Outdoor Lighting : physics, vision and perception

Contents Preface 1 Introduction: The function of outdoor lighting 1.1 Why lighting the outdoors? 1 1.2 Lighting engineering 3 1.3 The function of outdoor lighting 1.3.1 Road lighting, street lighting and public lighting 4 1.3.2 The advancement of human well-being 4 1.3.3 The function of road lighting 4 1.3.4 The driving task 6 (a) Driving task analysis 6..........(b) Task elements 7..........(c) Manoeuvres 7 1.4 Cognitive aspects of vision 9 1.5 Tools and methods 10 1.5.1 Models 10 1.5.2 Quick-and-dirty statistics 11 1.5.3 Scales in psycho-physiology 11 1.6 Conclusions 13 2 Physical aspects of light production 17 2.1 The physics of light 17 2.1.1 Definitions of light 17 2.1.2 Light rays 19 2.1.3 Waves and particles 20 (a) Waves 20..........(b) Particles 25..........(c) Photons 26 2.2 General aspects of light production 28 2.2.1 Principles of light generation 28 2.2.2 The efficacy of light sources 29 2.3 Incandescence 30 2.3.1 Thermal radiation 30 (a) The laws of black-body radiation 30..........(b) Grey bodies 33..........(c) Non-electric incandescent lamps 34..........(d) Electric incandescent filament lamps 35 2.3.2 Characteristics of electric incandescent lamps 38 (a) The filament 38..........(b) Filament evaporation and bulb blackening 38..........(c) Lamp life and design values 39..........(d) Balance between the efficacy and the lamp life 39 v 4 1 xiii 2.3.3 Halogen incandescent lamps 40 (a) The role of gas pressure in the bulb 40..........(b) The halogen cycle 41.......... (c) Characteristics of halogen incandescent lamps 41..........(d) Why use incandescent lamps? 42 2.4 Gas-discharge lamps 42 2.4.1 Quantum aspects of light 42 (a) Bosons, baryons, and fermions 42..........(b) The physics of metals 43..........(c) Quantum aspects of light; gas discharges 45..........(d) The construction of gas-discharge lamps 46...... lamps 51 2.4.2 Fluorescence 51 (a) Fluorescence in gas-discharge lamps 51..........(b) The conversion from UV radiation into light 53..........(c) The efficiency of the fluorescent process 55..........(d) Fluorescent materials 57 2.4.3 Types of gas-discharge lamps 59 (a) Four families of lamps 59........(b) Low-pressure mercury lamps 61..........(c) Lowpressure sodium lamps 62..........(d) High-pressure gas-discharge lamps 63..........(e) Highpressure mercury lamps 64..........(f ) Metal-halide lamps 64..........(g) High-pressure sodium lamps 65 2.5 Semiconductor light 65 2.5.1 The physics of semiconductors 65 (a) Intrinsic and extrinsic semiconductors 65..........(b) Semiconductor diodes 67.......... (c) Semiconductor light-emitting diodes 69 2.5.2 Anorganic LEDs 70 (a) The construction of anorganic LEDs 70..........(b) The colour of anorganic LEDs 71 ......(c) The performance of anorganic LEDs 71..........(d) Use of anorganic LEDs 74 2.5.3 Organic LEDs 75 2.6 Conclusions 78 3 Radiometry and photometry 85 3.1 Radiometry 85 3.1.1 Principles of radiometry 85 (a) The difference and the similarity between radiometry and photometry 85.......... (b) Radiant power 86..........(c) The basic formula of radiometry 86..........(d) Terminology 88 3.1.2 The solid angle 88 3.2 Basic photometric concepts 90 3.2.1 The SI-units 90 (a) Seven basic units 90..........(b) The photometric units 91..........(c) Units of the ISOphotometry 91 3.2.2 The luminous flux 92 (a) Definition 92..........(b) Reflectance, transmittance 92 3.2.3 The luminous intensity 93 3.2.4 The illuminance 94 (a) Definition 94..........(b) Horizontal, vertical and semicylindrical illuminance 95.......... (c) The average illuminance and the non-uniformity 96..........(d) The inverse square law 97..........(e) The distance law for large sources 98..........(f ) The distance law for bundled light 100..........(g) The cosine law 101..........(h) The cosine to the third law 102 Contents (e) The influence of the vapour pressure 48..........(f ) The main families of gas-discharge vi 3.2.5 The luminance 103 (a) General definition 103..........(b) The luminance of light-reflecting objects 105.......... (c) The luminance of light emitting objects 105 3.3 Conclusions 106 4 The mathematics of luminance 109 4.1 The field concept 109 4.1.1 Field theory 109 (a) Light fluid and light vectors 109..........(b) Fields 110..........(c) Forces and potentials 110.......... (d) Morphic fields 111 4.1.2 The light field 111 (a) The photic field 111..........(b) Fields of light rays 112..........(c) The speed of light 112.......... (d) The basic formula of photometry 114 4.2 Some aspects of hydrodynamics 118 4.2.1 The continuity principle 118 4.2.2 Bernoulli-fluids 119 4.2.3 The equation of continuity 120 4.2.4 Friction and diffraction 121 (a) The width of a light ray 121..........(b) Diffraction 121..........(c) The minimum separable 123 4.3 The luminance of real and virtual objects 124 4.3.1 The need for a proper definition of luminance 124 4.3.2 The general definition of luminance 125 (a) The direction aspects of the luminance 125..........(b) Light tubes 125..........(c) The physics of light tubes 127..........(d) The definition of the geometric flux 127..........(e) The throughput of light 129 4.4 The luminance of reflecting surfaces 131 4.4.1 The use of surface luminances 131 4.4.2 Definition of reflection 132 4.4.3 The luminance factor 134 (a) The reflection factor and the luminance factor 134..........(b) A description of the luminance factor 134..........(c) The luminance factor of a perfect diffuser 135..........(d) The definition of the luminance factor 135 4.4.4 The luminance factor of practical materials 137 4.5 Conclusions 138 5 Practical photometry 141 5.1 General aspects of photometry 141 5.1.1 Five stages in the history of photometry 141 5.1.2 Definition of measurement 143 (a) A general description of measurement 143..........(b) Measuring in nominal scales 143 ......(c) Measuring in ordinal scales 144..........(d) Measuring in quantitative scales 144.......... (e) The accuracy when measuring in different scales 145 5.1.3 The relation between radiometry and photometry reconsidered 145 5.1.4 Calibration 146 (a) Gauging and calibration 146..........(b) Standards 146 5.2 Traditional subjective photometry 148 Contents vii 5.2.1 Brightness estimation 148 5.2.2 Visual photometry 149 (a) The sensitivity of the eye 149..........(b) The photopic V..-curve 151..........(c) The determination of the V..-curve 154..........(d) Heterochromatic and isochromatic photometry 155..........(e) The contrast method of photometry 156..........(f ) Flicker effects 157..........(g) Flicker photometry 160 5.3 Traditional objective photometry 162 5.3.1 Instrumental photometry 162 (a) Counting photons 162..........(b) Sensors; Control and decision-making systems 162.......... (c) The S/N ratio 164 5.3.2 Detectors 165 (a) Photocells 165..........(b) Barrier-layer photo-effect 165..........(c) Photocells for internal photo-effects 167..........(d) Photocells for the external photo-effect 167..........(e) Photomultipliers 168 5.3.3 Measuring photometric quantities 170 (a) Basic considerations 170..........(b) Luxmeters 170..........(c) Luminance meters 171.......... (d) Measuring the luminous flux, and the light distribution 172..........(e) Accuracy 173.......... (f ) Examples of cosine and colour corrections for lux-meters 175 5.4 Modern objective photometry 177 5.4.1 CCDs 177 (a) CCDs for taking pictures 177..........(b) The properties of CCDs 178..........(c) The performance of CCDs 179..........(d) CCD data extraction and data processing 180 5.4.2 CCDs in photometry 181 5.5 Conclusions 181 6 The human observer; physical and anatomical aspects of vision 187 6.1 The ability to see 187 6.2 The nervous system 188 6.2.1 The structure of the nerve cells 188 (a) Neurones 188..........(b) Synapses 189 6.2.2 The central nervous system 191 6.3 The anatomy of the human visual system 191 6.3.1 The overall anatomy 191 6.3.2 The optical elements, the cornea 195 6.3.3 The optical elements, the eye lens 196 (a) The anatomy of the eye lens 196..........(b) Accommodation 197..........(c) Fourier optics 198..........(d) The point spread function or PSF 199.......... (e) Optical aberrations; monochromatic aberrations 200..........(f ) Optical aberrations; heterochromatic aberrations 200 6.3.4 The optical elements, the iris 202 (a) The anatomy of the iris 202..........(b) The Stiles-Crawford effect 203 6.3.5 The optical elements, the retina 204 (a) The anatomy of the retina 204..........(b) The photoreceptors 206..........(c) Cones and rods 207..........(d) The spatial distribution of rods and cones 209..........(e) Retinal ganglion cells 210 6.4 The optical nerve tracts 211 6.4.1 Image forming and non-image forming effects of light 211 viii Contents 6.4.2 The visual neural pathways 212 (a) The organization of the retinal visual system 212..........(b) The optical nerve 213.......... (c) Pathways for rod vision 215..........(d) Pathways for daylight levels 216..........(e) Movie tracks 218 6.4.3 The anatomy of the brain 219 (a) The main structure of the brain 219..........(b) Brain anatomy and brain functions 219 ......(c) The cerebrum 220..........(d) The cortex 221 6.5 Conclusions 223 7 The human observer; visual performance aspects 229 7.1 The functions of the human visual system 229 7.1.1 The sensitivity of the eye 229 (a) Standard observers 229..........(b) Assessing the sensitivity of the eye 231..........(c) Twodegree and ten-degree photometry 232 7.2 The sensitivity of the human visual system 233 7.2.1 The duplicity theorem 233 7.2.2 Photopic vision 233 (a) Three families of cones 233..........(b) The V..-curve 234..........(c) V.. as a function 235.......... (d) Tabulated values of V............ 7.2.3 The scotopic spectral sensitivity curve 236 7.2.4 Mesopic vision 237 (a) The limits of mesopic vision 237..........(b) The transition between photopic and scotopic vision 238..........(c) The high-mesopic region 239..........(d) The Purkinje-shift 240.......... (e) Mesopic spectral sensitivity curves 240..........(f ) Mesopic photometry 242.......... (g) Mesopic metrics 242..........(h) Mesopic brightness impression 243 7.3 Visual performance 244 7.3.1 Human performance and visual performance 244 (a) Ergonomic aspects 244..........(b) Task aspects 245 7.3.2 Visual performance and Weber’s Law 246 (a) The concept of visual performance 246..........(b) The law of Weber 246..........(c) Limits of Weber’s Law 247..........(d) Validity of Weber’s Law 249 7.4 The primary visual functions 250 7.4.1 Introducing the primary visual functions 250 7.4.2 Adaptation 251 7.4.3 Luminance discrimination 253 (a) The contrast 253..........(b) The minimum detectable contrast 254..........(c) Neural aspects of achromatic contrast phenomena 254..........(d) The laws of Ricco and Piper 255.......... (e) The relation between size and threshold contrast 258..........(f ) Lights with periodic brightness 259..........(g) The sensitivity to changes in the contrast 259..........(h) The RSCcurve 260 7.4.4 The visual acuity 262 (a) Visus 262..........(b) Measurement of the visual acuity 263..........(c) Visual acuity in relation to colour 265 7.5 Conclusions 266 8 The human observer; visual perception 273 8.1 Derived visual functions 273 Contents ix 8.1.1 Field of view 273 (a) The field of vision 273..........(b) The functional visual field 275..........(c) Binocular vision 275..........(d) Stereopsis 276..........(e) The stereoscopic range 277 8.1.2 The speed of observation; flicker-effects 278 (a) The discrimination in time 278..........(b) Flicker effects 279..........(c) Discomfort by flicker effects 280 8.1.3 Subjective brightness 281 8.1.4 Detection of movement 284 (a) Constancy 284..........(b) Movement detection 285 8.2 Blinding glare 286 8.3 Disability glare 287 8.3.1 Sources of disability glare 287 (a) Glare sources, the glare angle 287..........(b) Stray light in the eye 288..........(c) The equivalent veiling luminance 289..........(d) The nature of disability glare 289 8.3.2 Characteristics of disability glare 289 (a) The effect of the light veil 289..........(b) Colour effects of disability glare 290.......... (c) Practical implications of the colour effects 291..........(d) The four-component model 294..........(e) The ..-dependence 295..........(f ) Age effects of disability glare 296..........(g) The limits for the ..-dependence 297..........(h) The CIE Standard Glare Observer 301 8.4 Discomfort glare 303 8.5 Conclusions 305 9 The human observer; colour vision 313 9.1 Colour aspects 313 9.1.1 A description of colour 313 9.1.2 The importance of colour 314 9.1.3 Experiencing colours 315 9.2 Colour vision physiology 315 9.2.1 Three cone families 315 (a) The relative spectral sensitivity 315..........(b) Colour defective vision 318 (c) The absolute spectral sensitivity 320 9.2.2 The neural circuity in cone vision 322 (a) Colour vision theories 322..........(b) The opponent-process theory 323..........(c) The opponent-process theory circuitry 324..........(d) The construction of V.. of self-luminous objects 327 9.3 Colour metrics and colorimetry 328 9.3.1 Terminology 328 9.3.2 Colorimetry 329 (a) Additive and subtractive processes 329..........(b) The CIE system of colorimetry 329 ......(c) The 1931 CIE Standard Chromaticity Diagram 330..........(d) Standard conditions for colour vision 333..........(e) Colour names 335..........(f ) Colour points 335..........(g) The Munsell system 336..........(h) Metamerism 337 9.4 The colour characteristics of light sources 338 9.4.1 Chromatic adaptation effects 338 (a) The colour impression 338..........(b) Chromatic adaptation 338 9.4.2 The colour temperature 339 (a) The definition of the colour temperature 339..........(b) Incandescent light sources 340 x Contents ......(c) The locus of the black-body radiators 340..........(d) Near-white light sources 341.......... (e) Colour differences 342 9.4.3 The colour rendering 344 (a) The colour rendering in illuminating engineering 344..........(b) The colour rendition 345..........(c) The standard colours 345..........(d) The selection of the standard light source 346..........(e) The colour rendering of light sources 347 9.5 Conclusions 349 10 Road lighting applications 357 10.1 Geometric optics 358 10.1.1 Definitions of light 358 (a) Four models for the description of light 358..........(b) Light rays 358 10.1.2 Design of optical devices 359 (a) Principles of image-forming and lighting equipment 359..........(b) Image-forming equipment 360..........(c) Non-image forming equipment 363 10.2 Luminaire design 364 10.2.1 Optical elements 364 (a) Lamp and road axis 364..........(b) Road lighting luminaire light distributions 364.......... (c) Road lighting luminaire classification 366..........(d) The proposal of Narisada and Schreuder 368 10.2.2 The optics of road lighting luminaires 370 10.2.3 Ingress protection 372 10.3 Light pollution 373 10.3.1 Description of light pollution 373 (a) Light pollution and sky glow 373..........(b) Victims of light pollution 374.......... (c) Description of light pollution effects 375..........(d) Conspicuity of point sources 376.......... (e) Application of flat luminaire covers 376 10.3.2 Limits of light pollution 378 (a) The natural background radiation 378..........(b) Artificial sky glow 379..........(c) CIE Limits 379..........(d) IAU limits 382 10.3.3 Remedial measures 382 (a) Limiting sky glow 382..........(b) Switching off the lights 383..........(c) Gated viewing 383 ......(d) Light control 384..........(e) Reduction of reflection 384..........(f ) Using monochromatic light 385..........(g) Filtering the light 385 10.4 Reflection properties of road surfaces 385 10.4.1 Road reflection as a road lighting design characteristic 385 (a) The luminance technique in road lighting 385..........(b) Reflection characteristics 386.......... (c) Documentation of reflection characteristics 388 10.4.2 The classification of road surface reflection 388 10.4.3 Standard reflection tables 390 10.4.4 Field measurements of the road reflection 390 10.5 Conclusions 393 11 Road lighting design 401 11.1 Design methods for road lighting installations 401 11.1.1 Principles of lighting design 401 Contents xi 11.1.2 Design methods based on the road luminance 403 (a) Systems of road lighting quality assessment 403..........(b) The method using E-P diagrams 403..........(c) The basis of computer-assisted luminance-design methods 406.......... (d) LUCIE 407..........(e) Shortcomings of LUCIE 408 11.1.3 Alternative design parameters 410 (a) Illuminance 410..........(b) Road lighting design methods based on revealing power 411 ......(c) Visibility Level 411..........(d) Small Target Visibility 411..........(e) The Narisada visibilitybased design method for road lighting 412..........(f ) Guidance lighting 414..........(g) Visual comfort and city beatification 415..........(h) Fear for crime and subjective safety 417.......... (j) Cost-benefit considerations 418 11.2 Road lighting for developing countries 418 11.2.1 Recommendations 418 (a) The visibility approach 418..........(b) The traffic engineering approach 419 11.2.2 Low-maintenance lighting installations 420 (a) The maintenance of outdoor lighting installations 420..........(b) Open luminaire options 421..........(c) Comparing open and closed luminaires 422 11.3 Simplified design methods 425 11.3.1 Characteristics of simplified design methods 425 (a) The need for simplified design methods 425..........(b) Road classification 425..........(c) Lighted and unlit roads 426 11.3.2 A practical method for simplified lighting design 426 (a) The design approach 426..........(b) The effective road width 427..........(c) The mounting height 428..........(d) The spacing 428..........(e) The light level 428..........(f ) The utilization factor 428..........(g) The tabulated lighting design 429 11.4 Conclusions 430