual or thermal discomfort. This means that care has to be taken to control the admission of sunlight (see Chapter 7). Also, if electric lighting is used during daytime, it should be fitted with a control system that will minimise its use of energy. 11.2.3 Common lines of sight Formal teaching spaces have common lines of sight. For example, the lines of sight in a lecture hall are commonly from the seating towards the lecturer’s podium, demonstration bench and projection screen, and from the lecturer towards the seating area. These common lines of sight allow the lighting designer to pick the location and shielding of luminaires and windows so as to eliminate glare (Figure 11.2). Figure 11.2 Common lines of sight in formal teaching spaces

11.2.4 Flat or raked floor Small rooms in educational premises almost invariably have a flat floor but large lecture halls often have a raked floor. The problem these pose is that the effective height of the room decreases from the front to back of the lecture hall and this will influence the spacing of the luminaires if a constant illuminance is to be provided. 11.2.5 Presence of visual aids Today, the ‘chalk and talk’ approach to instruction is often supplemented by visual aids using television and computer screens or projected images. Uncontrolled lighting, both daylight and electric light, can make it difficult to see these aids. The presence of such aids makes it necessary to be able to dim the lighting of the classroom and to control the admission of daylight, particularly where daylight falls directly on the screen (see Section 11.3.3). 11.2.6 Surface finishes While strongly coloured surfaces can be stimulating, their use in classrooms should be limited to small areas (LRC, 1998). The majority of classroom surfaces should be finished in low chroma, high reflectance materials. This will increase the amount of inter-reflected light which, in turn, will distribute daylight more evenly across the room, and reduce the strength of any shadows and veiling reflections. 186


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11.3.1 Illuminances Table 11.1 summarises the minimum maintained illuminances recommended for the more common functional areas of educational premises. These illuminances should be provided on the relevant plane. For classrooms, this will be on the plane of the desks but for art rooms it may be the vertical plane of a canvas. High reflectance surface finishes will help distribute the light evenly on different planes. Table 11.1 Lighting recommendations for functional areas Room

Minimum Minimum maintained illuminance illuminance (lx) uniformity


Minimum CIE general colour rendering index

Classroom, lecture hall

300

0.8

19

80

Classroom used for adult education

500

0.8

19

80

IT room

300

0.8

19

80

Arts room

500

0.8

19

90

Science laboratory

500

0.8

22

80

Seminar room

300

-

19

80

Library

300

-

19

80

Assembly hall

300

0.8

19

80

Music room

300

-

19

80

Drama studio

300

-

19

80


11.3 Lighting recommendations

11.3.2 Illuminance uniformity Illuminance uniformity is important where the lighting needs to be perceived as uniform or where activities may take place anywhere within the lit area. So, for classrooms, lecture halls, IT rooms, art rooms, science laboratories and assembly halls a minimum illuminance uniformity of 0.8 is recommended. Where the space is likely to be obstructed, e.g. a library or where light should be centred on a performer, e.g. in a music room, the illuminance uniformity requirement is limited to the task area. Even where illuminance uniformity over the whole working plane is important, it may be necessary to provide additional lighting in a specific area to give emphasis e.g. on the whiteboard in a classroom. 11.3.3 Glare control Glare control should be applied to both luminaires and windows. For luminaires, this is a matter of limiting the light distribution so that the unified glare rating is 19 or less. One point that calls for care is the lighting of the teacher in a classroom or an instructor in a lecture hall. Figure 11.2 shows an instructor being illuminated with spotlights. The instructor will experience glare if the spotlights are positioned less than 60 degrees above the line of sight straight ahead. 187


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For windows, what is required is an ability to shut out a direct view of the sun and sky, preferably while leaving some view out. 11.3.4 Light source colour properties Light sources with a CIE general colour rendering index (CRI) of at least 80 should be used in all functional parts of a school. For circulation areas, light sources with a CRI of at least 60 are acceptable. As for colour appearance, the correlated colour temperatures (CCT) of light sources commonly used in schools varies from 3,000 K to 5,000 K and sometimes as high as 6,500 K. CCTs at the lower end of this range will give a warm appearance to the interior but do not blend well with daylight. Higher CCTs will blend better with daylight but give a cool colour appearance to the space. Very high CCTs will also produce a perception of greater brightness for the same luminance and enhance visual acuity. Whatever light source CCT is chosen, it should be used throughout the school. 11.3.5 Control systems Lighting controls should be installed in educational premises for three purposes: to minimise the use of electricity when there is sufficient daylight available to avoid the waste of energy by turning off the lighting when the space is empty to provide some flexibility in the use of the space. To minimise the use of electricity when there is sufficient daylight available, it is necessary to wire the installation so that luminaires at the same distance from the windows can be switched or dimmed together (Figure 11.3). Ideally, a dimming system should be used with a photosensor to detect the amount of daylight available.

lamps off

one lamp on

both lamps on

total illumination

electric light contribution

daylight contribution

Figure 11.3 Balancing daylight and electric light in a classroom To avoid the waste of energy by turning off the lighting when the space is unoccupied, motion sensors with an automatic switch off and a manual switch on should be used. To provide some flexibility in the space, a switching or dimming system should be provided under the control of the teacher or instructor. 188


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11.4.1 Classrooms and lecture halls Classrooms can be used for formal or informal teaching. Lecture halls are solely for formal teaching. In formal teaching, the students are all looking towards the teacher and the whiteboard or screen. In informal teaching, the students may be working in groups with the teacher circulating amongst them or the whole class may be arranged around the teacher. For classrooms used for formal teaching, a regular array of direct or direct/indirect fluorescent luminaires can be used, the long axis of the luminaires being arranged parallel to the windows. The use of direct/indirect luminaires is specifically recommended in some of the DCSF (formerly DfES) Building Bulletins. The whiteboard should be provided with its own lighting system designed to eliminate glare and veiling reflections. This can be done by mounting fluorescent luminaires on the ceiling, shielded from the students and located so that the light reaches all parts of the board at an angle of less than 30 degrees from the plane of the board. The teacher needs to be able to control the lighting. The windows should be fitted with blinds to facilitate the use of visual aids. Lecture halls often have raked seating and very little daylight. A regular array of dimmable luminaires shielded from students and arranged parallel to the seating is appropriate (Figure 11.2). The lighting of the instructor, any demonstration bench and the whiteboard should be provided by a separate installation. Both installations should be dimmable and under the control of the instructor.


11.4 Approaches to lighting educational premises

For classrooms dedicated to informal teaching, flexible lighting is desirable. This can take the form of a low level of ambient lighting from a regular array of fluorescent luminaires supplemented by dimmable spotlights mounted on track. 11.4.2 IT room The IT room is characterised by the installation of many computer screens for use by students (LRC, 2001a). The lighting of this room faces the same problems as a modern office and therefore should be lit in the same way, particularly as regards the methods used to minimise high luminance reflections from computer screens. The only difference is the need for the students to see a projected image of the instructor’s screen. This need implies that the lighting should be dimmable by the instructor. 11.4.3 Arts studio Arts studios have three special lighting requirements; good colour rendering, an emphasis on lighting vertical as well as horizontal planes to ensure good modelling and some flexibility in control (LRC, 2001b). Ideally, the windows in an arts room should deliver large amounts of north sky daylight. The electric lighting should blend with north sky daylight and should have a CIE general colour rendering index greater than 90. Both good modelling and flexibility can be delivered by an installation consisting of a low level of ambient lighting from a regular array of fluorescent luminaires supplemented by aimable and dimmable spotlights mounted on track. 11.4.4 Science laboratories Science laboratories require special lighting in that the atmosphere may be humid and corrosive. Luminaires should be sealed and proof against dirt and damp to IP44 (see Table 4.10). The electric lighting in a science laboratory should provide the required illuminance uniformly over the horizontal working plane. Supplementary task lighting may be needed. 189


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11.4.5 Seminar room The seminar room is rather like a small classroom used for informal teaching. The key word as far as the lighting is concerned is flexibility. This can take the form of a low level of ambient lighting from a regular array of fluorescent luminaires supplemented by dimmable spotlights mounted on track. At least one line of track on a separate control circuit should run parallel with the front of the room so that a more formal presentation can be made when desired. 11.4.6 Library The lighting of library spaces must be co-ordinated but appropriate to a number of different functions. In addition to general lighting, lighting for vertical book stacks, lighting for study, lighting for using computers and accent lighting for display purposes may be required. It is important that the lighting arrangements are designed so that there is no conflict between the appearance of the different parts of the installation or with the light distribution throughout the space. 11.4.7 Assembly hall The assembly hall is the one place where the whole school meets. As such it has an important social function. It may also be used for school ceremonies, concerts and theatrical performances as well as community events (LRC, 2001c). The general lighting should be designed to provide uniform illumination over the main seating area, using dimmable luminaires that blend with the architecture. Luminaires with louvres should not be used as they often vibrate during musical events. The stage should be lit using theatrical lighting techniques. 11.4.8 Music room Music rooms require illumination on many different planes, depending on the instrument being played, the position of the score and the location of the instructor. Daylight is desirable provided it does not cause glare and is evenly distributed around the room. Suspended direct/indirect lighting in a room with high surface reflectances is a good approach. Luminaires with louvres should not be used as they may vibrate during performances. 11.4.9 Drama studio The drama studio is essentially an open space in which different types of activity occur. The principle requirement for the lighting is variation in position, light distribution and amount. A series of mounting bars and a stock of theatrical lights combined with a control desk will provide the necessary flexibility. Ambient lighting using surface mounted fluorescent luminaires is also required for setting up and cleaning up.

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12.1 Functions of retail lighting For the retailer, lighting is an essential part of ‘setting out the stall.’ Lighting has four major roles in retail premises. They are: to attract attention to send a message to would-be shoppers about the nature of the shop to guide shoppers around the shop to display the merchandise to advantage.

Chapter Twelve: Retail lighting

Chapter 12: Retail lighting

Subsidiary lighting systems are needed to provide security after closing and to facilitate egress in an emergency (see Chapter 8). Examples of retail lighting design are available in Turner (1998).

12.2 Factors to be considered 12.2.1 Shop profile Retail premises differ on four dimensions: price, usage, range of products and sales style. It is the position on these four dimensions that determine the shop profile. Table 12.1 indicates the most common shop profiles. Table 12.1 Four common shop profiles Shop profile

Prices

Usage

Product range

Sales style

Low budget

Bargain

Weekly

Wide

Self service

Value for money

Low

Daily

Limited

Social contact

Quality

Higher

Impulse

Wide

Shopping as fun

Exclusive

Expensive

Deliberate

Exclusive

Personal service

Shop profiles matter because different profiles have different lighting styles. Low budget shops tend to be big box stores using high level uniform general lighting with no accent or display lighting (Figure 12.1). Exclusive shops tend to be much smaller and use low levels of general lighting combined with strong accent and/or display lighting on the merchandise (Figure 12.2). Value for money and quality shops lie between these extremes, with both general lighting and some accent lighting being used.

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Chapter Twelve: Retail lighting Figure 12.1 A budget retail store

Figure 12.2 A ‘high end’ retail outlet

12.2.2 Daylight or electric light Many retail premises do not allow much daylight penetration into the shop so this question is moot. However, in many out-of-town ‘shed’ stores, daylight may be admitted through roof lights. The use of daylight adds an attractive dynamic element to the store. 12.2.3 Nature of merchandise The type of lighting and the colour properties of the light sources used depend on the nature of the merchandise. Merchandise, such as bedding, needs to be displayed in a warm, cosy atmosphere. This calls for low light levels and a warm colour appearance. Conversely, free standing white goods are best shown at high light levels with light of a cool colour appearance, although when incorporated into displays simulating a home setting, lighting that looks like attractive home lighting is desirable. Merchandise such as meat, fish, fruit and vegetables needs lighting that emphasises whatever characteristic indicates freshness, e.g. redness for meat. Therefore, understanding the nature of the merchandise is essential when designing retail lighting. 12.2.4 Obstruction Some stores, such as DIY stores, have more in common with warehouses than shops. The store is divided into a large number of aisles and the merchandise is displayed in racks extending to head height and above. Where obstruction occurs, it is essential that the layout of the lighting and the merchandise is coordinated.

12.3 Lighting recommendations 12.3.1 Illuminances Retail lighting is essentially a balance between general lighting, accent lighting and display lighting. This balance itself depends on the shop profile. Therefore, the illuminances to be used depend on the shop profile. For low budget shops, where there is no accent or display lighting, the average illuminance should be in the range 500 to 1000 lx. This illuminance should be provided on the merchandise. For a supermarket, this means on the vertical faces of the shelves. 192


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For shops with value for money and quality profiles, where some accent lighting is used, the average general lighting illuminance should be in the range 250 to 500 lx and should be provided on the merchandise. 12.3.2 Illuminance uniformity Regardless of the shop profile, general lighting should be uniform. An illuminance uniformity (minimum/average) of at least 0.7 should be achieved by the general lighting alone. Where accent and display lighting is used, the overall illuminance uniformity is low, by design.


For a shop with an exclusive profile, which means the widespread use of accent and display lighting, the average general lighting illuminance should be in the range 100 to 200 lx. This lower illuminance is necessary for the accent lighting to be effective and should be provided on a horizontal plane at counter level.

12.3.3 Luminances For accent lighting to be effective, the luminance of the merchandise lit has to be higher than the luminance of its immediate background. Different luminance ratios will give different strengths of highlights and shadows. Table 12.2 indicates the luminance ratio for different strengths of accents. Table 12.2 Luminance ratios for different strengths of accent lighting Luminance ratio (accent/background)

Strength of accenting

1

None

2

Noticeable

5

Low theatrical

15

Theatrical

30

Dramatic

> 50

Very dramatic

12.3.4 Light source colour properties The colour appearance of the light used in a shop will contribute to the message the lighting sends to would-be shoppers. A cool light appearance tends to convey a business-like atmosphere while a warm colour appearance indicates a homely feel. As a general rule, the colour appearance of the light sources used changes from cool to warm as the shop profile moves from low budget to exclusive. Where daylight is used in the shop it is necessary to choose a light source colour appearance that blends well with it. For some merchandise, the colour appearance of the light used is important. Chiller cabinets look fresher and white goods look crisper and cleaner under a cool light source. Conversely, gold looks more attractive when illuminated by a warm light source. The other aspect of light source colour properties that needs attention is colour rendering. In general, light sources with a CIE general colour rendering index greater than 80 should be used in retail premises. 193


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This will often be satisfactory but where the merchandise is most likely to be seen under different lighting, e.g. a coat is most likely to be seen under daylight, it is wise to use lighting that does not distort the colour of the merchandise relative to how the merchandise will be seen in use. For some retailers, there can be a temptation to choose a light source that enhances the appearance of the merchandise. An example is the notorious butcher’s lamp, a lamp that exaggerates the redness of meat. This is a temptation that should be resisted. In other shops it will be important to choose a light source with colour rendering properties that give an appealing appearance to human skin, particularly in areas where an individual’s appearance may be closely examined, e.g. fitting rooms. While the CIE general colour rendering index is a useful guide, the final choice of light source is best made by viewing the lit objects of interest.

12.4 Approaches to retail lighting 12.4.1 General lighting General lighting in shops with a low budget or value for money profile is usually provided from a regular array of luminaires (Figure 12.1). These luminaires range from bare fluorescent lamp battens through recessed fluorescent louvres to pendant metal halide globes. The purpose of such general lighting is to produce a uniform illuminance over the relevant plane without causing glare. In shops with quality or exclusive profiles, the architecture is more likely to be a feature of the store and the general lighting will need to be integrated with it. This may involve the use of recessed downlights, cove lighting or suspended uplights rather than a regular array (Figure 12.2). Regardless of the lighting approach used, the appearance of the luminaires needs to be consistent with the style of the shop. 12.4.2 Accent lighting Accent lighting is designed to provide additional illuminance on some areas so as to emphasise specific items of merchandise and to provide a meaningful variation in brightness and shadow throughout the store. If well done, accent lighting can guide shoppers through the shop and draw their attention to merchandise. The best form of accent lighting depends on the area to be accented. For large area wall displays, wall washing luminaires fitted with fluorescent lamps are used (Figure 12.3). For gondola displays, the lighting can be built into the gondolas (Figure 12.4). For small area accent lighting, aimable spotlights attached to power track should be used (Figure 12.5). Whatever the form of accent lighting, some flexibility is required. This is because the nature and aiming of accent lighting will depend on the merchandise to be accented. As the nature and layout of the merchandise changes, the accent lighting will need to change.

Figure 12.3 Luminaires providing vertical illuminance

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Figure 12.4 Lighting of a gondola in a shop

Figure 12.5 A shop lit using spotlights on track

Where wall washing luminaires are used, the important characteristic of the luminaires is the light distribution, the ideal being a uniform illuminance from the top to the bottom of the wall. A similar consideration applies to accent lighting built into gondolas. The illuminance distribution from the top to the bottom of the gondola should be as even as possible. Where spotlights are used, the luminous intensity at the centre of the beam, the shape and dimensions of the resulting light spot with respect to the size and shape of the area to be lit are important. Accent lighting in shop windows has competition from daylight reflected from the window glass and from the windows of nearby shops. Depending on the shielding from daylight and the lighting of adjacent shops, the general lighting of the window during the day needs to be in the range 500 to 2000 lx, while accent lighting needs to be in the range 3000 to 10,000 lx. These illuminances should be reduced after dark. 12.4.3 Display lighting The function of display lighting in shop windows is to gain the attention of passersby and to make the merchandise look attractive. Inside the shop, the main purpose of display lighting is to emphasise the desirable features of specific merchandise. Inside the store, display lighting can be applied to merchandise open to examination (Figure 12.6) or to merchandise in showcases. 195


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Figure 12.6 Display lighting for mannequins

Display lighting is designed to gain attention by using an appropriate combination of brightness, colour and modelling. Relative brightness can be expressed in terms of the luminance ratios given in Table 12.2. The higher is the luminance ratio, the more likely the display is to gain attention. As for colour, strongly coloured light on an object of the same colour will deepen the colour whilst strongly coloured light on the background and surroundings will change the atmosphere. The modelling achieved depends on the relative strength of light delivered from different directions. Modelling is usually achieved by some combination of key-light, fill-light, back-light and up-light. Table 12.3 describes these techniques. Table 12.3 Descriptions of the components of display lighting

196

Light

Description

Function

Key-light

The principle source of directional illumination

To create sparkle and reveal texture

Fill-light

Supplementary illumination from a different direction

To soften shadows so as to get the contrasts in the display at the desired level

Back-light

Illumination from behind and usually above

To separate the object from its background, to reveal transparent elements

Up-light

Light accentuating parts of the display close to the floor

To soften shadows, can be used for dramatic effects


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Table 12.4 Common display lighting techniques for particular materials Materials

Display lighting technique

Uniformly transparent materials

Transmitted light from a lit background; up-lighting possibly in colour

Glass and crystal

Highlighting; up-lighting possibly in combination with translucent background lighting; coloured light

Transparent fibrous objects, e.g. fine textiles

Contour lighting from behind

Precious stones and jewellery

Small spotlights, black velvet background

Opaque, shiny objects, e.g. silver

Spotlights, black velvet background, highlighting

Opaque, textured objects

Light predominantly glancing across the surface


Different materials require different display lighting techniques. Table 12.4 lists some of the more common techniques for specific materials.

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Chapter Thirteen: Lighting for museums and art galleries

Chapter 13: Lighting for museums and art galleries 13.1 Functions of lighting in museums and art galleries Museums and art galleries come in many different forms, ranging from historic buildings to purpose-built facilities. Likewise, the objects they contain come in many different forms. Some are freestanding, some are wall mounted, some are contained in showcases and some are there to be experienced. Despite this diversity, the lighting of all types of museums and art galleries has five functions: to display the objects to advantage to minimise the damage done to the objects by exposure to light to show off the architecture of the facility to help maintain the security of the facility to provide assistance for egress in an emergency situation. Guidance on all these topics is given elsewhere (Loe et al, 1982; Phillips, 1997; Cuttle, 2007).

13.2 Factors to be considered 13.2.1 Daylight or electric light One of the first decisions the designer of lighting in a museum or art gallery has to take is what balance should be struck between daylight and electric light. For some exhibits, such as light art, daylight has to be excluded. For others, such as sculpture, daylight is preferred but the widespread use of daylight can be in conflict with conservation if the exhibits are sensitive to light. One compromise that is often used is to provide daylight and a view out through alcoves off the main display areas. When it is decided to use daylight as the primary light source, it is important that the designer should preserve the most attractive features of daylight, namely its changes in amount and colour. There is little point in controlling daylight so closely that it cannot be distinguished from electric lighting. Electric lighting will always be required for use after dark but can be adjusted during daytime when sufficient daylight is available (see Section 7.2). 13.2.2 Conservation of exhibits Exposure to light can cause damage to objects by radiant heating and by photochemical action. Radiant heating causes surface layers to expand and moisture in the object to be driven out. This results in cracking and lifting together with a loss of colour. Photochemical action is a chemical change produced by the absorption of photons. Symptoms of photochemical damage are pigment colour changes and loss of mechanical strength. The obvious first step to minimise such damage to exhibits is to shield them from both ultraviolet and infrared radiation. This radiation does not contribute to vision but does cause damage. The strongest source of ultra-violet radiation per lumen of light is daylight, even after passage through glass. The strongest sources of infrared radiation per lumen of light are the incandescent light sources. All sources of light should be filtered to minimise ultra-violet and infrared radiation unless required for display purposes.

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Table 13.1 Limiting illuminance (lx) and limiting exposure recommendations for objects with different levels of responsivity to light Responsivity to light

Limiting Limiting annual light illuminance (lx) exposure (lux-hours/year)

High responsivity objects, e.g. silk, newspapers, some colorants

50

15,000

Moderate responsivity objects, e.g. textiles, furs, lace, fugitive dyes, prints, watercolours, some minerals, feathers

50

150,000

Low responsivity sensitive objects, e.g. oil paintings, wood finishes, leather, some plastics

200

600,000

Irresponsive objects, e.g. metal, stone, glass, ceramic, most minerals

Unrestricted

Unrestricted


But radiation in the visible range can also cause damage particularly at the short wavelength end of the visible spectrum. To minimise damage from light, it is necessary to limit the light exposure. Table 13.1 shows the limiting illuminances and limiting annual light exposures recommended for objects with different levels of responsivity to light. Determining the responsivity of an object to light is the responsibility of the conservator. An illuminance of 50 lx is considered to be a minimum for displaying objects that require the perception of detail and colour. For high responsivity objects, using an illuminance of 50 lx implies restricting the annual hours of display to less than 300 hours.

13.2.3 Light source colour rendering properties Electric light sources vary in their ability to render colours accurately. Light sources with a CIE general colour rendering index greater than 80 should be used in all museums and art galleries. However, the CIE general colour rendering index is a single number describing a complex perception. Therefore, it is always advisable to view the objects to be displayed under the proposed light source before choosing the light source. 13.2.4 Adaptation The low light levels in the exhibit rooms of many museums and art galleries mean that visitors need time for their vision to adapt from the higher light levels usually present in entrances, cafes etc. To achieve this there should be a transition zone of slowly decreasing illuminance between the brighter lit areas and the exhibit areas. 13.2.5 Balance The balance between the lighting of the exhibits and the general lighting of the space can vary widely. At one extreme is the approach where the only lighting is the lighting of the exhibits, the general lighting of the space being achieved by spill light from the exhibits (Figure 13.1). Such lighting can be very dramatic but may pose problems for circulation. At the other extreme is a high level of diffuse ambient lighting without emphasis on the exhibits (Figure 13.2). This approach can be very bland. A reasonable compromise is to aim for an illuminance ratio between exhibit lighting and ambient lighting of 3:1. If a strong emphasis on the exhibits is required an illuminance ratio of at least 10:1 is suggested. 199



Figure 13.1 General lighting of exhibit space with spill lighting

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Figure 13.2 A high level of diffuse ambient lighting

13.2.6 Shadows and modelling The distribution of light around a three-dimensional exhibit determines the strength and form of the shadow pattern created and hence the strength of modelling. A large area luminaire and a high surface reflectance background will, together, minimise shadows and modelling. A narrow beam spotlight and a low reflectance background will, together, maximise shadows and modelling. What strengths of shadows and modelling are desired is a matter of judgment but exhibits with some modelling are considered more interesting and more attractive than those with none (Mangum, 1998). 13.2.7 Glare The widespread use of spotlights in museums and art galleries makes glare a distinct possibility. Glare from spotlights can usually be avoided if spotlights are aimed not more than 35 degrees above the downward vertical. 13.2.8 Veiling reflections and highlights Objects on display can vary dramatically in their reflection properties. A few are diffuse in reflection but many have a strong specular component. This means that high luminance reflections can be seen in the objects. The most usual sources of high luminance in a museum or art gallery will be windows and luminaires. Whether such high luminance reflections are desirable will depend on the object. For paintings and information presented on computer monitors, high luminance reflections are called veiling reflections and will reduce visibility. For silver and glass objects, high luminance reflections are called highlights and are essential for revealing the nature of the material. Whether high luminance reflections are present or absent will depend on the geometry between the luminaire, the object and the observer. By careful selection of the location of the luminaire relative to the object and control of its light distribution, high luminance reflections can be minimised or maximised. 13.2.9 Out-of-hours activities Prior to opening and after closing, there are numerous cleaning and curatorial activities that need to be undertaken. During this time, the display lighting should be extinguished and the museum and gallery lit by energy efficient ambient lighting. This is required by Part L of the Building Regulations for energy saving reasons.

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13.2.10 Security and emergency The objects contained in museums and art galleries are frequently valuable so the security of the building is important. Different security systems require different lighting. Where patrolling after closing is in use, lighting systems that enable the guard to move safely and effectively through the spaces is necessary. A minimum illuminance at floor level of 20 lx should be provided for safe movement. Museums and art galleries are open to the public, many of whom may be unfamiliar with the layout. Emergency lighting to help with egress, should it be necessary, is required by law (see Chapter 8). 13.2.11 Maintenance For any lighting system to be effective it has to be maintained. Access for maintenance needs to be considered when designing the lighting of museums and art galleries, as it may not be convenient to move exhibits. 13.2.12 Flexibility Many museums and art galleries change their displays regularly or house temporary exhibitions. Different displays or exhibitions require different lighting so it is essential to have flexibility. Flexibility of positioning can be provided by using a track system to power spotlights. Flexibility in the amount of light can be provided by having different elements of the lighting on different dimming circuits. Flexibility in light distribution can be achieved by using spotlights with different beam widths.

13.3 Lighting approaches for museums and art galleries


Further, extinguishing the display lighting will help to conserve those objects responsive to light exposure.

13.3.1 Wall mounted displays Lighting paintings hung on a wall requires care if veiling reflections and shadows are to be avoided. Uniform lighting over the whole wall can be achieved using wall washing luminaires. Uniform lighting over individual pictures can be achieved using spotlights. In this case, some spill light around each picture will soften the effect and illuminate any label. Where a painting is hung so that it can be viewed by a standing observer looking straight ahead, spotlights aimed so that the centre of the beam is on the centre of the painting and 30 degrees from the downward vertical usually produce satisfactory conditions. Where paintings are double hung, i.e. one above the other, the upper painting should be tilted down to minimise veiling reflections. 13.3.2 Three-dimensional displays Freestanding, three-dimensional objects need to be lit from several different directions. The usual approach is key-, fill-, background- and up-lighting (see Section 12.4). Back lighting determines the context in which the object will appear and sets the levels that will be required for key-, fill- and up-lighting to be noticeable. Key-lighting consists of a narrow beam aimed at the most important features of the object. This will create shadows and highlights on the object. Highlights reveal the nature of surfaces. Shadows reveal form and texture. However, excessive highlights can be glare sources and strong shadows can hide detail. Key-light is offset by fill-light and up-light, diffuse lighting that softens shadows and diminishes glare. By balancing key-, fill- and up-light in direction and amount relative to the back-light, a wide range of appearances can be created. 201


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The other problem with three-dimensional displays is avoiding glare to the viewer, not from the object but direct from the luminaires. When the object is at eye level or lower and is lit from all sides with the beam angles less than 30 degrees from the downward vertical glare should not occur. Where the object is large and requires the viewer to look upwards, glare is a possibility. This can be dealt with by restricting the directions from which the object is viewed, or using narrower beams for the key-light so that all the light is within the display or lighting from below as long as appearance is not distorted. 13.3.3 Showcase lighting Glazed showcases are used for displaying rare, valuable and delicate objects while protecting them from damage and theft. Showcases can be small or large; can be viewed from all sides or from a limited number of sides; and can be lit from outside the case or from inside. The problems of showcase lighting are reflections from the glazing, shadows produced by viewers and heat build up in the case. Reflections from the glazing and shadows caused by viewers are mainly problems with external lighting, particularly when the showcase has a low reflectance (dark) lining. Reflections can be dealt with by tilting or curving the glazing so that a dark surface is reflected or by creating a luminance ratio of 10:1 or greater between the interior and exterior or the showcase. Shadows have to be dealt with by using multiple light sources. Using carefully aimed interior lighting for the showcase will eliminate problems with reflections from the glazing. Whether shadows occur around and on the objects in the showcase will depend on how the objects are lit and the reflectance of the surfaces in the case. The more directional the lighting and the lower the reflectance of the interior, the more likely it is that shadows will occur around the object. One form of interior lighting is the light-box on top of the showcase. This can provide soft diffuse light using fluorescent lamps or directional lighting using adjustable spotlights. Lightboxes need to be ventilated to prevent heat build-up and have easy access to the lamps for maintenance. There should be a glass or plastic barrier between any fluorescent lamps in the light-box and the case interior to filter out ultra-violet and infrared radiation. For some tall or narrow showcases, the top lighting will need to be supplemented by lighting from the sides, back or bottom to provide good modelling of objects on the lower shelves and to alleviate shadows. Another form of interior lighting is small spotlights mounted in the corners of the showcase. Fibre-optic lighting has distinct advantages for such an approach. The light source can be mounted outside the showcase thereby avoiding heat build-up and the fibres can be filtered to eliminate ultra-violet and infrared radiation. Further, the fibres can be fitted with different light distribution devices and can be moved around the showcase as required.

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14.1 Functions of lighting in hospitals The lighting of hospitals has two main functions. The obvious and most important function is to meet the task requirements in each area of the hospital. Some of the tasks to be carried out will require exacting levels of visual performance. Indeed, the safety of the patients may depend on the level of visual performance achieved. The second and equally important function is to create an environment that is visually satisfying, wholly appropriate and ‘emotionally compatible.’ Lighting can influence human emotions and feelings of well-being. Good lighting will also help promote an air of quality and competence within the hospital. Extensive guidance on the lighting of hospitals is given in SLL Lighting Guide 2: Hospitals and health care facilities and other publications (Dalke et al., 2003).

14.2 Factors to be considered 14.2.1 Daylight The provision of some daylight and a view out is much appreciated by patients, so daylighting and access to windows should always be considered when designing the lighting of hospitals. However, care is necessary to limit sun penetration so that thermal and visual discomfort do not occur. Further, the amount of light coming through the windows at night needs to be restricted if sleep is to be undisturbed. This means that windows should be fitted with adjustable blinds. Where daylight makes a major contribution to the lighting of the space, the electric lighting should be fitted with an automatic switching or dimming system so that energy waste is avoided.

Chapter Fourteen: Lighting for hospitals

Chapter 14: Lighting for hospitals

14.2.2 Lines of sight Hospitals differ from many places in that some common lines of sight are unusual. For patients in hospitals, common lines of sight are towards the ceiling and the upper parts of the opposite walls. Such common lines of sight mean that special care is necessary to avoid glare to patients while still providing good visibility to doctors and nurses. 14.2.3 Colour rendering requirements Skin colour, eye colour and the colour of tissue and fluids can be important guides to diagnosis and treatment. Therefore, there are strict colour rendering requirements placed on the light sources used in the clinical areas of hospitals. Clinical areas include ward units, consulting rooms and operating departments. Ward units include bedded areas, ward corridors, nurses’ stations and treatment rooms. All fluorescent lamps within these areas should have a CIE general colour rendering index of at least 80. In specialist areas such as those used for examination or treatment, a minimum CIE general colour rendering index of 90 is recommended. However, these areas generally do not require the general illumination to be provided by such lamps, only the immediate task area. This task area lighting will usually be provided by dedicated fixed or mobile examination lamps. It is essential that light sources with different colour rendering or colour temperature characteristics are not used in the same area. If the bed head reading lights are intended to supplement the general illumination for the purposes of patient treatment, then the light sources used in the reading lights should have a CIE general colour rendering index of at least 90. 203


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14.2.4 Observation without disturbance to sleep Lighting in hospital wards suffers from a conflict of interest at night. The patients are trying to sleep, while the staff need to be able to see the patients, move around safely and do detailed work at the nurses’ station. The differences between the visual requirements of these activities means that ward lighting needs to be flexible. Crude flexibility can be achieved using switching. Fine flexibility can be designed using dimming. 14.2.5 Emergency lighting Emergency lighting is required for the movement of patients, staff and visitors to a safe location in an emergency. Some of the people in a hospital will almost certainly be physically incapacitated and/or could be mentally impaired. Because of the likely condition of patients, hospitals do not normally fully evacuate in an emergency. Patients are generally moved by a process called progressive horizontal evacuation from high risk areas to low risk areas while the emergency is brought under control. The emergency lighting should be sufficient to allow easy progressive horizontal evacuation, particularly in those areas where elderly patients may be present. Emergency lighting should be designed to meet the requirements of BS 5266. Design guidance can also be obtained from the SLL Lighting Guide 12: Emergency lighting design guide and from Chapter 8 of this Handbook. For hospitals, the minimum illuminance on the centre line of a 2 meter wide escape route should be 1 lx. A minimum illuminance of 0.5 lx should be provided on all non-designated escape route areas requiring emergency lighting. Fire muster points and dedicated refuge areas must be given special consideration to ensure they are illuminated to a minimum of 5 lx and are visible or stand out from the general surrounding area. Illuminated signs on the movement and escape routes should comply fully with BS 5499: Parts 1 and 4 and BS EN 50172. Standby lighting will be required in certain parts of the hospital to enable essential activities to be carried out in the event of a supply interruption. Hospitals normally work to two standards of illuminance for standby lighting. In critical areas, such as operating theatres, delivery rooms and high dependency units, the illuminance provided by the standby lighting should equal, or nearly equal 90 percent of the normal mains illuminance. Other non-critical but important areas will require standby lighting to a reduced illuminance, generally to 50 percent of the normal mains level. Where standby lighting is provided by a generator, there will always be a break in the continuity of supply as the engine runs-up so a battery back-up with a minimum of 3 hours capacity to power the lamp(s) should be provided to cover the start-up period and to cater for the possibility that the generator fails to start. 14.2.6 Luminaire safety All luminaires should comply with the relevant part of BS EN 60598. They should all carry a CE mark with the manufacturer’s declaration of conformity to all directives designated under the harmonised European Standards and certified to be in full compliance with the EMC Directive. In addition all luminaires intended for use within clinical areas of healthcare buildings should specifically comply with the requirements of BS EN 60598-2-25. Electrical safety should be considered a top priority for all electrical apparatus used within hospitals, especially in bed-head luminaires that are accessible to patients. Such luminaires should be either be of Class II construction or supplied from a safe extra-low voltage supply (SELV), as defined in BS EN 60598: Part I: Section 1.2.

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Hand-held switches at mains voltage can be dangerous to patients so an extra-low voltage relayactuated switch, at a maximum of 24 volts, should be incorporated into any nurse-call apparatus. Electrical connections should be accessible only with the use of tools. It is also worth noting that any recessed emergency luminaires used on an escape route will have to retain the fire integrity and the rate of fire spread of the surrounding ceiling system. In practice this means that any attachment used will have to withstand the 850 ˚C glow wire test and be manufactured from a self-extinguishing material such as polycarbonate or a TPa based polymer. 14.2.7 Cleanliness It is possible for airborne dust particles as small as 0.5 µm to transport harmful bacteria. Luminaires in common with other items of equipment can cause the transfer of infection by contact with the dust particles they may harbour. Therefore, luminaires for use in hospitals should have the minimum area of horizontal or near horizontal surfaces on which dust may settle and such dust should be easily removable by simple cleaning methods. In high risk areas it is advisable to use luminaires with no horizontal faces, only downward and vertical faces. It is also advisable to use theatre luminaires that have glass diffusers since glass cannot be penetrated by bacteria and is unaffected by sterilising materials and UV radiation. A further measure in preventing the transmission of infections is to ensure that any space requiring ingress protection between the void and room (especially theatre luminaires), uses a luminaire that has integral mechanical measures to ensure the seal between the ceiling and the luminaire frame and does not rely on the luminaire being manually held while it is fixed into place.


The construction should be robust and the luminaires should be capable of being securely mounted. Provision should be made for easy cleaning of the interior of enclosed luminaires without the risk of electrical shock.

14.2.8 Electro-magnetic compatibility (EMC) Many items of electrical equipment installed in hospitals can cause interference, either by radiation or by transients through the mains voltage supply. The prime nuisance factor from fluorescent luminaires is from radio interference. Suppressors, if fitted to the ballasts within the luminaires, should reduce the interference. The use of high frequency electronic control gear within the patient environment requires careful consideration with regard to EMC emissions and immunity. The testing and certification of a ballast by a manufacturer as an independent component is not sufficient to ensure that its use within another housing or product will meet the overall technical requirements. Tests need to be performed by manufacturers on the complete assembly, as it would be installed. BS EN 60601 defines the EMC test requirements for electrical medical equipment within the patient environment. The EMC elements of ISO 11197 should be observed for bed head service trunking systems that include lighting components.

14.3 Approaches for the lighting of different areas in hospitals The areas considered here are those most likely to be experienced by those visiting a hospital as patients. Hospitals contain many other areas. Details of the lighting required for all areas of hospitals are given in SLL Lighting Guide 2: Hospital and health care buildings.

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14.3.1 Entrance halls, waiting areas and lift halls In the main entrance of a hospital visitors will look for signage to direct them towards their destination. The lighting should be designed in conjunction with interior materials and finishes to clarify transit routes and points of arrival. A change of type, height or orientation of the luminaires can highlight the focal point of activity such as reception, waiting areas and lifts (Figure 14.1). This approach to design will also provide brightness variations that contribute to the pleasantness of the interior. A maintained illuminance of 200 lx on the floor is recommended.

Figure 14.1 A hospital entrance area

14.3.2 Reception and enquiry desks Maintained illuminances of 300 lx on the floor of the reception area and 500 lx on the task areas are recommended. The overall impression should be a welcoming one that avoids harsh contrasts (Figure 14.2). It is important to consider the vertical as well as the horizontal illumination, so that people’s faces within the reception areas are properly lit as this will provide good facial modelling and help with the process of lip reading.

Figure 14.2 A hospital reception area

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14.3.3 Hospital streets and general corridors Hospital streets form the major links between clinical departments and may include public waiting areas. They have a relatively high traffic density and can be in excess of 6 m wide . General corridors can vary from the minor, linking one or two offices, to the major, linking different departments (Figure 14.3). For both areas, a maintained illuminance of 200 lx on the floor is recommended. A lower maintained illuminance of 50 lx is recommended for use at night, the lower illuminance being achieved by either selective switching or, preferably, by dimming. If selective switching is used then care should be taken to maintain an illuminance uniformity (minimum/average) of at least 0.2. This will provide the staff with a more comfortable level for moving to and from dark wards and will also avoid the patients being disturbed by the glow of bright lights from the corridor. Low glare luminaires should be used, positioned to avoid alternating brightness patterns being viewed by trolley-borne patients.

Figure 14.3 Hospital corridor

14.3.4 Changing rooms, cubicles, toilets, bath, wash and shower rooms A maintained illuminance in the range of 100 to 150 lx on the floor is recommended. The lower illuminance is considered adequate for small, enclosed cubicles. In the interest of cleanliness, these areas should be lit to minimise shadows and no areas should have to rely solely on reflected light. Bathrooms and shower rooms are humid therefore special attention is required in the selection and the location of the luminaires. In changing areas, the luminaires should be sited between clothes racks or lockers to provide adequate light into the lockers. The positions of wall-mounted mirrors and of the general lighting should be chosen to avoid troublesome reflections. 14.3.5 Wards The lighting of wards must satisfy the requirements of both the patients and the nursing staff during the day, evening and night. In bed spaces, it is now common practice for the light levels required to administer medical or general patient care to be provided without the use of a separate portable luminaire. Lighting of bed spaces should be individually switched to encourage energy saving when the bed space is unoccupied. Lighting of the central ward area should be provided so as to enable safe circulation and general cleaning procedures to be carried out. Most importantly the lighting of the whole ward should aid in the provision of a general pleasant and amenable ambience. 207


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For nursing care to be performed efficiently the maintained illuminance over the general area of the bed should be at least 300 lx with a uniformity (minimum/average) of 0.5 or better. A combination of general and task lighting may be used. The maintained illuminance in the central space between the beds should be not less than an average of 100 lx at floor level. This level will be sufficient for the general activities of ambulant and recumbent patients without causing disturbance to other patients in the room who may want to rest. It is common practice that when patients are being attended to by nursing or medical staff, their bed curtains will be pulled around to provide an element of privacy. When the bed curtains are pulled around, the average illuminance within the curtained area for both the general level and the nursing care level must not be reduced by more than 25 percent when compared to the unscreened bedded area. A minimum acceptable mean illuminance of 75 lx for the general ward lighting should be maintained outside the bedded area when all the bed curtains within the ward are drawn around simultaneously. The lighting of wards can be done in several different ways. Ceiling mounted ward luminaires are usually required but these can be supplemented with bed lighting consisting of compact fluorescent lamps in ceiling-recessed luminaires positioned centrally over the bed area or linear fluorescent luminaires mounted on top of a strengthened curtain rail between beds to provide uplighting. This latter approach will not be appropriate where the distance between the curtain rail and the ceiling is less than 1 m and/or where the ceiling height is more than 3 m (Figure 14.4). Another possibility is to use luminaires that are integral within a wall-mounted bed-head services trunking system that also provides piped medical gas and cabled services. The optimum mounting height for such integrated luminaires is 1.8 m. Any luminaire mounted below 1.8 m will need careful light control if glare to patients and staff is to be avoided.

Figure 14.4 Ward and bedhead lighting

Ceiling mounted ward luminaires can be suspended, surface mounted or recessed. The minimum ceiling height required for suspended luminaires to be considered is 3.5 meters. This will ensure that adequate clearance is still possible for the use of mobile apparatus at the bedside. The mounting height above the floor should not be less than 2.7 m nor greater than 3.5 m. If the luminaire has an upward light component the suspension length should be between 700 mm and 1000 mm to achieve a satisfactory spread of light across the ceiling. For surface-mounted luminaires, the ceiling height may be 2.7 m or less. It is usually convenient to mount single-lamp fluorescent luminaires to coincide with the bed spaces. Twin-lamp luminaires may also be used, usually spaced at one and a half times the bed spacing. 208


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Recessed and semi-recessed luminaires may be used in ceilings between 2.4 m and 3 m high. Luminaire spacing should generally be as described for surface mounted luminaires. It is also possible to illuminate wards using wall mounted luminaires that combine an upward and downward component. This method has numerous advantages. The downward component allows patients to do visually demanding tasks like reading or jigsaw puzzles. The upward component provides non-glaring, soft illumination to the room allowing the patients to relax. When combined, the upward and downward components can provide the higher level of illumination required for examination or nursing care. Ward lighting should not cause glare to recumbent and ambulatory patients. Ceiling or wall mounted luminaires should be assessed for their average luminance value at elevation angles between and including angles (a) and (b) in Figures 14.5, 14.6. and 14.7. Ceiling mounted, surface luminaires should not exceed 1500 cd/m2 for all angles of azimuth. For all ceiling recessed or semi-recessed luminaires the value should be reduced to 1000 cd/m2. Wall mounted luminaires should be assessed for their average luminance value which should not exceed 700 cd/m2 for all angles of azimuth, between and including angles (a) and (b), as defined in Figure 14.7 where:


However, the illuminance in the circulation space could be less uniform and somewhat higher than the recommended value when using this method. In areas with ceiling heights between 2.4 m and 2.7 m, it is possible to provide the recommended illuminance at the bed head by using surface mounted luminaires alone.

(h1) is the minimum height of the mattress surface plus 200 mm (h2) is the maximum height of the mattress surface plus 600 mm (h3) is the height above floor level to the centre of the luminaire (d1) is the distance from the wall to the front edge of the pillow (d2) is the distance from the wall to front face of bed head (d3) is the distance from the wall to the luminaire centre. The average luminance value of 1500 cd/m2 (1000 cd/m2 for recessed or semi-recessed luminaires), is defined as the luminous intensity measured at each 5˚ angle between and including angles (a) and (b) divided by the sum of all the orthogonally projected luminous areas at each of the elevation angles. This average applies at all angles of azimuth. The average value of 700 cd/m2 for wall luminaires should not be exceeded anywhere between and including angles (a) and (b) for all angles of azimuth. The designer should use the measurement values relating to the actual or specific areas in question. However, in the absence of specific dimensional data for h1, h2, h3, d1, d2 and d3 the following values should apply; h1 = 850 mm h2 = 1450 mm h3= 2.7 m ceiling mounted, 2.0 m rail mounted, 1.8 m wall mounted d1 = 900 mm d2 = 450 mm d3 = 4.0 m ceiling mounte, 5.0 m rail mounted, 8.0 m wall mounted.

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d3

The average luminance value between and including angles (a) and (b) not to exceed 1500 cd/m2 for all angles of azimuth

d1

a

d2 h3

b

0˚

h2 h1

Figure 14.5 Elevation angles for ceiling mounted luminaires

b

d3 a

d1 d2

0˚ h3 The average luminance value should not to exceed 700 cd/m2 between and including angle (a) and (b) for all angles of azimuth

h2 h1

Figure 14.6 Elevation angles for bed head rail mounted luminaires

d3

b = 120˚ for luminaires mounted below 1.8 m b = 90˚ for luminaires mounted at 1.8 m but below 2.0 m

b = actual measured angle for luminaires mounted at or above 2.0 m d1 d2

a b h3

The average luminance value should not to exceed 700 cd/m2 between and including angle (a) and (b) for all angles of azimuth 0˚

Figure 14.7 Elevation angles for wall mounted luminaires 210

h2 h1


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Luminaires must not cause excessive luminance spots (bright patches), on the room surfaces when viewed by the patients. The average luminance of all the major reflecting surfaces should not exceed 600 cd/m2 and the maximum measured spot level should not exceed 1500 cd/m2. In addition there should be no sudden change in the values of luminance on any of the major reflecting surfaces, i.e. they should change gradually. 14.3.6 Reading lighting When reading, most people will rest with their head or back against the pillows. A reading light should provide an average illuminance of 300 lx over a horizontal area of 1m x 1m centred at the bed-head and directed towards the bottom of the bed at 1.0 m above floor level, after taking into account the shielding effect produced by the patient’s head and shoulders. The reading light switch should be conveniently positioned within reach of the patient. Suitable reading lights, especially if they are articulated, may also be used for general nursing activities at the beds. All reading lights should be cool to touch and easy to clean. Ideally, wall-mounted fixed bed-head type reading lights should be installed at a mounting height of 1.8 m but can be mounted below 1.8 m provided care is taken to control glare and shadows. Articulated wallmounted reading lights and ceiling-mounted reading lights can also be used.


For wall-mounted luminaires fixed at ≥ 2.0 m angle b shall be the actual measured value. At mounting heights of ≥ 1.8 m but less than 2.0 m from finished floor level, angle b shall always be 90 degrees. For mounting heights below 1.8 m angle b shall always be 120 degrees. The maximum luminance must not exceed 700 cd/m2 at any angle of azimuth between and including, the angles of elevation detailed in Figure 14.7 above.

14.3.7 Night lighting Night lighting needs to fulfill three functions: to provide enough light for the safe movement around the ward, to allow the nursing staff to see facial features and a patient’s general condition, and to allow patients to sleep. The average maintained illuminance for the central ward circulation space should be 5 lx on a 0.85 m high horizontal working plane, with a maximum illuminance measured on the pillow of 0.5 lx. To avoid disturbing glare, the luminance of any luminaire left on during the night within the ward should not exceed 30 cd/m2 at an angle of 35˚ and more from the downward vertical at all angles of azimuth. In addition, any luminaire positioned at the bed head or within the bedded area defined by the screening curtains should not exceed 30 cd/m2 at an angle of 20˚ and more from the downward vertical at all angles of azimuth. Moving shadows cast by car headlamps, trees or from nearby road lighting can be particularly disturbing to patients, it is recommended therefore that blinds or curtains be drawn over the windows at night where external sources are considered to be an issue. 14.3.8 Night observation lighting (watch lighting) Watch lighting may be required for the observation of a particular patient after the general lighting has been switched off. It should avoid any visual disturbance to other patients so it is unlikely that the general use of a patient’s reading light, which has not been designed for this purpose, will be successful. An illuminance of 15–20 lx at the bed head is considered adequate for this task, provided the night lighting is of the recommended level.

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14.3.9 Clinical areas and operating departments Clinical areas and operating departments are locations where surgical, clinical or medical procedures are carried out. The main function of lighting in such areas is to provide sufficient light for the critical examination of patients, for carrying out operating procedures and for the use of life support apparatus. It is essential that the general lighting should have a CIE general colour rendering index of 90 or more and should provide an even distribution of illuminance throughout the department. Ceilings and walls should have a semi-gloss or eggshell finish. The walls should not produce reflected images of the luminaires, especially where they might occur at the eye-height of operating theatre staff. The ceiling reflectance should be 0.7 to 0.9 which can be achieved by the use of off-white or a pale shade, other than blue or green. This will assist in controlling the luminance contrast between the ceiling and the general lighting luminaires. The walls should have a tinted finish, rather than white, with a reflectance of 0.5 to 0.8. The floor should have a light-tone finish with a reflectance of at least 0.3 to maintain an adequate inter-reflected light component, especially within the actual operating theatre. All luminaires used within a theatre complex should have ingress protection of at least IP 54. In addition all luminaires must be constructed to allow for easy cleaning. 14.3.10 Operating theatres European standard BS EN 60601-2-41: 2000 provides detailed information on the requirements of ‘luminaires for diagnosis’, ‘minor (treatment) surgical luminaires’ and ‘major and system surgical luminaires.’ The illuminance in the surgical field will be determined by the type of surgical procedure, the depth of the body cavity to be illuminated and the angle of illumination. Consequently different surgical procedures will require operating luminaires of varying luminous intensities and illuminated field sizes. In a large operating theatre suite each theatre may be equipped with an operating luminaire specifically suited to the type of surgery to be undertaken in each theatre. In smaller suites where various types of surgical procedures will be undertaken in the same theatre, it will be necessary to select an operating luminaire that will provide the best allround solution (Figure 14.8).

Figure 14.8 Operating theatre luminaires

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The general lighting is required to provide both horizontal and vertical components of illuminance, vertical being required for good visibility of swab count racks, wall-mounted equipment, life support equipment etc., the surfaces of which should not be glossy. For ophthalmic, ear, nose and throat (ENT), and micro-surgery, much lower levels of general illuminance will be required. A value of between 10 to 50 lx is recommended. Dimming will provide the flexibility that is often required in theatres to permit multi-functional use Surface mounted or, in some instances, wall mounted luminaires may be required where theatre ceilings are not suitable for recessed luminaires. If wall mounted luminaires are used care should taken to ensure that the minimum horizontal light requirement is achieved without glare to theatre staff.


The maintained illuminance for general lighting of operating theatres is 1000 lx. This is usually adequate for performance of ancillary tasks by theatre staff. To minimise the possibility of bacterial transmission the general theatre luminaires should have ingress protection of IP ≥ 65/54; that is IP65 void-to-room with the front frame fixed on and IP54 when the frame is off for lamp replacement.

Practice has shown that glare should not be a problem in the comparatively small areas of modern operating theatres provided that the recommended illuminances, colours and reflectances are used and linear recessed or surface fluorescent luminaires having a downward light output ratio of approximately 0.6 are specified. Failure of the lighting during an operation may have serious consequences and it is essential to provide sufficient and reliable standby lighting. Instantaneous change-over to the standby supply is required for the major surgical luminaire or surgical luminaire system.

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Chapter Fifteen: Quasi-domestic lighting

Chapter 15: Quasi-domestic lighting 15.1 Functions of quasi-domestic lighting Quasi-domestic lighting is found in places that seek to appear as private residences but which are, in fact, communal dwellings. Examples of such locations range from halls of residence for students through care homes for the elderly to hotels. The lighting in such locations has two main functions. The first is to enable the residents to see what they want to see, without discomfort. The second is to create a visual environment that is attractive and interesting or at least one that avoids looking ‘institutional.’ The balance between these two functions varies within and between each application. For example, in a hotel, the room lighting is dominated by the need to create an attractive and interesting visual environment although bed head lighting will also be designed to ensure that reading is easy. In contrast, in a home for the elderly, greater importance is attached to ensuring that the residents can see what they need to see, although the need for a non-institutional appearance should not be neglected.

15.2 Factors to be considered 15.2.1 Occupants’ capabilities Different communal dwellings may contain people with very different visual capabilities. The occupants of halls of residence at a university are mainly likely to be young with good visual systems. Conversely, the occupants of homes for the elderly will almost certainly be old and many may have some form of visual disability (see Section 2.8.2). Guidance on lighting for people with low vision is given in the SLL Factfile No 10: Providing visibility for an ageing workforce and elsewhere (LRC, 2001d; Goodman, 2008). A realistic assessment of the visual capabilities of the occupants and what it is they need to see is necessary before starting to design the lighting. 15.2.2 Daylight Access to daylight and a view out is strongly desired by most people. Therefore, daylighting and access to windows should always be considered when designing quasi-domestic lighting. The main limitation on this is the desire for privacy in some rooms such as bedrooms and bathrooms, although, even here, there is a desire for daylight some of the time. Privacy and some control of discomfort due to solar glare can be ensured by fitting windows with curtains or blinds. 15.2.3 Light source colour properties The appearance of the room décor is important in quasi-domestic lighting. The room décor may have been chosen with care to create the required ambience but the effect will be ruined if the appearance of the décor changes between daytime, when the room is daylit, and after dark, when it will be lit with electric light sources. Similarly considerations apply to skin colour. Skin colour is widely used as an indicator of health. Lighting which distorts skin tones will not be acceptable. Such considerations rarely cause a problem with incandescent light sources but they can when inappropriately chosen fluorescent light sources, such as those with a high correlated colour temperature (see Section 1.4.3), are used. To avoid such complications, any light source used in quasi-domestic dwellings should have a CIE general colour rendering index of 80 or greater and a correlated colour temperature of 3500 K or less. This is particularly important in bathrooms and bedrooms.

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15.2.5 Safety There are three particular aspects of safety that should concern the designer of quasi-domestic lighting. The first involves the use of recessed tungsten halogen downlights. These are an increasingly popular approach to domestic lighting. The problem is that these lamps get very hot with the result that flammable material should be kept well away from them, a fact that is sometimes forgotten once they have been inserted into a hole in the ceiling. Where downlights are installed in a ceiling there is concern about the preservation of the fire barrier represented by the ceiling and the transfer of sound between rooms. The easiest way to overcome these problems is to use downlights with built-in fire and acoustic protection. An alternative approach to minimising the fire hazard is to install covers over the back of the downlights to ensure each downlight is separated from other materials.


15.2.4 Energy efficiency Part L of the Building Regulations applies to quasi-domestic dwellings (SLL Factfile No.9, 2006). This imposes limits on the type and amount of lighting equipment that can be permanently installed although there is a useful loophole in that plug loads, such as table lamps, are unrestricted. Further, there are proposals to restrict the supply of conventional incandescent lamps over the next few years, the intention being to increase the use of light sources with higher luminous efficacies, such as tungsten halogen and compact fluorescent. When in the form of recessed downlights, tungsten halogen can pose a fire hazard if not properly installed, as discussed below, and compact fluorescents may not conform to the advice about light source colour properties given above.

The second applies to bathrooms and shower rooms where there are restrictions on the type of luminaire that can be installed in different locations (Table 15.1). These restrictions are designed to minimise the likelihood that someone will get an electric shock while in contact with water. Washbasins are not covered by the regulations but are usually treated as zone 2. Table 15.1 Zones identified for luminaires in bathrooms and shower rooms by the 17th edition of the IEE Wiring Regulations Zones

Location and limitation

0

Any luminaire installed inside a bath or shower tray which can hold water should be low voltage (maximum 12 V) and have an IP rating of IPX7

1

Any luminaire installed in the volume above a bath or shower tray to a height of 2.25 m from the bottom of the bath or shower tray or for a horizontal distance of 1.2 m from the center of a shower outlet and vertically up to the height of the shower outlet or 2.25 m, whichever is the higher, should have a minimum IP rating of IPX4 or be of safety extra-low voltage with the transformer beyond zone 2

2

Any luminaire installed outside zones 0 and 1 but inside the volume specified by a boundary set 0.60 m horizontally outside the perimeter of the bath or shower tray and 2.25 m vertically above the floor, should have a minimum IP rating of at least IPX4 or be safety extra-low voltage with the transformer located beyond zone 2

The third requires the installation of an emergency lighting system (see Chapter 8). Emergency lighting is required for the safe egress of residents in the event of an emergency. In some quasidomestic dwellings, such as care homes for the elderly, some of the residents will almost certainly be physically incapacitated and/or could be mentally impaired. 215


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For such situations, it would be better to follow the approach used in hospitals (see Chapter 14). General design guidance can also be obtained from the SLL Lighting Guide 12: Emergency lighting design guide. 15.2.6 Security One feature that distinguishes quasi-domestic buildings from private residences is that strangers may be encountered inside the building as they make their way to the room of the person they want to meet. This part private/part public nature of the building means that security is a specific concern, a concern that may be addressed by CCTV surveillance (see Section 18.2.5). For hallways, stairways and other communal areas, lighting that enables recognition of faces is essential to determine who belongs in the space and who doesn’t; who is perceived as safe and who may present a danger.

15.3 Lighting recommendations The lighting recommendations for quasi-domestic buildings are very simple. This is because the lighting is usually designed to fit around the furnishings, so concern with illuminance uniformity is often inappropriate. Where illuminance uniformity is a consideration, a minimum illuminance uniformity (minimum/average) of 0.8 is recommended. Further, many of the spaces are small so glare is not a problem because the luminaires are usually far away from the common lines of sight. Where glare is of concern it can usually be dealt with by ensuring the no part of the luminaire has a luminance greater than 300 cd/m2 when seen from common directions of view. As for the light source colour properties, these have been dealt with above. As a result of these considerations, the quantitative lighting recommendations are restricted to the minimum maintained illuminances that should be provided at particular locations (Table 15.2). These recommendations are applicable to quasi-domestic buildings occupied by young people. For quasi-domestic buildings where elderly people predominate, see the recommendations of the Thomas Pocklington Trust (Goodman, 2008). Table 15.2 Maintained illuminances recommended for different parts of some quasi-domestic buildings

216

Location

Plane of measurement

Maintained illuminance (lx)

Entrance

Floor

200

Reception desk

Working surface

300

Corridors

Floor

100

Stairs

Treads

100

Study bedroom

Desk

150

Study bedroom

Wash basin

100

Small kitchen

Worktops and cooker

150

Utility room

Worktops and washing machines

150

Lounges

Floor

150

TV lounge

Floor

50

Dining hall

Tables

150

Games rooms – billiards or snooker

Table

500

Games rooms – Table tennis

Table

300


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15.4.1 Entrances The first requirement for anyone approaching a building is the ability to identify the entrance. This can be ensured by lighting the entrance so that the doors and any sign identifying the building can be seen from a distance. The second is to move safely up to the entrance. For this purpose, the illuminance on the ground should be increased close to the entrance to the same level as that inside so as to provide a smooth transition zone between the exterior and the interior. This is particularly important for buildings where the elderly may be found because it allows more time for visual adaptation to occur. Where there are steps on the approach to the building, these should be lit after dark using column mounted urban area luminaires or bollards. Floodlights mounted low on the building should not be used as they tend to produce severe glare to those approaching the building. At the entrance, lighting should be provided both outside and inside. The purpose of such lighting is to make whoever is outside visible to the person opening the door and vice versa. For this to happen, there has to be a window or wide-angle viewer fitted in the door. As for the lighting, downlights mounted above the door should be avoided as they create shadows on the face that make identification difficult. A better approach is to use low luminance diffuse lighting placed on both sides of the door.


15.4 Approaches to lighting quasi-domestic buildings

The entrance hall gives the visitor a first impression of the building and provides important information about where to go. This information may be gained from display boards or from a reception desk. Display boards should have their own dedicated lighting. Reception desks should be lit to a higher illuminance than the rest of the space and the lighting should be designed to provide good vertical illuminances so that the faces of the receptionist and the visitor are clear. 15.4.2 Corridors and stairs In corridors, the aim of the lighting should be to light the walls as well as the floor. If linear light sources are used, the long axis should be oriented along the corridor. If the corridor is narrow, an alternative approach is to use cove lighting along one side of the corridor. The illuminance provided in a corridor should be at least 100 lx in daytime where there is no significant daylight contribution. After dark, but when people are still about, this can be reduced to 50 lx. Late at night, when most people are asleep a minimum of 5 lx is required provided there is some means to restore the illuminance to 50 lx on demand. Stairs should be lit so that there is a flow of light from top to bottom. This means that the treads will be illuminated but the risers will not. Figure 15.1 suggests what locations should and should not be used for luminaires. In addition to lighting, contrasting markings on the nosing of each tread are a useful safety feature. A+

B+

C+

D+

Figure 15.1 Staircase lighting: position A is recommended, B and C are to be avoided, and D can be used for wall-mounted luminaires on very long staircases 217


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15.4.3 Study bedrooms Study bedrooms require lighting that is flexible to enable the residents to have some individual control over what is essentially the only private space available to them. Sufficient flexibility can be provided by using adjustable local lighting on the desk and dimming of the main room light (Figure 15.2). The main room light should provide diffuse light of at least 100 lx at desk height. This will be easier to achieve if the room surfaces are of medium to high reflectance. Lighting of the en-suite facilities has to conform to the requirements for bathrooms and should be centred on the washbasin and mirror.

Figure 15.2 Lighting of study bedrooms for flexibility

15.4.4 Kitchens and utility rooms In many quasi-domestic buildings, kitchens and utility rooms are communal facilities. The lighting of these areas is utilitarian and should provide an average illuminance of 150 lx at the cooker/washing machine level. The luminaires used should be capable of withstanding water splashes (IP44). Light sources used in kitchens should have good colour rendering (CRI > 80). Bare light sources should not be used. Rather, enclosed luminaires that are easily cleaned and which ensure that if a light source brakes pieces of glass do not fall into the food are preferred. Luminaires with a diffuse light distribution and medium to high reflectance surfaces are required if people using the cooker or washing machine are not to be in their own shadow (Figure 15.3). As kitchens and utilities may be left unoccupied for some time, occupancy sensors should be fitted to avoid wasting energy.

Figure 15.3 Lighting of kitchens designed to avoid shadows

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15.4.6 Dining halls The dining hall is where residents gather for meals. The ambience can vary from that of an expensive restaurant to that of a youth hostel, although the latter is more common. Where meals are collected by the residents from a servery, on trays, the usual approach is to provide uniform lighting over the tables, although some interest may be created by lighting particular features of the dinning hall. Localised lighting is provided over the servery itself and infrared downlights are often used to keep the food warm. 15.4.7 Games room Games rooms may require special lighting depending on the games played and the standard at which they are played. Extensive advice is given in SLL Lighting Guide 4: Sports lighting. However, for games played primarily for amusement, uniform lighting producing a minimum maintained illuminance of 200 lx at floor level is sufficient. If fluorescent lighting is used, high frequency electronic control gear should be used. Further, the décor should be plain, particularly where high speed movement is involved, e.g. table tennis.


15.4.5 Lounges Lounges are social areas where people may gather to talk, read or watch television. The lighting should contribute to a relaxing atmosphere. This can be achieved by providing sufficient light for reading in some areas, low light levels in others, taking care to avoid reflections of light in the TV screen, and by providing some emphasis on important features of the space, such as pictures. Illuminance uniformity is not important for lounges but the integration of the lighting with the architecture is. Flexibility through preset ‘scenes’ provided by a preprogrammed control system is an attractive option.

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Chapter Sixteen: Road lighting

Chapter 16: Road lighting 16.1 Road classification Road lighting is divided into three classes; traffic routes where the needs of the driver are dominant, subsidiary roads where the lighting is primarily intended for the pedestrian and the cyclist, and urban centres, where the lighting is designed to do what can be done for public safety and security, while also providing an attractive nighttime environment. The photometric recommendations for all types of road lighting in the UK are given in BS EN 13201: Part 2. Advice on the implementation of these recommendations is given in BS 5489-1 together with Amendment 2.

16.2 Lighting for traffic routes Lighting for traffic routes is lighting designed primarily to meet the requirements of the driver of a motorised vehicle. Road lighting recommendations identify three distinct situations; traffic routes where motorised vehicles are dominant and move without conflict, the edges of roads where pedestrians and cyclists may be at risk, and conflict areas where streams of motorised vehicles intersect with each other or with pedestrians and cyclists. 16.2.1 Lighting recommendations for traffic routes The primary function of the lighting of traffic routes is to make other vehicles on the road visible. Road lighting does this by producing a difference between the luminance of the vehicle and the luminance of its immediate background, the road surface. This difference is achieved by increasing the luminance of the road surface above that of the vehicle so that the vehicle is seen in silhouette against the road surface. The criteria used to define lighting for traffic routes are: Average road surface luminance: The luminance of the road surface averaged over the carriageway (cd/m2). Overall luminance uniformity (Uo ): The ratio of the lowest luminance at any point on the carriageway to the average luminance of the carriageway. Longitudinal luminance uniformity (Ul ): The ratio of the lowest to the highest luminance found along a line along the centre of a driving lane. For the whole carriageway, this is the lowest longitudinal luminance uniformity found for the driving lanes of the carriageway. Threshold increment: A measure of the loss of visibility caused by disability glare from the road lighting luminaires. Quantitatively, percentage threshold increment is given by the expression TI = 65 (Lv / L0.8) where : Lv = equivalent veiling luminance (cd/m2) (see section 2.6.3) L = average road surface luminance (cd/m2) Surround ratio: The average illuminance just outside the edge of the carriageway in proportion to the average illuminance just inside the edge of the carriageway.

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Table 16.1 Lighting classes for traffic routes Road name

Road characteristic

Detailed description

Motorway

Limited access

Routes for fast moving, long distance traffic. Fully grade separated and restrictions on use Main carriageway in complex interchange areas Main carriageway with interchanges at < 3 km

Strategic route

Trunk roads and some main A roads between primary destinations

< 40,000 > 40,000

ME1 ME1 ME2 ME1

< 40,000 > 40,000

Emergency lanes

-

ME4a

< 15,000 > 15,000

ME3a ME2

Routes for fast moving, long distance traffic with little frontage access or pedestrian traffic. Speed limits are usually in excess of 40 mph and there are few junctions. Pedestrian crossings are either segregated or controlled and parked vehicles are usually prohibited

Dual carriageway Major urban network and inter-primary links, short to medium distance traffic

< 40,000 > 40,000

Lighting class

Main carriageways with interchanges > 3 km

Single carriageway

Main distributor

ADT

Routes between strategic routes and linking urban centres to the strategic network with limited frontage access. In urban areas, speed limits are usually 40 mph or less, parking is restricted at peak times and there are positive measures for pedestrian safety reasons Single carriageway Dual carriageway

< 15,000 > 15,000

< 15,000 > 15,000 < 15,000 > 15,000


Traffic routes are divided into different classes. The different classes are based on the type of road, the average daily traffic flow (ADT), the speed of vehicles, the type of vehicles in the traffic and the frequency of conflict areas and pedestrians. Table 16.1 specifies the different classes and identifies the recommend lighting criteria. Details of the recommended lighting criteria for dry roads are given in Table 16.2. These are the lighting criteria usually adopted in the UK.

ME2 ME2

ME3a ME2

ME3a ME2 ME3a ME2 221


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Table 16.1 Lighting classes for traffic routes Road name

Road characteristic

Detailed description

Secondary distributor

Classified road (B or C road) and unclassified urban bus route, carrying local traffic with frontage access and frequent junctions

Rural areas (Environmental zones 1 or 2). These roads link larger villages and HGV generators to the strategic and main distributor network

Link road

< 7,000 7,000–15,000 > 15,000

ME4a ME3b ME3a

< 7,000 7,000–15,000 > 15,000

ME3c ME3b ME2

Rural areas (Environmental zones 1 or 2). These roads link smaller villages to the distributor network. They are of varying width and not always capable of carrying two-way traffic

Any

ME5

Urban areas (Environmental zone 3). These roads are residential or industrial interconnecting roads with 30 mph speed limits, random pedestrian movements and uncontrolled parking

Any

ME4b or S2

Any with high pedestrian or cyclist traffic

S1

Urban areas (Environmental zone 3). These roads have 30 mph speed limits and very high levels of pedestrian activity with some crossing facilities including zebra crossings. On-street parking is generally unrestricted except for safety reasons

Road linking the main and secondary distribution network with frontage access and frequent junctions

Lighting class

ADT

Table 16.2 Lighting recommendations for traffic routes

222

Lighting class

Minimum maintained average road surface luminance (cd/m2)

Minimum overall luminance uniformity

Minimum longitudinal luminance uniformity for the carriageway

Maximum threshold increment (%) (note 1)

Minimum surround ratio (note 2)

ME1

2.0

0.40

0.70

10

0.50

ME2

1.5

0.40

0.70

10

0.50

ME3a

1.0

0.40

0.70

15

0.50

ME3b

1.0

0.40

0.60

15

0.50

ME3c

1.0

0.40

0.50

15

0.50

ME4a

0.75

0.40

0.60

15

0.50

ME4b

0.75

0.40

0.50

15

0.50

ME5

0.50

0.35

0.40

15

0.50


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Note 2. The surround ratio criterion should only be applied where there are no traffic areas with their own criteria adjacent to the carriageway.

In some situations, it may not be possible to calculate the maximum threshold increment. An alternative method to limit disability glare is to select a luminaire according to the classes given in Table 16.3. The different classes are defined by the luminous intensity of the luminaire, in candelas/1000 lumens of bare light source output, at 70, 80 and 90 degrees from the downward vertical, in any direction, and the luminous intensity above 95 degrees, in any direction. Class G3 corresponds to a cutoff luminaire. Class G6 corresponds to a full cutoff luminaire.


Notes to Table 16.2 Note 1. A five percentage point increase in minimum threshold increment is permitted where low luminance light sources, such as low pressure sodium and fluorescent, are used.

Table 16.3 Luminaire classes for the control of disability glare Lighting class

Maximum luminous Maximum luminous Maximum luminous intensity/1000 intensity/1000 intensity/1000 lumens at 70° lumens at 80° lumens at 90° (cd/1000 lm) (cd/1000 lm) (cd/1000 lm)

Luminous intensity above 95° (cd)

G1

-

200

50

-

G2

-

150

30

-

G3

-

100

20

-

G4

500

100

10

0

G5

350

100

10

0

G6

350

100

0

0

16.2.2 Lighting recommendations for areas adjacent to the carriageway People and objects adjacent to the carriageway need to be seen by the driver. Such locations include unmade verges, footways and cycle paths and the emergency lanes of motorways. For all traffic routes other than heavily used footways and cycle tracks and the emergency lanes of motorways, lighting of the area adjacent to the carriageway should conform to the surround ratio (Table16.2). For traffic routes with heavily trafficked footways and cycle tracks an appropriate lighting criterion should be selected from Table 16.4. Which criterion is selected will depend on the lighting class used for the carriageway. To ensure adequate illuminance uniformity, the actual maintained average horizontal illuminance should not be more than 1.5 times greater than the minimum maintained average horizontal illuminance. Emergency lanes on motorways should be lit to lighting class ME4a (see Table 16.2).

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Table 16.4 Lighting recommendations for areas adjacent to the carriageway Lighting class

Minimum maintained average horizontal illuminance (lx)

Minimum maintained horizontal illuminance (lx)

S1

15

5

S2

10

3

S3

7.5

1.5

S4

5

1

S5

3

0.6

S6

2

0.6

16.2.3 Lighting recommendations for conflict areas A conflict area is one in which traffic flows merge or cross, e.g. at intersections or roundabouts, or where vehicles and other road users are in close proximity, e.g. on a shopping street or at a pedestrian crossing. Lighting for conflict areas is intended for drivers rather than pedestrians. The criteria used to define lighting for conflict areas are based on the illuminance on the road surface rather than road surface luminance. This is because drivers’ viewing distances may be less than the 60 m assumed for traffic routes and there are likely to be multiple directions of view. The criteria used for the lighting of conflict areas are: Average road surface illuminance: the illuminance of the road surface averaged over the carriageway (lx). Overall illuminance uniformity (Uo): the ratio of the lowest illuminance at any point on the carriageway to the average illuminance of the carriageway. The recommendations for the different lighting classes for conflict areas are given in Table 16.5. These recommendations can be applied to all parts of the conflict area or only to the carriageway when separate recommendations are used for pedestrians or cyclists (see Section 16.2.2). The choice of lighting class has to be matched to the lighting of the traffic routes approaching the conflict area. Guidance is given in Table 16.6. Table 16.5 Lighting recommendations for conflict areas

224

Lighting class

Minimum maintained average road surface illuminance (lx)

Minimum overall illuminance uniformity

CE0

50

0.4

CE1

30

0.4

CE2

20

0.4

CE3

15

0.4

CE4

10

0.4

CE5

7.5

0.4


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16.2.4 Coordination It is obviously important that the lighting of conflict areas should be coordinated with that of the traffic routes. Table 16.6 indicates the compatible lighting classes for traffic routes and conflict areas. Where two traffic routes lit to different classes lead into a conflict area, the match should be made to the higher traffic route class.


A specific form of conflict area is the pedestrian crossing. Where a pedestrian crossing is close to a junction it is treated simply as part of the conflict area but where it occurs in isolation there are two possibilities for lighting. One is to use the normal lighting of the traffic route with the crossing positioned at the midpoint between luminaires. The other is to use additional local lighting. The local lighting approach is recommended when the traffic routes are lit to less than lighting class ME3 (see Table 16.2) or the crossing is located on a bend, on the brow of a hill or where the relative positions of the crossing and road lighting luminaires cannot be coordinated. The local lighting should illuminate the crossing to a higher illuminance than is provided on the roads approaching the crossing. A suitable lighting class for horizontal illuminance can be selected from Table 16.5. The local lighting should have strong vertical component to ensure that pedestrians are positively illuminated but care must be taken to control glare towards drivers (Table 16.3).

Table 16.6 Compatible lighting classes for conflict areas on traffic routes Traffic route lighting class

Conflict area lighting class

ME1

CE0

ME2

CE1

ME3

CE2

ME4

CE3

ME5

CE4

16.2.5 Traffic route lighting design Fundamental The design process for traffic route lighting consists of the following stages: Selection of the lighting class and definition of relevant area: the lighting class of the carriageway is selected (Table 16.1). The nature and extent of adjacent areas and any conflict areas are identified and the lighting approach to be used chosen. The compatible lighting classes for adjacent areas and conflict areas are selected (Table 16.6). Collection of preliminary data: the following data is required before calculation can start: mounting height, luminaire type and optic setting, lamp type, initial luminous flux of lamp, IP rating of luminaire, cleaning interval planned for luminaire, pollution category for location, luminaire maintenance factor, lamp replacement interval, lamp lumen maintenance factor at replacement interval, maintenance factor, luminaire tilt, width of carriageway, width of driving lane, width of adjacent areas, luminaire transverse position relative to the calculation grid, luminaire arrangement, road surface r-table.

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The emphasis given to maintenance factors in this list arises from the fact that the lighting recommendations are made in terms of minimum maintained values. Table 16.7 sets out typical luminaire maintenance factors to be applied for different locations, luminaires and cleaning intervals. In this table, high pollution generally occurs in the centre of large urban areas and heavy industrial areas; medium pollution occurs in semi-urban, residential and light industrial areas while low pollution occurs in rural areas. Luminaires are classified by the protection against foreign objects and dust number used in the IP system (see Table 4.10). Table 16.7 Typical luminaire maintenance factors Luminaire IP class/pollution level

Cleaning interval = 12 months




IP2X/High

0.53

0.48

0.45

0.42

IP2X/Medium

0.62

0.58

0.56

0.53

IP2X/Low

0.82

0.80

0.79

0.78

IP5X/High

0.89

0.87

0.84

0.76

IP5X/Medium

0.90

0.88

0.86

0.82

IP5X/Low

0.92

0.91

0.90

0.88

IP6X/High

0.91

0.90

0.88

0.83

IP6X/Medium

0.92

0.91

0.89

0.87

IP6X/Low

0.93

0.92

0.91

0.90

The reflection properties of a road surface are quantified by an r-table. This consists of a matrix of values of q cos3 γ, where q is the luminance coefficient of the pavement material and γ is the angle of incidence of light from the upward vertical, in degrees (see Figure 16.1). This quantity is called the reduced luminance coefficient (r). The two dimensions of the r-table are the angle β, the angle between the vertical plane of incidence and the vertical plane of observation and the tangent of the angle γ, the angle of incidence from the upward vertical (see Figure 16.1). Each cell in the r-table contains a value for the reduced luminance coefficient multiplied by 10,000.

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δ γ

β


S

α

Figure 16.1 Angles upon which the luminance coefficient is dependent In principle, the relevant angles for characterising the reflection properties of the road surface are: α = angle of observation from the horizontal, β = angle between the vertical planes of incidence and observation, γ = angle of incidence from the upward vertical, and δ = angle between the vertical plane of observation and the road axis. In practice, for lighting of traffic routes, it is assumed that α has a fixed value of 1 degree corresponding to a viewing distance of about 60 m and δ is irrelevant because the reflection properties of road surfaces are isotropic. Although different road materials have different reflection properties, and those properties change over time and with wear, there are only two r-tables commonly used in the UK, one for asphalt-based roads and one for concrete roads. The r-table for the asphalt-based roads is called the representative British road surface. r-tables are characterised by two parameters, one concerned with lightness and one concerned with specularity. The parameter for lightness is the average luminance coefficient, Q0; this is highly correlated to the average luminance produced on the road surface. The parameter for specularity is S1 = r (0, 2) / r (0, 0) where: r (0, 2) is the reduced luminance coefficient for β = 0 degrees and tan γ = 2 r (0, 0) is the reduced luminance coefficient for β = 0 degrees and tan γ = 0

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The representative British road surface is characterised as Qo = 0.07 and S1 = 0.97. For concrete road surfaces the corresponding values are Qo = 0.10 and S1 = 0.24. There are other r-tables available for different pavement materials. Where it is required to design for a frequently wet road, the calculations described below should be made using r-tables for both dry and wet surfaces. Calculation of design spacing The design of road lighting for traffic routes to meet the selected criteria uses information on the luminous intensity distribution of the luminaire, the layout of the luminaires relative to the carriageway and the reflection properties of the road surface. The luminous intensity distribution of the luminaire is supplied by the manufacturer. The layout of the luminaires for two-way roads is usually single-sided, staggered or opposite. In a single sided installation all the luminaires are located on one side of the carriageway. The single-sided layout is used when the width of the carriageway is equal to or less than the mounting height of the luminaires. The luminance of the lane on the far side of the carriageway is usually less than that on the near side. In a staggered layout, alternate luminaires are arranged on opposite sides of the carriageway. Staggered layouts are typically used where the width of the carriageway is between 1 to 1.5 times the mounting height of the luminaires. With this layout, care should be taken that the luminance uniformity criteria are met. In the opposite layout, pairs of luminaires are located opposite each other. This layout is typically used when the width of the carriageway is more then 1.5 times the mounting height of the luminaires. The layout of luminaires for dual carriageways and motorways is usually central twin, central twin and opposite or catenary. In a central twin layout, pairs of luminaires are located on a single column in the central reservation. This layout can be considered as a single-sided layout for the two carriageways. Where the overall width of the road is wider, either because the central reservation is wider or there are more lanes, the central twin and opposite layout can be used. In this, the central twin luminaires alternate with the opposite luminaires to form a staggered layout. In the catenary layout, luminaires are suspended from a catenary cable along the central reservation. The catenary layout offers good luminance uniformity, less glare because the luminaires are viewed axially, and excellent visual guidance. With an r-table matched to the pavement material, the luminous intensity distribution for the luminaire and the layout of the luminaires relative to the carriageway, the luminance produced by a single luminaire at any point P on the road surface can be calculated using the equation: L=

Ir h2

where: L = luminance at the point P produced by the luminaire (cd/m2) I = luminous intensity in the direction from the luminaire to the point P (cd) r = reduced luminance coefficient at point P h = mounting height of luminaire (m) This process can then be repeated for adjacent luminaires and the contributions from all luminaires summed to get the luminance at that point for the whole lighting installation. This process can then be repeated over an array of points on the road so as to get the luminance metrics used to characterise the road lighting for traffic routes. 228


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Table 16.8 Minimum set-back of lighting columns from the edge of the carriageway Design speed for road (km/h)

Minimum horizontal set-back from the edge of the carriageway (m)

50

0.8

60

1.0

100

1.5

120

1.5


Although this process can be done manually, for straight roads it is almost always done using software. This allows the designer to access the photometric file for the selected luminaire and then to manipulate the mounting height, clearance, set-back, tilt and layout of the luminaires necessary to determine the spacing required to meet the appropriate lighting criteria. Of these variables, clearance and set-back have limits. To allow safe passage, the clearance of all parts of the lighting equipment above the carriageway should be at least 5.7 m. To reduce the risk of death or injury caused by collision with a lighting column, the minimum set-back of the lighting column from the edge of the carriageway is related to the design speed of the road, as listed in Table 16.8.

Bends in the road with a radius greater than 300 m can be considered as straight as far as lighting is concerned. For bends with smaller radii, the layout of the luminaires should be designed to ensure the necessary road surface luminance and good visual guidance. Where the width of the carriageway is less the 1.5 times the mounting height of the luminaires, the luminaires should be arranged in a single sided plan on the outside of the bend. For wider roads, an opposite layout should be used. A staggered layout should not be used on bends as it gives poor visual guidance. The spacing of luminaires on a bend is less than on a straight road, typically half to three quarters of the spacing on a straight road. To check that the road surface luminance criteria are met for bends, an isoluminance template can be used. This consists of a contour on the road where the luminance from a single luminaire is at 12.5% and 25% of the maximum road surface luminance. Given a layout of luminaire positions, the luminance templates of the individual luminaires can be superimposed on the plan of the road to determine the luminance uniformity. Further details of this approach are given in BS 5489: Part 1. Conflict areas have different shapes and use illuminance as a criterion rather than luminance. The illuminance produced at a point P from a single luminaire is given by the formula:

E=

I cos3 γ h2

where: E = illuminance at the point P from the luminaire (lx) I = luminous intensity in the direction from the luminaire to the point P (cd) γ = angle of the direction of I from the downward vertical (degrees) h = mounting height of luminaire (m) 229


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This process can be repeated for adjacent luminaires and the contributions from all luminaires summed to get the illuminance at that point for the whole lighting installation. This process can then be repeated over an array of points on the road so as to get the illuminance metrics used for the lighting of conflict areas. Alternatively, manufacturers often provide a relative isolux diagram, this being the illuminance pattern provided on the road surface by a single luminaire relative to the maximum illuminance and plotted in terms of mounting height. Given a layout of luminaires around a conflict area, the mounting height and information about the maximum illuminance, the overall illuminance pattern can be generated. Some suggested luminaire layouts for commonly occurring conflict areas, e.g. roundabouts, are given in BS 5489: Part 1 as is advice for special locations, such as bridges, elevated roads and around airfields. BS 5489: Part 2 provides guidance on the lighting of tunnels. Plotting of luminaire positions Having determined the ideal spacing, the luminaire positions are identified, starting with the conflict areas. After these are settled, the luminaire positions for the traffic routes and adjacent areas are identified.

16.3 Lighting for subsidiary roads 16.3.1 Lighting recommendations for subsidiary roads Subsidiary roads consist of access roads and residential roads and associated pedestrian areas, footpaths and cycle tracks. The main function of lighting of subsidiary roads and the areas associated with them is to enable pedestrians and cyclists to orientate themselves and to detect vehicular and other hazards, and to discourage crime against people and property. The lighting in such areas can provide some help to drivers but it is unlikely to be sufficient for revealing objects on the road without the use of headlamps. The main purpose of lighting footpaths and cycle tracks separated from roads is to show the direction the route takes, to enable cyclists and pedestrians to orientate themselves, to detect the presence of other cyclists, pedestrians and hazards, and to discourage crime against people and property. Illuminance on the horizontal is used as the lighting criterion for subsidiary roads and associated areas. The illuminances associated with each lighting class are given in Table 16.4. The lighting class to be used is determined by the traffic flow, the environmental zone, the level of crime and the colour rendering of the light source used (Table 16.9). In this table, low traffic flow refers to areas where traffic is typical of a residential road and solely associated with adjoining properties. Normal traffic flow refers to areas where traffic flow is equivalent to a housing estate access road. High traffic flow refers to areas where traffic usage is high and can be associated with local amenities such as clubs, shopping facilities and pubic houses. The crime rates should be considered relative to the local area. The environmental zones (E1 to E4) are as defined in Table 6.1. The divide in CIE general colour rendering index (CRI) at 60 means that the use of low pressure sodium or high pressure sodium light sources calls for a higher illuminance than fluorescent and metal halide light sources. The S-class may be increased one step where there are traffic calming measures.

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Crime rate

CRI

Low

< 60

Low traffic flow/E1 or E2

≥ 60

Low Moderate Moderate High High

< 60 ≥ 60 < 60 ≥ 60

Normal Normal High traffic traffic traffic flow/E3 flow/E1 flow/E1 or E4 or E2 or E2

High traffic flow/E3 or E4

S5

S4

S3

S3

S2

S6

S5

S4

S4

S3

S4

S3

S2

-

S1

S3

S4

S3

-

S2

S2

S2

S1

-

S1

S3

S3

S2

-

S2


Table 16.9 Lighting classes for subsidiary roads and associated areas, footpaths and cycle tracks

The area over which these illuminances should be applied varies with the application. When considering roads with associated areas, it is recommended that a single lighting class be applied to the carriageway and any adjacent footway and verge, from boundary to boundary. If a road is a shared surface residential road, the relevant area is the shared surface only. When considering footpaths and cycle tracks separated from roads, consideration should be give to extending the lit area beyond the width of the footpath or cycle track so as to give a wider field of view. Glare from luminaires should be controlled. To limit disability glare, where luminaires have clear bowls or reflectors, these should conform to at least class G1 of Table 16.3. For discomfort glare, the simplest approach is to select a luminaire where the light source is not visible, either directly or as an image, from any relevant direction. If a more quantitative approach is desired, glare index can be used. This is calculated from the equation: Glare index = I × A–0.5 where: I = maximum luminous intensity at 85° from the downward vertical, in any direction (cd) A = apparent area of the luminous parts of the luminaire on a plane perpendicular to the direction of I (m2). Table 16.10 shows the glare index classes appropriate for subsidiary roads, footpaths and cycle tracks. Table 16.10 Lighting classes based on glare index Lighting class

Maximum glare index

D1

7,000

D2

5,500

D3

4.000

D4

2.000

D5

1.000

D6

500 231


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16.3.2 Lighting design for subsidiary roads The design process for lighting of subsidiary roads and associated areas, footpaths and cycle tracks consists of the following stages: Selection of the lighting class and definition of relevant area: the lighting class is selected (Table 16.9) and the relevant areas defined. Collection of preliminary data: the following data is required before calculation can start: Mounting height, luminaire type and optic setting, lamp type, initial luminous flux of lamp. IP rating of luminaire, cleaning interval planned for luminaire, pollution category for location, luminaire maintenance factor, lamp replacement interval, lamp lumen maintenance factor at replacement interval, maintenance factor, luminaire tilt, width of relevant area, luminaire transverse position relative to the calculation grid, luminaire arrangement, glare index of luminaire. Calculation of design spacing: the calculation procedure for subsidiary roads and associated areas, footpaths and cycle tracks is given in BS EN 13201: Part 3, Section 7. Plotting of luminaire positions: having determined the ideal spacing, the luminaire positions are identified, starting with T-junctions, areas of traffic calming measures, and severe bends. After these are settled, the luminaire positions for the straight sections of the roads, paths or tracks are fitted to match. Finally, a check is made to determine if the luminaire positions are compatible with possible column positions.

16.4 Lighting for urban centres and public amenity areas Urban centres and public amenity areas are used by pedestrians, cyclists and drivers. In such places, the lighting of the road surface for traffic movement is not the only or even the main consideration. Rather, the functions of lighting in urban centres and public amenity areas are to do what can be done for public safety and security, while also providing an attractive nighttime environment. To fulfill these functions, a master plan should be produced to meet some or all of the following objectives: to provide safety for pedestrians from moving vehicles to deter anti-social behaviour to ensure the safe movement of vehicles and cyclists to match the lighting design and lighting equipment to the architecture and environment to control illuminated advertisements and integrate floodlighting, both permanent and temporary to illuminate road and directional signs to blend light from private and public sources to limit light pollution to maintain lighting installations and protect them from vandalism to facilitate CCTV surveillance. 232


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Guidance on some of the techniques used to light urban centres and public amenity areas are given in CIBSE LG 6: The outdoor environment and ILE/CIBSE Lighting the environment – A guide to good urban lighting. Table 16.11 Recommended lighting classes for city and town centres Type of traffic

Normal traffic flow/E3

Normal traffic flow/E4

High traffic flow/E3

High traffic flow/E4

Pedestrian only

CE3

CE2

CE2

CE1

Mixed vehicle and pedestrian with separate footways

CE2

CE1

CE1

CE1

Mixed vehicle and pedestrian on the same surface

CE2

CE1

CE1

CE1


This battery of objectives and the individual nature of each site ensure that there is no standard method of lighting urban centres and public amenity areas, nor any universally applicable recommendations. What can be given are some general recommendations for the illuminances to be used in city and town centres, although even these may need to be adjusted for a particular site, depending on the ambient environment, the level of crime, street parking etc. Table 16.11 lists the lighting classes recommended for city and town centres, based on the type of traffic, the traffic flow, and the environmental zone (see Table 6.1). The minimum maintained illuminances associated with each lighting class are given in Table 16.5.

16.5 Tunnel lighting A tunnel can be defined as a section of road that is not exposed to the sky. Tunnels shorter than 25 m do not need lighting. Tunnels longer than 200 m will need lighting by day and night. Tunnels between 25 and 200 m in length may need lighting by day and night. The nature of lighting provided will depend on the tunnel class, classes ranging from 1 to 4 depending on the traffic density and traffic mix. The purpose of tunnel lighting is to enable drivers to see vehicles and obstructions within the tunnel. The lighting of tunnels has to address two different problems. The first is the black-hole effect experienced by a driver approaching a tunnel. The second is the black-out effect caused by a lag in adaptation on entering the tunnel. Neither of these problems occurs at night, because then the average road surface luminance inside the tunnel is recommended to be at least 1 cd/m2, a value similar to if not greater than that of the road surface outside the tunnel (BSI 5489-2: 2003). By day, this is not the case. By day, the luminances around the tunnel portal will be much higher than those inside the tunnel so both the black-hole effect and the black-out effect may be experienced and driver safety may suffer. The black-hole effect refers to the perception that from the distance at which a driver needs to be able to see vehicles and obstructions in the entrance to the tunnel, that entrance is seen as a black hole. The major cause of the black-hole effect is the reduction in luminance contrasts of the retinal images of vehicles and obstructions in the tunnel entrance caused by light scattered in the eye. There are two approaches that can be used to alleviate the black-hole effect. The first is to reduce the luminance of the surroundings to the tunnel. This can be done by ensuring that the tunnel portal is of low reflectance, by shading the tunnel portal and the road close to the tunnel entrance with louvres designed to exclude sunlight, by using low reflectance road surface materials outside the tunnel and by landscaping to shield the view of high-luminance sources, such as the sky.

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The second is to increase the luminance contrast of vehicles and obstacles inside the tunnel entrance. This can be done by the choice of materials used in the tunnel entrance. The road surface inside the tunnel entrance should be of higher reflectance than that immediately outside and the walls of the tunnel up to a height of 2 m, against which vehicles in the tunnel are usually seen, should have a luminance within the range of 60 to 100 percent of the average road surface luminance, the actual minimum depending on the tunnel class. The black-out effect occurs because although the approach to the tunnel starts the process of visual adaptation there is no guarantee that this process will be complete by the time the tunnel entrance is reached. The approach used to diminish the black-out effect is to gradually decrease the road surface luminance from a threshold zone, starting at the tunnel portal, through a transition zone, to the interior zone. The length of these zones is determined by the stopping distance (SD), this being the distance required to bring a vehicle travelling at the maximum allowed speed to a complete halt. The length of the threshold zone is one SD. The average road surface luminance of the threshold zone is determined by the access zone luminance. The access zone is the part of the road approaching the tunnel within one SD of the entrance portal. The access zone luminance is the average luminance of a conical field of view subtending 20 degrees at the eye of a driver located at the start of the access zone and looking at the entrance portal. The threshold luminance ranges from 3 to 10 percent of the access zone luminance depending on the tunnel class and the speed limit. The length of the transition zone is determined by the assumed vehicle speed, the distance being set so as to allow about 18 seconds for adaptation. The road surface luminance of the interior zone in daytime depends on the speed and density of traffic in the tunnel and covers a range of 0.5 to 10 cd/m2, the higher the speed limit, the higher the traffic density and the more mixed the traffic, the higher the average road surface luminance recommended in the interior zone. The minimum overall uniformity ratio along each lane of the tunnel should be 0.4 and the minimum longitudinal uniformity ratio is in the range 0.6 to 0.7 depending on the tunnel class. Disability glare from lighting in the tunnel is controlled by limiting the threshold increment to less than 15 percent. At the end of the interior zone is an exit zone where drivers leave the tunnel. The length of the exit zone in metres is numerically equal to the speed limit in kilometres/hour. The road surface luminance of the exit zone should be five times the average road surface luminance of the interior zone. Detailed guidance on the lighting of tunnels can be obtained from BS 5489-2: 2003. As for the type of lighting used to provide the luminances in the tunnel, the light source most commonly used is one of the discharge sources, because of their high luminous efficacy, long life and robustness. The luminaires used in tunnels have to be of rugged construction to deal with vibration, dirt, chemical corrosion and washing with pressure jets. Three types of light distribution are used, symmetrical, counter-beam and pro-beam lighting. Symmetrical light distributions produce uniform luminance lighting throughout the tunnel so vehicles of different reflectances will have either positive or negative luminance contrasts with the road. Counter-beam light distributions are those where the light is directed predominantly against the traffic flow. This gives a high pavement luminance so that vehicles tend to be seen in negative contrast, but there is some risk of the driver experiencing discomfort and disability glare. Pro-beam light distributions are those where the light is directed predominately in the direction of the traffic flow. This gives a low road surface luminance but high luminances for vehicles so the vehicles tend to be seen in positive contrast. Various claims have been made about the benefits of these different systems but no consensus about the best system has been reached.

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Finally, it is necessary to consider the potential for flicker and the consequent discomfort and distraction to the driver. When tunnel lighting is provided by a series of regularly-spaced, discrete luminaires, there is always a possibility of flicker being perceived. It is recommended that care be taken to avoid spacing individual luminaires so that drivers moving at representative speeds in the tunnel are not exposed to flicker in the range 2.5–15 Hz. Of course, flicker is only a consideration if the lighting is provided by discrete luminaires. An alternative system based on a continuous linear luminaire through the tunnel avoids any flicker problem and provides good visual guidance for the tunnel, a feature that is particularly valuable where the tunnel curves.

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Chapter Seventeen: Exterior workplace lighting

Chapter 17: Exterior workplace lighting 17.1 Functions of lighting in exterior workplaces Exterior workplaces occur in many different forms. There are those that involve the movement of people, such as airports; those that involve the storage and movement of goods, such as container terminals; those that involve the operation of large plant, such as an oil refinery; and those that exist temporarily as happens during the construction of a building. Regardless of the purpose of the site, the lighting systems of exterior workplaces have common aims. In all exterior workplaces, the lighting is designed to ensure the safety of people working on the site and to enable the work to be done quickly and easily, without discomfort.

17.2 Factors to be considered When designing lighting for exterior workplaces, there are a number of factors that need to be considered. 17.2.1 Scale The scale of the equipment to be used on the site is important in determining the lighting approach. Some industries, such as the chemical industry, have plant that is large and complex so there is no possibility of separating the lighting from the plant. As a result, the lighting has to be integrated into the plant (Figure 17.1). Figure 17.1 Lighting of a chemical complex

Others are large and simple and can be lit by simple area floodlighting. Yet others are small and have a limited number of lines of sight, e.g. loading bays. 17.2.2 Nature of work The nature of the work in exterior workplaces can vary widely. All exterior workplaces require lighting for safe movement but beyond that the need for fine visual discrimination and where it is needed is uncertain and may vary from day to day. In these circumstances, consideration should be given to using localised lighting where fine visual discrimination is always needed and mobile lighting for places where fine visual discrimination may be needed in different locations at different times. Some lighting will also be required where working at night exposes the workers to danger (Figure 17.2). 236


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17.2.3 Need for good colour vision Where colour is used to convey information, lighting with good colour rendering properties is required. For example, in chemical plants, it is common to use colour to identify the contents of pipes. For such applications, a light source with a CIE general colour rendering index of at least 60 is recommended.


Figure 17.2 A mobile luminaire used to provide lighting in a temporary work zone

17.2.4 Obstruction Many exterior workplaces contain obstructions, e.g. stacked shipping containers. Obstructions tend to produce shadows. Shadows can be minimised by: using high mounted floodlights with a wide light distribution so that light reaches every point from more than one direction having high-reflectance surfaces such as concrete rather than tarmac hard standing providing local lighting of the shadowed area. 17.2.5 Interference with complementary activities Some common exterior workplaces are interfaces between one mode of transport and another, e.g. railway yards, airports and docks. Care should be taken to ensure that train drivers, aircraft pilots and ships’ pilots approaching the facility can see and understand all the relevant signals. They may experience difficulty in doing this either because of low visibility caused by disability glare or because of confusion caused by similarity between signal lights and the workplace lighting. 17.2.6 Hours of operation Not all exterior workplaces operate throughout the night. If this is the case, consideration should be given to switching to security lighting after the end of work (see Section Chapter 18). Even when the site is active throughout the night, it is often the case that the number of staff involved is small. If this is the situation, consideration should be given to a switching system which allows different parts of the site to be lit or unlit according to the needs of the work. 237


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17.2.7 Impact on the surrounding area Exterior workplace lighting should be limited to the site. Stray light from a site may be considered to be light trespass by neighbours and a source of sky glow by others (see Section 6.2.9 and SLL Factfile 7: Environmental considerations for exterior lighting). 17.2.8 Atmospheric conditions Some exterior workplaces are difficult environments for lighting equipment. Chemical plants may produce a corrosive atmosphere. Oil refineries have a flammable environment. Coastal container terminals will expose luminaires to a high level of salt.

17.3 Lighting recommendations 17.3.1 Illuminance and illuminance uniformity The recommendations for exterior workplace lighting involve maintained mean illuminance, illuminance uniformity, glare control and light source colour properties. The maintained mean illuminances listed are minima on the relevant plane. The illuminance uniformity is measured over the relevant area which can range from the whole site to a small part of the site. Exterior working activities are very diverse. Table 17.1 gives some lighting recommendations for generic activities. Recommendations for specific industries can be found below and in the SLL Code for lighting and the SLL Lighting Guide 1: Industrial lighting. Table 17.1 Illuminance recommendations for exterior workplaces

238

Activity

Minimum maintained mean illuminance (lx)

Illuminance uniformity (minimum/ average)

Typical applications

Safe pedestrian movement in low risk areas

5

0.15

Industrial storage areas with only occasional traffic

Safe movement of slow vehicles

10

0.25

Open storage areas served by fork lift trucks

Safe movement in medium risk areas

20

0.25

Vehicle storage areas, container terminals with frequent traffic

Normal traffic

20

0.4

Road lighting in container terminals, marshalling yards

Very rough work

20

0.25

Excavation and site clearance

Rough work

50

0.25

Handling timber

Safe movement in high risk areas

50

0.4

Critical area within chemical plants, oil refineries etc

Normal work

100

0.4

Brick laying, carpentry

Fine work

200

0.5

Painting, electrical work


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GR = 27 + 24 ln

Lv L0.9 e

where: Lv = equivalent veiling luminance produced by the luminaires at the eye (cd/m2) Le = equivalent veiling luminance produced by the environment at the eye (cd/m2) See Section 2.6.3 for more information on the calculation of equivalent veiling luminance. For many applications, Le is approximated by the formula Le = 0.035 E ρ / π where ρ is the reflectance of the surface, e.g. a sports field, and E is the illuminance on the field (lx). For grass sports fields, a reflectance in the range 0.15 to 0.25 is appropriate. The higher the glare rating, the greater is the visual discomfort. It is necessary to calculate glare rating for all critical viewing directions. 17.3.3 Light source colour properties Light source colour properties are important for naming colours, something that can be significant where colour coding is used for identification. The ability to name colours accurately and confidently is determined by the light source spectral power distribution and the illuminance. Any light source with a CIE general colour rendering index greater than 60 will allow accurate and confident colour naming at the illuminances recommended for public spaces at night. High pressure sodium lamps allow accurate but less confident colour naming at the higher illuminances recommended for public spaces but both the accuracy and confidence decline at lower illuminances. Low pressure sodium lamps do not allow accurate colour naming under any illuminance and any confidence felt about being able to name colours is misplaced.


17.3.2 Glare control Glare control for outdoor lighting is quantified by the glare rating. Glare rating (GR) is given by the formula

17.3.4 Loading areas Many industrial premises have a loading bay (Figure 17.3). The two key points to remember about a loading bay is that there should be no glare to the driver backing up to the loading bay and when backed up the vehicle may cause shadows over the working area. Luminaires on a loading bay are exposed to the weather so they should have the appropriate IP rating (see Table 4.10). For loading bays with a canopy height less than 6 m, a suitable approach is to use pairs of luminaires fitted with fluorescent lamps, one mounted either side of the bay door. Where the canopy is more than 6 m high, luminaires using high intensity discharge lamps can be used instead of fluorescent lamps provided care is take to avoid glare to the driver. An alternative mounting position for such luminaires is at the front of the canopy aimed towards the bay door. To enable workers to see inside a vehicle it can be helpful to place a low wattage floodlight above the loading bay door. These luminaires should not be switched on until after the vehicle has been backed up. Care should be taken to minimise glare to workers leaving the vehicle. Outdoor loading areas are usually lit by area floodlighting, either mounted on a building or on poles or masts. Such lighting should provide uniform illumination without glare to people working in the area, particularly fork lift truck drivers whose viewing direction may frequently be upward. 239


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Figure 17.3 Lighting of a loading bay

Table 17.2 Lighting recommendations for loading Application

Horizontal illuminance (lx)

Horizontal illuminance uniformity

Maximum glare rating


Loading bay

150

-

-

40

Outdoor loading area

100

0.5

45

20

17.3.5 Chemical and fuel industries Some parts of these industries have large outdoor facilities. Some such facilities are open e.g. a coal stockyard, while others are complex structures with platforms at many different levels e.g. an oil refinery. For the former, lighting is usually done by conventional area floodlighting techniques. For the latter, lighting is done by integrating luminaires into the plant. Luminaires in these facilities are often exposed to adverse conditions. These may range from a very dirty atmosphere, as in a coal and ash handling area, through corrosive atmospheres, as in some chemical plants, to risks of fire and/or explosion, as in the oil and gas industries where whole plants are considered hazardous areas. Luminaires that are capable of dealing with the prevailing conditions need to be used (see Section 4.3.2). Consideration also needs to be given to ensuring easy access to luminaires for maintenance. The lighting recommendations for the chemical and fuel industries are given in Table 17.3. The approach to designing lighting for the outdoor areas of these industries is discussed in Section 17.4.

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Activity





Handling servicing tools, adjusting manual valves, starting and stopping motors, lighting of burners, operating switch gear

20

0.25

55

20

Moving on walkways

50

-

-

-

Filling and emptying trucks and wagons with risk free substances, inspection of pipes and packages

50

0.4

50

20

Fuel loading and unloading sites

100

0.4

45

20

Filling and emptying trucks and wagons with dangerous substances, replacement of pump packing, general service work, reading of instruments

100

0.4

45

40

Repairs of machines and electric devices

200

0.5

45

60


Table 17.3 Lighting recommendations for chemical and fuel industries

17.3.6 Sidings, marshalling yards and goods yards These railway facilities can cover large areas. Lighting is usually done by conventional area floodlighting but there are two features that require special attention. The first is the level of obstruction caused by the closeness of wagons on adjacent lines. The second is the need to ensure good visibility of all signals. To avoid shadows between wagons, confusion with signals and glare to workers, a high mast lighting installation is commonly used. The masts should be positioned near to those areas that require higher illuminances (see Table 17.4). The floodlights should be aimed along the tracks. This aiming minimises shadows between adjacent wagons and takes advantage of specular reflections to reveal the run of the rails. Where lighting has to be across tracks, reflections from wagon sides make an important contribution to the illumination between wagons. This contribution will only be important if the angle of incidence is more than 45 degrees (Figure 17.4). The lateral spacing of floodlights should not be more than twice the difference between the height of the floodlights and the height of the wagons.

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Figure 17.4 High mast lighting of a railway yard with reflections from wagons

Hm

Max 45˚

Hw

S

Table 17.4 Lighting recommendations for sidings and railway yards

242

Location





Railway yards, flat marshalling, retarder and classification yards

10

0.4

50

20

Hump areas

10

0.4

45

20

Freight track, short duration operations

10

0.25

50

20

Open platforms in freight areas

20

0.4

50

20

Servicing trains and locomotives

20

0.4

50

40

Railway yards handling areas

30

0.4

50

20

Coupling area

30

0.4

45

20

Covered platforms in freight areas, short duration operations

50

0.4

45

20

Covered platforms in freight operations, continuous operations

100

0.5

45

40


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17.4.1 High mast floodlighting Many large area sites, such as container terminals, railway marshalling yards and car storage areas use high mast floodlighting. A smaller number of high masts are preferred over a larger number of lower masts for reasons of economy and because they allow greater freedom of movement in the area illuminated. The most economical mast height is usually between 20 and 30 m. At greater heights, the costs of the masts increase greatly while at lower heights, the numbers of masts, lamps and luminaires increase dramatically. A lower mast height can be justified where there is extensive obstruction. The usual light sources for high mast lighting are either high pressure sodium or metal halide discharge lamps. The luminaires used are floodlights with the light distribution matched to the proposed spacing of the masts. The luminaires should be suitable for the atmospheric conditions. This means that, at the very least, the luminaire should have the necessary IP number (see Table 4.10) and may require protection against corrosion and explosive atmospheres. 17.4.2 Integrated lighting Oil refineries, cement plants and similar sites are usually lit by integrating the lighting into the plant (Figure 17.5). This is typically done by selecting a luminaire with a very wide light distribution, both up and down, and bolting it onto convenient parts of the structure so as to light all parts of the structure. The result is that too often the plant is lit up like a Christmas tree.


17.4 Approaches to exterior workplace lighting

Figure 17.5 A cement plant with lighting integrated into the structure

Increased sensitivity to light pollution should mean that this approach is no longer acceptable. It is still necessary to integrate the lighting into the structure but to reduce light pollution it is necessary to be more careful about the type of luminaire selected, more informed about suitable locations for those luminaires and more adventurous about the control of the lighting at night. The luminaire selected should provide a predominantly downward light distribution, ideally within 70 degrees about the downward vertical. This more restricted light distribution will require more care in the positioning of adjacent luminaires to ensure they are providing enough light for safe access and work, without leaving dark spots. As for controls, the number of people working at night to keep the plant running is often small and they are unlikely to want access to all parts of the plant at all times. Simple switching controls located in a control room can be used to light those parts of the plant in which people are working, as necessary. 243


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17.4.3 Localised lighting In many exterior workplaces, the places where detailed visual work is carried out are limited. In this situation, there is little point in lighting the whole site to the level necessary for the detailed work. A better approach is to light the whole site to the level necessary for safe movement and to use localised lighting for the work areas. This localised lighting may be permanent, for a fixed working area, or temporary, for a construction site. The latter lighting may be powered from a generator.


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18.1 Functions of security lighting Security lighting is installed to help protect people and property from criminal acts. Other forms of lighting, such as outdoor display lighting, decorative floodlighting, shop window lighting and park lighting, can contribute to this goal, but they are designed with additional criteria in mind (see CIBSE Lighting Guide 6: The outdoor environment). Lighting can help to protect people and property from criminal activities because of its effect on vision (Boyce 2003). In public spaces, good security lighting is designed to help everyone see clearly all around. This means that people approaching can be easily identified and that other people’s activities can be seen from a distance. This has the effect of shifting the odds in favour of the law-abiding and against the criminal. The law-abiding are unlikely to be taken by surprise, while criminals are more uncertain about whether their activities have been witnessed or they have been recognised. In secure spaces to which the public does not have access, it is possible to use lighting to enhance the vision of guards while hindering the vision of potential intruders.

Chapter Eighteen: Security lighting

Chapter 18: Security lighting

Lighting is only one part of a security system. The complete system usually includes a physical element, such as fences, gates and locks; a detection element, involving guards patrolling or remote surveillance; and a response element, which determines what is to be done after detection occurs. Unless security lighting is integrated into the complete system, it is unlikely to be successful. For example, good lighting in a storage area that nobody is watching, and hence in which there is no possibility of a response, will simply help intruders do what they want to do, more quickly.

18.2 Factors to be considered The characteristics of the lighting to be used as part of the security system will be determined by various features of the site. The factors that always need to be considered are the following. 18.2.1 Type of site Sites can be conveniently classified by the extent to which people have access to the site and the presence or absence of physical defences such as fences. Broadly, there are three types of site. secure areas, where there are physical defences and to which access is controlled, such as a fenced storage yard (Figure 18.1) public areas, where people may be present at any time and which have no physical defences, such as a shopping centre car park (Figure 18.2) private areas, where there are no physical defences but where the general public is not expected to be present, such as a house (Figure 18.3).

245



Figure 18.1 Lighting of a secured area, a fenced storage yard

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Figure 18. 2 Lighting of a public area, a shopping centre car park

Figure 18.3 Lighting of a private area, a house driveway 18.2.2 Site features One feature of a site that can have a major influence on the type of security lighting adopted is the extent to which the site is obstructed. Where a single building occupies a significant part of the site and contains the only items of value, it may be more effective to floodlight the building rather than to light the whole site. Where there are multiple obstructions, as in a container terminal, the whole site should be lit in a way that minimises shadows. Another important feature is the average reflectance of the surfaces within the site. High reflectance surfaces increase the amount of inter-reflected light and this diminishes both shadows and glare. Figure 18.4 shows what happens when glare is combined with obstruction and low reflectance surfaces.

Figure 18.4 A business yard lit by two high power floodlights. The combination of a narrow light distribution, obstruction and low surface reflectances results in strong shadows and glare

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18.2.4 Crime risk The frequency and nature of crimes occurring in different locations can vary widely. The level of risk will already be built into the level of defences used on secure sites but this is not possible in public areas. In public areas, increasing risk of crime is associated with increasing illuminances used for security lighting. 18.2.5 CCTV surveillance CCTV cameras are widely used for remote surveillance of large areas. The amount of light required for effective operation of CCTV cameras can vary dramatically from starlight to highlevel security lighting. Manufacturers specify a minimum illuminance needed for their cameras to produce a clear picture. These values usually assume an incandescent lamp. Higher illuminances may be required for other light sources with different spectral power distributions. Further, if moving objects are to be easily seen, illuminances above the minimum will be required, whatever the light source. The manufacturer should be consulted before selecting the light source to be used if there is any doubt about the sensitivity of the camera.


18.2.3 Ambient light levels The illuminances produced by the security lighting need to at least match or preferably exceed the illuminances of the surrounding area. Unless, this is done, the area covered by the security lighting will look dimly lit.

The other aspect of cameras that needs care is their rather limited dynamic range. A high level of illuminance uniformity is necessary if dark areas in the CCTV image are to be avoided. Further, care should be taken to mount CCTV cameras in positions where they do not receive any light directly from the luminaires as such light will sometimes cause a ‘white-out’ of that part of the image. 18.2.6 Impact on the surrounding area Security lighting should be limited to the protected area. Stray light from a security lighting installation may be considered to be light trespass by neighbours and a source of sky glow by others (see Section 6.2.9). Further, where signal lights are used to control traffic on roads and railways, care should be taken to avoid confusion caused by either disability glare to the observer, veiling reflections on the signals, or the identification of the security lighting itself as a signal.

18.3 Lighting recommendations 18.3.1 Illuminance and illuminance uniformity The recommendations for security lighting involve maintained mean illuminance, illuminance uniformity, glare control and light source colour properties. The maintained mean illuminance and illuminance uniformity recommendations are given for secure areas and public areas separately. The recommendations for glare control and light source colour properties are applicable to both. The maintained mean illuminances listed are minima. It may be necessary to increase these illuminances where the ambient light levels and the risks of crime are high.

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Table 18.1 Illuminance recommendations for security lighting of secure areas Application



Notes

Large open areas, e.g. storage yards

5

0.1

The illuminance is measured on the horizontal surface of the area, using the method given in BS 5489-1

Building facades

5

0.1

The illuminance is measured on the building facade

Fences

5

0.1

The illuminance is measured on the ground on either side of the fence

Entrances/gatehouses

100

-

The illuminance is measured at ground level. In addition, a vertical illuminance of 25 lx should be provided at the level of the vehicle driver

Table 18.2 Illuminance recommendations for security lighting of public areas

248

Application



Notes

Light traffic and low crime risk car parks

5

0.25

The illuminance is measured on the ground, using the method given in BS 5489-1

Medium traffic or medium crime risk car parks

10

0.25


Heavy traffic or high crime risk car parks

20

0.25


Public parks

10

0.25

The illuminance is measured on the ground of pathways

Service station, pump area

50

0.33

The illuminance is measured on the ground

Service station, store front

30

0.33

The illuminance is measured on the ground


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It is important when designing security lighting to be clear about the value of glare. Where clear visibility at a distance is important to those guarding a secure area or those using a public area, glare needs to be carefully controlled. A glare rating of 30 or less is recommended. This can usually be achieved by eliminating any direct view of the light source for all luminaires mounted below 5 m. Where the security lighting is to be used to make it difficult for potential intruders to see into a site, glare is a positive so a direct view of the light source and a low mounting height are encouraged. For such applications, a glare rating of 70 or greater is recommended.


18.3.2 Glare control Glare control for outdoor lighting is quantified by the glare rating. The glare rating is calculated using the method set out in CIE Publication 112: 1994 (see Section 17.3.2 for details) and in the SLL Code for lighting. The glare rating will vary with viewing direction. For altitude, it is usually assumed that the observer is looking 2 degrees below the horizontal. For azimuth, calculations are done in 45 degree steps around the observation point.

18.3.3 Light source colour properties Light source colour properties are important for naming colours, an element in many witness statements. The ability to name colours accurately and confidently is determined by the light source spectral power distribution and the illuminance. Any light source with a CIE general colour rendering index greater than 60 will allow accurate and confident colour naming at the illuminances used in public spaces at night. High pressure sodium lamps allow accurate but less confident colour naming at the higher illuminances used for public spaces but both the accuracy and confidence decline at lower illuminances. Low pressure sodium lamps do not allow accurate colour naming under any illuminance and any confidence felt about being able to name colours is misplaced (Saalfield, 1995).

18.4 Approaches to security lighting 18.4.1 Secure areas The first question to consider is whether to light the space at all. It can be argued that lighting a secure area advertises the presence of something worth taking and hence attracts criminals, so keeping the area dark is a better approach. However, if the criminal already knows the area contains valuable materials, then the absence of lighting makes the secure area more difficult to defend. Thus the choice of whether to light or not depends on the owner’s assessment of risk. If the risk of criminal activity is high, lighting is desirable. If the risk of criminal activity is low, then providing lighting may be counterproductive. Area lighting: area lighting is commonly used in large open areas such as storage yards and container terminals. Typically, these sites are lighted uniformly by floodlighting or roadway luminaires on poles 10 m or more in height. For typical roadway and floodlighting luminaires mounted singly on poles, the desired illuminance uniformity can be achieved by spacing the luminaires at six times their mounting height. The actual spacing will depend on the luminous intensity distribution of the luminaire. If the area is unobstructed by trees, structures or topography, the most economic installation will be one very tall pole carrying many high-wattage lamps. However, this solution is a false economy as it also produces the poorest illuminance uniformity, the harshest shadows, and the greatest amount of light trespass. If the area contains obstructions, as in container terminals, a design utilising multiple source locations will reduce shadowing. 249


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This is especially true if the luminaires are positioned within the site, between obstructions, and with overlapping light patterns. Reflectance of site materials can also be used to advantage. If the owner uses containers that are painted a highly reflective colour, or paves the area with concrete rather than asphalt, light diffusely reflected from these surfaces will diminish the depth of shadows. Building facades: security lighting for building exteriors is based on the principle that all points of entry to the building and the areas around them should be easily seen. Depending on the construction of the building, the points of entry can consist of walls and roof as well as doors and windows. The most comprehensive approach is to light the whole building. Security lighting for buildings is more effective if the building has a high reflectance facade and the area adjacent to the building also has a high reflectance.

Figure 18.5 Lighting of a complete building facade

The building can be lighted by luminaires set in the ground, mounted on the building or mounted on poles (Lyons, 1980; Leslie and Rodgers, 1996). Ground-mounted floodlights can provide uniform building lighting but they are very accessible and hence can easily be sabotaged. Luminaires mounted on the building are more economical than pole-mounted luminaires, since the expense of the pole is eliminated and wiring costs are reduced. However, for anything other than a simple rectangular building, it is difficult to adequately illuminate all of the building surfaces without using an excessive number of luminaires. Polemounted luminaires are usually the best option for uniformly lighting the surfaces of buildings and the surrounding area. Perimeter fences: the purpose of lighting perimeter fences is to enable guards to detect intruders loitering outside the fence or attempting to get over or through the fence. Fences come in several different forms from masonry through steel palisades to chain link. The form of lighting used will depend on the possibility of seeing through the fence and whether one or both sides of the fence line are to be patrolled. If the fence is solid, there is no possibility of seeing through it. Nonetheless, if both sides of the fence are to be guarded, lighting can be provided on both sides by positioning a luminaire directly above the top of the fence. The luminaire should be located well above the top of the wall to reduce the shadowed area at the base of the wall. If a view through the fence is possible, and if the fence is patrolled from either inside or outside the secure area, it is useful to be able to see both sides of the fence from one side. For this to happen, light needs to be provided on both sides. This can be done from polemounted fixtures set back from the fence (Lyons, 1980). 250


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Lighting designed to deliberately produce disability glare to people outside a fence can be used for perimeter fences enclosing large areas, in remote locations where there is no other site lighting (Lyons, 1980). In this system, a line of high-luminance luminaires is mounted at eye level and aimed outward from the secure area. For glare lighting to be effective, the secure area should not be otherwise illuminated, any fence material should be of low reflectance and the luminaires should be closely spaced. Further, patrol roads or paths should be located within the perimeter fence, behind the line of the glare lighting luminaires. Care should be taken to locate the luminaires far enough inside any perimeter fence line to guarantee that the intruder cannot get between the luminaire locations and still view the secure area from outside the fence. This approach should be used with caution because of the likelihood of light trespass to nearby residents and visual discomfort to passers-by.


The lighting will be most effective if the luminance of the fence is lower than the luminance of the area on the side being viewed through the fence (Boyce, 1979). This objective can be achieved by using a low-reflectance fence material such as black or dark green-coated chainlink. If galvanised chain link is used, care should be taken with the aiming of the luminaires to reduce the illuminance directly onto the fence.

Entrances and gatehouses: access to a secure area is usually controlled by security personnel whose duty is to stop and inspect people and vehicles entering and leaving the site. At most exposed locations, a gatehouse will be provided. The entrance should be equipped with multiple luminaires so the loss of any one luminaire will not seriously degrade the lighting available to the guard on duty (Leslie and Rodgers, 1996). All vehicle entrances should have luminaires located so as to facilitate complete inspection of vehicles and their contents. Lights should be located to illuminate the vehicle license plate. Where on-coming vehicles approach the guardhouse, signs may be appropriate instructing drivers to turn off headlamps. In high security areas, some luminaires should be mounted at or near ground level to facilitate inspection of the underside of the vehicle. These luminaires can be controlled with a manual switch or remote sensing device. Having a concrete road surface to increase the reflected light will help in the inspection of the underside of vehicles. Consideration should be given to providing back-up power supplies for use during electrical outages. Care should be taken to provide good vertical illuminance so as to allow for facial identification, inspection of credentials, and packages without use of auxiliary hand-held devices such as flashlights. Illumination inside the guardhouse should be limited to the minimum required for the completion of assigned tasks, such as report writing and equipment use. The ability to reduce the illuminance is necessary to allow the guard to see clearly through the windows at night and to limit the ability of someone approaching the gatehouse to see what the guard is doing inside. Well-shielded task luminaires are essential to avoid reflections on any surveillance monitors and the windows of the gatehouse. Fitting the gatehouse with specular-reflecting, low-transmission glass at a tilted angle, painting the inside of the gatehouse in dark colours and ensuring that illumination can be dimmed will all help limit the view into the gatehouse (Lyons, 1980).

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18.4.2 Public spaces The ultimate aim of the lighting of public spaces is to make the space look attractive and safe and hence encourage its use at night (Leslie and Rodgers, 1996). Lighting can contribute to this perception by allowing action at a distance. What this means is that by enhancing the visibility of people and faces, suspicious or threatening behaviour may be detected early enough for an escape to be made. Similarly, greater visibility provided by lighting may enable people behaving in a suspicious manner to be recognised or at least described. Such observations at a distance are a benefit to the law-abiding and a disadvantage to the criminal. Lighting designed to allow action at a distance requires that attention be paid to the illuminance provided, the uniformity of illuminance, the presence of disability glare and the spectral power distribution of the light source. For people to have a reasonable perception of safety at night in car parks and on business streets, the horizontal illuminance on the ground should lie somewhere between 10 and 50 lx depending on the ambient illuminance (Figure 18.6). Below 10 lx, perceptions of safety deteriorate rapidly. Above 50 lx, perceptions of safety are close to the maximum possible, so there is little more to gain from higher illuminances (Boyce et al, 2000).

5

Degree of agreement

3

1

–1

= Male = Female = Male

–3

–5

0

= Female

50

100

150

200


Figure 18.6 Mean levels of agreement with the statement ‘This is a good example of security lighting’ plotted against horizontal illuminance, for sites in New York City and Albany, NY, for male and female subjects separately. A value of +5 indicates strong agreement and –5 indicates strong disagreement (after Boyce et al., 2000). As for illuminance uniformity, if the principal of action at a distance is to be followed, it is essential that excessive variations in illuminance be avoided. Close spacing of luminaires is particularly important if excessive variation in the vertical illuminances on faces is to be avoided. To avoid excessive variation in vertical illuminance, the spacing used should be less than two thirds of the maximum spacing suggested by manufacturers. The most common sources of disability glare at night are luminaires in unsuitable locations, poor aiming of luminaires or poor luminaire design. This last problem is particularly common in ‘historic’ luminaires, which combine little shielding of the light source with low mounting heights. Care in the selection of luminaires, their aiming and mounting heights are essential if disability glare is to be avoided. 252


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Parks: parks and similar areas are intended for the pleasure and relaxation of the public but it is difficult to relax if one is worried about the possibility of assault. Lighting of such sites requires that people visiting the park should be able to see clearly all around them without destroying the ambience of the park. There are many different approaches that can be used, ranging from conventional path lighting to landscape lighting (Figure 18.7) (CIBSE Lighting Guide 6: The outdoor environment; Leslie and Rodgers, 1996).


Car parks: the recommended minimum maintained mean illuminance for car parks depends on the level of traffic and the risk of crime (Table 18.2). Where traffic is light and the risk of crime is low, a minimum maintained mean illuminance of 5 lx is adequate. More traffic or greater crime risk implies higher illuminances for security lighting (CIBSE Factfile 2: Car park lighting – A dilemma resolved). Car parks are usually lit by pole-mounted luminaires arranged around and within the car park (Leslie and Rodgers, 1996).

Figure 18.7 Lighting in a small park

Service stations and mini-marts: these locations are often round-the-clock operations. A minimum maintained mean illuminance of 50 lx on the ground is recommended for all parking and customer use areas, including petrol pumps and islands, and air and water stations. Surrounding areas should be illuminated to a minimum maintained mean illuminance of 30 lx. A minimum vertical illuminance of 10 lx at 1.5 m above ground level should be provided for lighting faces (Figure 18.8).

Figure 18.8 Lighting of a service station

18.4.3 Private areas Security lighting for private houses differs from the lighting provided for secure areas and public spaces because houses usually do not have the physical defences of secure spaces although it is not desirable to have the public using the space. The size of the house, the distance from neighbours, the nature of the terrain and whether the house is in a rural, suburban or urban area are all factors to be considered. Deterrence is usually the number one priority in residential security, followed by detection, recognition and, if all else fails, a signal for help. 253


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Illumination at the front entrance is mainly for the identification of callers. Luminaires on either side of the door aid recognition by lighting the face from two directions (Figure 18.9). Luminaires should not be located directly above or behind where a person at the door would be standing. The minimum vertical illuminance at head height should be 10 lx (Van Bommel and Van Dyk, 1984).

Figure 18.9 A recessed doorway with lighting at the sides of the door

The front, back and sides of the house are best illuminated using luminaires mounted on the building itself. This method increases the illumination on the face if the correct luminaires are selected and should be controlled with a motion sensor. As a person approaches, the sensor will activate the luminaires, confronting an intruder with a well-lit environment. The minimum maintained vertical illuminances for the surfaces of a private house should be in the range 5 to 20 lx, the actual illuminance being determined by the risk of crime and the ambient illuminance. The minimum maintained minimum/average illuminance ratio for all surfaces is 0.25. 18.4.4 Multi-occupancy dwellings Multi-occupancy dwellings present additional security lighting challenges to those posed by single-family houses. Outside the dwelling, the challenges are the same as for single-family houses and can be dealt with as described above (Leslie and Rodgers, 1996) but when the occupants are inside the building, they are not in a totally secure environment. The building is accessible to the other residents and their guests so occupants may be at risk when moving about within the building. For hallways, stairways and laundry rooms, lighting that enables recognition of faces is essential to determine who belongs in the space and who doesn’t; who is perceived as safe and who may present a danger. Corridors tend to be dark in many multi-occupancy dwellings. A minimum maintained illuminance of 100 lx should be provided at floor level.

18.5 Lighting equipment 18.5.1 Light sources Most general-purpose light sources can be used for security lighting (see Chapter 3). HID lamps tend to be used for all-night security lighting because they have high luminous efficacies and long lives, they are unaffected by the ambient operating temperature and are available in a wide range of lumen ratings, colours and wattages. 254


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The longer run-up and restrike times of HID lamps make them unsuitable when the lighting is only energised when an intruder is detected or a brief period of darkness occurring in the event of a power failure is unacceptable. In these situations, an incandescent or fluorescent light source is preferred. 18.5.2 Luminaires The selection of the luminaire will be based on the light source to be used, the desired luminous intensity distribution, aesthetics and the degree to which the luminaire will be exposed to the environment. Environmental factors to be considered include exposure to wind, rain and salt; temperature extremes; luminaire mounting location; and the level of vulnerability of the luminaire to damage by attack.


Against these advantages, they require bulkier luminaires, control of light output is more difficult, initial cost is higher and mounting may be more complex. These disadvantages can be offset by the benefits of needing far fewer fixture locations or mounting multiple luminaires in a single location.

Any fixture mounted in an area that will be exposed to the weather should have an appropriate international protection (IP) rating (see Table 4.10). Luminaires that are located in areas that are not temperature controlled may need special components depending on the light source used. Fluorescent light sources are most affected by ambient temperature extremes. Any luminaire mounted on a ceiling or wall less than 3 m above the ground is likely to be the subject of vandalism. Vandal resistant lighting should be considered in these applications. A vandal resistant luminaire should incorporate the following features: The base of the luminaire should be structurally designed, i.e. have a step or flanged base, and be solidly mounted to the building structure or mounting accessory. An electrical junction box should never be used as the sole luminaire support in a security lighting installation. The lens or diffuser of the luminaire should be of a one-piece wraparound, injection moulded construction using ultraviolet (UV) stabilised polycarbonate. Exposed hardware, such as that needed to secure the lens to the body of the luminaire, should be tamperproof. Light sources and sockets should be protected against mechanical shock and never located close to the interior wall of the lens. The luminaire should have the ability to withstand repeated blows from a heavy rubber mallet or hammer. 18.5.3 Lighting columns The higher luminaires are mounted from the ground, the fewer columns and luminaires will be required to light a given area and the less likelihood of vandalism. As column heights are reduced, more columns with lower wattage luminaires are required to avoid glare and nonuniform lighting patterns. Steel and concrete columns are most resistant to attack. 255


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Aluminum and fibreglass columns can be damaged by forced oscillation. Columns made of these materials should be avoided in areas where vandalism is prevalent. 18.5.4 Lighting controls Security lighting should always be controlled automatically; activation should never be made the responsibility of an individual. System design should consider the possibility of power outages and lamp failure. Redundancy should be considered when assigning luminaires to ‘zones’ of control so that the failure of one luminaire does not leave a large area unlit. HID systems should be designed to be energised prior to darkness by a time suitable for the run-up period of the lamp. Lighting controls should be designed to energise the lighting system when the ambient natural light level is 1.6 times the maintained mean illuminance design value or 15 lx, whichever is higher. This will ensure that designed illuminances will be met during dusk as well as after dark. Types of automatic controls suitable for security lighting operation include time switches, photo-cells, dimmers and motion detectors. Time switches: these are generally used to control large areas from one location, such as shopping centre car parks. Astronomical time switches can be programmed to adjust on-off times with the changes of season. These types of switches can be quite expensive, and still may not be able to readjust by themselves if darkness is hastened by cloud cover. All time switches should include a battery back-up. Photocontrols: these are used to control individual or small groups of luminaires on circuits that are always energised. They can be designed to automatically energise luminaires during dark periods regardless of time of day. They have the added advantage of not needing to be re-set after power outages or at the changes to and from daylight savings time. Photocontrols should not be mounted where the light sensing area is accessible to flashlight or vehicle headlight beams. Dimmers: these can be used to reduce illumination and power demand by approximately 50 percent during low traffic periods in such applications as office car parks during working hours or shopping centre car parks late at night. By dimming all luminaires, the entire area remains uniformly illuminated. This contrasts with the ‘spotty’ appearance commonly caused when half of the luminaires are switched off to save electricity. Dimmable fluorescent and HID luminaires require special ballasts. Dimmed HID sources may not have the same colour characteristics as when they are operated at 100 percent light output. This can have implications for camera surveillance as well as the ambiance of the space. Motion detectors: these are used to switch on specific luminaires when motion is detected. Motion detectors can employ infrared or ultrasonic technology. Passive infrared detectors are the predominant choice outdoors, due to the sensitivity of ultrasonic detectors to movement caused by wind. The designer should review the coverage pattern with the manufacturer’s data to determine suitability for the application. Due to the run-up time of HID light sources, motion detectors should only be used with incandescent and fluorescent light sources. 18.5.5 Maintenance No security lighting system can remain effective without regularly scheduled maintenance. A planned maintenance program should include: Immediate replacement of failed lamps, repair or replacement of vandalised luminaires, regular cleaning and cutting back of any encroaching vegetation.

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19.1 Functions of lighting for sports The function of lighting for sports is primarily to make what is going on highly visible to participants and spectators, without discomfort to either. Sports can be played both outdoors and indoors. Outdoor facilities range from large multi-use stadia to village tennis courts. Indoor facilities range from multi-use sports halls to single-use swimming pools. Some sports, such as football, rugby, cricket, tennis and golf are big business while others, such as archery and curling are specialist interests. Big businesses often depend on sales of television rights for a significant proportion of their income. In such circumstances, the lighting also has to serve the needs of television transmission so that the spectators watching via a screen can see what is going on. The guidance given here is for the most popular sports. Detailed guidance on lighting for a wider range of sports can be obtained from the SLL Lighting Guide 4: Sports lighting. The governing bodies of some sports make their own lighting recommendations. These recommendations may exceed those given here. The recommendations given here, and in SLL Lighting Guide 4: Sports lighting, should be treated as minima.

Chapter Nineteen: Sports lighting

Chapter 19: Sports lighting

19.2 Factors to be considered Sports facilities come in many different forms. They can be private or public. They can be large or small. They can cater for thousands of spectators or for the players alone. The sports themselves can call for fine discrimination of rapidly moving targets or simply the ability to see a stationary target in a known position. The directions of view can vary widely from predominantly upward, as in badminton, to predominantly downward as in snooker, and anywhere in between, as in football. Despite the variability faced by the designer of sports lighting, the objectives are the same everywhere. They are: to facilitate a high level of performance by the players to enable spectators, both present and remote, to see clearly what is going on to enable the sport to be played after dark to create a safe environment for both players and spectators to create a comfortable visual environment for both players and spectators. To meet these objectives it is necessary to consider many aspects of the situation. Those listed below are relevant to all sports lighting applications. 19.2.1 Standard of play and viewing distance Any sport can be played at different levels, from the completely professional to the gross amateur. Providing lighting suitable for the gross amateur in a facility used by the completely professional is a disservice to the sport. Equally, providing the lighting necessary for the professional in a facility used by the gross amateur is a waste of money. Therefore, sports lighting recommendations are divided into three classes according to the players’ level of skill. Another factor that influences sports lighting recommendations are the distances from which spectators have to view the sport. The greater the distance from which spectators view the activity and the finer the detail that has to be seen, the higher the class of lighting recommended.

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The three classes of lighting recommendations are: Lighting class I International and national competition Large numbers of spectators with long viewing distances Top level supervised training Lighting class II Mid-level competition, principal local clubs and county regional competition Medium numbers of spectators with medium viewing distances High level supervised training Lighting class III Low-level competition; local or small club competition Minimal or no spectator provision General training; school sports or recreational activities. The nature of some sports, particularly the speed with which visual information needs to be processed, means there is some overlap in the lighting recommendations for different sports at different levels. 19.2.2 Playing area The nominal playing area is the marked out area of the ‘court’ or ‘pitch’ for the sport. However, for some sports, such as tennis, there is a larger area surrounding the nominal playing area within which play may occur. Further, even when play is confined to the nominal playing area, there is a surrounding area that a player may enter, e.g. the area around a football pitch. The total area to be lit includes the actual playing area and the safety zone around the actual playing area. Advice on nominal playing areas and total areas for different sports can be obtained from the governing bodies of the sports and, for some sports, from SLL Lighting Guide 4: Sports lighting. 19.2.3 Luminaires Luminaires used to light some sports facilities, such as sports halls, are at risk of damage from flying objects. To minimise this risk, luminaires should be located outside the main activity zone and adequately protected by nets, wire mesh etc. Further, luminaires and the associated protection should be designed so as not to contain any traps for balls, shuttlecocks etc. Luminaires used in swimming pools may be subject to a corrosive atmosphere. Careful selection of luminaires is necessary to minimise this problem. 19.2.4 Television Television cameras cannot match the human eye neither for its sensitivity nor for its ability to adjust rapidly to sudden changes in luminance and colour. This means that where television cameras are regularly used at a sports facility, the lighting design needs to be more stringent. The illuminance required for different sports will depend on the type and sensitivity of the camera, lens angle and speed of play. For classification purposes, sports are divided into three groups, A, B and C (see SLL Lighting Guide 4: Sports lighting for the group appropriate for specific sports). For each group, a range of minimum maintained vertical illuminances is given, the value chosen for each sport depending on the maximum shooting distance (Figure 19.1).

258


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1400

C

Figure 19.1 For each group, a range of minimum maintained vertical illuminances is given, the value chosen for each sport depending on the maximum shooting distance

1200 B 1000

Ev (lx)

A

800 600 400 200 0 0

25

50

75

100

125

150

175

200

Shooting distance in metres

While the average illuminance is an important metric, other metrics of equal importance to sports lighting where TV cameras are to be used are those concerned with illuminance uniformity. There are five such metrics. They are as follows.


1600

The ratio of mean horizontal and mean vertical plane illuminances should be between 0.5 and 2.0, inclusive. On planes facing a sideline bordering a main camera area or facing a fixed camera position, the vertical illuminance uniformity ratio (minimum/maximum) should be equal to or greater than 0.4. At a single point on the four planes facing the sides of a playing area, the vertical illuminance uniformity ratio (minimum /maximum) should be equal to or greater than 0.3. The horizontal illuminance ratio (minimum /maximum) should be equal to or greater than 0.5. On large playing fields, such as football pitches, the maximum gradient in horizontal illuminance should not be greater than 25 percent every 5 m. As for light source colour properties where television is used, for outdoor facilities the correlated colour temperature of the light should be in the range 4,000 K to 6,500 K. Where there is little contribution from daylight, the correlated colour temperature of the lighting can be within the range 3,000 K to 6,500 K. For both outdoor and indoor facilities, the CIE general colour rendering index of the light source used should be greater than 65 and preferably have a minimum value of 80. Further advice on the lighting of sports events for television broadcasting can be found in CIE Publication 169-2005. 19.2.5 Coping with power failures Emergency lighting is required to cope with power failures. This can take two basic forms, emergency escape lighting and standby lighting. Emergency escape lighting is designed to enable people to exit a building quickly, without panic. The requirements for emergency escape lighting are given in Chapter 8 of this Handbook and in SLL Lighting Guide 12: Emergency lighting design guide. Standby lighting for sports facilities can also take two forms. The first is safety lighting, which is designed to ensure that the event can be stopped without injury to the players. The second is continuation lighting, which is designed to enable the event to continue. 259


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Safety lighting is not necessary in all sports, only those where rapid motion is likely to be occurring at the instant of power failure, for example gymnastics, ice hockey and horse racing. The illuminance requirements for safety lighting are usually specified as a percentage of the normal illuminance recommendation for a set number of seconds. The safety lighting requirements for specific sports are given in Section 19.3. Continuation lighting requires the provision of a secondary lighting system powered from a generator or a central battery. A typical system would consist of a number of luminaires connected to both the mains supply and to a change-over switch that can detect the power failure and connect the luminaire to the generator or battery unit. If the light source being used is not incandescent or fluorescent, it will also be necessary to use a hot-restrike system. If a generator is to power the secondary lighting system it may also be necessary to have a battery system to provide instant power to cover the run-up time of the generator which can be as long as 20 seconds. For continuation lighting to be successful, it should provide illuminances at least to the level of those provided for Class III of that sport (see Section 19.3). 19.2.6 Obtrusive light Because of the high illuminances required, outdoor sports facilities are a common source of complaints about light pollution. Such complaints can take two forms, light trespass and skyglow. Complaints about light trespass are usually made by the owners of adjacent properties. Criteria to determine if such complaints are justified are given in Section 6.2.9. If the complaints are justified, the source of complaint can often be removed by carefully aiming of the lighting or by bespoke shielding of the luminaires to prevent any direct light from the installation reaching the windows of the complainant (Figure 19.2). Light pollution in the form of light trespass is a recognised statutory nuisance under the Clean Neighbourhoods and Environment Act 2005.

Figure 19.2 Special shielding of floodlights on a tennis court designed to avoid light trespass on nearby properties

Complaints about sky glow are more likely to be made by pressure groups that object to the use of the facilities at night. It is not the job of lighting designers to justify the use of sports facilities at night but it is their job to minimise the amount of sky glow. This can be done by the careful selection and aiming of luminaires and the advocacy of a curfew system for the use of the lighting. Advice on designing outdoor lighting with minimum sky glow is given in the Society of Light and Lighting Factfile 7, Environmental considerations for exterior lighting and in the references CIE Publication 150-2003 and ILE Guidance notes on the reduction of obtrusive light. 260


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The following tables summarise the recommendations for the lighting of sports facilities in the different lighting classes. The recommendations are given for sports of majority interest. Recommendations for lighting sports of minority interest are available in the SLL Lighting Guide 4: Sports lighting. The following notes are essential for interpreting the recommendations. The horizontal and vertical illuminances given are both minimum maintained average values. Horizontal illuminance is for the playing surface. Vertical illuminance is usually on a specified plane at a given height above the ground. Methods for measuring or calculating the mean illuminance are given in SLL Lighting Guide 4: Sports lighting. Illuminance uniformity is the ratio of minimum illuminance to the mean illuminance over the actual playing area. Methods for measuring or calculating the illuminance uniformity are given in SLL Lighting Guide 4: Sports lighting.


19.3 Lighting recommendations

For indoor facilities, glare control is achieved by specifying a maximum unified glare rating (UGR). For outdoor facilities, glare control is achieved by specifying a maximum glare rating (see Section 17.3.2 and CIE Publication 112-1994). 19.3.1 Athletics Athletics can take place outdoors in a stadium or indoors in an arena. The lighting in both sorts of facility should be adequate for both field and track events. Where sports involving flying missiles such as the discus, javelin and hammer are to take place, the lighting should ensure the missile is visible throughout its flight. For the track, the vertical illuminance at the finishing line should be at least 1000 lx to enable the photo-finish equipment to operate. For class III outdoor tracks, the recommended horizontal illuminance can be reduced to 50 lx for jogging. Athletics falls into TV group A. Table 19.1 Lighting recommendations for indoor athletics Class


Illuminance uniformity

Colour rendering index

I

500

0.7

60

II

300

0.6

60

III

200

0.5

20

Table 19.2 Lighting recommendations for outdoor athletics Class




Glare rating

I

500

0.7

60

50

II

200

0.7

60

50

III

100

0.5

20

55 261


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19.3.2 Bowls Bowls requires the players to be able to see the jack, the lie of the woods around the jack and the run of a live wood. To achieve this, a high level of illuminance uniformity is necessary and glare needs to controlled. An illuminance gradient of not more than 5 percent per metre is recommended. Bowls falls into TV group A. For indoor bowls, the usual lighting approach is to use fluorescent luminaires mounted at least 3 m above the floor, ideally on either side of the lanes (Figure 19.3). Glare is controlled by the choice of luminaire and ensuring that the reflectances of the walls and ceiling are at least 0.4 and 0.6 respectively.

Figure 19.3 For indoor bowls, the usual lighting approach is to use fluorescent luminaires mounted at least 3 m above the floor, ideally on either side of the lanes

For outdoor bowls, the usual lighting system is floodlights mounted at the corners of the green. Light should reach all parts of the green from at least two directions if good modelling is to be provided. Glare is controlled by careful selection of mounting height and aiming of floodlights. Table 19.3 Lighting recommendations for indoor bowls Class




I

500

0.8

60

II

500

0.8

60

III

300

0.5

20

Table 19.4 Lighting recommendations for outdoor bowls

262

Class




Glare rating

I

200

0.7

60

50

II

200

0.7

60

50

III

100

0.7

20

55


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For indoor cricket, which can take the form of games and training nets, the usual lighting approach is to use fluorescent luminaires, taking care to minimise glare. The luminaires are protected by nets hung at least 1 m below the luminaires, ideally on either side of the lanes (Figure 19.4).


19.3.3 Cricket Cricket is played with a hard ball delivered at high speed. The bowler needs to have a clear view of the pitch and wicket. The batsman needs to have a clear view of the bowler’s action and runup. The fielders need to be able to see the flight of the ball. To meet these objectives more light is usually provided more uniformly in the square near the wicket than in the outfield and glare needs to be limited as far as possible. Cricket is in TV group C.

Figure 19.4 Lighting for indoor cricket

For outdoor cricket, the usual lighting system uses high-mounted floodlights. Light should reach all parts of the field from at least two directions. Glare is controlled by careful selection of mounting height and aiming of floodlights. A white ball is often used to after dark to give a better contrast against the night sky. Table 19.5 Lighting recommendations for indoor cricket Class




I

750

0.7

60

II

500

0.7

60

III

300

0.7

20

Table 19.6 Lighting recommendations for indoor cricket training nets Class




I

1500

0.8

60

II

1000

0.8

60

III

750

0.8

20 263


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Table 19.7 Lighting recommendations for outdoor cricket Class

Horizontal illuminance on wicket square (lx)

Illuminance uniformity on wicket square

Horizontal illuminance on outfield (lx)

Horizontal illuminance uniformity on outfield

Glare rating


I

750

0.7

500

0.5

50

60

II

500

0.7

300

0.5

50

60

III

300

0.5

200

0.3

55

20

19.3.4 Five-a-side football (indoor) In this sport, players must be able to follow the movement of both the ball and other players. This sport usually takes place in multi-use sports halls (Figure 19.5). The lighting usually consists of a regular array of ceiling mounted luminaires spaced to provide the necessary illuminance uniformity. The luminaires need to be protected from the ball. Glare can be reduced by ensuring the ceiling has a reflectance in the range 0.6 to 0.9. This sport is in TV group B.

Figure 19.5 For five-a-side football, the lighting usually consists of a regular array of ceiling mounted luminaires spaced to provide the necessary illuminance uniformity

Table 19.8 Lighting recommendations for indoor five-a-side football Class




I

750

0.7

60

II

500

0.7

60

III

200

0.5

20

19.3.5 Fitness training Fitness training involves the use of equipment such as weights, treadmills and rowing machines. The purpose of the lighting is to allow safe operation of the equipment and to provide a comfortable environment. Usually, the lighting consists of a regular array of ceiling mounted luminaires. The reflectance of the ceiling should 0.6 or more so as to buffer the brightness of the luminaires viewed directly by someone looking upwards. 264


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Class




I, II and III

500

0.8

60

19.3.6 Football (Association, Gaelic and American) Football involves the rapid passage of a ball combined with physical contact between players. At high levels, these sports attract large numbers of spectators which means that attention should be paid to emergency lighting and the lighting requirements may be specified by UEFA or FIFA. For lower classes, football is in TV group B. The purpose of the general lighting is to provide uniform illumination of the pitch, with good modelling of players and without shadows or glare to players or spectators. This purpose can be met by a number of different approaches, from pole-mounted floodlights to continuous lines of floodlights mounted on the roofs of grandstands. If the former approach is used, it is important to note that for Association and Gaelic football, lighting masts should not be located within 10 degrees of the goal line axis.


Table 19.9 Lighting recommendations for fitness training

Table 19.10 Lighting recommendations for Association, Gaelic and American football Class



Glare rating


I

500

0.7

50

60

II

200

0.6

50

60

III

75

0.5

55

20

19.3.7 Lawn tennis The main visual requirements in tennis are for the players, match officials and spectators to see the ball, player and court clearly. The flight of the ball indoors will be seen easily if the ball is seen against a dark background. The reflectance of any vertical fabrics or surfaces surrounding the court should not be greater than 0.5. The ceiling above the court and extending 3 m behind the base lines should be kept free from luminaires. Typical lighting systems for indoor courts use luminaires that are mounted parallel to the sidelines, extend beyond the baselines and are outside the court area. For outdoor courts, sharp cutoff floodlights mounted on columns to the sides of the court are the usual choice. The choice of light source depends on the material forming the court. For both indoor and outdoor courts, the Lawn Tennis Association has specific illuminance requirements for the total area and the principal area (see Section 19.2.2). Lawn tennis is in TV group B. Table 19.11 Lighting recommendations for tennis (indoor) Class




I

750

0.7

60

II

500

0.7

60

III

300

0.5

20

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Table 19.12 Lighting recommendations for tennis (outdoor) Class




Glare rating

I

500

0.7

60

50

II

300

0.7

60

50

III

200

0.6

20

55

19.3.8 Rugby (Union and League) Rugby involves the rapid passage of a ball combined with physical contact between players. At high levels, these sports attract large numbers of spectators, which means that attention should be paid to emergency lighting. The purpose of the general lighting is to provide uniform illumination of the whole pitch, with good modelling of players and without shadows or glare to players or spectators. This purpose can be met by a number of different approaches, from pole-mounted floodlights to continuous lines of floodlights mounted on the roofs of grandstands. If pole-mounted floodlights are used, they should be positioned so that they do not obstruct the view of spectators. If floodlights mounted on the roofs of stands are used care should be taken that shadows are not cast onto the pitch. For rugby, it is permissible to place floodlights in line with the try line. Rugby is in TV group B. Table 19.13 Lighting recommendations for rugby (union and league) Class



Glare rating


I

500

0.7

50

60

II

200

0.6

50

60

III

75

0.5

55

20

19.3.9 Swimming Swimming is not a sport that requires the participants to undertake difficult visual tasks. The purpose of the lighting of swimming pools is to ensure safety and to provide a pleasant ambience. The safety requirement will be met by lighting that provides sufficient illuminance with careful control of reflections from the water surface (see Section 19.4.4). To ensure safety in the event of a power failure, safety lighting that produces 5 percent of the recommended illuminance for at least 30 seconds should be provided. Diving areas require special consideration with regard to glare and modelling. Swimming is in TV group A. Table 19.14 Lighting recommendations for swimming in indoor and outdoor pools

266

Class


Horizontal Colour illuminance uniformity rendering index

Horizontal/vertical illuminance ratio for diving area

I

500

0.7

60

50

II

300

0.7

60

50

III

200

0.5

20

55


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19.4.1 Multi-use sports halls As its name implies, a multi-use sports hall is an indoor facility where many different sports are played, sometimes simultaneously and where there is only limited provision for spectators. The essential characteristics of the lighting of multi-use sports halls are enough illuminance provided uniformly without glare. Given the multiple uses of the sports hall, this implies some flexibility in the lighting through switching (Figure 19.6). The usual design approach is to first identify the sports that will need to be accommodated and the potential for non-sporting uses. The lighting requirements for each sport need to be established and the relative importance of the sports listed. The lighting approach most commonly used is a ceiling-mounted regular array general lighting system with switching arrangements for different activities, levels of play or simultaneous use. With such a system, the illuminance on the walls and ceiling should be at least 50 percent and 30 percent respectively of the illuminance on the playing area. It is important for the layout of the playing areas and the type and layout of the lighting to be planned together. Where the different sports have been prioritised, the lighting should be designed to meet the requirements of the highest priority sport while ensuring that, as far as possible, all other activities are catered for. Where there is limited information on expected usage or badminton is one of the sports to be catered for, the lighting should be designed to suit the layout of the badminton courts. Badminton has the most exacting visual requirements of the sports played in multi-use sports halls and a lighting scheme that satisfies the requirements for badminton and is matched to the court layouts will often cater adequately for a wide range of other sports.


19.4 Lighting in large facilities

Figure 19.6 Lighting of a multi-sport hall

19.4.2 Small sports stadia A small sports stadium is an outdoor sports ground consisting of a central field area surrounded by an athletics track and sometimes a cycle track. The central area may be used for field athletics and other sports such as football, rugby and hockey. The spectator capacity is typically less then 5,000, usually in a grandstand located on one side. The sports taking place in small sports stadia are usually at the level of lighting classes II and III. Floodlights mounted on masts either at the four corners of the stadium or located around the perimeter of the track, except in front of the grandstand, are the most common approaches. Floodlights can also be mounted on the grandstand provided care is taken to avoid casting shadows onto the track and central area. Care should also be taken to avoid glare to participants in field events involving throwing and jumping. 267


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19.4.3 Indoor arenas Indoor arenas are usually built to cater for a variety of events, some sporting and some not. Permanent spectator seating is arranged around the event floor with temporary seating being placed on the floor as required. Given the variety of uses, the temptation is to design the lighting to meet all possibilities but experience suggests that the best approach is to provide permanent lighting for the main sports event and for setting up, using temporary lighting for any specific event that calls for something different (Figure 19.7).

Figure 19.7 Lighting of an indoor arena

The usual approach for lighting the sports area of indoor arenas is to use floodlights similar to those used for outdoor stadia. The design is built up from overlapping beams until the whole area is covered. Higher illuminances are created by adding more layers. Some flexibility is needed to cover different sports that use different parts of the sport area. This can be achieved by switching different layers of light. Given the different uses to which an arena may be put, there will be a need for frequent changes of the floor. This requires a separate lighting installation for setting up, a lighting installation that provides 100 lx on the floor. If the set-up lighting is also used as house lighting, a light source with a CIE general colour rendering index of 80 should be used. If the set-up lighting is not used as house lighting, a separate lighting installation will be needed over the permanent seating providing a similar illuminance to the set-up lighting. This lighting may need to be dimmed during the events. 19.4.4 Swimming pools Swimming pools vary widely in design but they all have a problem with high luminance reflections from the water surface. This is important because such reflections tend to mask what is happening beneath the water. The reflectance of water increases rapidly as the angle of incidence exceeds 70 degrees. In principle, it should be easy to eliminate high luminance reflections by ensuring that the angle of incidence is below 70 degrees. However, movement of the water means that the angle of incidence can vary dramatically.

268

For indoor pools, a good approach is to use indirect lighting designed to ensure that there are no high luminances to be reflected, apart from any views of the sky and sun through windows or skylights (Figure 19.8). There are two factors that influence the location of indirect luminaires. The first is the need to maintain the luminaires. Luminaires should not be located over the pool unless they are accessible from catwalks or from behind the ceiling. The second is the need to avoid glare to spectators and pool attendants, both of whom may be sitting some height above the water. Luminaires in indoor pools should be constructed to withstand high temperatures, humidity and corrosion. A minimum IP number of IP54 is recommended.


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Figure 19.8 Lighting of a swimming pool

For outdoor pools, lighting is usually provided by floodlights mounted on masts around the pool. The mounting height should be such that the angle of incidence on the far side of the pool is more than 50 degrees and preferably 60 degrees. Both indoor and outdoor pools may have underwater lighting. This reduces the effect on visibility of high luminance reflections from the water surface. Underwater lighting takes two forms, dry and wet. Dry underwater lighting has the luminaires behind watertight portholes. Wet underwater lighting has the luminaires in the water but with cables long enough so that they can be serviced from the poolside. Narrow beam floodlights are used for underwater lighting, with the beam axis aimed approximately 10 degrees above the horizontal. Almost total internal reflection takes place at the surface of the water so there is no risk of glare to surface swimmers, judges or spectators. Underwater lighting should not be used for races or for water polo.

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Chapter Twenty: Lighting performance verification

Chapter 20: Lighting performance verification 20.1 The need for performance verification Verifying the performance of a lighting installation is desirable for three reasons. First, anyone who has paid for a new lighting installation should be interested to know if they have got what they paid for. Second, anyone who has designed a lighting installation and has seen it installed should be concerned with how well the actual installation matches what was expected from the design. Discrepancies between the design and reality can indicate problems with the design process or with the data used in the design. Third, lighting installations change as they age (see Chapter 21). Light sources tend to produce less light with increasing hours of use. Luminaires emit less light and can change their light distribution as they get dirty. The amount of interreflected light can change as surface reflectances change. For applications where minimum standards of lighting are specified, being able to measure the current performance of a lighting installation is desirable to schedule maintenance correctly. The verification of the performance of a lighting installation requires a field survey. Such a survey requires decisions about the relevant operating conditions, the use of photometric instruments and the selection of an appropriate measurement procedure.

20.2 Relevant operating conditions It is essential when making field measurements to keep a complete and accurate record of the state of the lighting installation and the interior in general at the time the measurements are made. Particular attention should be given to the lamp type and age, the level and stability of the supply voltage, the state of maintenance of the lamps and luminaires, the surface reflectances, the degree of obstruction and any other factors that could influence the measurement. Photographs of the interior are a valuable supplement to a written record. Before carrying out a field survey, it is necessary to decide on the lighting conditions that are of interest. For example, is daylight to be admitted and, if it is, what type of control is to be used? Are the measurements to be concerned with average values over the whole interior or only over individual workplaces? Should the measurements around the workplace be taken with the people present, etc? It is also necessary to identify the appropriate measurement plane; horizontal and vertical and at what height or orientation. Before starting to take measurements it is first necessary to ensure that the lamps have been burnt for at least 100 hours. If this has been done, then the first step in measurement is to stabilise the performance of the lamps, luminaires and instrumentation. The time required to stabilise the light output of an installation depends on the type of light source and luminaire. Installations using discharge lamps, including tubular fluorescent, require at least 20 min, and ideally one hour, to stabilise before measurements are made. To stabilise the reading of some instruments the photocell should be exposed to the approximate illuminances to be measured for about 5 min before making the first measurement. Daylight is rarely stable and hence the illuminance and luminance it produces can rapidly vary over a very large range. For this reason when measurements of the electric lighting installation alone are required, daylight must be excluded from the interior or the measurements must be made after dark.

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Field measurements of lighting are usually undertaken with two basic instruments, an illuminance meter and a luminance meter. 20.3.1 Illuminance meters Illuminance meters usually consist of a selenium or silicon photovoltaic cell connected directly, or indirectly via an amplifier, to an analogue or digital display (Figure 20.1). The quality of an illuminance meter is determined by a number of factors including calibration uncertainty, nonlinearity, spectral correction error, cosine correction error, range change error and temperature change error. All these errors are discussed in detail in BS 667: Specification for illuminance meters. This standard defines two types of meter, type L mainly designed for laboratory use and type F designed for field use. The total uncertainty for a type L meter is ±4% and ±6% for a type F meter. These error limits assume the measurement of nominally white light. Measurements of highly coloured light sources, such as some light emitting diodes, may show much greater errors because of the poor fit of the spectral sensitivity of the meter to the CIE Standard Photopic Observer at particular wavelengths.


20.3 Instrumentation

Figure 20.1 An illuminance meter

Illuminance meters are available for measuring illuminance from 0.1 lux to 100,000 lux, i.e. from emergency lighting conditions to daylight conditions. It is important to use an illuminance meter with a range matched to the illuminances to be measured. 20.3.2 Luminance meters A luminance meter consists of an imaging system, a photoreceptor, and a display (Figure 20.2). The optical imaging system is used to form an image of the object of interest on the photoreceptor. The photoreceptor produces a signal that is dependent on the average luminance of the image it receives. The object of interest must be in focus and fill the photoreceptor aperture in order to obtain valid readings. This signal is amplified and displayed in either analogue or digital form. By changing the imaging system it is possible to alter the field of view of the photoreceptor to give different areas of measurement. The photoreceptors used in luminance meters may be photovoltaic cells or photomultiplier tubes. The photovoltaic cells, as in illuminance meters, need to be colour corrected and used with associated circuitry to give a linear response and operate acceptably over a range of ambient temperature.

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Figure 20.2 A luminance meter

BS 7920: Specification for luminance meters discusses in detail the uncertainties that luminance meters may be subject to and specifies limits for the uncertainties for two classes of luminance meter. The two types of meter are type L, laboratory meters and type F, field meters. A meter that just meets the standard would have a best measurement capability of ±5% (Type L) or ±7% (Type F). The uncertainties for measurements of highly coloured light sources may be greater. Luminance meters are available which provide measurements over a range of 10-4 to 108 cd/m2 for areas varying from a few seconds of arc to several degrees. It is important to use a luminance meter with appropriate sensitivity and measurement area for the application.

20.4 Methods of measurement The lighting recommendations given in this Handbook, the SLL Code for lighting and the SLL Lighting Guides usually involve some combination of average illuminance; some measure of illuminance variation, either illuminance diversity or illuminance uniformity; some measure of glare limitation which can be a maximum luminance, a unified glare rating (UGR) for interior lighting or a glare rating (GR) for exterior lighting; and a colour rendering index (CRI). Of these, only the average illuminance, illuminance diversity, illuminance uniformity and surface luminance can be measured in a field survey. Both UGR and GR have to be calculated for given viewing positions and directions, and CRI is a property of the light source. 20.4.1 Average illuminance The average illuminance over an interior is usually measured to check if an installation has achieved its design specification. For design calculations using computers it is practical to obtain a print-out of illuminance over a large number of closely spaced grid points. With site measurements, for logistical reasons the aim must be to obtain acceptably accurate results from a minimum number of points. To do this, the following procedures are recommended after the installation has been operating for an appropriate time at the design supply voltage. For discharge lamps this time is 100 hours, but it will be less for incandescent lamps. 20.4.2 Interior lighting For interior lighting, there are two possible methods of measurement of average illuminance. The first is based on a full grid of measurement points over the working plane or specific task areas, as required. The same grid may be used in the measurement of illuminance variation. The second is a two-line method of measurement for average illuminance that may be used for a limited range of installations. 272


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25 m

10 m

20 m

Figure 20.3 An L-shaped room with the distribution of cells required for the measurement of average illuminance 15 m


Full grid of measurement points When this method is applied to an interior lighting installation, the interior is divided into a number of equal size cells that should be as square as possible.

The illuminance at the centre of each cell is measured and the mean value for all the cells is calculated. This gives an estimate of the average illuminance. The accuracy of the estimate depends on the number of cells and the variation of illuminance. Table 20.1 relates the room index (RI) to the number of cells necessary to give an error of less than 10%; the data in Table 20.1 are valid for spacing-to-height ratios up to 1.5:1. Table 20.1 Minimum number of cells to form a full grid when measuring average illuminance in an interior Room index (RI)

RI < 1

1 > RI < 2

2 > RI < 3

RI >3

Number of cells

9

16

25

36

The only limitation on the use of the above is when the grid of cells coincides with the grid of lighting points; large errors are then possible and more cells than the number given should be used. The numbers of cells suggested are minima, and it may be necessary to increase their number to obtain a symmetrical grid to suit a particular room shape. The following examples illustrate the use of the method: (a) An interior measuring 20 m × 20 m and with luminaires mounted 4 m above the working plane has a room index of 2.5. A minimum of 25 cells is therefore required, i.e. a 5 × 5 grid spaced at 4 m × 4 m. (b) If the room measures 20 m × 33 m with the luminaires mounted at the same height, the room index of 3.1 indicates that a minimum of 36 cells would suffice. To give a grid which is acceptably ‘square’, 40 cells could be used, spaced at 4 m × 4.125 m. 273


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(c) Re-entrant room shapes may be divided into separate, smaller rectangular areas and the closest spacing arrived at by the above method applied to the whole room (Figure 20.3). Thus a room of 25 m × 20 m with a 10 m × 10 m re-entrant portion at one corner may be considered as two areas of 20 m x 15 m and 10 m × 10 m. For a luminaire mounting height of 3 m the larger area has a room index of 2.8, suggesting a minimum number of cells of 4 × 6 = 24 at a grid spacing of 3.75 m × 3.3 m. The smaller area has a room index of 1.7 indicating a minimum number of points as 16 at a spacing of 2.5 m × 2.5 m. A grid of points spaced at 2.5 m would be applicable to the whole space. Illuminance measurements should be made at the centre of each cell, at the height of the working plane, over the whole space or over the task area, as required. If the working plane is not specified, measurements should be taken on a horizontal plane at 0.8 m above the floor. A portable stand or tripod is useful to support the photocell at the required height and inclination. Care should be taken not to cast a shadow over the photocell when taking the readings. Two-line method This method applies to rectangular interiors lit by a regular layout of ceiling-mounted luminaires that are installed at or below the manufacturers’ maximum spacing-to-height ratios. It is not suitable for measurement of average illuminance in non-uniform installations, installations with a mixture of mounting heights, other unconventional layouts or those consisting of mixtures of different ceiling mounted luminaires or uplighters. In such cases the full grid measurement method must be used. In the two-line method, measurements are taken at evenly spaced intervals along two perpendicular lines parallel to the two axes of the room. The spacing of the measurements may be at any convenient distance but must not exceed the spacing of the cells calculated from Table 20.1 and must include a reading at the intersection of the two lines. The intersection point should be chosen to avoid positions exactly below or midway between luminaires. The average illuminances along the two lines of measurement are calculated. The overall average illuminance of the installation (Eav) is then given by: Eav = Ex Ey / Eis where: Eis is the illuminance at the intersection point of the two lines Ex is the average illuminance along line x Ey is the average illuminance along line y 20.4.3 Exterior lighting For exterior lighting installations, a full grid of measurements should be used. The cells are usually rectangular and the cell size in each axis should be a whole number. The illuminance is measured at the centre of each cell. The maximum cell size may be determined from the equation p = 0.2 × 5log d where: p = grid interval d = size of the longer reference axis

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p

Figure 20.4 A full grid of measurements should be used for exterior lighting installations

The number of cells in the larger dimension is given by the nearest odd whole number to the quotient of the size of the longer reference axis (d) and the grid interval (p). This result is then used to calculate the nearest odd whole number of cells in the smaller dimension. In a symmetrical but localised situation, as on an athletics track, the larger dimension d is given by one quarter of the distance of the overall inner track limit (Figure 20.5).


d

Figure 20.5 Calculation for an athletics track For the special case of road lighting, further guidance on measurement procedures is given in ILE Technical Report 28: Measurement of Road Lighting Performance on Site.

20.5 Measurement of illuminance variation To confirm compliance with the recommendations on illuminance variation, measurements of illuminances over the whole working plane are needed to calculate illuminance diversity and over task areas and their immediate surrounds to calculate illuminance uniformity. 20.5.1 Illuminance diversity For a wide range of commercial and industrial interiors where the visual task may be adversely affected by excessive variations in illuminance, the full grid measurement method should be used. This will provide a coarse grid of points over the whole working plane. Additional measurements are then required, centred on selected points to check for local maximum and minimum illuminances. These additional measurements are made on a 3 × 3 grid of points at about 1 m centres. In this procedure any measurement locations within 0.5 m of room walls or large fixed obstructions are ignored. 275


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20.5.2 Illuminance uniformity To measure illuminance uniformity, a 0.25 m square grid of measurement points is established over the task area and its immediate surround at a number of representative positions. Task illuminance uniformity is assessed using the area-weighted arithmetic average of the measurement points within each task area and the minimum grid point illuminance value within that area. The lowest values of illuminance uniformity calculated from the measured values at the selected positions is taken as representative of the whole installation. For measurement in an unfurnished area where there is no information on the task area and immediate surround dimensions, the grid should be applied to the whole working plane.

20.6 Luminance measurements Luminance measurements are often made in response to complaints about glare. In these circumstances the conditions that are the subject of complaint should be established and luminance measurements made from the position of the people who are complaining. In this way the source of the complaints may be identified. When measuring the luminance of light sources or luminaires, the meter should be mounted on a tripod and it is essential that the area of interest must fill the complete photoreceptor aperture of the meter. If a luminance meter is not available, an estimate of the luminance of matte room surfaces can be obtained indirectly by measuring the reflectance of the surface and the illuminance (lux) on it and then calculating the luminance (cd/m2).

20.7 Measurement of reflectance Sometimes it is necessary to measure the reflectance of a surface, e.g. to determine if the reflectance is outside the recommended range or to establish if the reflectance assumed in a calculation is reasonable. There are a number of ways to do this. One is to measure the illuminance falling on the surface and the luminance of the surface at the same point. The reflectance is then given by the expression:

R=

Eπ L

where: R is the reflectance of the surface at the measurement point E is the illuminance on the surface at the measurement point (lx) L is the luminance of the surface at the measurement point (cd/m2) Another method is to use a luminance meter and a standard reflectance surface made from pressed barium sulphate or magnesium oxide. The luminances of the surface of interest and the standard reflectance surface are measured at the same appropriate position. Then the reflectance of the surface of interest is given by the expression: R = Rs L1 / Ls where: R is the reflectance of the surface of interest L1 is the luminance of the surface of interest (cd/m2) Ls is the luminance of the standard reflectance surface (cd/m2) Rs is the reflectance of the standard reflectance surface 276


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If a luminance meter is not available, then an approximate measure of the reflectance of a surface can be obtained by making a match between the surface of interest and a sample from a range of colour samples of known reflectance as described in SLL Lighting Guide 11: Surface reflectance and colour.


This method can also be used to obtain the luminance factor (or gloss factor) for non-matte surfaces where local values of luminance, from defined viewing positions, are of interest. This has little or no relevance to the average value of the inter-reflected illuminance received on the working plane or other room surfaces.

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Chapter Twenty One: Lighting maintenance

Chapter 21: Lighting maintenance 21.1 The need for lighting maintenance A lighting installation starts to deteriorate from the moment it is first switched on. Maintenance keeps the performance of the system within the design limits and promotes safety and the efficient use of energy. Maintenance includes replacement of failed or deteriorated lamps and control gear, the cleaning of luminaires and the cleaning and redecoration of room surfaces. Detailed advice on lighting maintenance can be found in CIE Publications 97-2005 and 154-2003.

21.2 Lamp replacement There are two factors to be considered when determining the timing of lamp replacement, the change in light output and the probability of lamp failure. The relative weight given to these two factors depends on the light source. Mains and low voltage tungsten filament and tungstenhalogen lamps usually fail before the decline in light output becomes significant. Therefore the replacement time for these lamps is determined by the probability of lamp failure alone. All other electric light sources show a significant reduction in light output before a large proportion fail. For these lamps, both the decline in light output and the probability of lamp failure are important in determining the lamp replacement time. For the majority of lighting installations, the most sensible procedure is to replace all the lamps at planned intervals. This procedure, which is known as group replacement, has visual, electrical and financial advantages over the alternative of ‘spot replacement’, e.g. replacing individual lamps as they fail. Visually, group replacement ensures that the installation maintains a uniform appearance. Electrically, group replacement reduces the risk of damage to the control gear caused by the faulty operation of lamps nearing the end of their life. Financially, by having the lamp replacement coincide with luminaire cleaning and doing both at a time when it will cause the minimum of disturbance, the cost of maintenance can be minimised. Group replacement is an appropriate procedure for routine maintenance and the frequency with which the procedure is carried out will have a direct bearing on the installed electrical load. However, in any large installation, a few lamps can be expected to fail prematurely. These lamps should be replaced promptly on an individual basis. For many installations the most economic time for group replacement is when the light output of the lamps has fallen below 80% of the initial value and the lamp failures are becoming significant to the loss of average illuminance. The latest time for group replacement is when the designed ‘maintained illuminance’ has been reached. As light source development proceeds there is a temptation to replace one light source with another that is superficially similar but of higher luminous efficacy. However, it is essential to establish that the replacement light source and the existing control gear are compatible physically, electrically and photometrically. Before replacing any discharge light source with another of a different type or the same type but from a different manufacturer, advice on compatibility should be sought.

21.3 Cleaning luminaires

278

The rate at which dirt is deposited on and in a luminaire depends on the amount and composition of the dirt in the atmosphere, and on the type of luminaire. Over the same period and in the same location, dust-proof (IP5X) and dust-tight (IP6X) luminaires and open reflectors with slots in the top will collect less dirt than louvred luminaires with closed tops, or luminaires with unsealed diffusers (see Sections 21.7 and 21.8).


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The appropriate cleaning interval for luminaires and the lamps they contain is a basic design decision. The factors that need to be considered are the cost and convenience of cleaning at a particular time and the illuminance at that time in relation to the design maintained illuminance. As a general guide, luminaires should be cleaned at least once a year but for some locations this will not be sufficient. A wide range of materials is used in luminaires. Table 21.1 summarises the most suitable cleaning methods for different materials. Additionally, equipment manufacturers provide useful information on the most appropriate cleaning methods, or guidance can be obtained from specialist cleaning product suppliers. Table 21.1 Methods for cleaning materials used in luminaires Materials

Cleaning methods

Anodized aluminium

Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral detergent in warm water which does not leave a residue and then allowed to air dry.


For particularly dirty atmospheres or where access is difficult, the best choice would be dustproof or dust-tight luminaires, ventilated luminaires that are designed to use air currents to keep them clean, or lamps with internal reflectors. Even the most protected luminaires, e.g. dust-tight luminaires, will collect dirt on their external surfaces. Therefore even these luminaires will need cleaning regularly.

Ultrasonic cleaning techniques. Severe staining or contamination should be removed first by metal polish. Stainless steel

Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral detergent in warm water and then the surface dried with a clean cloth, following the grain of brushed finishes where applicable. Surface lustre may be restored by applying an oil-based cleaning compound with a cloth and wiping off all surplus.

Galvanized steel, natural aluminium

Surfaces should be cleaned with a neutral-based detergent and wiped dry.

Enamel paint finish, polyester powder coat

Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral detergent in warm water and the surface dried with a clean cloth. Solvent-based cleaners should not be used.

Glass

Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral detergent in warm water that does not leave a residue, then wiped and allowed to air dry.

Acrylic, polycarbonate, glass-polyester, reinforced plastic

Remove loose dirt and dust with a vacuum cleaner. Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral-based detergent that does not leave any residue, then rinsed and wiped dry with warm water containing an anti-static solution. Solvent-based cleaners should not be used under any circumstances. Ultrasonic cleaning techniques. 279


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21.4 Room surface cleaning All room surfaces should be cleaned and redecorated regularly if a dirty appearance and light loss is to be avoided. Regular cleaning is particularly important where light reflected from the room surfaces makes an important contribution to the lighting of the interior, e.g. where daylight from the side windows is used or where the electric lighting installation has a high indirect component such as uplighting (see Section 21.7).

21.5 Maintained illuminance The illuminance recommendations in the SLL Code for lighting and in this Handbook are all given in terms of maintained illuminance. Maintained illuminance is defined as the average illuminance over the reference surface at the time maintenance is carried out. In other words, maintained illuminance is the minimum illuminance that the lighting installation will produce, on that surface, during its life. Using maintained illuminance for recommendations implies that the designer must obtain a decision from the client on the maintenance policy to be implemented throughout the life of the installation in order to determine the maintenance factor to be used in their calculations. If this cannot be achieved, the designer must clearly state the assumed maintenance programme used in the design calculations.

21.6 Designing for lighting maintenance The maintenance requirements for a lighting installation must be considered at the design stage. Three aspects are particularly important: The maintenance factor used in the calculation of the number of lamps and luminaires needed to provide the maintained illuminance. Maintenance factor is defined as the ratio of maintained illuminance to initial illuminance. The closer the maintenance factor is to unity, the smaller the number of lamps and luminaires that will be needed. This approach demands a commitment to regular and frequent maintenance. Unless this commitment is fulfilled the installation will not meet the recommended maintained illuminance during its life. Practical access and handling. Good maintenance will only occur if access to the lighting installation is safe and easy, and the lighting equipment is straightforward to handle. Equipment selection. The dirtier the operating environment, the more important it is to select equipment that is resistant to dirt deposition.

21.7 Determination of maintenance factor for interior lighting The quantity used to take account of the planned maintenance schedule when designing a lighting installation is the maintenance factor. The maintenance factor (MF) for an indoor lighting installation is a multiple of four factors: MF = LLMF × LSF × LMF × RSMF where: LLMF is the lamp lumen maintenance factor LSF is the lamp survival factor LMF is the luminaire maintenance factor RSMF is the room surface maintenance factor. 280


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Manufacturers’ data will normally be based on British Standards test procedures which specify the ambient temperature in which the lamp will be tested, with a regulated voltage applied to the lamp and, if appropriate, a reference set of control gear. If any of the aspects of the proposed design are unusual, e.g. high ambient temperature, vibration, switching cycle, operating attitude etc., the manufacturer should be made aware of the conditions and will advise if they affect the life and/or light output of the lamp. Typical values of LLMF after a range of operating times, for some commonly used discharge light sources are given in Table 21.2. Table 21.2 Typical values of lamp lumen maintenance factor (LLMF) for some commonly used discharge light sources after a range of hours of use Light source


21.7.1 Lamp lumen maintenance factor (LLMF) The luminous flux from all electric light sources reduces with time of operation. The rate of decline varies for different light sources so it is essential to consult manufacturers’ data. From such data it is possible to obtain the lamp lumen maintenance factor for a specific number of hours of operation. The lamp lumen maintenance factor is the proportion of the initial light output that is produced after a specified time. Where the decline in light output is regular, LLMF may be quoted as a percentage reduction per thousand hours of operation.

Hours of use (thousands) 0.1

0.5

1.0

1.5

2

4

6

8

10

12

14

Triphosphor/multiphosphor fluorescent

1

0.98 0.96

0.95 0.94 0.91 0.87 0.86 0.85 0.84 0.83

Halophosphor fluorescent

1

0.97 0.94

0.91 0.89 0.83 0.80 0.78 0.76 0.74 0.72

Mercury

1

0.99 0.97

0.95 0.93 0.87 0.80 0.76 0.72 0.68 0.64


1

Improved colour high pressure sodium

1

Low pressure sodium

1

1

0.98

0.99 0.97 1

0.99

0.97 0.96 0.93 0.91 0.89 0.88 0.87 0.86 0.95 0.94 0.89 0.84 0.81 0.79 0.78

-

0.98 0.98 0.98 0.97 0.97 0.96 0.96 0.96

21.7.2 Lamp survival factor (LSF) Lamp survival factor is defined as the proportion of lamps of a specific type that are expected to be emitting light after a number of hours of operation. Lamp survival factor should only be used in the calculation of maintenance factor when group lamp replacement, without spot replacement, is to be done. As with lamp lumen maintenance factor it is essential to consult manufacturers’ data. These data will be based on assumptions such as switching cycle, supply voltage and control gear. If the expected operating conditions depart from these assumptions, manufacturers should be informed and asked for advice on how the actual conditions might affect lamp survival. Typical values of LSF after a range of operating times, for some commonly used discharge light sources are given in Table 21.3.

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Table 21.3 Typical values of lamp survival factor (LSF) for some commonly used discharge light sources after a range of hours of use Light source

Hours of use (thousands) 0.1

0.5

1.0

1.5

2

4

6

8

10

12

Triphosphor/multiphosphor fluorescent

1

1

1

1

1

1

0.99 0.95 0.85 0.75 0.64

Halophosphor fluorescent

1

1

1

1

1

1

0.99 0.95 0.85 0.75 0.64

Mercury

1

1

1

1

0.99 0.98 0.97 0.95 0.92 0.88 0.84


1

1

1

1

0.99 0.98 0.96 0.94 0.92 0.89 0.85

Improved colour high pressure sodium

1

1

1

0.99 0.98 0.96 0.90 0.79 0.65 0.50

14

-

21.7.3 Luminaire maintenance factor (LMF) Dirt deposited on or in a luminaire will cause a reduction in light output from the luminaire. The rate at which dirt is deposited depends on the construction of the luminaire, the nature of the dirt and the extent to it is present in the atmosphere. The luminaire maintenance factor (LMF) is the ratio of the light output of a luminaire at a given time to the initial light output. Tables 21.4 to 21.6 give typical values of LMF for six different types of luminaires and six different luminaire cleaning intervals, for clean, normal and dirty environments respectively. Clean environments are found in such locations as clean rooms, computer centres, electronic assembly areas and hospitals. Normal environments are found in offices, shops, schools, laboratories, restaurants, warehouses and so on. Dirty environments are common in steelworks, chemical works, foundries, woodwork areas and similar locations.


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Time between luminaire cleaning (years) Luminaire type

0.5

1.0

1.5

2.0

2.5

3.0

Bare lamp batten

0.95

0.93

0.91

0.89

0.87

0.85

Open top reflector (ventilated)

0.95

0.90

0.87

0.84

0.82

0.79

Closed top reflector (unventilated)

0.93

0.89

0.84

0.80

0.77

0.74

Enclosed (IP2X)

0.92

0.88

0.85

0.83

0.81

0.79

Dustproof (IP5X)

0.96

0.94

0.92

0.91

0.90

0.90

Indirect uplighter

0.92

0.86

0.81

0.77

0.73

0.70

Table 21.5 Typical luminaire maintenance factors (LMF) for a range of luminaires, and a range of cleaning intervals, in normal environments


Table 21.4 Typical luminaire maintenance factors (LMF) for a range of luminaires, and a range of cleaning intervals, in clean environments

Time between luminaire cleaning (years) Luminaire type

0.5

1.0

1.5

2.0

2.5

3.0

Bare lamp batten

0.92

0.89

0.87

0.84

0.82

0.79


0.91

0.86

0.83

0.80

0.76

0.74


0.89

0.81

0.74

0.69

0.64

0.61

Enclosed (IP2X)

0.87

0.82

0.79

0.77

0.75

0.73

Dustproof (IP5X)

0.93

0.90

0.88

0.86

0.85

0.84

Indirect uplighter

0.89

0.81

0.73

0.66

0.60

0.55

Table 21.6 Typical luminaire maintenance factors (LMF) for a range of luminaires, and a range of cleaning intervals, in dirty environments Time between luminaire cleaning (years) Luminaire type

0.5

1.0

1.5

2.0

2.5

3.0

Bare lamp batten

0.88

0.83

0.80

0.78

0.75

0.73


0.88

0.83

0.79

0.75

0.71

0.68


0.83

0.72

0.64

0.59

0.54

0.52

Enclosed (IP2X)

0.83

0.77

0.73

0.71

0.68

0.65

Dustproof (IP5X)

0.91

0.86

0.83

0.81

0.80

0.79

Indirect uplighter

0.85

0.74

0.65

0.57

0.51

0.45 283


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21.7.4 Room surface maintenance factor (RSMF) Changes in room surface reflectance caused by dirt deposition will cause changes in the illuminance produced by the lighting installation. The magnitude of these changes is governed by the extent of dirt deposition and the importance of inter-reflection to the illuminance produced. Inter-reflection is closely related to the distribution of light from the luminaire and the room index. For luminaires that have a strongly downward distribution, i.e. direct luminaires, inter-reflection has little effect on the illuminance produced on the horizontal working plane. Conversely, indirect lighting is completely dependent on inter-reflections. As for room index, the smaller is the room index, the greater is the contribution of inter-reflected light. Tables 21.7 to 21.9 show the typical changes in the illuminance from an installation that occur with time due to dirt deposition on the room surfaces, for clean, normal and dirty conditions, in small, medium or large rooms, lit by direct, direct/indirect and indirect luminaires. Clean environments are found in such locations as clean rooms, computer centres, electronic assembly areas and hospitals. Normal environments are found in offices, shops, schools, laboratories, restaurants, warehouses and so on. Dirty environments are common in steelworks, chemical works, foundries, woodwork areas and similar locations. Table 21.7 Room surface maintenance factor (RSMF) for direct, direct/indirect and indirect luminaires in rooms of different room indices, for a range of cleaning intervals, in clean environments Interval between cleaning (years) Room index

Luminaire type

0.5

1.0

1.5

2.0

2.5

3.0

0.7

Direct

0.97

0.97

0.96

0.95

0.94

0.94

0.7

Direct/indirect

0.94

0.90

0.89

0.87

0.85

0.84

0.7

Indirect

0.90

0.85

0.83

0.81

0.77

0.75

2.5 to 5

Direct

0.98

0.98

0.97

0.96

0.96

0.96

2.5 to 5

Direct/indirect

0.95

0.92

0.90

0.89

0.87

0.86

2.5 to 5

Indirect

0.92

0.88

0.86

0.84

0.81

0.78

Table 21.8 Room surface maintenance factor (RSMF) for direct, direct/indirect and indirect luminaires in rooms of different room indices, for a range of cleaning intervals, in normal environments Interval between cleaning (years)

284

Room index

Luminaire type

0.5

1.0

1.5

2.0

2.5

3.0

0.7

Direct

0.96

0.94

0.94

0.93

0.92

0.92

0.7

Direct/indirect

0.88

0.86

0.83

0.82

0.80

0.79

0.7

Indirect

0.84

0.78

0.75

0.73

0.70

0.68

2.5 to 5

Direct

0.97

0.96

0.96

0.95

0.95

0.95

2.5 to 5

Direct/indirect

0.90

0.88

0.86

0.85

0.84

0.82

2.5 to 5

Indirect

0.87

0.82

0.79

0.77

0.74

0.72


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Interval between cleaning (years) Room index

Luminaire type

0.5

1.0

1.5

2.0

2.5

3.0

0.7

Direct

0.95

0.93

0.92

0.90

0.89

0.88

0.7

Direct/indirect

0.84

0.82

0.80

0.78

0.75

0.74

0.7

Indirect

0.80

0.73

0.69

0.66

0.63

0.59

2.5 to 5

Direct

0.96

0.95

0.95

0.94

0.94

0.94

2.5 to 5

Direct/indirect

0.86

0.85

0.83

0.81

0.79

0.78

2.5 to 5

Indirect

0.83

0.77

0.74

0.70

0.67

0.64

21.8 Determination of maintenance factor for exterior lighting The maintenance factor (MF) for an outdoor lighting installation is a multiple of three factors: MF = LLMF × LSF × LMF


Table 21.9 Room surface maintenance factor (RSMF) for direct, direct/indirect and indirect luminaires in rooms of different room indices, for a range of cleaning intervals, in dirty environments

where: LLMF is the lamp lumen maintenance factor LSF is the lamp survival factor LMF is the luminaire maintenance factor. Typical values of LLMF are given in Table 21.2. Typical values of LSF after different hours of operation are given in Table 21.3. Typical values of luminaire maintenance factor (LMF) for luminaires with different levels of dust proofing installed in different levels of atmospheric pollution and with different luminaire cleaning intervals are given in Table 21.10. The level of dust proofing is given by the IP class to which the luminaire belongs (see Table 4.10). Low atmospheric pollution occurs in rural areas. Medium atmospheric pollution occurs in semiurban, residential and light industrial areas. High atmospheric pollution occurs in large urban areas and heavy industrial areas. Table 21.10 Typical luminaire maintenance factor (LMF) for luminaires of different IP classes, in different levels of atmospheric pollution over a range of cleaning intervals Luminaire cleaning interval (years) Luminaire IP class

Atmospheric pollution

1.0

1.5

2.0

3.0

IP2X

Low

0.82

0.80

0.79

0.78

IP2X

Medium

0.62

0.58

0.56

0.53

IP2X

High

0.53

0.48

0.45

0.42

IP5X

Low

0.92

0.91

0.90

0.88

IP5X

Medium

0.90

0.88

0.86

0.82

IP5X

High

0.89

0.87

0.84

0.76

IP6X

Low

0.93

0.92

0.91

0.90

IP6X

Medium

0.92

0.91

0.89

0.87

IP6X

High

0.91

0.90

0.88

0.83 285


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21.9 Disposal of lighting equipment Until recently, the disposal of lighting equipment was rarely discussed. However, the introduction of the Waste Electrical and Electronic Equipment (WEEE) Regulations have made it necessary for the designer to consider how lighting equipment is to be disposed of at the end of life. The purpose of the WEEE regulations is to reduce the impact of electrical and electronic equipment on the environment but encouraging recycling and reducing the amount of such waste that goes to landfill. With the exception of lighting equipment in households and filament light sources anywhere, all lighting equipment, lamps, luminaires and control systems, is now considered hazardous waste. Recently two organisations have been established in the UK, which can advise on the disposal of redundant lighting equipment. They are Recolight (www.recolight.co.uk) for lamp disposal and Lumicon (www.lumicon.co.uk) for luminaire disposal. Guidance on the implementation of the WEEE Regulations as they apply to lighting is available from the Lighting Industry Federation.


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22.1 Changes and challenges Lighting practice does not exist in a vacuum. Rather, lighting practice occurs within a business and social environment and that environment is always changing. The resulting changes and challenges can be gradual or sudden; technical, economic or political, but all are likely to result in adjustments in lighting practice. This chapter is concerned with the sort of changes and challenges that are already on the horizon and that are likely to impact lighting practice in the foreseeable future.

22.2 The changes and challenges facing lighting practice 22.2.1 Costs Costs have always been an important consideration for lighting applications, the balance between first and operating costs changing as the price of electricity has changed. The price of electricity varies with the source of fuel. In the UK, recent increases in demand for oil and gas and reductions in supply have resulted in dramatic increases in the price of electricity. Whatever the cause, any increase in the cost of electricity implies a shift in emphasis to operating costs and enthusiasm for technologies that minimise electricity consumption and maximise energy efficiency, together with a closer examination of the basis of many lighting recommendations.

Chapter Twenty Two: On the horizon

Chapter 22: On the horizon

22.2.2 Technologies Light emitting diodes (LEDs) Lighting is unique amongst technologies in that the first electric light source invented, the incandescent lamp, is still the most widely used. This is in spite of the ingenuity of the lighting industry, which has produced a dazzling array of new light sources with much greater luminous efficacies, longer lives and a wide range of colour properties. However, the reign of the incandescent lamp is under threat from influential forces and new technology. The influential forces are those who see the elimination of the cheap but inefficient incandescent lamp as desirable for environmental, political or commercial reasons. The new technology is the LED. LEDs have already displaced the incandescent lamp from many signs and signals, are starting to appear in near field lighting installations such as reading lamps, and are poised to make the breakthrough into general illumination. When they do they will not only show improvements on existing criteria, such as luminous efficacy and lamp life, but also offer new possibilities, such as luminaires which allow changes in light level, light distribution and light spectrum to be made quickly and easily. Lighting controls Lighting control systems are becoming more sophisticated. This is now possible for a number of reasons. First, enormous amounts of computer power are now available in very small packages. Second, developments in wireless communication have enhanced flexibility and removed the need for expensive rewiring. Third, there are a number of widely recognised communication protocols that enable equipment from different manufacturers to work together. As a result of these changes the integration of daylight and electric lighting is much easier, individual control of electric lighting is a real possibility, and the dimming of road lighting at night as traffic flows diminish is being seriously considered (Walker, 2007). 22.2.3 New knowledge There are a number of areas in which research is revealing an understanding that has important implications for lighting practice. 287


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Light and health For most of the last century, light was considered solely in terms of its impact on our ability to see. However, it has been known for some time that exposure to optical radiation can have both positive and negative impacts on human health, impacts that can become evident soon after exposure or only after many years. Optical radiation covers the ultra-violet, visible and infrared regions of the electromagnetic spectrum (see Figure 1.1). An example of the impact of optical radiation is the production of vitamin D following exposure of the skin. Vitamin D is essential for healthy bones and influential in many other aspects of health (Holick, 2005). Unfortunately, optical radiation incident on the skin and eye is also known to produce tissue damage, both acute and chronic, through either thermal or photochemical routes. There exist occupational safety guidelines limiting the exposure to optical radiation (ACGIH, 2004) and methods for evaluating electric light sources for their potential to cause tissue damage (IESNA, 1996). These effects are well known, so it is the more recent discovery of a new class of photoreceptor in the retina of the eye that has renewed interest in light and health (Brainard et al, 2001; Thapan et al, 2001). The output from these photoreceptors is linked to the suprachiasmatic nuclei in the brain. These nuclei are believed to form the master clock for the body’s circadian system. The relevance of this finding for lighting practice is evident from the fact that patterns of light exposure have been shown to alleviate problems associated with diminished operation of the circadian system. For example, people with Alzheimer’s disease show a fractured sleep/wake cycle, often being active at night. It has been shown that exposure to bright light during the day and little light at night restores the sleep/wake cycle to a more stable state (van Someren et al., 1997). Similarly, some people suffer from timing problems with sleep, young people having delayed sleep phase syndrome and elderly people having advanced sleep phase syndrome. Exposure to bright light at the correct time has been shown to correct these timing problems, the exposure being in the morning for the young and the evening for the elderly (Czeisler et al., 1988; Campbell et al., 1993). There is also the presently unexplained phenomenon of the use of light treatment to overcome seasonally affective disorder (SAD), a condition in which people feel depressed during a specific season, usually winter, but not during the rest of the year. Exposure to bright light has been shown to diminish this depression in a significant number of people. Guidance on its use has been developed (Lam and Levitt, 1999). But it is not all good news. Concern has also been raised about the impact of light exposure at night on the development of breast cancer (Figueiro et al, 2006). A lot more needs to be known about how the circadian system and all the other bodily functions linked to it might be influenced by light exposure before advocating the widespread use of light exposure for purposes other than vision (Boyce, 2006; Figueiro et al, 2006). Once that knowledge is gained, then lighting is likely to be designed not just for vision but for human health as well. Individual control Lighting has usually been specified and designed on a one-size-fits-all basis. However, research has shown that when office workers are given individual control of their lighting, the preferred illuminances can vary widely but the bulk of the illuminances chosen are below the levels recommended (Boyce et al, 2006a). These findings have two implications. The first is that onesize-fits-all lighting cannot hope to satisfy everyone, a fact made evident by the finding that for the most common form of office lighting in North America, only about 70% of occupants finding the lighting comfortable (Eklund and Boyce, 1996). The second is that the change in office work produced by the almost universal use of self-luminous displays represents an opportunity to re-examine lighting recommendations.

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Mesopic vision Much exterior lighting provides conditions such that the visual system is in the mesopic state yet the measurements used to describe photometric conditions are all based on the photopic response. As a result, light sources that are calculated to be equal may be very different in reality. This is of particular concern for road lighting where interest is focused on the possibility that metal halide light sources may provide equal visibility at lower illuminances than the high pressure sodium light sources widely used at present (Fotios and Cheal, 2007a and b). Unfortunately, there is no internationally agreed system of mesopic photometry. Previous attempts to identify a standard observer for mesopic vision were based on the perception of brightness (CIE, 1989) but recently, alternative approaches based on reaction times (Rea et al, 2004) and performance measurements related to driving (Elohoma and Halonen, 2006) have been published. A comparison between these two systems suggests that there is little difference between them at the luminances typically produced by exterior lighting (Rea and Bullough, 2007). The CIE is attempting to develop a system for dealing with mesopic vision based on these findings. Once such a system has been developed, a major reassessment of exterior lighting practice is to be expected.


Scotopically enhanced lighting Research has demonstrated that light sources that more effectively stimulate the rod photoreceptors of the eye improve visual acuity (Berman et al, 2006). This improvement is caused by the smaller pupil size produced and hence the improvement in retinal image quality. This finding suggests that light sources with a high scotopic/photopic ratio can be used at lower illuminance than those with a lower scotopic/photopic ratio to achieve equal visual performance. This is certainly true for tasks that are limited by visual acuity but not for tasks limited by other factors (Boyce et al, 2003b) or for applications where appearance is more important than visual performance. Nonetheless, this research has demonstrated that light spectrum has an impact on task performance beyond simply colour rendering.

Replacement of the CIE general colour rendering index (CRI) Although the CIE General CRI has been used to characterise light sources for many years it does have a number of limitations. First, just because two light sources have the same general CRI, it does not mean that they render colours the same way. The general CRI is an average and there are many combinations of special CRI values that give the same average. Second, different light sources are being compared with different reference light sources. This makes the meaning of comparisons between different light sources uncertain, yet comparing light sources is what the general CRI is most widely used to do. Third, there is considerable argument about the method used to correct for chromatic adaptation. What has made the search for a replacement urgent is the development of improved or new light sources with different colour properties but which the general CRI is unable to separate. It is likely that any replacement for the general CRI will involve abandoning the use of a single number to describe a phenomenon as complex as colour perception and the acceptance of something more sophisticated such as colour vector maps (van Kemenade and van der Burgt, 1988) or the colour gamut (see Section 1.4.5). Replacement of daylight factor Daylight factor has been used to quantify the proportion of daylight available in an interior for many years. Unfortunately, daylight factor suffers from a serious limitation, namely that it assumes a uniform overcast sky. This is a problem in that real skies vary greatly from day to day and from climate to climate. Thus, a realistic evaluation of the energy impact of any proposed daylighting scheme demands that account be taken of the typical climate in which the building is situated as well as the orientation of the building. 289


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Alternative climate-based metrics, such as useful daylight illuminance, are being developed (Madaljevic, 2006). Such metrics would make the adoption of daylight as the primary light source in buildings easier to achieve. Lighting the space Current lighting practice is divided into two parts. Where the appearance of the space is important to the impression given, e.g. for hotel foyers, the lighting designer is allowed free reign to use the lighting of the space to deliver the required ‘message’. In applications where function is the main consideration, attention is focused on visual performance of tasks with the result that the appearance of the space is often ignored. This dichotomy has triggered two different streams of research. One is the search for the cues that people use in generating their impression of a space (Loe et al, 1994, 2000). By identifying the parts of the space that are important for perception and the aspects of light distribution and colour appearance that influence perception, it is hoped to improve the quality of lighting design. The other is an attempt to demonstrate the value of lighting the space by measuring individual task performance under different types of interior lighting. This has been largely unsuccessful (Boyce et al 2006b). While it has been shown that people can identify better quality lighting and prefer it, there is no effect of lighting quality on task performance other than where there are differences in task visibility. This failure to find an effect of lighting quality beyond visibility is most likely to be because the simulated work studies used measure what we can do, not what we might choose to do. To measure what people choose to do, studies have to be conducted in the field where real people do real work. Until such studies are done and the possibility that lighting the space may have an effect at an organisational level is investigated, the importance of lighting the space on task performance is a matter of belief and exhortation rather than proof. 22.2.4 External influences Lighting practice is under pressure from a number of external interests. The fact that lighting is a major consumer of electricity together with the relatively short time scales within which lighting practice can be changed has attracted the attention of those concerned with energy conservation, global warming and sustainability. The aim of these interests is to reduce the amount of electricity used for lighting. One way to achieve this is to make daylight the primary light source in buildings with electric lighting being used as a supplement when necessary. Another is to ban the sale of inefficient light sources and luminaires. Legislative, regulatory and promotional activities in these areas are to be expected. Another interest group influencing lighting practice is one concerned with light pollution for its effects on the night sky and the surrounding flora and fauna. Light pollution can be considered at two levels, the local, where it tends to be related to light trespass, and the regional, where attention is given to sky glow. This group wishes to change lighting practice to reduce the amount and distribution of light used at night. There are a number of approaches being developed to reduce light pollution, varying from the simple advice to use full cutoff luminaires to the more sophisticated design tool that seeks to limit the amount of light leaving the boundary of the site (Brons et al, 2008). It is likely that concerns about light pollution will carry greater weight in the design of exterior lighting in the future.

22.3 The evolution of lighting practice Given that lighting practice faces a number of changes and challenges and is likely to be influenced by the interests of a number of groups whose concerns are more with the consequences of lighting than with lighting itself, what can be done to guide how lighting practice evolves? 290


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The basic framework for understanding what motivates people is given by Maslow’s hierarchy of needs (Maslow and Lowery, 1998). Graphically, this consists of a triangle formed of eight levels (Figure 22.1). The lower four are called deficiencies. They represent needs that must be met. The lowest need is simply the physiological need for food, water, sleep, warmth etc. The second is the need for safety. The third is the need to belong, to be accepted as a member of some group. The fourth is the need for esteem from others. The fifth to eight levels are called the growth levels and represent needs that are optional. They are, respectively, the need to know and understand, aesthetic needs, self-actualisation which means finding fulfillment, and transcendence, where the individual connects to something beyond the ego.


This question can be addressed through two other questions, what is it that motivates people to want some form of lighting and how should lighting practitioners react to external interests?

Transcendence

Selfactualisation

Aesthetic needs

Need to know and understand

Esteem needs

Belongingness and love needs

Safety needs

Physiological needs

Figure 22.1 Maslow’s hierachy of needs Within this structure, the lower needs must be met before moving to a higher level. Everyone starts from the bottom and works their way up. Fewer and fewer reach each level. Anyone who achieves transcendence is a saint. The question now is what has lighting got to contribute to these needs? The answer is that lighting at its most basic contributes to the physiological need to see and to the need for safety. Lighting also has a role to play in the need to belong, because lighting as an element of fashion can be used to define groups. It might also be argued that lighting has a role in satisfying aesthetic needs, but the number of people who have achieved this elevated level is small. 291


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Overall, this is not a very encouraging picture. The contribution to the first and second levels should ensure that there will always be mass support for simple forms of lighting but the failure to be an essential component in the next levels suggests that attempts to develop mass aesthetic appreciation of lighting will meet with limited success. The one ray of hope in all this is a growth in our understanding of how exposure to light influences human health. The concern with health operates at the first or second level and so could generate mass support for developments in lighting practice. The other possibility for mass support is to form an alliance with the groups who are concerned with the consequences of lighting rather than lighting itself. This increases the number of people for whom lighting operates at the third level. In a sense, lighting practitioners should be flattered by the attentions of these other groups. It means that like war and generals, lighting has become too important to be left to lighting practitioners alone. Further, using emerging technologies and knowledge to meet the desires of groups concerned with sustainability and light pollution represents an opportunity for lighting practitioners to demonstrate added value. Of course, such a course of action will require compromises from all parties but surely it is better to use our wits to work together rather than to defend the indefensible. So, how will lighting evolve? There will always be a niche market for sophisticated lighting, but for the bulk of lighting practice, the answer is one of two directions. In one direction the prospect is of lighting as a commodity driven solely by price with a limited range of standard equipment and designs. In the other the prospect is of a more sophisticated approach in which new technology, new understanding and new objectives combine to produce lighting better suited to the needs and concerns of mankind in the 21st century. Which of these directions lighting moves in will depend on the willingness of lighting practitioners to take advantage of new knowledge and technology and to cooperate with rather than confront apparently conflicting interests.

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23.1 Standards British Standards Institution BS 667: 2005: Illuminance meters. Requirements and test methods, London: BSI. British Standards Institution BS 5266-1: 2005: Emergency lighting. Code of practice for the emergency lighting of premises, London: BSI. British Standards Institution BS 5266-10: 2008: Guide to the design and provision of emergency lighting to reduce the risks from hazards identified by The Regulatory Reform (Fire Safety) Order 2005 risk assessment, London: BSI. British Standards Institution BS 5394:1988, EN 55015: 1987: Specification for limits and methods of measurement of radio interference characteristics of fluorescent lamps and luminaires, London: BSI.

Chapter Twenty Three: Bibliography

Chapter 23: Bibliography

British Standards Institution BS 5489-1: 2003+A2: 2008: Code of practice for the design of road lighting. Lighting of roads and public amenity areas, London: BSI. British Standards Institution BS 5489-2: 2003+A1: 2008: Code of practice for the design of road lighting. Lighting of tunnels, London: BSI. British Standards Institution BS 5499: Safety signs, including fire safety signs, London: BSI. British Standards Institution BS 6387: 1994: Specification for performance requirements for cables required to maintain circuit integrity under fire condition, London: BSI. British Standards Institution BS 7846: 2000: Electric cables. 600/1000 V armoured fire-resistant cables having thermosetting insulation and low emission of smoke and corrosive gases when affected by fire, London: BSI. British Standards Institution BS 7920: 2005: Luminance meters. Requirements and test methods, London: BSI. British Standards Institution BS 8206-2: 2008: Lighting for buildings: Code of practice for daylighting, London: BSI. British Standards Institution BS EN 12193: 2007: Light and lighting. Sports lighting, London; BSI. British Standards Institution BS EN 12464-1: 2002: Light and lighting. Lighting of work places. Indoor work place, London; BSI. British Standards Institution BS EN 13201-2: 2003: Road lighting. Performance requirements, London: BSI. British Standards Institution BS ISO 15469: 2004: Spatial distribution of daylight. CIE standard general sky , London; BSI. 293


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British Standards Institution BS EN 50171: 2001: Central power supply systems, London: BSI. British Standards Institution BS EN 50172:2004, BS 5266-8: 2004: Emergency escape lighting system, London: BSI. British Standards Institution BS EN 55016: Specification for radio disturbance and intensity measuring apparatus and method, London: BSI. British Standards Institution BS EN 60061: Specification for lamp caps and holders together with gauges for the control of interchangeability and safety, London: BSI. British Standards Institution BS EN 60064: 1995+A4: 2007: Tungsten filament lamps for domestic and similar general lighting purposes. Performance requirements, London: BSI. British Standards Institution BS EN 60081: 1998, IEC 60081: 1997: Double-capped fluorescent lamps. Performance specifications, London: BSI. British Standards Institution BS EN 60192: 2001, IEC 60192: 2001: Low pressure sodium vapour lamps. Performance specifications, London: BSI. British Standards Institution BS EN 60238: 2004: Edison screw lampholders, London: BSI. British Standards Institution BS EN 60357: 2003: Tungsten halogen lamps (non-vehicle). Performance specification, London: BSI. British Standards Institution BS EN 60400:2000, IEC 60400: 1999: Lampholders for tubular fluorescent lamps and starterholders, London: BSI. British Standards Institution BS EN 60432: Incandescent lamps. Safety specifications, London: BSI. British Standards Institution BS EN 60570: 2003: Electrical supply track systems for luminaires, London: BSI. British Standards Institution BS EN 60598: Luminaires, London: BSI British Standards Institution BS EN 60601: Medical electric equipment: general requirements for human safety and essential performance, London: BSI. British Standards Institution BS EN 60601-2-41: Particular requirements for the safety of surgical luminaires and luminaires for diagnosis, London: BSI. British Standards Institution BS EN 60702: Mineral insulated cables and their terminations with a rated voltage not exceeding 750 V, London: BSI. British Standards Institution BS EN 60838: Miscellaneous lampholders, London: BSI. British Standards Institution BS EN 60896: Stationary lead acid batteries, London: BSI.

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British Standards Institution BS EN 60901:1996+A4: 2008: Single-capped fluorescent lamps. Performance specifications, London: BSI.


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British Standards Institution BS EN 60921: Ballasts for tubular fluorescent lamps. Performance requirements, London: BSI. British Standards Institution BS EN 60923: 2005: Auxiliaries for lamps. Ballasts for discharge lamps (excluding tubular fluorescent lamps). Performance requirements, London: BSI. British Standards Institution BS EN 60924: 1991: Specification for general and safety requirements for d.c. supplied electronic ballasts for tubular fluorescent lamps, London: BSI. British Standards Institution BS EN 60925: 1991: Specification for performance requirements for d.c. supplied electronic ballasts for tubular fluorescent lamps, London: BSI. British Standards Institution BS EN 60927: 2007: Auxiliaries for lamps. Starting devices (other than glow starters). Performance requirements, London: BSI.


British Standards Institution BS EN 60920: 1991: Ballasts for tubular fluorescent lamps. General and safety requirements, London: BSI.

British Standards Institution BS EN 60920: 1991: Ballasts for tubular fluorescent lamps. General and safety requirements, London: BSI. British Standards Institution BS EN 60969: 1993: Self-ballasted lamps for general lighting services. Performance requirements, London: BSI. British Standards Institution BS EN 61000: Safety requirements for electronic equipment for measurement, control and laboratory use, London: BSI. British Standards Institution BS EN 61047: 2004: D.C. or A.C. supplied electronic step-down convertors for filament lamps. Performance requirements, London: BSI. British Standards Institution BS EN 61048: 2006: Auxiliaries for lamps. Capacitors for use in tubular fluorescent and other discharge lamp circuits. General and safety requirements, London: BSI. British Standards Institution BS EN 61049: 1993: Specification for capacitors for use in tubular fluorescent and other discharge lamp circuits. Performance requirement, London: BSI. British Standards Institution BS EN 61056: Portable lead-acid cells and batteries (valve regulated type), London: BSI. British Standards Institution BS EN 61184:1997, IEC 61184: 1997: Bayonet lampholders, London: BSI. British Standards Institution BS EN 61195:2000, IEC 61195: 1999: Double-capped fluorescent lamps. Safety specifications, London: BSI. British Standards Institution BS EN 61199:2000, IEC 61199: 1999: Single-capped fluorescent lamps. Safety specifications, London: BSI. Industry Committee for Emergency Lighting (ICEL) ICEL: 1004: 2003: Requirements for the re-engineering of luminaires for emergency lighting use, London: ICEL. 295


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International Standards Organisation BS EN ISO 11197: 2004: Medical supply units, Geneva: ISO

23.2 Guidance American Conference of Governmental Industrial Hygienists (ACGIH), (2004) TLVs and BEIs Threshold limit values for chemical substances and physical agents, biological exposure indices, Cincinnati, OH: ACGIH. Chartered Institution of Building Services Engineers CIBSE Lighting Guide 6: The outdoor environment, London: CIBSE. Chartered Institution of Building Services Engineers CIBSE Factfile 2: Car park lighting — dilemma solved, London: CIBSE. Chartered Institution of Building Services Engineers CIBSE Technical Memorandum 35: Environmental performance toolkit for glazed facades, London: CIBSE. Commission Internationale de l’Eclairage CIE Publication 15:2004: Colorimetry, Vienna: CIE. Commission Internationale de l’Eclairage CIE Publication 107: 1994 : Review of the official recommendations of the CIE for the colors of signal lights, Vienna: CIE. Commission Internationale de l’Eclairage CIE Publication 112: 1994: Glare evaluation systems for use with outdoor sports and area lighting, Vienna: CIE. Commission Internationale de l’Eclairage CIE Publication 150: 2003: Guide on the limitation of the effects of obtrusive light from outdoor lighting installations, Vienna: CIE. Commission Internationale de l’Eclairage CIE Publication 154:2003: Maintenance of outdoor lighting systems, Vienna: CIE. Commission Internationale de l’Eclairage CIE S 015/E: 2005: Lighting of outdoor workplaces, Vienna: CIE. Commission Internationale de l’Eclairage CIE Publication 169: 2005: Practical design guidelines for the lighting of sports events for colour television and filming, Vienna: CIE. Commission Internationale de l’Eclairage CIE Publication 97: 2005: Guide on the maintenance of indoor electric lighting systems, Vienna: CIE. Department for Education and Science Building Bulletin 90, BB90, Lighting design for schools, London: DfES (now the Department for Children, Schools and Families). Department for Education and Science Building Bulletin 87, BB87, Guidelines for environmental design in schools, London: DfES (now the Department for Children, Schools and Families). Department for Education and Science Building Bulletin 77, BB77, Designing for pupils with special educational needs and disabilities in schools, London: DfES (now the Department for Children, Schools and Families).

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Illuminating Engineering Society of North America, The IESNA Lighting Handbook, 9th Edition, New York: IESNA. Illuminating Engineering Society of North America, ANSI/IESNA RP-27-96, Recommended practice for photobiological safety for lamps and lamp systems, New York: IESNA. Institution of Lighting Engineers, Guidance notes for the reduction of obtrusive light, ILE, Rugby. Institution of Lighting Engineers Technical Report 28: Measurement of road lighting performance on site, ILE, Rugby. Joint statement (SLL, ECA, ILE, LIF) Means of assessing equal and approved, 2004. Lighting Industry Federation, LED Guide – Light from the light emitting diode, 2005.


EBV Electronik, see www.ebv.com/thequintessence

Lam, RW, and Levitt, AJ, (1999) Canadian consensus guidelines for the treatment of seasonal affective disorder, Vancouver, BC: Clinical and Academic Publishing. NHS Estates Health Technical Memorandum 2022: Medical gas pipelines, London: NHS. Philips Lumileds Lighting Company, see www.philipslumileds.com Society of Light and Lighting SLL Code for lighting, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 1: Industrial lighting, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 2: Hospital & health care buildings, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 4: Sports lighting, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 5: Lecture, teaching and conference rooms, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 7: Office lighting, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 10: Daylighting and window design, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 11: Surface reflectance and colour, London: CIBSE. Society of Light and Lighting SLL Lighting Guide 12: Emergency lighting design guide, London: CIBSE. Society of Light and Lighting SLL Factfile 7: Environmental considerations for exterior lighting, London: CIBSE. Society of Light and Lighting SLL Factfile 9: Lighting and the 2006 Building regulations, London: CIBSE.

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Society of Light and Lighting SLL Factfile 10: Providing visibility for an ageing workforce, London: CIBSE.

23.3 References Berman, S.M., (1992) Energy efficiency consequences of scotopic sensitivity, Journal of the Illuminating Engineering Society, 21, 3–14. Berman, S.M., Navvab, M., Martin, M.J., Sheedy, J. and Tithof, W., (2006) A comparison of traditional and high colour temperature lighting on the near acuity of elementary school children, Lighting Research and Technology, 38, 41–52. Blackwell, H.R., (1959) Development and use of a quantitative method for specification of interior illumination levels on the basis of performance data, Illuminating Engineering, 54, 317–353. Boff, K.R., and Lincoln, J.E., (1988) Engineering data compendium: Human perception and performance, Wright-Patterson AFB, OH: Harry G. Armstrong Aerospace Medical Research Laboratory. Boyce, P.R., (1979) The effect of fence luminance on the detection of potential intruders, Lighting Research and Technology, 11, 78–84. Boyce, P.R., (2003) Human Factors in Lighting, London: Taylor and Francis. Boyce, P.R., (2006) Lemmings, light and health, Light and Engineering, 14, 24–31. Boyce, P., Eklund, N., Mangum, S., Saalfield, C., and Tang, L., (1995) Minimum acceptable transmittance of glazing, Lighting Research and Technology, 27, 145–152. Boyce, P.R., Eklund, N.H., Hamilton, B.J., and Bruno, L.D., (2000) Perceptions of safety at night in different lighting conditions, Lighting Research and Technology, 32, 79–92. Boyce, P.R., Hunter, C.M., and Howlett, O., (2003a) The benefits of daylight through windows, Troy, NY: Lighting Research centre. Boyce, P.R., Akashi, Y., Hunter, C.M. and Bullough, J.D., (2003b) The impact of spectral power distribution on the performance of an achromatic visual task, Lighting Research and Technology, 35, 141–161. Boyce, P.R., Veitch, J.A., Newsham, G.R., Jones, C.C, Heerwagen, J., Myer, M. and Hunter, C.M., (2006a) Switching and dimming behaviour in offices, Lighting Research and Technology, 38, 358–378. Boyce, P.R., Veitch, J.A,, Newsham, G.R., Jones, C.C., Heerwagen, J., Myer, M. and Hunter, C.M., (2006b) Lighting quality and office work: Two field simulation experiments, Lighting Research and Technology, 38, 191–223. Brainard, G.C., Hanifin, J.P., Greeson, J.M., Byrne, B., Glickman, G., Gerner, E. and Rollag, M.D., (2001) Action spectrum for melatonin regulation in humans: Evidence for a novel circadian photoreceptor. Journal of Neuroscience 21, 6405–6412.

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Campbell, S.S., Dawson, D. and Anderson, M.W., (1993) Alleviation of sleep maintenance insomnia with timed exposure to bright light, J. Am. Geriartr. Soc., 41,829–836. Commission Internationale de l’Eclairage (CIE) (1989) CIE Publication 81: Mesopic photometry: History, special problems and practical solutions, Vienna: CIE. Crisp, V.H.C. and Henderson, G., (1982) The energy management of artificial lighting, Lighting Research and Technology 14, 193–206. Cuttle, C., (1979) Subjective assessments of the appearance of special performance glazing in offices, Lighting Research and Technology, 11, 140–149. Cuttle, C, (2003) Lighting by design, London: Architectural Press.


Brons, J.A., Bullough, J.D. and Rea, M.S., (2008) Outdoor site-lighting performance: A comprehensive and quantitative framework for assessing light pollution, Lighting Research and Technology, 40, 201–224.

Cuttle, C. (2007) Light for Art’s Sake: Lighting for artworks and museum displays, London: Butterworth-Heinemann. Czeisler, C.A., Kronauer, R.E., Johnson, M.P., Allen, J.S. and Dumont, M., (1988) Action of light on the human circadian pacemaker: Treatment of patients with circadian rhythm sleep disorders, in J.Horn (ed) Proc. Conf. Sleep '88. Stuttgart, Germany: Verlag. Dalke, H., Littlefair, P. and Loe, D, (2003) Lighting and colour design for hospital environments, Watford: Building Research Establishment. Dubois, M-C, (2003) Shading devices and daylight quality: An evaluation based on simple performance indicators, Lighting Research and Technology, 35, 61–76. Eklund, N.H. and Boyce, P.R., (1996) The development of a reliable, valid, and simple office lighting survey, Journal of the Illuminating Engineering Society, 25, 25–40. Elohoma, M and Halonen, L., (2006) New model for mesopic photometry and its application to roadway lighting, Leukos, 2, 263–293. Figueiro, M.G., Rea, M.S. and Bullough, J.D., (2006) Does architectural lighting contribute to breast cancer, Journal of Carcinogenesis, 5. 20. Fotios, S.A. and Cheal, C., (2007a) Lighting for subsidiary streets – lamps of different SPD, Part 1 – Visual performance, Lighting Research and Technology, 39, 215–232. Fotios, S.A. and Cheal, C., (2007b) Lighting for subsidiary streets – lamps of different SPD, Part 1 – Brightness, lighting research and technology, 39, 233–249. Goodman , C. Housing for people with sight loss: A Thomas Pocklington Trust design guide EP84, Bracknell: IHS BRE Press, 2008. Hawkes, R.J., Loe, D.L. and Rowlands, E., (1979) A note towards the understanding of lighting quality, Journal of the Illuminating Engineering Society, 8, 111–120. 299


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absorption filters 91 accent lighting 96, 193, 194 accommodation, visual 26 acoustic characteristics 93–94 adaptation, visual 24–25, 29, 121 adaptation glare 37 air handling luminaires 91–92 aluminium 85, 89, 279 amalgams 62 ambient temperature 79 aperture mode 43 arc tubes 70, 72 architectural integration 120, 126 area lighting emergency lighting 142–143 exterior workplaces 241–243 security lighting 248, 249–250 see also floodlighting art galleries 198–202 arts studios 187, 189 assembly halls 187, 190 atria 136 autoleak transformer 111–112 automatic controls 127–128, 158 awnings 139

Index

Index

baffles 89–90 ballasts 103, 104, 109–112 see also electronic control gear battery powered systems 145, 153 beam spread 105 bedrooms 216, 218 borrowed light 137 brightness perception 42, 133 British Standards (BS) daylight requirements 133 emergency lighting 140–141, 142 luminaires 102–104 road lighting luminaires 106 building facades 248, 250 building management systems 147 Building Regulations 118, 140 building services, integration with 126 bulb forms and materials fluorescent lamps 61, 63 high pressure mercury lamps 65–66 high pressure sodium lamps 73 incandescent lamps 58 low pressure sodium lamps 70 metal halide lamps 68 tungsten halogen lamps 60 burning position 79 cabling see electrical circuits candles 82 canteens 163, 167, 181–182 capacitors, standards 103, 104 car parks 248, 253 care homes 214–219 cathodoluminescence 52 CCT see correlated colour temperatures (CCT) CCTV surveillance 247 CE mark 101, 102–104 ceilings height 158–159, 169 luminous 172 ceramics 86 certification 100–104, 155

303


Index 304

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chemical industries 240–241 chemiluminescence 52 choke ballasts 110 chromaticity, glazing 134 chromaticity diagrams 8–10 chromium, reflectance 89 CIE chromaticity diagrams 7–10 classification, indoor luminaires 105 Colour Matching Functions 7–8 colour rendering index (CRI) 12–13, 289 colour spaces 10–11 daylight spectra 56 publication list 296 Spectral Luminous Efficiency Functions 2 standard observers 1–2 standard sky types 54–55 CIELAB 11 CIELUV 11 circulation areas hospitals 206, 207 industrial premises 181 offices 164, 167 quasi-domestic lighting 216 classification, luminaires 105–108, 148 classrooms 187, 189 cleaning 278–280 clerestory windows 135 colour appearance 63, 119, 167–168 see also correlated colour temperatures (CCT) colour filters 90–91 colour gamut 13 Colour Matching Functions 7–8 colour order systems 14–15 colour perception 42 colour properties 78 fluorescent lamps 63 high pressure mercury lamps 66 high pressure sodium lamps 74 lamp types 80–81 light emitting diodes (LEDs) 76 low pressure sodium lamps 70 metal halide lamps 69 colour rendering index (CRI) 289 colour rendering requirements 118, 119 educational premises 187 exterior workplaces 239 hospitals 203 industrial lighting 175 offices 167, 168 retail premises 193–194 security lighting 249 colour spaces 10–11, 14–15 colour stability 68 colour temperatures see correlated colour temperatures (CCT) colour thresholds 28, 31 colour vision 23–24, 44–45 colourimetry 7–15 commissioning, emergency lighting 154–155 communal dwellings 214–219 compact fluorescent lamps 63–64 computer rooms 187, 189 computer screens see display screens conservation lighting 198–199 Construction Products Directive 140 contrast, luminance 26–27, 47 control gear 109–114 requirement by lamp type 80–81 standards 102


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Index

control room lighting 178–180 control systems 115–116, 125, 287 educational premises 188 emergency lighting 147 security lighting 256 correlated colour temperatures (CCT) 11–12 daylight 56–57 lamp types 80–81 offices 167–168 costs 121, 287 cove lighting 171 CRI (colour rendering index) 289 DALI systems 116 daylight 52–57 availability 55–56, 131–133 colour temperatures 56–57 luminance distribution 54–55, 131–132 spectrum 56 sun path and position 52–54 daylight factor 131–133, 289–290 daylighting 129–139 advantages and disadvantages 129–130 contribution to room brightness 133 educational premises 186 hospitals 203 industrial lighting 174 integration with 120, 126–128 maintenance 137–139 museums and galleries 198 offices 158, 172 quasi-domestic lighting 214 remote distribution 136–137 retail premises 192 roles 124 task illumination 133 thermal problems 139 types 133–135 visual problems 137–139 diffuse reflectors 88, 89 digital control systems 116 dimming dimmers 256 lamp types 79, 80–81 photo-electric controls 128 dining halls 216, 219 direct lighting 94, 168–169 direct/indirect lighting 95, 170 discharge tubes ballasts 109–112 compact fluorescent 63–64 diameters and lengths 62 electronic control gear 112–114 fluorescent lamps 61, 62, 63–64 high pressure mercury lamps 65 high pressure sodium lamps 72 low pressure sodium lamps 70 metal halide lamps 68 display lighting 195–196 display screens 156–157, 165–166, 178–180 see also veiling reflections disposal of lighting equipment 79, 94, 286 DMX 512 116 downlights 96 drama studios 187, 190 ducted exhaust systems 91–92 dysprosium lamp 67

305


Index 306

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earthing 85 economic service life see service life educational premises 185–190 efficacy see luminous efficacy efficiency, luminaires 91 electric discharges 49–50 electrical circuits emergency lighting 146–147 luminaires 84–85 electrical connections, luminaires 84–85 electrical insulation 84, 108 electrical protection 107–108, 147, 215 electrical safety hospital lighting 204–205 luminaire classification 107–108 quasi-domestic lighting 215 standards 100–103 electrical standards 100–103 electrical testing, emergency lighting 154–155 electrodes, lamp 61, 65, 72 electroluminescence 51 electroluminescent (EL) panels 76–77 electro-magnetic compatibility (EMC) 146, 205 Electro-Magnetic Compatibility (EMC) Directive 100, 101, 102 electromagnetic control gear 109–112 electronic control gear 112–114 emergency lighting 140–155, 259–260 control rooms 179 hospitals 204 industrial premises 177 quasi-domestic premises 215–216 standards 103 emergency power sources 145–146 EN (Euronorm) standards 100–104 end caps 72 ENEC mark 101, 103–104 energy consumption 126–127 see also power demand energy efficiency 120, 215, 290 entrances hospitals 206 office buildings 164 quasi-domestic buildings 217 security lighting 248, 251 environmental conditions 106–107, 174 environmental issues disposal of lighting equipment 79, 94, 286 integration with the surroundings 128 light trespass 122–123, 238, 260 skyglow 123–124, 238, 243, 290 environmental zones 122, 124 escape route lighting 141–142 Euronorm (EN) standards 100–104 European Union Directives 100–102 emergency lighting 140 lamp recycling 94 exterior lighting 98–100 classification 105–108 glare control 249 illuminance measurement 274–275 integration with the surroundings 128 light trespass and skyglow 122 maintenance factor 285 public amenity areas 232–233 workplace lighting 236–244 see also security lighting; sports lighting eye movements 17–18


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Index

fibre-optic lighting 202 filament design 58 filling gas see gas filling filters 90–91 fire protection 108, 215 fire safety lighting see emergency lighting flammability, mounting surfaces 108 flicker 41 floodlighting 243 luminaires 99–100, 105 fluorescence see luminescent light sources fluorescent lamps 60–64 baffles 89 colour appearance and rendering 63 compact 63–64 diameters and lengths 62 electromagnetic control gear 109–111 gas filling 61–62 induction lamps 74–75 summary of characteristics 80 fuel industries 240–241 games rooms 216, 218 gas filling fluorescent lamps 61–62 high pressure mercury lamps 65 high pressure sodium lamps 73 incandescent lamps 58–60 low pressure sodium lamps 70 metal halide lamps 66–67 gas lighting 83 gatehouses 248, 251 general colour rendering index (CRI) see colour rendering index (CRI) General Lighting Service (GLS) lamp 57–58 generators 146 glare 37–39 glare control 118 daylighting 137–138 educational premises 187 exterior workplaces 239 industrial lighting 176, 181 office lighting 166–167 road lighting 223 security lighting 249 glass absorption filters 91 luminaires 85 spectral transmittance 91, 134 glazing see windows glossiness perception 43 glow starters 110 GLS (General Lighting Service) lamp 57–58 halls of residence 214–219 halophosphates 61 hazardous situations 144, 174, 177 health issues 288 daylighting 130 visual discomfort 37–44 high intensity discharge (HID) lamps control gear 111–114 high mast floodlighting 243 high pressure mercury lamps 64–66, 80 high pressure sodium lamps 70–74, 81, 112 high risk areas see hazardous situations hospitals 203–213 housing see multi-occupancy dwellings; private houses hue perception 43

307


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Index

ignition see starters/ignitors illuminance 4 daylighting 131 distribution 119, 275–276 daylighting 138 exterior lighting 98–100 interior lighting 94–97 measurement 272–275 offices 164–165 optical control 86–91 maintained illuminance 280 measurement 155, 272–276 meters 271 units 5–6 uniformity 37, 118, 276 visual performance 33–34 illuminances, recommended 118 educational premises 187 emergency lighting 143–144 exterior workplaces 238 hospitals 206–213 industrial lighting 177–182 museums and galleries 199 offices 162–166 quasi-domestic lighting 216 retail premises 192–193 road lighting 220–225 security lighting 247–248 sports lighting 261–266 illuminant mode 43 incandescence 48–49 incandescent lamps 57–58, 80 indirect lighting 158–159, 169–170 luminaires 95 individual control 288 indoor arenas 268 indoor lighting see interior lighting induction lamps 74–75 industrial lighting 172 inspection, emergency lighting 153–154 installation, emergency lighting 153 instrumentation 271–272 insulation see electrical insulation integrated lighting 243 integration issues 125–128 interference filters 91 interior design 126 interior lighting architectural integration 120, 126 classification 105 illuminance measurement 272–274 maintenance factor 280–285 types 94–97 visual function 118 International Protection (IP) system 106–107 ionised gas discharge 49–50 IT rooms 187, 189 kitchens 163, 216, 218 laboratory lighting 187, 189 lamp lumen maintenance factor (LLMF) 281 lamp replacement 278 lamp size 79 lamp survival factor (LSF) 78, 149, 281–282 lampholders, standards 103 lecture halls 187, 189 LEDs (light emitting diodes) 75–76, 81, 114, 287

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Index

legal requirements 118 emergency lighting 140 industrial lighting 173–174 office lighting 156–157 libraries 163, 167, 187, 190 life see service life light distribution see illuminance, distribution light emitting diodes (LEDs) 75–76, 81, 114, 287 light oscillation 177 light output ratio (LOR) 91 light pipes 136–137 light pollution see light trespass; skyglow light radiation 48–52 electric discharges 49–50 luminescence 51–52 spectral power distribution 48–49 light shelves 138 light spectrum 1 light trespass 122–123, 238, 260 light-boxes 202 lighting columns 98–99, 255–256 see also road lighting lighting controls see control systems lighting design 117–128, 288–290 lightness perception 42, 43 LLMF (lamp lumen maintenance factor) 281 LMF (luminaire maintenance factor) 282–283 loading bays 239–240 localised lighting exterior workplaces 244 industrial lighting 183 offices 170–171 see also task lighting LOR (light output ratio) 91 louvres baffles 90 solar shading 138–139 low pressure sodium lamps 69–70, 81, 111–112 low voltage light sources 114 Low Voltage (LV) Directive 100, 101 LSF (lamp survival factor) 78, 149, 281–282 lumen maintenance 78, 281 luminaire maintenance factor (LMF) 282–283 luminaires 84–108 certification 100–104, 155 classification 105–108, 148 cleaning 278–280 construction 86 efficiency 91 electrical connections 84–85 emergency lighting 145, 147–149 exterior lighting 98–100 interior lighting 94–97 maintenance 226 materials 85–86 optical control 86–91 self-contained 145, 147 standards 100–106 substitutions 128 thermal characteristics 91–93, 108 luminance 4 daylighting 131–132 measurement 276 meters 271–272 units 5–6 luminance coefficient 4, 226–228 luminance contrast 26–27, 47 luminescent light sources 51–52, 149

309


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Index

luminous ceilings 172 luminous efficacy 78, 80–81 luminous efficiency functions 2, 20 luminous exitance 6 luminous flux 3, 77 distribution, luminaire classification 105 as a function of temperature, fluorescent lamps 62 lamp types 80–81 luminous intensity distribution, luminaire classification 105–106 emergency lighting 143 measurement 3 LV (Low Voltage) Directive 100 magnifiers 184 maintained illuminance 280 maintenance 278–286 daylighting 139 emergency lighting 153–154 lighting design 121, 280 road lighting 226 maintenance factor (MF) 280–285 manual switching 115, 126–127 materials, luminaires 85–86 measurement methods 3–6, 272–277 measurement units 5–6 meeting rooms 167, 187, 190 mercury gas discharge 50 mercury vapour lamps see fluorescent lamps; high pressure mercury lamps mesopic vision 25, 121, 289 mess rooms 181–182 metal halide lamps 66–69, 80, 112 MF (maintenance factor) 280–285 modes of appearance 42–44 Modified Photopic Observer 2 motion detectors see presence detectors mounting surfaces, flammability 108 multi-occupancy dwellings 254 multi-phosphors 61, 63 museums 198–202 music rooms 187, 190 night vision 2 noise rating (NR) 93–94 object modes 43 occupant controls 126–127, 288 office lighting 156–172 oil lamps 82–83 operating conditions hazardous situations 144, 174, 177 industrial lighting 174 luminaire classification 106–107 performance verification 270 operating theatres 212–213 operational costs 121, 287 optical control, luminaires 86–91 output ranges, lamp types 80–81 overhangs 138 overheating 108, 215 painted surfaces 89, 161, 279 parks see public areas PCA (polycrystalline alumina) 72 pedestrian areas 224–225, 230–233 luminaires 98–99 see also public areas perception, visual 41–44

310


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Index

performance standards 104 verification 270–277 visual 32–34 perimeter fences 248, 250–251 petrochemical industries 240–241 phosphor coatings 61 photochemical adaptation 25 photo-electric controls 115, 127–128, 256 photoluminescence see luminescent light sources photometric testing 155 photometry 3–6, 272–277 photopic vision 2, 3, 14, 25, 121 plant rooms 164, 167, 182 plastics 85, 91, 279 plenum exhaust systems 91–92 ‘ply-glass’ tube 70 polycrystalline alumina (PCA) 72 post top luminaires 98–99 power demand 77, 120 see also energy consumption power factor 77–78 power ranges, lamp types 80–81 presence detectors 115, 256 privacy problems, daylighting 139 private houses, security lighting 253–254 protection, luminaire classification 106–107 public areas 248 amenity areas 232–233 public parks 248, 253 security lighting 248, 252–253 see also pedestrian areas radioluminescence 51 railway sidings and yards 241–242 reception areas 164, 206, 216 recycling regulations 94 reflectance 4–5 computer screens 156–157 luminaire reflectors 89 measurement 276–277 units 5–6 road surfaces 226–228 surface finishes 159–161 reflectors 86–88 refractors 88 relative visual performance (RVP) 34 residential accommodation 214–219 restaurants 163, 167 Restriction of Hazardous Substances Directive (RoHS) 94 restrike time 79 retail lighting 191–197 road lighting 220–235 luminaires 98, 106, 228–230 road surfaces, reflection properties 226–228 RoHS (Restriction of Hazardous Substances Directive) 94 rooflights 135–136 room surface maintenance factor (RSMF) 284–285 rotating machinery 177 RSMF (room surface maintenance factor) 284–285 run-up 65, 78–79, 80–81 RVP (relative visual performance) 34 safety hospital lighting 204–205 industrial lighting 177 quasi-domestic lighting 215 standards 100–103 see also electrical safety; emergency lighting; fire protection

311


Index 312

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Page 56

safety signs 142, 149 saturation perception 43 scandium lamp 67 schools see educational premises science laboratories 187, 189 scotopic vision 2, 3, 14, 25 scotopically enhanced lighting 289 scotopic/photopic ratio 14 secondary reflector luminaires 99 security lighting 201, 216, 245–256 selection process 124–125 self-contained luminaires 145, 147 seminar rooms 167, 187, 190 service life 78, 149 lamp replacement 278 lamp types 80–81 service stations 248, 253 shading devices, glare reduction 138–139 shadows 40–41 shape perception 42 shops see retail lighting showcase lighting 202 signage, escape routes 142 Signs Directive 140 size perception 42 sky types, CIE standard 54–55 skyglow 123–124, 238, 243, 290 skylight 54–57 skylights 135–136 slave luminaires 147–148 Society of Light and Lighting (SLL) Lighting Guides 297 sodium gas discharge 50 sodium lamps see low pressure sodium lamps solar gain 139 solar shading 135, 138–139 see also daylight; sun path and position spatial thresholds 26–27, 28–30 Spectral Luminous Efficiency Functions 2 spectral power distribution 3, 7–8, 48–49 high pressure sodium lamps 71 metal halide lamps 67 scotopic/photopic ratio 14 spectral radiant exitance 48 spectral sensitivity 1–2, 7–8, 14, 20 spectral transmittance 91, 134 specular reflectors 86–88, 89 sports lighting 257–269 spotlights 96, 105 spread reflectors 88, 89 stable running 65 stadia see sports lighting Standard Photopic Observer 1–2 Standard Scotopic Observer 2 standard sky types 54–55 standards daylight requirements 133 emergency lighting 140–141, 142 luminaires 100–106 references 293–296 road lighting luminaires 106 standby lighting 144 starters/ignitors fluorescent lamps 110 high intensity discharge (HID) lamps 112 high pressure mercury lamps 65 standards 103, 104 see also electronic control gear steel 85, 279


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Index

storage areas 164, 180–181, 182 street lighting, standards 103 see also pedestrian areas; road lighting stroboscopic effects 177, 184 study bedrooms 216, 218 substitutions 128 sun path and position 52–54 suprathreshold performance 32–34 surface mode 43, 44 surface reflectance see reflectance surfaces see mounting surfaces surge-protection devices 147 sustainability issues 120–121, 290 see also environmental issues swimming pools 266, 268–269 switching behaviour 126–127 system choice 124–125 task lighting 170–171 daylighting 133 requirements 118 task lights 97 visual inspection 183–184 task performance 33 television sports broadcasting 258–259 temperature, running 79 temporal thresholds 28, 30–31 testing, emergency lighting 153–154 thermal characteristics, luminaires 91–93 thermal problems overheating 108, 215 solar gain 135, 139 thermoluminescence 52 three colour metal halide lamp 67 through wiring 85 thulium lamp 67 timers 115, 256 tin halide lamp 67 track systems, standards 103 traffic route lighting 225–226 transformers low voltage light sources 114 standards 103, 104 transparency perception 43 tri-phosphors 61, 63 tritium powered signs 149 trunking systems 84–85 tubes see discharge tubes tungsten halogen lamps 59–60, 114 tunnel lighting 233–235 types of system luminaires 94–100 Unified Glare Rating (UGR) 39 uninterruptible power supplies (UPS) 145–146 units of measurement 5–6 urban centres 232–233 see also public areas utility rooms 218 veiling reflections 39–40 daylighting 137 museums and galleries 200 see also display screens vision, human 16–47 visual accommodation 26 visual acuity 27 visual adaptation 24–25, 29, 121 visual aids 184, 186

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Index

visual amenity 119–120, 290 visual anomolies 44–47 visual attributes 42–43 visual discomfort 37–44 visual field 16–17 visual function 118 visual impairment 45–47 visual inspection, lighting for 183–184 visual perception 41–44 visual performance 32–34 visual problems 37–44 see also glare control; veiling reflections visual search 34–36 visual thresholds 26–32, 45–47 volume mode 43, 44 wall washers 97, 195 wallpacks 100 warehouses 180–181 Waste Electrical and Electronic Equipment Directive (WEEE) 94 white high pressure sodium lamp 74 windows 133–134 blinds 139, 161 glare reduction 137 maintenance issues 139 wiring see electrical circuits Workplace Directive 140 workshops 164, 167, 175–176, 182 workstation lighting 170–171 see also display screens

314

The SLL Lighting Handbook

The SLL Lighting Handbook

IESNA Lighting Handbook

The Automated Lighting Programmer's Handbook

Set Lighting Technicians Handbook

The Automated Lighting Programmer's Handbook, Second Edition

Handbook Of Interior Lighting Design

IESNA Lighting Handbook 9th Ed

The design of lighting

Handbook Of Interior Lighting Design E

Lighting the Way

Solar Lighting

LED Lighting: A Primer to Lighting the Future

Interior lighting

Garden lighting

LED Lighting: A Primer to Lighting the Future

Set Lighting Technician's Handbook, Third Edition: Film Lighting Equipment, Practice, and Electrical Distribution

Photographic Lighting Simplified

Photographic Lighting Simplified

Lighting efficiency applications

LightWave v9 lighting

Emergency and Security Lighting

LightWave 3D 8 Lighting

Photographic Lighting: Essential Skills

Lighting Modern Buildings

Lighting by Design

Basics Photography: Lighting

LightWave 3D 7.5 Lighting

Digital Lighting & Rendering

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The SLL Lighting Handbook