The Institution of Lighting Engineers
`
`The Outdoor
`Lighting Guide
`
`Ultravision's Exhibit No. 2019, IPR2020-01638
`Page 001
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`

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`The Outdoor Lighting Guide
`
`The Institution of Lighting Engineers (ILE) is the UK and Ireland’s largest
`and most influential professional lighting association, dedicated solely to
`excellence in lighting. Founded in 1924 as the Association of Public Lighting
`Engineers and licensed by the Engineering Council, the ILE has evolved to
`include lighting designers, architects, consultants and engineers amongst its
`2,500-strong membership.
`
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`The Outdoor Lighting Guide
`
`The Institution of Lighting Engineers
`
`Ultravision's Exhibit No. 2019, IPR2020-01638
`Page 004
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`

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`First published 2005
`by Taylor & Francis
`2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN
`Simultaneously published in the USA and Canada
`by Taylor & Francis
`711 Third Ave, New York, NY 10017
`Taylor & Francis is an imprint of the Taylor & Francis Group
`© 2005 The Institution of Lighting Engineers
`Typeset in Sabon by
`Integra Software Services Pvt. Ltd, Pondicherry, India
`
`All rights reserved. No part of this book may be reprinted or
`reproduced or utilised in any form or by any electronic, mechanical, or
`other means, now known or hereafter invented, including photocopying
`and recording, or in any information storage or retrieval system, without
`permission in writing from the publishers.
`British Library Cataloguing in Publication Data
`A catalogue record for this book is available
`from the British Library
`Library of Congress Cataloging in Publication Data
`A catalog record for this book has been requested
`
`ISBN 978-0-4153-7007-3
`
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`Contents
`
`xi
`xiv
`xv
`
`1
`
`Foreword
`Disclaimer
`Abbreviations and symbols for quantities, units and notation
`
`1 Visual effects of lighting
`1.1
`Introduction 1
`1.2
`Light 1
`1.2.1 Lighting levels 1
`1.2.2 Task performance 1
`1.2.3 Appearance 2
`Flux, intensity, illuminance, luminance and brightness 2
`1.3
`1.4 Glare 3
`1.5
`Positive and negative contrast 4
`1.6
`Absorption and reflection 4
`1.7
`Radiation 4
`1.8
`Apparent colour 5
`1.9
`Colour rendering 7
`1.10 Daytime appearance 8
`1.11 The outdoor environment 8
`
`10
`
`2 Social and environmental elements
`2.1
`Introduction 10
`2.2
`Crime and disorder 11
`2.2.1 Introduction 11
`2.2.2 The effects of street lighting on crime and disorder 11
`2.2.3 Improved street lighting and crime
`prevention: Are there alternatives? 13
`2.2.4 The role of lighting in the
`development of crime control strategies 14
`Light pollution 16
`2.3.1 Adverse effects of outdoor lighting 16
`2.3.2 Influence of surrounding environment 17
`2.3.3 Relevant lighting parameters 18
`
`2.3
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`vi Contents
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`Recommended limits for lighting parameters 19
`2.3.4
`2.3.5 Design guidelines 19
`2.3.6 Methods of mitigation 21
`2.3.7
`Illustrations of luminaire
`accessories for limiting obtrusive light 22
`2.4 Strategic urban lighting plans 24
`2.4.1
`Introduction 24
`2.4.2 Origins of the urban lighting plan 24
`2.4.3
`Lighting strategy methodology 25
`2.4.4
`The aims of a strategic urban lighting plan 27
`2.4.5
`The main factors in the success of lighting strategies 27
`2.4.6
`The effectiveness of lighting strategies 31
`2.4.7
`Conclusions 32
`2.5 Health and Safety 33
`2.5.1
`Introduction 33
`2.5.2
`The body of law 34
`2.5.3 Duty of Care 34
`2.5.4 Qualified and absolute duties 35
`2.5.5 Health and Safety hierarchy 35
`2.5.6
`The Health and Safety at Work etc. Act 35
`2.5.7
`The Management of Health
`and Safety at Work Regulations 36
`The Provision and Use of
`Work Equipment Regulations 38
`The Lifting Operations and
`Lifting Equipment Regulations 39
`2.5.10 The Construction, Design
`and Management Regulations 39
`2.5.11 The Construction (Health,
`Safety and Welfare) Regulations 41
`2.5.12 The Electricity at Work Regulations 41
`2.5.13 Electricity Safety, Quality and
`Continuity (ESQC) Regulations 43
`2.5.14 Lighting and Health and Safety Legislation 43
`2.5.15 BS 7671 – Requirements for Electrical
`Installations (The IEE Wiring Regulations) 44
`2.5.16 The ILE Code of Practice for
`Electrical Safety in Highway Operations 44
`2.5.17 National (Scottish) Vocational
`Qualification NVQ/SVQ 45
`2.5.18 Waste management 45
`2.6 Waste management 45
`2.6.1
`Introduction 45
`2.6.2
`Legislation 47
`
`2.5.8
`
`2.5.9
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`Contents
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`vii
`
`55
`
`Responsible bodies 50
`2.6.3
`2.6.4 Waste 51
`
`3 Equipment
`3.1 Introduction 55
`3.2 Light sources 55
`3.2.1
`Introduction 55
`3.2.2
`Lamp characteristics 56
`3.2.3
`Light generation 58
`3.2.4
`Principal lamp type characteristics 59
`3.2.5 Other light sources 69
`3.3 Control gear 71
`3.3.1
`Introduction 71
`3.3.2
`Role of control gear 71
`3.3.3
`Requirement for control gear 72
`3.3.4
`Important characteristics 72
`3.3.5
`Potential problems 75
`3.4 Luminaires 76
`3.4.1 General 76
`3.4.2
`Luminaire types 76
`3.4.3 Materials and construction 98
`3.4.4
`Light control 107
`3.4.5
`Performance and standards 115
`3.5 Switching controls 118
`3.5.1
`Introduction 118
`3.5.2
`Considerations 118
`3.5.3
`Choice of control 118
`3.5.4
`Recommendations 122
`3.6 Supports 123
`3.6.1
`Introduction 123
`3.6.2
`Building mountings 123
`3.6.3
`Illuminated bollards 124
`3.6.4
`Lighting columns 124
`3.6.5
`Poles 131
`3.6.6 Hinged lighting columns 132
`3.6.7 High masts 133
`3.6.8
`Catenaries 136
`3.6.9
`Corrosion protection 136
`3.6.10 Foundations 137
`3.6.11 Inspection and maintenance 137
`3.7 Maintenance 138
`3.7.1
`Introduction 138
`3.7.2 Maintenance schedule 138
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`145
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`viii Contents
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`3.7.3 Reactive maintenance 138
`3.7.4 Preventative maintenance 140
`
`4 Techniques for particular applications
`4.1 Introduction 145
`4.2 Town and city centres 145
`4.2.1 Introduction 145
`4.2.2 The visual needs of pedestrians 147
`4.2.3 Traffic lighting versus pedestrian lighting 148
`4.2.4 The role of anti-pollution measures 150
`4.2.5 New lighting in practice 151
`4.2.6 Conclusions 152
`4.2.7 Recommendations 152
`4.3 Lighting and closed circuit television (CCTV) 153
`4.3.1 Introduction 153
`4.3.2 CCTV applications 153
`4.3.3 CCTV systems 154
`4.3.4 Recommendations 157
`4.4 Transport interchanges 160
`4.4.1 General 160
`4.4.2 Daylight 161
`4.4.3 Colour 162
`4.4.4 Information displays, advertisements and CCTV 162
`4.4.5 Controls 162
`4.4.6 Emergency lighting 163
`4.4.7 Heritage buildings 163
`4.4.8 Characteristics of different interchanges 163
`4.4.9 Recommendations 165
`4.5 Effect lighting 168
`4.5.1 Introduction 168
`4.5.2 Scope 168
`4.5.3 Prime considerations 171
`4.5.4 Techniques in design 181
`4.5.5 Water features 186
`4.5.6 Assessment of completed projects 187
`4.5.7 Summary 188
`4.5.8 Recommendations 188
`4.6 Exterior work areas 189
`4.6.1 Introduction 189
`4.6.2 General considerations 189
`4.6.3 Building sites 191
`4.6.4 Rail – sidings/marshalling yards/goods depots 191
`4.6.5 Sea – dockyards/container terminals/jetties 193
`4.6.6 Sales areas – car forecourts 194
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`Contents
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`ix
`
`4.8
`
`Coal mining – open cast 194
`4.6.7
`Loading bays 195
`4.6.8
`Sewage/water treatment works 196
`4.6.9
`Petrol stations 197
`4.6.10
`Recommendations 198
`4.6.11
`4.7 Hazardous areas 200
`4.7.1
`Introduction 200
`4.7.2
`Hazardous area classifications 200
`4.7.3
`Standards 204
`4.7.4
`Types of protection for lighting systems 207
`4.7.5
`Selection of equipment for use in hazardous areas 209
`4.7.6
`Recommendations 211
`Sport 211
`4.8.1
`Introduction 211
`4.8.2
`Standards and codes of practice 211
`4.8.3
`The visual task 213
`4.8.4
`Principles 213
`4.8.5
`Design considerations 216
`4.9 High mast lighting 219
`4.9.1
`Introduction 219
`4.9.2
`Use of high mast lighting 223
`4.9.3
`General design recommendations 224
`4.9.4
`Practice in relation to type of location 226
`4.10 Festival lighting 229
`4.10.1
`Introduction 229
`4.10.2
`Various forms of festival decorations 229
`4.10.3 Health and Safety 230
`4.10.4
`Approval for erection of decorations 231
`4.10.5 Highway safety 231
`4.10.6
`Switch-on 231
`4.10.7 Maintenance 232
`4.10.8
`Removal 232
`4.11 Traffic routes 232
`4.11.1 General principles 232
`4.11.2
`Road surfaces 233
`4.11.3
`Appearance 233
`4.11.4 Wet conditions 234
`4.11.5
`Considerations 235
`4.11.6
`Choice of lamp type 235
`4.11.7
`Choice of luminaire 236
`4.11.8
`Supports 236
`4.11.9
`Advantages of road lighting 238
`4.11.10 Recommendations 238
`4.11.11 Vehicular tunnels 242
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`x Contents
`
`4.12 Residential areas 244
`4.12.1
`Introduction 244
`4.12.2
`Considerations 245
`4.12.3
`Choice of lamp type 245
`4.12.4
`Choice of luminaire 245
`4.12.5
`Supports 246
`4.12.6
`Recommendations 247
`4.12.7
`Footpaths 248
`4.12.8
`Cycle tracks 249
`4.12.9
`Traffic calming 250
`4.12.10 Parking areas 251
`4.12.11 Pedestrian underpasses 252
`4.13 Car parks 255
`4.13.1 General 255
`4.13.2
`Environmental issues 255
`4.13.3
`Choice of equipment 255
`4.13.4
`Light sources 256
`4.13.5 Design considerations 256
`4.13.6 Hours of operation 257
`4.13.7 Maintenance 258
`4.13.8
`Recommendations 258
`4.14 Security lighting 258
`4.14.1 General 258
`4.14.2
`Environmental issues 259
`4.14.3
`Choice of equipment 259
`4.14.4
`Light sources 260
`4.14.5 Design considerations 261
`4.14.6
`Lighting to deter 262
`4.14.7
`Lighting to reveal 262
`4.14.8 Open spaces 263
`4.14.9 Hours of operation 263
`4.14.10 Security of supply 263
`4.14.11 Installation methods 263
`4.14.12 Maintenance 264
`4.14.13 Recommendations 264
`4.14.14 Domestic security lighting 264
`
`Appendix
`Glossary
`Notes
`Bibliography
`Index
`
`266
`303
`352
`354
`372
`
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`Foreword
`
`Outdoor lighting is used for a variety of purposes in modern society.
`It enables people to see essential detail so they can be active at night. Good
`lighting can enhance the safety and security of persons or property, empha-
`sise features of architectural or historical significance, or call attention to
`commercial premises by means of area lighting or signs. Unfortunately, poor
`lighting practice is extensive. Much bad lighting can be blamed on the fact
`that the user is unaware of the issues of visibility and its usefulness. Care-
`less and excessive use of artificial light in our outdoor environments causes
`extensive damage to the aesthetics of the night-time environment, while at
`the same time it often compromises safety and usefulness, the very reason
`for its installation. Bad lighting hurts everyone. The loss of the dark star-
`filled sky is of tragic consequence for the environment and for the human
`soul, akin to the loss of our forested landscapes and other natural trea-
`sures. On the other hand, quality lighting brings substantial benefits. Lack
`of glare and excessive contrast brings improved visibility, especially for the
`ageing eye. Elimination of wasted light saves money, energy and resources,
`which in turn reduces air pollution and carbon dioxide emissions caused by
`energy production and resource extraction. Quality lighting improves the
`appearance of our communities, returning a sense of balance to the night
`and giving a more attractive appearance to our cities, towns and villages.
`So good lighting can make a significant contribution to the outdoor
`environment whereas poor lighting can damage it.
`This positive contribution is not limited to the hours of darkness, as
`the reduction in crime effects are now known to extend to the daytime.
`In August 2002 the British Home Office published two research studies
`on crime prevention: ‘Effects of improved street lighting on crime: A sys-
`tematic review’, and HORS 251 ‘Crime prevention effects of closed circuit
`television: A systematic review’, HORS 252.1
`In international experiments one of the main points to emerge from the
`street lighting study is that where street lighting had been improved there
`had been an overall reduction in recorded crime of 20 per cent. In the British
`studies there was a 30 per cent decrease in crime. The authors conclude
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`xii
`
`Foreword
`
`that lighting improvements increase community pride and confidence and
`strengthen informal social control, and that this explains the impact, rather
`than increased surveillance or deterrent effects. Furthermore, improvements
`in street lighting offer a cost-effective crime reduction measure.
`The Closed-Circuit Television (CCTV) study summarised the findings of
`previous studies from both Britain and the USA and concluded that where
`CCTV had been installed there had been an overall reduction in recorded crime
`of 4 per cent across all the experimental areas. It was found that CCTV had no
`effect on violent crimes but had a significant desirable effect on vehicle crimes.
`Both studies together demonstrate that improved lighting is between five
`andseventimesmoreeffectiveatreducingcrimethantheinstallationofCCTV.
`In 1999 the Technical Committee of the Institution, then under the chair-
`manship of Stuart Bulmer, recognised the need to bring together various
`elements of good outdoor lighting practice. Some were already contained
`within Institution documents but others were not yet committed to paper.
`A panel of experts was set up under the leadership of the incoming Techni-
`cal Committee chairman David McNair to cover the range of topics. The
`aim of the project was to produce a comprehensive outdoor lighting guide.
`It was to be a one-stop shop: able to suitably educate any engineer (of
`whatever persuasion) or other related professional who cares to examine
`it; and, to document current good practice, target lighting levels, unifor-
`mity and glare control required for the different applications. It was to be
`comprehensive yet only explain what is necessary, with reference made to
`further documents to assist those with more expertise.
`The panel contributed in their field of expertise to the various Parts of the
`document. As expected there were multiple overlaps between the sections
`and the authors.
`The panel members were as follows:
`
`John S. Anderson
`John Brewis
`David S. Black
`David Burton
`David Coatham
`Jason Ditton
`Robert Divall
`Allan Howard
`Carl Gardner
`Arthur Gibbons
`Ian Graves
`Clive Lane
`William Marques
`David G. McNair (Chairman)
`Nigel Parry
`
`Whitecroft Road and Tunnel Lighting
`Institution of Lighting Engineers
`South Lanarkshire Council
`Ashfield Consultancy Services
`Institution of Lighting Engineers
`University of Sheffield
`Thorn Lighting
`Mouchel Consulting
`Institution of Lighting Engineers
`Dron and Dickson Group
`Philips Lighting
`CU Phosco Lighting
`CU Phosco Lighting
`South Lanarkshire Council
`City of Westminster
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`Foreword xiii
`
`Nigel E. Pollard
`Gareth Pritchard
`Malcolm Richards
`Bryan Shortreed
`
`NEP Lighting Consultancy
`Pudsey Diamond Engineering Ltd
`D.W. Windsor
`Urbis Lighting Ltd
`
`The Institution is grateful for the support of the contributors and their
`affiliated bodies, without whom the compilation of this book would not
`have been possible.
`The Chairman, working to the guidance of a strategy group, drew
`together the various contributions into what hopefully readers will find a
`coherent structure. This would not have been possible without the extensive
`and invaluable effort of David Coatham.
`The strategy group members were as follows:
`
`Patrick Baldrey
`David Coatham
`David McNair
`Gareth Pritchard
`Derek Rogers
`
`Urbis Lighting Ltd
`Institution of Lighting Engineers
`South Lanarkshire Council
`Pudsey Diamond Engineering Ltd
`Derek Rodgers and Associates
`
`For final checking John Brewis joined the strategy group. In addition the
`Institution wishes to acknowledge the assistance received from Steve Lain
`and Roger Heyworth, who started but were unable to complete sections
`due to changes in their employment; Alastair Scott of Urbis Lighting, who
`provided extensive and invaluable assistance in accessing diagrams and pho-
`tographs; Richard Leonard of Philips Lighting, who carried out many cal-
`culations; and Colin Rowley of the Dron and Dickson Group, who was too
`busy to contribute, but commissioned Arthur Gibbons to work in his place.
`CU Lighting and South Lanarkshire Council provided diagrams. Philips
`Lighting, South Lanarkshire Council, Thorn Lighting, D.W. Windsor and
`Urbis Lighting provided photographs. Extracts from the work of Ken Pease
`and the International Dark-Sky Association are gratefully acknowledged, as
`are the words added by Kate Painter. The ‘Slipstream’ sculpture in Chapter 4
`is by Joseph Ingleby and the photographs of it by Ruth Clark. The book
`was prepared for publication by David Coatham.
`It is hoped this book will give readers a better understanding of the principles
`of good lighting, act as a reference source where good practice can be identified
`and in some cases explain the limitations under which designers work.
`Finally, this document is a building block for the future. As techniques
`develop, as knowledge is acquired and as experience is gained it will have
`to be updated. If readers have any comments, suggestions for improvement,
`requests for inclusion of contributions towards future editions or wish to
`view what others are posting, they are invited to visit www.ile.org.uk.
`
`David McNair
`
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`Disclaimer
`
`This publication has been prepared on behalf of the ILE Technical Commit-
`tee for study and application. The document reports on current knowledge
`and experience within the specific fields of light and lighting described
`and is intended to be used by the ILE membership and other interested
`parties. It should be noted, however, that the status of this document is
`advisory and not mandatory. The views expressed are not necessarily those
`of the contributors. The ILE should be consulted regarding possible sub-
`sequent amendments. Any mention of organisations or products does not
`imply endorsement by the ILE. Whilst every care has been taken in the
`compilation of any lists, up to the time of going to press, these may not
`be comprehensive. Compliance with any recommendations does not itself
`confer immunity from legal obligations.
`
`The Institution of Lighting Engineers
`The objective of the Institution is to promote, encourage and improve the
`science and art of lighting for the benefit of the public.
`
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`

`Abbreviations and symbols for
`quantities, units and notation
`
`A
`ABS
`BS EN
`BSI
`cd
`CE
`CIE
`CRI
`CCT
`DLOR
`¯E
`E
`EEC
`EMC
`EN
`ENEC
`EPDM
`GLS
`GRP
`HID
`HPS
`HQI
`Hz
`IP
`IR
`I
`I table
`ILCOS
`K
`¯L
`L
`LDL
`
`Ampere
`Acrylonitrile-butadiene-styrene
`British Standard European Norm
`British Standards Institute
`Candela
`European conformity mark
`Commission Internationale de l’Eclairage
`Colour rendering index
`Correlated colour temperature
`Downward light output ratio
`Illuminance
`Average illuminance
`European Economic Community
`Electromagnetic compatibility
`European Norm
`European Norm electrical certificate
`Ethylene propylene diene monomer
`General lighting service
`Glass-reinforced polyester
`High intensity discharge
`High pressure sodium
`Metal Halide
`Hertz
`Ingress protection
`Infrared
`Luminous intensity
`Luminous intensity distribution table
`International lamp coding system
`Kelvin
`Luminance
`Average luminance
`Lighting design lumens
`
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`xvi Abbreviations and symbols for quantities, units and notation
`
`lm
`LOR
`lx
`MICC
`MF
`PAR
`PC
`PCA
`PFC
`PIR
`PMMA
`PVC
`R table
`Ra
`RAL
`RCD
`SIP
`SON
`SOX
`sr
`TI
`ULOR
`ULR
`UV
`Ul
`Uo
`V
`W
`
`Lumen
`Light output ratio
`Lux
`Mineral insulated copper conductors
`Maintenance factor
`Parabolic reflector
`Polycarbonate
`Polycrystalline alumina
`Power factor correction capacitor
`Passive infrared
`Acrylic (polymethylmethacrylate)
`Polyvinylchloride
`Reflectance table
`Colour rendering index
`Reichs-Ausschus fur Lieferbedingungen
`Residual current device
`Superimposed pulse
`High pressure sodium
`Low pressure sodium
`Steradian
`Threshold increment
`Upward light output ratio
`Upward light ratio
`Ultraviolet
`Longitudinal uniformity
`Overall uniformity
`Volt
`Watt
`
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`Chapter 1
`Visual effects of lighting
`
`1.1 Introduction
`Lighting has three primary functions:
`
`1 To improve visual performance;
`2 To improve safety; and
`3 To improve the visual environment.
`
`Each of these functions is equally applicable to both indoor and outdoor
`environment, however; the outdoor environment is a very different place
`from the indoor environment. It is subject to more extreme environmental
`conditions and human behaviour. Whilst there is some overlap of task there
`is a complete overlap of lighting principles and visual effects.
`
`1.2 Light
`
`1.2.1 Lighting levels
`
`The human eye perceives objects by the light that is emitted or reflected by
`them. With the exception of light sources, the light reaching an observer
`(the luminance of the object) is the reflected light and is dependent on the
`light incident on the object (the illuminance), the reflective properties of the
`object and the position of the observer with relation to the object. These
`variables give a very large number of possible luminance requirements.
`
`1.2.2 Task performance
`
`The ability to perform a visual task is influenced by the size of the task,
`the contrast and the vision of the viewer. Whereas a difficult task cannot
`be made into an easy task, increasing the illuminance generally improves
`visual performance for a specified task. However, saturation occurs, and
`beyond a certain value any further increase is superfluous and results in
`an unnecessary use of energy. The point at which saturation occurs will be
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`2 Visual effects of lighting
`
`I5 μsr
`
`4.8 μsr
`
`Figure 1.1 Relationship of relative visual performance with retinal illuminance in trolands
`and contrast, for task sizes of 15 (cid:1)sr (a) and 4.8 (cid:1)sr (b).
`
`higher the more difficult the task e.g. tasks involving very small objects or
`those carried out at high speed. Saturation is illustrated in Figure 1.1.
`
`1.2.3 Appearance
`
`In a limited number of outdoor locations the appearance of the lighting will
`be more important than the task performed. Indeed the actual task may be
`viewing the appearance of a lit object or the lit environment. Examples are the
`illumination of buildings and structures and the lighting of town squares. The
`lighting here is intended to create mood, interpret architecture or give visual
`stimulation. The art of good lighting becomes as important as the science, and
`designers have to take account of colour, form, texture and perception.
`
`1.3 Flux, intensity, illuminance, luminance and brightness
`Flux is the total quantity of light that a source (e.g. a lamp) emits. It is mea-
`sured in lumens and is the starting point for general lighting calculations.
`The quantity of light emitted in a specified direction is the luminous
`intensity or simply the intensity of the light in that direction. The existence
`of luminous intensity diagrams or tables for luminaires allows detailed
`lighting calculations to be carried out. It is measured in candelas, which are
`lumens per unit solid angle in the specified direction.
`Illuminance is the magnitude of light incident on a surface. It cannot be
`seen because it has not reached the eye yet. Illuminance is the objective
`
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`Visual effects of lighting 3
`
`Luminous Flux
`
`(Lumen)
`
`Luminous Intensity
`
`(Candela)
`
`Illuminance
`
`(Lux)
`
`Luminance
`
`(Candela per square metre)
`
`Figure 1.2 Flux, intensity, illuminance and luminance.
`
`quantity that is most commonly used to specify lighting levels because in
`most applications it is not possible to specify the position of the observers,
`the lit objects and the light sources with sufficient accuracy to use lumi-
`nance, or there are multiple observer positions. Illuminance is measured in
`lux, which are lumens incident on a point per area of the point.
`However, lighting practitioners think in terms of luminance, contrast and
`glare. The amount of light that reaches the eye by reflection or by direct emis-
`sion from a light source is called luminance. The light reflected from any
`surface is dependent on the quantity of illuminance, the reflective properties
`of the surface and the position of the observer with relation to the surface.
`Luminance is measured in candelas per square metre, which is the luminous
`intensity per area of the solid angle of the object when viewed by the observer.
`Figure 1.2 illustrates all the four terms. Brightness is the subjective
`response created by the brain’s interpretation of what the eye sees.
`
`1.4 Glare
`Glare occurs when one part of the visual scene is much brighter than the
`remainder. The most common causes of glare are inappropriate orientation
`of luminaires, and the poor selection of luminaire and mounting height
`combination. In a road environment, dipped vehicle headlamps can cause
`substantial glare even if the road is well lit. Glare impairs vision, causes
`discomfort and reduces task performance.
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`4 Visual effects of lighting
`
`1.5 Positive and negative contrast
`Contrast is the assessment of the difference in appearance of two or more
`parts of a field seen simultaneously or successively. It is the key to vision: if
`there is no contrast between an object and its background then the object
`will not be detected. The luminance contrast of an object is
`
`C = L2 − L1
`
`L1
`
`where L2 is the luminance of the object; and L1 is the luminance of the
`background.
`Where the object is brighter than the background, there is a positive
`contrast and the object is seen by direct vision. And where the object is
`darker than the background, there is a negative contrast and the object is
`seen by silhouette vision.
`
`1.6 Absorption and reflection
`Any light falling on to a surface that is not reflected is either absorbed or
`transmitted through the object.
`If the material does not transmit light, all non-reflected light disappears
`into the surface and is converted into heat. This is called absorption. The
`amount of absorption varies according to the angle of incidence, the colour
`of the light and the physical characteristics (colour, texture, density) of
`the material. Generally, for higher angles of incidence more light will be
`reflected.
`The colour of a surface is dependent on the light reflected from it, for
`example a blue surface will reflect incident light in the blue wavelengths of
`the spectrum and absorb light with other wavelengths.
`
`1.7 Radiation
`Light forms part of a complex of physical phenomena included under the
`heading ‘electromagnetic radiation’. It is therefore closely related to, for
`example, radio and TV signals, infrared (IR) and ultraviolet (UV) radiations,
`X-rays and other radiations. These emissions occur at different wavelengths.
`The major difference between light and these other phenomena is that
`humans and animals use a collection of the wavelengths to ‘see’ and this is
`called the visible spectrum. Some animals also use wavelengths in the IR or
`UV ranges to extend their range of vision.
`‘White’ light is a collection of different wavelengths between approxi-
`mately 380 and 780 nm, which in combination are perceived as white. Most
`lamps that emit a ‘white’ light do not emit a continuous spectrum of wave-
`lengths but a series of wavelengths of different amplitude. Figure 1.3 shows
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`Visual effects of lighting 5
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`380 400
`
`500
`
`600
`Wavelength (nm)
`
`700
`
`760
`
`VISIBLE
`LIGHT
`
`GAMMA RAYS X(cid:3)-(cid:3)RAYS
`
`ULTRA-
`VIOLET
`
`INFRA - RED
`
`RADIO
`
`-12
`
`10
`
`-10
`10
`
`-8
`
`10
`
`-(cid:25)
`
`10
`
`-4
`
`10
`
`Wavelength (m)
`
`-2
`10
`
`1
`
`2
`10
`
`Figure 1.3 Visible portion of electromagnetic spectrum. (see Colour Plate 1)
`
`the relationship between the visible portion of electromagnetic spectrum i.e.
`visible light and the non visible portions of the spectrum. Figure 1.4 shows
`the range and proportions of the emission spectrum of a typical fluorescent
`lamp.
`
`1.8 Apparent colour
`Colour temperature describes how a lamp appears when lit. It is the temper-
`ature of a black body radiator that emits radiation of the same chromaticity
`as the lamp being considered. For complete accuracy, the chromaticity must
`be on the black body (full radiator) locus, the power radiation curve of a
`black body.
`As very few lamps have chromaticity on the locus, the more useful corre-
`lated colour temperature (CCT) is used. It is based on similar chromaticity
`to a black body radiator. This is red at 800 K, warm yellowish ‘white’ at
`2800 K, daylight ‘white’ at 5000 K and bluish daylight ‘white’ at 8000 K.
`CCT is good for comparing incandescent lamps because they emit a con-
`tinuous spectrum. It is not so good for comparing discharge lamps because
`their spectrum is not necessarily continuous. Some discharge lamps with the
`same CCT can have different effects on illuminated objects (Figure 1.5).
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`500
`400
`700 nm
`600
`Figure 1.4 Emission spectrum of a typical fluorescent lamp. (see Colour Plate 2)
`
`(a)
`
`Figure 1.5 Effect of different colour temperature: (a) under SOX light and (b) under
`‘white’ light. (see Colour Plate 3)
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`Visual effects of lighting 7
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`(b)
`
`Figure 1.5 (Continued).
`
`1.9 Colour rendering
`The ability of a light source to render colours of surfaces correctly is quan-
`tified by the CIE Group and the colour rendering index (Table 1.1). This
`index is based on how close a set of test colours are reproduced by the lamp
`under evaluation, relative to how they are reproduced by an appropriate
`standard light source of the same CCT. Perfect matching is given value
`of 100.
`
`Table 1.1 CIE colour rendering groups
`
`Colour rendering
`groups
`
`1A
`1B
`
`2
`3
`4
`
`CIE general colour
`rendering index
`Ra ≥ 90
`90 ≥ Ra ≥ 80
`80 ≤ Ra ≤ 60
`60 ≤ Ra ≤ 40
`40 ≤ Ra ≤ 20
`
`Typical applications
`
`Critical colour matching
`Accurate colour judgements required for
`appearance
`Moderate colour rendering required
`True colour recognition of little significance
`Not recommended for colour matching
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`8 Visual effects of lighting
`
`1.10 Daytime appearance
`It should be remembered that lighting is a very visible service. Its appearance
`to the user is just as vital a design parameter as its performance. Lighting
`equipment can be chosen to be inconspicuous, both in its design and the
`way it is installed, or selected to be a feature. At night the lit appearance of
`the products used, including their supporting structures, whether brackets,
`lighting columns, towers or background, needs considering as well as the
`lit scene’s appearance and technical performance. The choice of product
`includes style and scale, colour and finish. By day the lighting equipment
`is usually visible in the environment and the luminaire together with the
`bracket and lighting column or other means of support and fixing must be
`considered as a whole – they form a single item visually. What is seen, at
`night and during the day, is usually a collection of luminaires and their sup-
`ports; the way these are seen together, their dominance, clutter, confusing
`or untidy combinations, for example, must be taken into account.
`
`1.11 The outdoor environment
`Lighting the outdoor environment is relatively simple during the hours of
`daylight as even in poor weather conditions the sky generally has sufficient
`luminance to provide adequate light for human observers who do not have
`significant visual impairment. Luminance is above 10 cd m−2 allowing full
`operation of the cone receptors. Vision is in photopic mode with full colour
`differentiation. Relative sensitivity to different wavelengths is shown on the
`right-hand curve of Figure 1.6.
`However, during the hours of darkness and where no artificial light is
`available, luminances drop to below 10−2 cd m−2. Vision is in the scotopic
`
`Scotopic Vision
`
`Photopic Vision
`
`1.0
`0.9
`0.8
`0.7
`0.6
`0.5
`0.4
`0.3
`0.2
`0.1
`0.0
`400
`
`Spectral Luminous Efficiency
`
`450
`
`550
`500
`Wavelength λ (nm)
`
`600
`
`650
`
`700
`
`Figure 1.6 Spectral response of human eye.
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`Visual effects of lighting 9
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`range where only the rod receptors are operational, with no colour dif-
`ferentiation provided. Peripheral detection is superior to foveal detection,
`as the rods are concentrated in the peripheral areas of the eye. The peak
`sensitivity of the eye shifts to a lower wavelength of light. As a consequence
`the eye is relatively more sensitive to light in the blue are