[Architecture eBook] Handbook of Interior Lighting Design(2)

7/30/2019 [Architecture eBook] Handbook of Interior Lighting Design(2)

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Handbook ofLighting Design

E EditionRdiger Ganslandt

Harald Hofmann

Vieweg

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Rdiger GanslandtBorn in 1955. Studied German, Art and theHistory of Art in Aachen, Germany.Member of theproject team on imaginaryarchitecture. Book publications on topicsrelating to sciences and humanities,article on lighting design. Joined Erco in1987, work on texts and didacticconcepts. Lives in Ldenscheid, Germany.

Harald HofmannBorn in 1941 in Worms, Germany. StudiedElectrical Engineeringat Darmstadt Uni-versity of Technology from 1961 to 1968.Gained a doctorate in 1975. Worked asan educator and researcher in theLightingTechnology department at DarmstadtUniversity of Technology until 1978.Joined Erco in 1979 as Head of LightingTechnology. Professor of Lighting Techno-logy in the Faculty of Architecture atthe Darmstadt University of Technologysince 1997.


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Title Handbook of Lighting Design

Authors Rdiger GanslandtHarald Hofmann

Layout and otl aicher andgraphic design Monika Schnell

Drawings otl aicherReinfriede BettrichPeter GrafDruckhaus Maack

Reproduction Druckhaus Maack, LdenscheidOffsetReproTechnik, BerlinReproservice Schmidt, Kempten

Setting/printing Druckhaus Maack, Ldenscheid

Book binding C. FikentscherGrobuchbinderei Darmstadt

ERCO Leuchten GmbH, LdenscheidFriedr. Vieweg & Sohn Verlagsgesell-schaft mbH, Braunschweig/Wiesbaden1. edition 1992

The Vieweg publishing company is a Ber-telsmann International Group company.

All rights reserved. No part of this publi-cation may be reproduced in any form orby any means without permission fromthe publisher. This applies in particular to(photo)copying, translations, microfilmsand saving or processing in electronicsystems.

Printed in Germany


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Handbook ofLighting Design

EEditionRdiger Ganslandt

Harald Hofmann

Vieweg


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About this book Wide interest has developed in light andlighting, not least because the growingawareness of architectural quality has gi-ven rise to an increased demand forgood architectural lighting. Standardisedlighting concepts may have sufficedto light the concrete architecture of therecent past, but the varied and distinctivearchitecture of modern-day buildingsrequires equally differentiated and distinc-tive lighting.

An extensive range of light sourcesand luminaires are available for this task;with technical progress the scope oflighting technology has expanded, andthis has in turn led to the developmentof increasingly more specialised lightingequipment and tools. It is this factthat makes it increasingly difficult for thelighting designer to be adequatelyinformed regarding the comprehensiverange of lamps and luminaires availableand to decide on the correct technicalsolution to meet the lightingrequirementsof a specific project.

The Handbook of Lighting Designcovers the basic principles and practiceof architectural lighting. It exists asmuch as a teaching aid, e.g. for studentsof architecture, as a reference book forlighting designers. The Handbook doesnot intend to compete with the existingcomprehensive range of specialistliterature on lighting engineering, nor tobe added to the limited number ofbeautifully illustrated volumes containingfinished projects. The Handbook aimsto approach and deal with the subject ofarchitectural lighting in a practical

and comprehensible manner. Backgroundinformation is provided through a chapterdedicated to the history of lighting.The second part of the Handbook dealswith the basics of lighting technologyand surveys light sources, control gearand luminaires available. The third partdeals with concepts, strategies and theprocesses involved in lighting design.In the fourth part there is a comprehensivecollection of design concepts for themostfrequent requirements of interior lighting.The glossary, index and bibliographyprovided to assist users of this Handbookin their daily work facilitate the search forinformation or further literature.


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Foreword

1.0 History

1.1 The history of architectural lighting 12

1.1.1 Daylight architecture 121.1.2 Artificial lighting 131.1.3 Science and lighting 151.1.4 Modern light sources 161.1.4.1 Gas lighting 171.1.4.2 Electrical light sources 181.1.5 Quantitative lighting design 221.1.6 Beginnings of a new age kind lighting design 221.1.6.1 The influence of stage lighting 241.1.6.2 Qualitative lighting design 241.1.6.3 Lighting engineering and lighting design 25

2.0 Basics

2.1 Perception 28

2.1.1 Eye and camera 282.1.2 Perceptual psychology 292.1.2.1 Constancy 312.1.2.2 Laws of gestalt 332.1.3 Physiology of the eye 362.1.4 Objects of peception 38

2.2 Terms and units 40

2.2.1 Luminous flux 402.2.2 Luminous efficacy 402.2.3 Quantity of light 402.2.4 Luminous intensity 402.2.5 Illuminance 422.2.6 Exposure 422.2.7 Luminance 42

2.3 Light and light sources 43

2.3.1 Incandescent lamps 452.3.1.1 Halogen lamps 492.3.2 Discharge lamps 522.3.2.1 Fluorescent lamps 532.3.2.2 Compact fluorescent lamps 542.3.2.3 High-voltage fluorescent tubes 552.3.2.4 Low-pressure sodium lamps 562.3.2.5 High-pressure mercury lamps 572.3.2.6 Self-ballasted mercury lamps 582.3.2.7 Metal halide lamps 592.3.2.8 High-pressure sodium lamps 60

2.4 Control gear and control equipment 65

2.4.1 Control gear for discharge lamps 652.4.1.1 Fluorescent lamps 652.4.1.2 Compact fluorescent lamps 662.4.1.3 High-voltage fluorescent tubes 662.4.1.4 Low-pressure sodium lamps 662.4.1.5 High-pressure mercury lamps 662.4.1.6 Metal halide lamps 672.4.1.7 High-pressure sodium lamps 672.4.2 Compensation and wiring of discharge lamps 672.4.3 Radio-interference suppression and limiting other

interference 672.4.4 Transformers for low-voltage installations 682.4.5 Controlling brightness 712.4.5.1 Incandescent and halogen lamps 71

Contents


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2.4.5.2 Low-voltage halogen lamps 712.4.5.3 Fluorescent lamps 712.4.5.4 Compact fluorescent lamps 722.4.5.5 Other discharge lamps 722.4.6 Remote control 722.4.7 Lighting control systems 722.4.7.1 Lighting control systems for theatrical effects 73

2.5 Light qualities and features 74

2.5.1 Quantity of light 742.5.2 Diffuse light and directed light 762.5.2.1 Modelling 772.5.2.2 Brilliance 782.5.3 Glare 792.5.4 Luminous colour and colour rendering 83

2.6 Controlling light 85

2.6.1 The principles of controlling light 852.6.1.1 Reflection 852.6.1.2 Transmission 852.6.1.3 Absorption 872.6.1.4 Refraction 872.6.1.5 Interference 872.6.2 Reflectors 882.6.2.1 Parabolic reflectors 892.6.2.2 Darklight reflectors 902.6.2.3 Spherical reflectors 902.6.2.4 Involute reflectors 902.6.2.5 Elliptical reflectors 902.6.3 Lens systems 912.6.3.1 Collecting lenses 912.6.3.2 Fresnel lenses 912.6.3.3 Projecting systems 912.6.4 Prismatic systems 922.6.5 Accessories 92

2.7 Luminaires 94

2.7.1 Stationary luminaires 942.7.1.1 Downlights 942.7.1.2 Uplights 972.7.1.3 Louvred luminaires 972.7.1.4 Washlights 1002.7.1.5 Integral luminaires 1012.7.2 Movable luminaires 1022.7.2.1 Spotlights 1022.7.2.2 Wallwashers 1032.7.3 Light structures 1042.7.4 Secondary reflector luminaires 1052.7.5 Fibre optic systems 105

3.0 Lighting design

3.1 Lighting design concepts 110

3.1.1 Quantitative lighting design 1103.1.2 Luminance-based design 1123.1.3 The principles of perception-oriented lighting design 1153.1.3.1 Richard Kelly 1153.1.3.2 William Lam 1173.1.3.3 Architecture and atmosphere 118

3.2 Qualitative lighting design 119

3.2.1 Project analysis 1193.2.1.1 Utilisation of space 1193.2.1.2 Psychological requirements 1223.2.1.3 Architecture and atmosphere 122


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3.2.2 Project development 1233.3 Practical planning 126

3.3.1 Lamp selection 1263.3.1.1 Modelling and brilliance 1273.3.1.2 Colour rendering 1273.3.1.3 Luminous colour and colour temperature 1283.3.1.4 Luminous flux 1283.3.1.5 Efficiency 1283.3.1.6 Brightness control 1303.3.1.7 Ignition and re-ignition 1303.3.1.8 Radiant and thermal load 1303.3.2 Luminaire selection 1323.3.2.1 Standard product or custom design 1323.3.2.2 Integral or additive lighting 1323.3.2.3 Stationary or movable lighting 1363.3.2.4 General lighting or differentiated lighting 1363.3.2.5 Direct or indirect lighting 1363.3.2.6 Horizontal and vertical lighting 1383.3.2.7 Lighting working areas and floors 1383.3.2.8 Wall lighting 1393.3.2.9 Ceiling lighting 1413.3.2.10 Luminance limitation 1413.3.2.11 Safety requirements 1433.3.2.12 Relation to acoustics and air conditioning 1433.3.2.13 Accessories 1433.3.2.14 Lighting control and theatrical effects 1443.3.3 Lighting layout 1443.3.4 Switching and lighting control 1503.3.5 Installation 1523.3.5.1 Ceiling mounting 1523.3.5.2 Wall and floor mounting 1543.3.5.3 Suspension systems 1543.3.6 Calculations 1543.3.6.1 Utilisation factor method 1543.3.6.2 Planning based on specific connected load 1573.3.6.3 Point illuminance 1583.3.6.4 Lighting costs 1593.3.7 Simulation and presentation 1603.3.8 Measuring lighting installations 1683.3.9 Maintenance 169

4.0 Examples of lighting concepts

4.1 Foyers 1734.2 Lift lobbies 1804.3 Corridors 1844.4 Staircases 1884.5 Team offices 1924.6 Cellular offices 1984.7 Executive offices 2034.8 Conference rooms 2074.9 Auditoriums 2134.10 Canteens 2174.11 Cafs, bistros 2214.12 Restaurants 2254.13 Multifunctional spaces 2294.14 Museums, showcases 2364.15 Museum, galleries 2414.16 Vaulted ceilings 2494.17 Sales areas, boutiques 2524.18 Sales areas, counters 2564.19 Administration buildings, public areas 2594.20 Exhibitions 264

5.0 Appendix

Illuminance recommendations 270Classification of lamps 271Glossary 272, bibliography 282, acknowledgements 286, index 287


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History1.0


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For the most part of the history of mankind,from the origins of man up to the 18.century, there were basically two sourcesof light available. The older one of thesetwo is daylight, the medium by whichwesee and towhose properties the eye hasadaptedovermillionsofyears.Aconsiderabletime elapsed before the stone age, withits development of cultural techniques andtools, added the flame as a second,artificial light source. From this timeon lighting conditions remained the samefor a considerable time. The paintingsinthe caveof Altamirawere created tobeviewedunderthesamelightasRenaissanceand Baroque paintings.

Lighting was limited to daylight andflame and it was for this very reason thatman has continued to perfect the appli-cation of these two light sources for tensof thousands of years.

1.1.1 Daylight architecture

In the case of daylight this meant consi-stently adapting architecture to therequirements for lighting with natural light.Entire buildings and individual roomswere therefore aligned to the incidence ofthe suns rays. The size of the roomswas also determined by the availability ofnatural lighting and ventilation. Differentbasic types of daylight architecturedeveloped in conjunction with the lightingconditions in the various climatic zonesof the globe. In cooler regions witha predominantly overcast sky we seethe development of buildings with large, tallwindows to allow as much light into thebuilding as possible. It was found thatdiffuse celestial light produced uniformlighting; the problems inherent to brightsunshine cast shadow, glare andoverheating of interior spaces wererestricted to a few sunny days in the yearand could be ignored.

In countries with a lot of sunshinethese problems are critical. A majorityof the buildings here have small windowslocated in the lower sections of the buil-dings and the exterior walls are highlyreflective. This means that hardly any directsunlight can penetrate the building. Eventoday the lighting is effected in the mainby the light reflected from the buildingssurfaces, the light being dispersed inthe course of the reflection process and alarge proportion of its infrared componentdissipated.

Whenitcametothequestionofwhetherthere was sufficient light, aspectsrelating to aesthetic quality and perceptualpsychology were also taken into accountwhen dealing with daylight, which isevident in the way architectural details aretreated. Certain elements were designeddifferently according to the light availableto promote the required spatial effectthrough the interplay of light and shadow.In direct sunlight reliefs, ledges and the

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1.1 History1.1.1 Daylight architecture

The historyof architecturallighting

1.1

Daylight architecture:large, tall windows.

Sunlight architecture:small, low windows,

reflective outer walls.


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1.1 History1.1.2 Artifical lighting

flutingoncolumnshaveathree-dimensionaleffect even if they are of shallow depth.Such details require far more depth underdiffuse light to achieve the same effect.Facades in southern countries thereforeonly needed shallow surface structures,whereas the architecture of morenorthern latitudes and the design ofinterior spaces was dependent on morepronounced forms and accentuationthrough colour to underline the structureof surfaces.

But light does not only serve to renderspatial bodies three-dimensional. It is anexcellent means for controlling ourperception on a psychological level. In oldEgyptian temples e.g.in the sun templeof Amun Re in Karnak or in Abu Simbel you will not find light in the form ofuniform ambient lighting, but as a meansto accentuate the essential colonnadesthat gradually become darker allowtheviewer toadapt to lower lighting levels,the highlighted image of the god thenappearing overwhelmingly bright in con-trast. An architectural construction canfunction similar to an astronomical clock,with special lighting effects only occurringon significant days or during particularperiods in the year, when the sun risesor sets, or at the summer or the wintersolstice.

Inthecourseofhistorytheskilltocreatepurposefully differentiated daylightingeffects has been continually perfected,reaching a climax in the churches ofthe Baroque period, e.g. the pilgrimagechurch in Birnau or the pilgrimage churchdesigned by Dominikus Zimmermannin Upper Bavaria , where the visitorsgaze is drawn from the diffuse brightnessof the nave towards the brightly litaltar area, where intricate wood carvingsdecorated in gold sparkle and standout in relief.

1.1.2 Artificial lighting

A similar process of perfection also tookplace in the realm of artificial lighting,a development that was clearly confined bythe inadequate luminous power providedby the light sources available.

The story began when the flame, thesource of light, was separated from fire,the source of warmth - burning brancheswere removed from the fire and used fora specific purpose. It soon became obviousthat it was an advantage to select piecesof wood that combust and emit lightparticularly well, and the branch wasreplaced by especially resinous pine wood.The next step involved not only relyingon a natural feature of the wood, but, inthe case of burning torches, to applyflammable material to produce more lightartificially. The development of the oillamp and the candle meant that man thenhad compact, relatively safe light sourcesat his disposal; select fuels were used eco-

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Theinfluence of lightonnorthern and southernarchitectural design. Inthe south spatial formsare aligned to thecorrelation of the steepangle of incident sun-light and light reflectedfrom the ground. In thenorth i t i s the lowangle of the suns raysthat affects the shapeof the buildings.

Greek oil lamp, a massitem in the ancientworld

Oil lamp made of brass


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1.1 History1.1.2 Artificial lighting

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Lamps andburners da-ting back to thesecond half of the 19.century, copper engra-ving. Based on theconstruction of theArgand burner, the oillamp was adaptedthrough numeroustechnical innovationsto meet a wide varietyof requirements.The differences between

lamps with flat wicksand those with themore efficient tubularwicks are clearlyevi-dent. In later paraffinlamps the light fuel

was transported to theflame via the capillaryaction of the wickalone, earlier lampsthat used thick-bodiedvegetable oils requiredmore costly fuel supplysolutions involvingupturned glass bottlesor spring mechanisms.In the case of especi-ally volatile or thick-bodied oils there were

special wickless lampsavailable that producedcombustible gaseousmixtures throughthe inherent vapourpressure producedby the volatile oil or byexternal compression.


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1.1 History1.1.3 Science and lighting

nomically in these cases, the torch holderwas reduced to the wick as a means oftransport for wax or oil.

The oil lamp, which was actually de-velopedin prehistorictimes, representedthe highest form of lighting engineeringprogress for a very long time. The lampitself later to be joined by the candlestick continued to be developed. All sortsof magnificent chandeliers and sconceswere developed in a wide variety of styles,but the flame, and its luminous power,remained unchanged.

Comparedto modern day light sourcesthis luminous power was very poor,and artificial lighting remained a make-shift device. In contrast to daylight, whichprovided excellent and differentiatedlighting for an entire space, thebrightnessof a flame was always restricted to itsdirect environment. People gatheredaround the element that provided lightor positioned it directly next to the objectto be lit. Light, albeit weak, began tomark mans night-time. To light interiorsbrightly after dark required largenumbers of expensive lamps and fixtures,which were only conceivable for courtlygatherings. Up to the late 18th centuryarchitectural lighting as we know it todayremained the exclusive domain of day-lighting.

1.1.3 Science and lighting

The reason why the development of effi-cient artficial light sources experienceda period of stagnation at this point in timelies in mans inadequate knowledge in thefield of science. In the case of the oillamp, it was due to mans false conceptionof the combustion process. Until thebirth of modern chemistry, the belief laiddown by the ancient Greeks was takento be true: during the burning processa substance called phlogistos was released.According to the Greeks, any materialthat could be burned therefore consistedof ash and phlogistos (the classicalelements of earth and fire), which wereseparated during the burning process phlogistos was released as a flame, earthremained in the form of ash.

It is clear that the burning processcould not be optimised as long as beliefswere based on this theory. The roleof oxidation had not yet been discovered.It was only through Lavoisiers experimentsthat it became clear that combustionwas a form of chemical action and thatthe flame was dependent on the presenceof air.

Lavoisiers experiments were carriedout in the 1770s and in 1783 the new fin-dings were applied in the field of lighting.Francois Argand constructed a lamp thatwas to be named after him, the Argandlamp. This was an oil lamp with a tubularwick, whereby air supply to the flamewas effected from within the tube as wellas from the outer surface of the wick.

Improved oxygen supply together with anenlarged wick surface meant a huge andinstantaneous improvement in luminousefficiency. The next step involved surroun-ding wick and flame with a glass cylinder,whereby the chimney effect resultedin an increased through-put of air anda further increase in efficiency.The Argandlamp became the epitome of the oillamp. Even modern day paraffin lamps workaccording to this perfected principle.

Optical instruments have been recognisedas aids to controlling light from very earlytimes. Mirrors are known to have beenused by ancient Greeks and Romans andthe theory behind their application setdown in writing. There is a tale aboutArchimedes setting fire to enemy shipsoff Syracuse using concave mirrors.And there are stories of burning glasses,in the form of water-filled glass spheres.

At the turn of the first millennium,there were a number of theoretical worksin Arabia and China concerning the effectof optical lenses. There is in fact concreteevidence of these lenses dating fromthe 13th century. They were predominantlyused in the form of magnifying glassesor spectacles as a vision aid. The materialfirst used was ground beryl. This costlysemi-precious stone was later replaced byglass, manufactured to a sufficiently clearquality. The German word for glassesis Brille, demonstrating a clear semanticlink to the original material used for thevision aid.

In the late 16th century the first tele-scopes were designedby Dutch lens grinders.In the 17th century these instrumentswere then perfected by Galileo, Keplerand Newton; microscopes and projectorequipment were then constructed.

At the same time, some basic theoriesabout the nature of light originated.Newton held the view that light wasmade up of numerous particles a viewthat can be retraced to ancient time.Huygens, on the other hand, saw light asa phenomenon comprising waves. The twocompeting theories are substantiated bya series of optical phenomena and existedside by side. Today it is clear that lightcan neither be understood as a purelyparticle or wave-based phenomenon,but only through an understanding of thecombination of both ideas.

With the development of photometrics the theory of how to measure light and illuminances through Boguer andLambert in the 18th century, the mostessential scientific principles for workablelighting engineering were established.The application of these various correlatedfindings was restricted practically exclu-sively to the construction of optical in-struments such as the telescope and themicroscope, to instruments therefore thatallow man to observe, and are dependenton external light sources. The activecontrol of lightusing reflectors and lenses,known to be theoretically possible and

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Christiaan Huygens. Isaac Newton.

Paraffin lampwith Argand burner.


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1.1 History1.1.4 Modern light sources

occasionally tested, was doomed to faildue to the shortcomings of the lightsources available.

In the field of domestic lighting thefact that there was no controllable,centrally situated light available was notconsidered to be a concern. It was com-pensated for by family gatherings aroundthe oil lamp in the evenings. This short-coming gave rise to considerable problemsin other areas, however. For example,in lighting situations where a considerabledistance between the light source andthe object to be lit was required, aboveall, therefore, in street lighting and stagelighting, and in the area of signalling,especially in the constructionof lighthouses.It was therefore not surprising thatthe Argand lamp, with its considerablyimproved luminous intensity not onlyserved to light living-rooms, but waswelcomed in the above-mentioned criticalareas and used to develop systems thatcontrol light.

This applied in the first place to streetand stage lighting, where the Argandlamp found application shortly after itsdevelopment. But the most important usewas for lighthouses, which had previouslybeen poorly lit by coal fires or by usinga large number of oil lamps. The proposalto light lighthouses using systems compri-sing Argand lamps andparabolic mirrorswas made in 1785; six years later the ideawas used in Frances most prominentlighthouse in Cordouan. In 1820 AugustinJean Fresnel developed a compositesystem of stepped lens and prismatic ringswhich could be made large enoughto concentrate the light from lighthouses;this construction was also first installedin Cordouan. Since then Fresnel lenses havebeen thebasis for all lighthouse beaconsand have also been applied in numeroustypes of projectors.

1.1.4 Modern light sources

The Argand lamp marked the climax ofa development which lasted tens of thou-sands of years, perfecting the use of theflame as a light source. The oil lamp at itsvery best, so to speak. Scientific progress,which rendered this latter developmentpossible, gave rise to the developmentof completely new light sources , whichrevolutionised lighting engineering at anincreasingly faster pace.

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Beacon with Fresnellenses and Argandburners.

Augustin Jean Fresnel.

Fresnel lenses andArgand burners. Theinner section of theluminous beam is con-centrated via a steppedlens, the outer sectiondeflected by meansof separate prismaticrings.


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1.1.4.1 Gas lighting

ThefirstcompetitortotheArgandlampwasgas lighting. People had known ofthe existence of combustible gases sincethe 17th century, but gaseous substanceswere first systematically understoodand produced within the framework ofmodern chemistry. A process for recoveringlighting gas from mineral coal wasdeveloped in parallel to the Argand lampexperimentation.

Towards the end of the 18th centurythe efficiency of gas lighting was demon-strated in a seriesof pilotprojects a lecturehall in Lwen lit by Jan Pieter Minckellaers;a factory, a private home and evenan automobile lit by the English engineerWilliam Murdoch. This new light sourceachieved as yet unknown illuminancelevels. It was, however, not yet possible tointroduce this new form of lighting ona large scale due to the costs involved inthe manufacture of the lighting gas andin removing the admittedly foul-smellingresidues. A number of small devices weredeveloped, so-called thermo-lamps,which made it possible to produce gas forlighting and heating in individual house-holds. These devices did not prove tobe as successful as hoped. Gas lighting onlybecame an economic proposition withthe coupling of coke recovery and gasproduction, then entire sections of townscould benefit from central gas supply.Street lighting was the first areato be connected to a central gas supply,followed gradually by public buildingsand finally private households.

As is the case with all other lightsources a series of technical developmentsmade gas lighting increasingly moreefficient. Similar to the oil lamp a varietyof different burners were developedwhose increased flame sizes providedincreased luminous intensity. The Argandprinciple involving the ring-shaped flamewith its oxygen supply from both sidescould also be applied in the case ofgas lighting and in turn led to unsurpassedluminous efficacy.

The attempt to produce a surplus ofoxygen in the gas mixture by continuingto develop the Argand burner produceda surprising result. As all the carbon con-tained in the gas was burned off to pro-duce gaseous carbon dioxide, the glowingparticles of carbon that incorporated thelight produced by the flame were no longerevident; this gave rise to the extraor-dinarily hot, but barely glowing flame ofthe Bunsen burner. There was thereforea limit to the luminous intensity of self-luminous flames; for further increasesin efficiency researchers had to fall backon other principles to produce light .

One possibility for producing highly efficientgas lighting was developed through thephenomenon of thermo-luminescence, theexcitation of luminescent material by

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Lighting shop windows

using gas light (around1870).

Carl Auer v. Welsbach.

Drummonds limelight. The incandescentmantle as invented by

Auer v. Welsbach.


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heating. In contrast to thermal radiation,luminous efficacy and colour appearancein this process were not solely dependenton the temperature, but also on the kindof material; more and whiter lightwas produced using temperature radiationmethods.

The first light source to work accordingto this principle was Drummondslimelight, which was developed in 1826.This involved a piece of limestone beingexcited to a state of thermo-luminescencewith the aid of an oxy-hydrogen burner.Limelight is admittedly very effective, butrequires considerable manual control withthe result that it was used almost exclu-sively for effect lighting in the theatre.It was only in 1890 that Austrian chemistCarl Auer von Welsbach came up witha far more practical method for utilisingthermo-luminiscence. Auer von Welsbachsteeped a cylinder made of cotton fabricin a solution containing rare earths sub-stances that, similar to limestone, emita strong white light when heated. Theseincandescent mantles were applied toBunsen burners. On first ignition the cottonfabric burned, leaving behindnothing butthe rare earths the incandescent mantle ineffect. Through the combination of theextremely hot flame of the Bunsen burnerand incandescent mantles comprising rareearths, the optimum was achieved inthe field of gas lighting. Just as the Argandlamp continues to exist today in theform of the paraffin lamp, the incandescentor Welsbach mantle is still used for gaslighting, e.g. in camping lamps.

1.1.4.2 Electrical light sources

Incandescent gas light was doomed to gothe way of most lighting discoveries thatwere fated to be overtaken by new lightsources just as they are nearing perfection.This also applies to the candle, whichonly received an optimised wick in 1824to prevent it from smoking too much.Similarly, the Argand lamp was pipped atthe post by the development of gaslighting, and for lightingusing incandescentmantles, which in turn had to competewith the newly developed forms of electriclight.

In contrast to the oil lamp and gaslighting, which both started life as weaklight sources and were developed to be-come ever more efficient, the electric lampembarked on its career in its brightestform. From the beginning of the 19thcentury it was a known fact that by crea-ting voltage between two carbon electrodesan extremely bright arc could be pro-duced. Similar to Drummonds limelight,continuous manual adjustment wasrequired, making it difficult for this newlight source to gain acceptance, addedto the fact that arc lamps first had to beoperated on batteries, which was a costlybusiness.

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Hugo Bremers arclamp. A simple springmechanism automati-cally controls the dis-tance between thefour carbon electrodesset intheshape ofa V .

Jablotschkows version

of the arc lamp, ex-posed and with glassbulb.

Arc lighting at thePlace de la Concorde.


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Siemens arc lampdating back to 1868.According to the des-cription: an adjustablespotlight complete withconcave mirror, car-riage, stand and anti-dazzle screen" the oldest luminairein Siemens archivesdocumentedin the form

of a drawing.


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About mid-century self-adjusting lampswere developed, thereby eliminating theproblem of manual adjustment. Generatorsthat could guarantee a continuous supplyof electricity were now also available.It was, however, still only possible to operateone arc lamp per power source; seriesconnection splitting the light, as it wascalled was not possible, as the differentburning levels of the individual lampsmeant that the entire series was quicklyextinguished. This problem was onlysolved in the 1870s. The simple solutionwas provided by Jablotschkows versionof the arc lamp, which involved twoparallel carbon electrodes set in a plastercylinder and allowed to burn simulta-neously from the top downwards. A morecomplex, but also more reliable solutionwas provided by the differential lamp,developed in 1878 by Friedrich v. Hefner-Alteneck, a Siemens engineer, wherebycarbon supply and power constancy wereeffected via an electromagnetic system.

Now that light could be divided upthearc lamp became an extremely practicallight source, which not only foundindividual application, but was also usedon a wide scale. It was in fact appliedwherever its excellent luminous intensitycouldbeputtogooduseonceagaininlighthouses, for stage lighting; and, aboveall, for all forms of street and exteriorlighting. The arc lamp was not entirelysuitable for application in private homes,however, because it tended to producefar too much light a novelty in the fieldof lighting technology. It would takeother forms of electric lighting to replacegas lighting in private living spaces.

It was discovered at a fairly early stage,that electrical conductors heat up to pro-duce a sufficiently great resistance, andeven begin to glow; in 1802 eight yearsbefore his spectacular presentation of thefirst arc lamp Humphrey Davy demon-strated how he could make a platinum wireglow by means of electrolysis.

The incandescent lamp failed to esta-blish itself as a new light source fortechnical reasons, much the same as thearclamp. There were only a few substancesthat had a melting point high enough tocreate incandescence before melting.Moreover, the high level of resistancerequired very thin filaments, which weredifficult to produce, broke easily andburnt up quickly in the oxygen in the air.

First experiments made with platinumwires or carbon filaments did not producemuch more than minimum service life.The life time could only be extended whenthe filament predominantly madeof carbon or graphite at that time wasprevented from burning up by surroundingit with a glass bulb, which was eitherevacuated or filled with inert gas.Pioneers in this field were Joseph WilsonSwan, who preceded Edison by sixmonths with his graphite lamp, but above

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Heinrich Goebel, experi-mental incandescent

lamps (carbon fila-ments in air-void eau-de-cologne bottles).

Joseph Wilson Swan,Swans version of theincandescent lampwith graphite filamentand spring base.

Thomas Alva Edison,Edison lamps, platinumand carbon filament

version, as yet withoutthe typical screw cap.


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all Heinrich Goebel, who in 1854 producedincandescent lamps with a service lifeof 220 hours with the aid of carbonizedbamboo fibres and air-void eau-de-colognebottles.

The actual breakthrough,however, wasindeed thanks to Thomas Alva Edison,who in 1879 succeeded in developing anindustrial mass product out of theexperimental constructions created by hispredecessors. This product correspondedin many ways to the incandescentlampas weknow ittoday right down tothe construction of the screw cap.The filament was the only element thatremained in need of improvement.Edison first used Goebels carbon filamentcomprising carbonized bamboo. Latersynthetic carbon filaments extruded fromcellulose nitrate were developed. The lu-minous efficacy, always the main weaknessof incandescent lamps, could, however,only be substantially improved withthe changeover to metallic filaments. This iswhere Auer von Welsbach, who hadalready made more efficient gas lightingpossible through the development of theincandescent mantle, comes into his ownonce again. He used osmium filamentsderived through a laborious sinteringprocess. The filaments did not prove to bevery stable, however, givingway to tantalumlamps, which were developed a littlelater and were considerably more robust.These were in turn replaced by lampswith filaments made of tungsten, a mate-rial still used for the filament wire inlamps today.

Following the arc lamp and the incandes-cent lamp, discharge lamps took theirplace as the third form of electric lighting.Again physical findings were availablelong before the lamp was put to anypractical use. As far back as the 17thcentury there were reports about luminousphenomena in mercury barometers.But it was Humphrey Davy once againwho gave the first demonstration of howa discharge lamp worked. In fact, atthe beginning of the 18th century Davy ex-amined all three forms of electric lightingsystematically. Almost eighty yearspassed, however, before the first trulyfunctioning discharge lamps were actuallyconstructed, and it was only after theincandescent lamp had established itselfas a valid light source, that the firstdischarge lamps with the prime purposeof producing light were brought ontothe market. This occured at aroundthe turn of the century. One of thesewas the Moore lamp a forerunner of themodern-day high voltage fluorescenttube. It consisted of long glass tubes ofvarious shapes and sizes, high voltageand a pure gas discharge process. Anotherwas the low-pressure mercury lamp,which is the equivalent of the fluorescentlamp as we know it today, except that ithad no fluorescent coating.

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Cooper-Hewitts l ow-pressure mercury lamp.This lamp workedmuch like a modern-day fluorescent tubebut did not containany fluorescent mate-rial, so only very littlevisible light was pro-duced. The lamp wasmounted in the centrelike a scale beam, be-cause it was ignitedby tippingthe tubes bymeans of a drawstring.

Theatre foyer lit byMoore lamps.


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1.1 History1.1.5 Quantitative lighting design1.1.6 Beginnings of new lighting design

The Moore lamp like the high-voltage fluorescent tube today wasprimarily used for contour lighting in archi-tectural spaces and for advertising purpo-ses; its luminous intensity was too lowto be seriously used for functional lighting.The mercury vapour lamp, on the otherhand, had excellent luminous efficacyvalues, which immediately established it asa competitor to the relatively inefficientincandescent lamp. Its advantages were,however, outweighed by its inadequatecolour rendering properties, which meantthat it could only be used for simplelighting tasks.

There were two completely differentways of solving this problem.Onepossibilitywas to compensate for the missingspectral components in the mercuryvapour discharge process by adding lumi-nous substances. The result was the flu-orescent lamp, which did produce goodcolour rendering and offered enhancedluminous efficacy due to the exploitationof the considerable ultra-violet emission.

The other idea was to increase thepressure by which the mercury vapourwas discharged. The result was moderatecolour rendering, but a considerable in-crease in luminous efficacy. Moreover, thismeant that higher light intensitiescould be achieved, which made the high-pressure mercury lamp a competitor to thearc lamp.

1.1.5 Quantitative lighting design

A good hundred years after scientific re-search into new light sources beganall the standard lamps that we know todayhad been created, at least in their basicform. Up to this point in time, sufficientlight had only been available duringdaylight hours. From now on, artificiallight changed dramatically. It was no longera temporary expedient but a formof lighting to be taken seriously, rankingwith natural light.

Illuminance levels similar to those ofdaylight could technically now be pro-duced in interior living and working spacesor in exterior spaces, e.g. for the lightingof streets and public spaces, or forthe floodlighting of buildings. Especially inthe case of street lighting, the temptationto turn night into day and to do awaywith darkness altogether was great. In theUnited States a number of projects wererealised in which entire towns were lit byan array of light towers. Floodlightingon this scale soon proved to have more dis-advantages than advantages due to glareproblems and harsh shadows. The daysof this extreme form of exterior lightingwere therefore numbered.

Both the attempt to provide comprehen-sive street lighting and the failure ofthese attempts was yet another phase inthe application of artificial light. Whereas

inadequate light sources had been themain problem to date, lighting specialistswere then faced with the challengeof purposefully controlling excessiveamounts of light. Specialist engineersstarted to think about how muchlight was to be required in which situationsand what forms of lighting were to beapplied.

Task lighting in particular was examinedin detail to establish how great aninfluence illuminance and the kind oflighting applied had on productivity.The result of these perceptual physiologicalinvestigations was a comprehensivework of reference that containedthe illuminance levels required for certainvisual tasks plus minimum colour renderingqualities and glare limitation require-ments.

Although this catalogue of standardswas designed predominantly as an aidfor the planning of lighting for workplaces,it soon became a guideline for lightingin general, and even today determineslighting design in practice. As a planningaid it is almost exclusively quantity-oriented and should, therefore, not beregarded as a comprehensive planning aidfor all possible lighting tasks. The aimof standards is to manage the amount oflight available in an economic sense,based on the physiological research thathad been done on human visual require-ments.

The fact that the perception of anobject is more than a mere visual task andthat, in addition to a physiological process,vision is also a psychological process,was disregarded. Quantitative lightingdesign is content with providing uniformambient lighting that will meet there-quirements of the most difficult visualtask to be performed in the given space,while at the same time adhering to thestandards with regard to glare limitationand colour distortion. How we see archi-tecture, for instance, under a given light,whether its structure is clearly legible andits aesthetic quality has been enhancedby the lighting, goes beyond the realm ofa set of rules.

1.1.6 Beginnings of a new kind oflighting design

It was, therefore, not surprising thatalongside quantative lighting technologyand planning a new approach to designingwith light was developed, an approachthat was related far more intenselyto architectural lighting and its inherentrequirements.

This developed in part within theframework of lighting engineering as itwas known. Joachim Teichmller, founderof the Institute for Lighting Technologyin Karlsruhe, is a name that should be men-tioned here. Teichmller defined theterm Lichtarchitektur as architecture that

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American light tower(San Jos 1885).


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1.1 History1.1.6 Beginnings of new lighting design

conceives light as a building material andincorporates it purposefully into the over-all architectural design. He also pointedout and he was the first to do so that,with regard to architectural lighting,artificial light can surpass daylight, if it isapplied purposefully and in a differentiatedway.

Lighting engineers still tended topractise a quantative lighting philiosophy.It was the architects who were nowbeginning to develop new concepts forarchitectural lighting. From time imme-morial, daylight had been the definingagent. The significance of light and shadowand the way light can structurea building is something every architectis familiar with. With the development ofmore efficient artificial light sources,the knowledge that has been gained of day-light technology was now joined bythe scope offered by artificial light. Lightno longer only had an effect coming fromoutside into the building. It could lightinterior spaces, and now even light frominside outwards. When Le Corbusierdescribed architecture as the correct andmagnificent play of masses broughttogether in light, this no longer onlyapplied to sunlight, but also included theartificially lit interior space.

This new understanding of light hadspecial significance for extensively glazedfacades, which were not only openingsto let daylight into the building, but gavethe architecture a new appearance atnight through artificial light. A Germanstyle of architecture known as GlserneKette in particular interpreted the buildingas a crystalline, self-luminous creation.Utopian ideas of glass architecture,luminous cities dotted with light towersand magnificent glazed structures, laPaul Scheerbart, were reflected in a numberof equally visionary designs of spar-kling crystals and shining domes. A littlelater, in the 1920s, a number of glassarchitecture concepts were created; largebuildings such as industrial plants ordepartment stores took on the appearanceof self-illuminating structures afterdark, their facades divided up via the inter-change of dark wall sections and lightglazed areas. In these cases, lightingdesign clearly went far beyond the merecreation of recommended illuminances.It addressed the structures of the litarchitecture. And yet even this approachdid not go far enough, because it regardedthe building as a single entity, to beviewed from outside at night, and dis-regarded users of the building and theirvisual needs.

Buildings created up to the beginningof the second world war were thereforecharacterised by what is, in part , highlydifferentiated exterior lighting. All this,however, made little difference to thetrend towards quantitative, unimaginativeinterior lighting, involving in the mainstandard louvred fittings.

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Joachim Teichmller.

Wassili Luckhardt

(18891972): Crystalon the sphere. Cultbuilding. Second ver-sion. Crayon, around1920.

J. Brinkmann, L. C. van derVlugt and Mart Stam:Van Ne lle tobacco factory,Rotterdam 192630.


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In order to develop more far-reachingarchitectural lighting concepts, manhad to become the third factor alongsidearchitecture and light. Perceptual psycho-logy provided the key. In contrast tophysiological research, it was not simply aquestion of the quantitative limiting va-lues for the perception of abstract visualtasks. Man as a perceiving being wasthe focus of the research, the question ofhow reality perceived is reconstructed inthe process of seeing. These investigationssoon led to evidence that perceptionwas not purely a process of reproducingimages,not a photographing of ourenviron-ment. Innumerable optical phenomenaproved that perception involves a complexinterpretation of surrounding stimuli,that eye and brain constructed rather thanreproduced an image of the world aroundus.

In view of these findings lightingacquired a totally new meaning. Light wasno longer just a physical quantity thatprovided sufficient illumination; it becamea decisive factor in human perception.Lighting was not only there to renderthings and spaces around us visible,it determined the priority and the wayindividual objects in ourvisual environmentwere seen.

1.1.6.1 The influence of stage lighting

Lighting technology focussing on man as aperceptive being acquired a number ofessential impulsesfrom stage lighting. In thetheatre, the question of illuminance levelsand uniform lighting is of minor impor-tance. The aim of stage lighting is notto render the stage or any of the technicalequipment it comprises visible; whatthe audience has to perceive is changingscenes and moods light alone can beapplied on the same set to create the im-pression of different times of day, changesin the weather, frightening or romanticatmospheres.

Stage lighting goes much furtherin its intentions than architectural lightingdoes it strives to create illusions, where-as architectural lighting is concernedwithrendering real structures visible.Never-theless stage lighting serves as an examplefor architectural lighting. It identifiesmethods of producing differentiatedlighting effects and the instruments re-quired to create these particular effects both areas from which architecturallighting can benefit. It is therefore notsurprising that stage lighting began toplay a significant role in the developmentof lighting design and that a large numberof well-known lighting designers have theirroots in theatre lighting.

1.1.6.2 Qualitative lighting design

A new lighting philosophy that no longerconfined itself exclusively to quantitative

aspects began to develop in the USAafter the second world war. One of thepioneers in the field is without doubtRichard Kelly, who integrated existing ideasfrom the field of perceptual psychologyand stage lighting to create one uniformconcept.

Kelly broke away from the idea ofuniform illuminance as the paramountcriterion of lighting design. He substitutedthe issue of quantity with the issue ofdifferent qualities of light, of a series offunctions that lighting had to meet toserve the needs of the perceiver. Kelly dif-ferentiated between three basic func-tions: ambient light , focal glow and playof brilliance.

Ambient light corresponded to whathad up to then been termed quantitativelighting.General lighting was providedthat was sufficient for the perception ofthe given visual tasks; these mightinclude the perception of objects andbuilding structures, orientation within anenvironment or orientation while inmotion.

Focal glow went beyond this generallighting and allowed for the needs of manas a perceptive being in the respectiveenvironment. Focal glowpicked out relevantvisual information against a backgroundof ambient light; significant areas wereaccentuated and less relevant visualinformation took second place. In contrastto uniform lighting, the visual environ-ment was structured and could be perceivedquickly and easily. Moreover, the viewersattention could be drawn towardsindividual objects, with the result thatfocal glow not only contributed towardsorientation, but could also be used forthe presentation of goods and aestheticobjects.

Play of brilliance took into accountthe fact that light does not only illuminateobjects and express visual information,but that it could become an objectof contemplation, a source of information,in itself. In this third function lightcould also enhance an environment inan aesthetic sense play of brilliance froma simple candle flame to a chandeliercould lend a prestigious space life andatmosphere.

These three basic lighting categoriesprovided a simple, but effective andclearly structured range of possibilitiesthat allowed lighting to address thearchitecture and the objects within anenvironment as well as the perceptual needsof the users of the space. Starting inthe USA, lighting design began to changegradually from a purely technical disci-pline to an equally important and indis-pensible discipline in the architecturaldesign process the competent lightingdesigner became a recognised partnerin the design team, at least in the case oflarge-scale, prestigious projects.

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Ambient light.


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1.1.6.3 Lighting engineering and lightingdesign

The growing demand for quality lightingdesignwasaccompaniedbythedemandfor quality lighting equipment. Differen-tiated lighting required specialisedluminaires designed to cope with specificlighting tasks. You need completely diffe-rent luminaires to achieve uniform wash-light over a wall area, for example,than youdo foraccentuatingone individualobject, or different ones again for thepermanent lighting in a theatre foyerthan for the variable lighting required ina multi-purpose hall or exhibition space.

The development of technical possibi-lities and lighting application led toa productive correlation: industry had tomeet the designers demands for newluminaires, and further developments inthe field of lamp technology and luminairedesign were promoted to suit particularapplications required by the lightingdesigners.

New lighting developments served toallow spatial differentiation and moreflexible lighting. Exposed incandescent andfluorescent lamps were replaced by avariety of specialised reflector luminaires,providing the first opportunity to directlight purposefully into certain areasor onto objects from theuniform lightingof extensivesurfaces using wall or ceilingwashers to the accentuation of a preciselydefined area by means of reflector spot-lights. The development of track lightingopened up further scope for lightingdesign, because it allowed enormous flexibi-lity. Lighting installationscouldbe adap-ted to meet the respective requirementsof the space.

Products that allowed spatial differen-tiation were followedby new developmentsthat offered time-related differentiation:lighting control systems. With the useof compact control systems it has becomepossible to plan lighting installationsthat not only offer one fixed application,but are able to define a range of lightscenes. Each scene can be adjusted to suitthe requirements of a particular situation.This might be the different lightingconditions required for a podiumdiscussion or for a slide show, but it mightalso be a matter of adapting to changeswithin a specific environment: the changingintensity of daylight or the time of day.Lighting control systems are therefore alogicalconsequenceofspatialdifferentiation,allowing a lighting installation to beutilised to the full a seamless transitionbetween individual scenes, which is simplynot feasible via manual switching.

There is currently considerable researchand development being undertaken inthe field of compact light sources: amongthe incandescents the halogen lamp,whose sparkling, concentrated lightprovides new concepts for display lighting.Similar qualities are achieved in the field

of discharge lamps with metal halidesources. Concentrated light can be appliedeffectively over larger distances. Thethird new development is the compactfluorescent lamp, which combines theadvantages of the linear fluorescent withsmaller volume, thereby achievingimproved optical control, ideally suited toenergy-efficient fluorescent downlights,for example.

All this means that lighting designershave a further range of tools at theirdisposal for the creation of differentiatedlighting to meet the requirements ofthe specific situation and the perceptualneeds of the people using the space.It can be expected in future that progressin the field of lighting design will dependon the continuing further developmentof light sources and luminaires, but aboveall on the consistent application of thishardware in the interest of qualitativelighting design. Exotic solutions usingequipment such as laser lighting orlighting using huge reflector systems will remain isolated cases and will notbecome part of general lighting practice.

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Play of brilliance

Focal glow.


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Basics2.0


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2.1 Perception2.1.1 Eye and camera2.1

Most of the information we receive aboutthe world around us is through our eyes.Light is not only an essential prerequisiteand the medium by which we are ableto see. Through its intensity, the way it isdistributed throughout a space andthrough its properties, light creates specificconditions which can influence ourperception.

Lighting design is, in fact, the planning ofour visual environment. Good lightingdesign aims to create perceptual con-ditions which allow us to work effectivelyand orient ourselves safely while pro-moting a feeling of well-being in a parti-cular environment and at the same timeenhancing that same enviroment in anaesthetic sense. The physical qualities ofa lighting situation can be calculated andmeasured. Ultimately it is the actualeffect the lighting has on the user ofa space, his subjective perception, thatdecides whether a lighting concept is suc-cessful or not. Lighting design can there-fore not be restricted to the creationof technical concepts only. Human per-ception must be a key consideration in thelighting design process.

2.1.1 Eye and camera

The process of perception is frequentlyexplained by comparing the eye witha camera. In the case of the camera,an adjustable system of lenses projects thereversed image of an object onto a light-sensitive film. The amount of light iscontrolled by a diaphragm. After developingthe film and reversing the image duringthe enlarging process a visible, two-dimensional image of the object becomesapparent.

Similarly, in the eye, a reversed imageis projected onto the inner surface ofthe eye, the so-called fundus oculi,via a deformable lens. The iris takes on thefunction of the diaphragm, the light-sensitive retina the role of the film.The image is then transported via theopticnerve from the retina to the brain,where it is adjusted in the cortex and madeavailable to the conscious mind.

Comparing the eye with the camera inthis way makes the process of vision fairlyeasy to understand, but it does not con-tribute to our comprehensionof perception.The fault lies in the assumption thatthe image projected onto the retina isidentical to the perceived image. The factthat the retina image forms the basis forperception is undisputed, but there areconsiderable differences between what isactually perceived in our field of visionand the image on the retina.

Firstly, the image is spatially distortedthrough its projection onto the curvedsurface of the retina a straight line is asa rule depicted as a curve on the retina.

Perception

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Spherical aberration.Projected images aredistorted due to thecurvature of the retina.

Chromatic aberration.Images are blurreddue to the variousdegrees of refractionof spectral colours.


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2.1 Perception2.1.2 Perceptual psychology

This spherical misrepresentation is ac-companied by clear chromatic aberration light of various wavelengths is refractedto varying degrees, which producescoloured rings around the objects viewed.

The eye is therefore a very inadequateoptical instrument. It produces a spatiallydistorted and non-colour corrected imageon the retina. But these defects are notevident in our actual perception of theworld around us. This means that theymust somehow be eliminated while theimage is being processed in the brain.

Apart from this corrective process thereare a number of other considerable diffe-rences between the image on the retinaand what we actually perceive. If we per-ceive objects that are arranged within aspace, this gives rise to images on the re-tina whose perspectives are distorted.A square perceived at an angle, for example,will produce a trapezoidal image on theretina. This image may, however, also havebeen produced by a trapezoidal surfaceviewed front on, or by an unlimited num-ber of square shapes arranged at anangle. The only thing that is perceived isone single shape the square that thisimage has actually produced. This percep-tion of a square shape remains consistent,even if viewer or object move, althoughthe shape of the image projected on theretina is constantly changing due to thechanging perspective. Perception cannottherefore only be purely a matter ofrendering the image on the retina availableto our conscious mind. It is more a resultof the way the image is interpreted.

2.1.2 Perceptual psychology

Presenting a model of the eye to demon-strate the similarities to theworkings ofa camera does not provide any explanationas to how the perceived imagecomes intobeing it only transports the object tobe perceived from the outside world to thecortex. To truly understand what visualperception is all about, it is not so muchthe transport of visual information that isof significance, but rather the processinvolved in the interpretation of this infor-mation, the creation of visual impressions.

The next question that arises iswhether our ability to perceive the worldaround us is innate or the result of a lear-ning process, i.e. whether it has tobe developed through experience. Anotherpoint to be considered is whether senseimpressions from outside alone arere-sponsible for the perceived image orwhether the brain translates these stimuliinto a perceivable image through theapplication of its own principles of order.

There is no clear answer to this que-stion. Perceptual psychology is divided onthis point. There are, in fact, a number ofcontradictory opinions, each of which canprovide evidence of various kinds to prove

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Perceptual constancy:perception of a shape

in spite of the fact thatthe image on the retinais changing with thechanging perspective.

Perception of a shapebased on shadow for-

mation alone whencontours are missing.

Recognising an overallshape by revealingessential details.

Matching a colour tothe respective patternperceived. The colour ofthe central grey pointadjusts itself to theblack or white colour ofthe respective perceivedpattern of five


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their point. But not one of these schoolsof thought is able to give a plausibleexplanation for all the phenomena thatoccur during the visual process.

There is an indication that the spatialaspect of perception is innate. If youplace new-born animals (or six-month-old babies) on a glass panel that overlapsa step, they will avoid moving onto thearea beyond the step. This indicates thatthe innate visual recognition of depthand its inherent dangers have priorityover information relayed via the sense oftouch, which tells the animal, or baby,that they are on a safe, flat surface.

On the other hand, it can be demon-strated that perception is also dependenton previous experience. Known shapesare more easily recognised than unknownones. Once interpretations of complexvisual shapes have been gained, theyremain, and serve as a source of referencefor future perception.

In this case experience, and the ex-pectations linked with it, may be sostrong that missing elements of a shapeareperceivedas complete or individualdetails amended to enable the object tomeet our expectations.

When it comes to perception, there-fore, both innate mechanisms and experi-ence have a part to play. It may bepresumed that the innate componentis responsible for organising or structuringthe information perceived,whereas onahigher level of processing experience helpsus to interpret complex shapes and struc-tures.

As for the issue of whether impressionsreceived via the senses alone determineperception or whetherthe informationalso has to be structured on a psychicallevel, again there is evidence to proveboth these concepts. The fact that a greyarea will appear light grey if it is edgedin black, or dark grey if it is edged inwhite can be explained by the fact that thestimuli perceived are processed directly brightness is perceived as a resultof the lightness contrast between thegrey area and the immediate surroundings.What we are considering hereis a visual impression that is based ex-clusively on sensory input which is not in-fluenced by any criteria of order linkedwith our intellectual processing of thisinformation.

On the other hand, the fact thatverticallines in a perspective drawingappear to be considerably larger furtherback in the drawing than in the fore-ground, can be explained by the fact thatthe drawing is interpreted spatially. A linethat is further away, i.e. in the back-ground, must be longer than a line in theforeground in order to produce an equi-valently large retina image in the depthof the space a line of effectively thesame length will therefore be interpretedand perceived as being longer.

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Constancy with regardto perception of size.

Due to the perspectiveinterpretation of thisillustration the lumi-naires are all perceivedas being the same sizein spite of the variati-ons in size of the retinaimages.

In this case the per-spective interpretation

leads to an optical il lu-sion. The vertical lineto the rear appearsto be longer than aline of identical lengthin the foreground dueto the perspectiveinterpretation of thepicture.

The continuous lumi-nance gradient acrossthe surface of thewalls is interpreted asa property of thelighting of the wall.The wall reflectancefactor is assumed to beconstant. The grey ofthe sharply framedpicture is interpretedas a property of thematerial, although theluminance is identicalto the luminance ofthe corner of the room.

The perception of thelightness of the greysurface depends on itsimmediate surroundings.If the surroundingfield is light an identical

shade of grey will appearto be darker than whenthe surrounding fieldis dark.


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Our apparent knowledge of distanceratios therefore gives rise to a changein the way we perceive things. As thedistances in the drawing are however fic-titious, we can say that there is evidencethat the brain is able to perform inter-pretative processes that are not dependenton external stimuli. Perception thereforecannot be attributed to one principlealone, but results from various mecha-nisms.

2.1.2.1 Constancy

Even if there is not one simple explanationfor the way perception works, the questionregarding which objective the variousmechanisms serve remains an interestingone.Optical illusions providean opportunityto examine the effects and aims ofperception. Optical illusion is not a caseof a perceptual faux pas, but can beregarded as the border case of a mechanismthat provides essential information undereveryday conditions. This indicates thatboth phenomena described above, boththe changing perception of brightnesson identical surfaces and the erroneousperception of lines of equal length, can beexplained as stemming from one commonobjective.

One of the most important tasks of per-ception is to differentiate betweenconstantobjectsand changesin our surroun-dings in the continuously changingshapes and distribution of brightnessof the image on the retina. Since constantobjects also produce retina images ofvarying shapes, sizes and brightnessarising due to changes in lighting,distanceor perspective, this indicates that mecha-nisms must exist to identify these objectsand their properties and to perceive themas being constant.

Our misinterpretation of lines of the samelength shows that the perceived size ofan object does not depend on the size of the retina image alone, but that the dis-tance of the observer from the objectis significant. Vice versa, objects of knownsizes are used to judge distances orto recognise the size of adjacent objects.Judging from daily experience thismechanism is sufficient to allow us to per-ceive objects and their size reliably. A per-son seen a long way away is thereforenot perceived as a dwarf and a house onthehorizon not as a small box. Only inextreme situations does our perceptiondeceive us: looking out of an aeroplane ob-jects on the ground appear to be tiny; theviewing of objects that are considerablyfarther away, e.g. the moon, is much moredifficult for us to handle.

Just as we have mechanisms that handlethe perception of size we have similarmechanisms that balance the perspective

distortion of objects. They guarantee thatthe changing trapezoidal and ellipsoidalforms in the retina image can be perceivedas spatial manifestations of constant,rectangular or round objects, while takinginto consideration the angle at which theobject is viewed.

When it comes to lighting designthere is a further complex of constancyphenomena that are of significance;those which control the perception ofbright-ness. Through the identification ofthe luminous reflectance of a surfaceit becomes apparent that a surface reflectslight differently depending on the inten-sity of the surrounding lighting, i.e. theluminance of a surface varies. The illumi-nated side of a unicoloured object has ahigher luminance than the side thatreceives no direct light; a black object insunlight shows a considerably higher levelof luminance than a white object in aninterior space. If perception depended onseen luminance, the luminous reflectancewould not be recognised as a constantproperty of an object.

A mechanism is required that deter-mines the luminous reflectance of asurface from the ratio of the luminances ofthis surface to its surroundings. Thismeans that a white surface is assumed to bewhite both in light and shade, becausein relation to the surrounding sufacesit reflects more light. There is, however, theborderline case, as indicated above, wheretwo surfaces of the same colour are per-ceived as being of a different brightnessunder the same lighting due to differentsurrounding surfaces.

The ability of the perceptual process torecognise the luminous reflectanceof objects under different illuminance levelsis actually only half the story. There mustbe additional mechanisms that go beyondthe perception of luminous reflectance,while processing varying gradients andsharp differences in luminance.

We are familiar with changing luminancelevels on the surfaces around us. Theymay be the result of the type of lighting:one example of this is the gradualdecrease in brightness along the rear wallof a space that is daylit from one sideonly. Or they may arise from the spatialform of the illuminated object: examplesof this are the formation of typicalshadows on spatial bodies such as cubes,cylinders or spheres. A third reasonfor the presence of different luminancesmay lie in the quality of the surface.Uneven reflectance results in unevenluminance even if the lighting is uniform.The aim of the perceptual process isto decide whether an object is of a singlecolour, but not lit uniformly, or whetherit is spatially formed or a uniformlylit object with an uneven reflection factor.

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The spatial impressionis determined by theunconscious assump-tion that l ight comesfrom above. By inver-ting the picture theperception of elevationand depth is changed.

The spatial quality ofan object can berecognised purely fromthe gradient of theshadows.


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The example shown here serves to explainthis process. As a rule the folded card isperceived as if it is being viewed from theoutside (fold to the front). In this case itappears to be uniformly white but lit fromone side. If the card is seen as beingviewed from inside (fold to the rear), it isperceived as being uniformly lit butwith onehalf coloured black. The luminancepattern of the retina image is thereforeinterpreted differently: in one case itis attributed to a characteristicblack/whitecoloration of the perceived object; in theother case perception does not coverthe different luminance in the perceptionof the apparently uniformly white card;it is taken to be a feature of the lightingsituation.

One characteristic feature of perceptionis, therefore, the preference for simpleand easily comprehensible interpretations.Differences in luminance are effectivelyeliminated from the perceived images to alarge extent or especially emphasized de-pending on whether they are interpretedas a characteristic feature of the objector as a feature of the surroundings in thiscase, of the lighting.

These mechanisms should be taken intoconsideration when designing thelighting for a space. The first conclusionthat can be drawn is that the impressionof uniform brightness does not dependon totally uniform lighting, but thatit can be achieved by means of luminancegradients that run uniformly.

On the other hand irregular or unevenluminances can lead to confusing lightingsituations. This is evident, for example,when luminous patterns created on thewalls bear no relation to the architecture.The observers attention is drawn to aluminance pattern thatcannot be explainedthrough the properties of the wall, noras an important feature of the lighting.If luminance patterns are irregular theyshould, therefore, always be in accordancewith the architecture.

The perception of colour, similar to theperception of brightness, is dependent onsurrounding colours and the qualityof the lighting. The necessity to interpretcolours is based on the fact that colourappearances around us are constantlychanging.

A colour is therefore perceived asbeing constant both when viewed in thebluish light of an overcast sky or in warmerdirect sunlight colour photographstaken under the same conditions, however,show the colour shifts we expect underthe particular lighting.

Perception is therefore able to adjustto the respective colour properties of thelighting, thereby providing constantcolour perception under changing condi-tions. This only applies, however, when

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Change of perceptionfrom light/dark toblack/white if the spa-tial interpretationof the figure changes.

Light distribution thatis notaligned with thearchitectural structureof the spaceis perceived

as disturbing patternsthat do not relate tothe space.

The position of theluminous beam deter-mines whether itis perceived as back-ground or as a distur-bing shape.

The lighting distributionon an unstructured

wall becomes adominant feature,whereas the samelighting distributionon a structured wal l isinterpreted as back-ground and not per-ceived.


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the entire environment is lit with light ofthe same luminous colour and thelighting does not change too rapidly.If different lighting situations can be com-pared directly, the contrast due to differentluminous colours will be perceived.This becomes evident when the observermoves through spaces that are lit diffe-rently, but above all when different lightsources are used within one room orif the observer is in a space comprisingcoloured glazing and in a position tocompare the lighting inside and outsidethe building. Lighting a space usingdifferent luminous colours can be doneeffectively, if the change of luminouscolour bears a clear relation to the re-spective environment.

2.1.2.2 Laws of gestalt

The main theme of this chapter so far hasbeen thequestion of how the properties ofobjects size, form, reflectance andcolour are perceived as being constantin spite of changing retina images.These considerations did not include howthe object itself is perceived.

Before properties can be attributed toan object, the object itself must be recog-nised, that is to say, distinguished from itssurroundings. The process of identifyingthis object in the profusion of continuouslychanging stimuli on the retina is no lessproblematic than the perception ofobjects. Or to put it in more general terms:how does the perceptual process definethe structures its attentionhas been drawnto and how does it distinguish them fromtheir surroundings.

An example will serve to illustrate thisprocess. In the drawing on the left mostpeople spontaneously see a white vaseagainst a grey background. On closer ex-amination two grey heads facing eachother against a white background becomeapparent. Once the hidden faces havebeen discovered, there is no difficulty inperceiving the vase or the faces, but itis impossible to see both at the same time.

In both cases we perceive a figure eitherthe vase or the two faces against a back-ground of a contrasting colour. The sepa-ration of gestalt (form) and environment,of motif and background, is so completethat if you imagine that the form ismoved, the background does not move inunison. In our example the backgroundis therefore an area behind the form andfills the entire drawing. Apart from itscolour and its function as an environmentno other properties are attributed to thebackground area. It is not an object in itsown right and is not affected by changesinherent to the form. This impression isnot influenced by the knowledge that the"background" in our example, is in fact,another form, or gestalt the perceptual

mechanism is stronger than our consciousreasoning.

This example shows that the complex andinconsistent patterns of the retina imageare ordered in the course of the perpetualprocess to enable us to interpretwhatwe perceive easily and clearly. In ourexample, a portion of these patternswithin one picture are grouped togetherto form an image, i.e. an object of interestwhile the rest of the patterns are regardedas the background and their propertiesby and large ignored.

Moreover, the fact that of the two in-terpretations the vase is the preferred oneshows that this process of interpretionis subject to certain rules; that is to say,that it is possible to formulate lawsaccording to which certain arrangementsare grouped together to form shapes,i.e. objects of perception.

These rules are not only of value when itcomes to describing the perceptual pro-cess, they are also of practical interest forthe lighting designer. Every lightinginstallation comprises an arrangementof luminaires on the ceiling, on the wallsor in the space. This arrangement isnot perceived as such, but is organised intoforms or groups in accordance with thelaws of gestalt. The architectural settingand the lighting effects produced bythe luminaires give rise to further patterns,which are included in our perceptionof the overall situation.

It might occur that these structuresare reorganised visually to such an extentthat we do not perceive the patternsas intended, but other shapes and forms.Another, negative effect may be forexample, in the case of a chessboard pat-tern that gestalt and backgroundcannot be clearly identified. The resultis continuously shifting focus selection.It is therefore necessary to considerto the laws of gestalt when developinglighting design concepts.

33

Depending on howyou view this drawing,you will see a vase ortwo heads facing eachother.


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An initial and essential principle of theperception of gestalt, is the tendency tointerpret closed formsas a figure.

Closed forms need not possess a continuouscontour. Elements arranged closetogether are grouped according to an-other law of gestalt, the law of proximity,and form a figure. The example on theleft demonstrates that we first see a circleand then an arrangement of luminaires.The circles are arranged in such a strictorder that the imaginary linking linesbetween them is not straight, but formsa circle; the resulting shape is not a poly-gon but a perfect circle.

Apart from the effect produced by proxi-mity, there is another mechanismvia which shapes that are not competelyclosed can be perceived as a gestalt.A closed shape is always seen as being onthe insideof the linking line the forma-tive effect therefore only works in onedirection. This inner side is usually identicalto the concave, surrounding side ofthe line that encloses the figure. This inturn leads to a formative effect evenin the case of open curves or angles, rende-ring a figure visible inside the line, thatis to say in the partly enclosed area. If thisleads to a plausible interpretationof theinitial pattern, the effect of the inner sidecan be significant.

Patterns frequently possess no shapes thatcan be arranged according to theprinciples of closure or proximity, or theinner line. But in such cases there arelaws of gestalt that allow certain arrange-ments to appear as a shape. The percep-tion of a form as a pure shape is based onsimple, logical structure, whereas morecomplex structures belonging to the samepattern disappear into an apparently con-tinuous background. One example ofthe this logical structuring of specific shapesis symmetry.

Shapes ofequal width have a similareffect. This is not strictly a case ofsymmetry. A principle of order and orga-nisation is, however, evident, and thisallows us to perceive a shape.

If a pattern contains no symmetry orsimilar widths, uniform stylecan still beenough to render a shape a gestalt.

Apart from providing the ability to dis-tinguish shapes from their surroundings, i.e.figures from their background, perceptionalso clarifies the relation of figuresto each other; be it the grouping togetherof individual shapes to form one large shapeor the inter-relationship of a numberof shapes to form a group. The basic princi-ple that lies behind our ability to distin-guish between shapes and background isonce again evident here: our unconscioussearch for order in our visual field.

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Law of gestalt relatingto proximity. Luminairesare grouped in pairs.

Law of gestalt relatingto proximity. Fourpoints are grouped toform a square, fromeight points upwards acircle is formed.

The downlights are ar-ranged in two linesin accordance with thelaw of pure form. Whentwo modular luminairesare added the arrange-

ment is reorganisedaccording to the law ofsymmetry to form twogroups of five.


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A basic law of gestalt is to prefer to per-ceive lines as steady continuous curvesor straight lines, and to avoid bends anddeviations. The preferance to perceivecontinuous lines is so great that it caninfluence the overall interpretation of animage.

When it comes to two-dimensional shapesthe law of the continuous line conformswith the law of pure form. In this case,too, shapes are organised to create figuresthat are as simple and clearly arranged aspossible.

When a given number of individual shapesare put together to form groups, similarlaws of gestalt come into play as with thefocal selection of figure and background.The proximityof shapes is an equallyessential principle in this regard.

A further criterion for the formulation ofgroupsis symmetry. Especiallyin the caseof axial symmetry (arrangements arounda vertical axis) the mirrored shapes arealways grouped in pairs. This effect can beso strong that the grouping of adjacentshapes according to the law of proximitybecomes irrelevant.

Besides spatial layout, the structure of theshapes themselves is also responsible forthe formation into groups. The shapes inthe adjacent drawing are not organisedaccording to proximity or axial symmetry,but in groups of identical shapes. Thisprinciple ofidentityalso applies when theshapes in a group are not absolutely iden-tical but only similar.

The final law of gestalt for the arrangementof groups is a special case, as it involvesthe element of movement. In the case ofthe law of"common destiny"it isnot the similarity of structure, but rathera mutual change, predominantly of thespatial position, which assembles thefigures into groups. This becomes apparentwhen some of the forms that wereoriginally attributed to a previously well-organised group, move in unison, becausein contrast to the remaining figures,it is as if they are drawn on a transparentoverlay, which is placed on the originalpattern. The common movement ofthe group in contrast to the immovabilityof the other figures renders their belongingtogether in any purposeful sense soprobable that the original image is sponta-neously reinterpreted.

At first glance these laws of gestaltappear to be very abstract and of l itt lesignificance for the lighting designer.But these laws of gestalt do playan important role in the development ofluminaire arrangements. The actuallighting effect produced by a plannedarrangement of luminaires may deviatetotally from the original design,if the concept it is based on ignores themechanisms inherent to perception.

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Law of gestalt relatingto continuous lines.The arrangement isinterpreted as two linescrossing.

Law of gestalt relatingto pure form. The arran-gement is interpreted astwo superimposed rec-tangles.

Law of gestalt relatingto similarity. Luminairesof the same typeare grouped together.


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Choroid membrane forblood supply to the eye

Retina, location of thelight-sensitive receptors

Sclera

Fovea

Optical nerve

Cornea

Cavity

Lens

Vitreous body

Iris with pupil as thevisual aperture

Ciliary muscle foradaptation of lens todifferent viewingdistances (accommo-dation)

2.1 Perception2.1.3 Physiology of the eye

36

Sectional view of theeye, representationshowing the parts ofthe eye which are sig-nificant in the physio-logy of vision:


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1,0

0,8

0,6

0,4

0,2

400 500 600 700 (nm)800

VV'

60 40 20 0 20 40 60

Blind spotConesRods

temporal nasal

16.104

N

8.104

12.104

4.104

2.1 Perception2.1.3 Physiology of the eye

2.1.3 Physiology of the eye

The information presented in this chapteris based on the consideration that it isinadequate to portray theeye as an opticalsystem when describing human perception.The process of perception is not a matterof how an image of our environmentis transferred to the retina, but how theimage is interpreted, how we differentiatebetween objects with constant propertiesin a changing environment. Althoughthis means that priority will be given hereto theprocessby which the image is createdboth physiologically and psychologically,the eye and its fundamental propertiesshould not be ignored.

The eye is first and foremost an opticalsystem creating images on the retina.Wehave described this systembycomparingthe eye with a camera, but more interestingby far is the surface on which the imageoccurs - the retina. It is in this layerthat thepattern of luminances is translatedinto nervous impulses. The retina has,therefore, to possess light sensitivereceptors that are numerously sufficientto allow a high resolution of the visualimage.

On close examination it is evident that thesereceptors are not arranged in a uniformpattern; the retina is a very complicatedstructure: firstly there are two differenttypes of receptor, the rods and the cones,which are not distributed evenly overthe retina. At one point, the so-calledblind spot, there are no receptors at all,as this is the junction between the opticnerves and the retina. On the otherhand there is an area calledthefovea, whichis at the focal point of the lens.Here there is the greatest concentrationof cones, whereas the density of the conesreduces rapidly towards the peripheralarea. This is where we find the greatestconcentrationof rods, which are notevidentat all in the fovea.

The reason for this arrangement of differentreceptor types lies in the fact thatour eyes consist of two visual systems. Theolder of these two systems, from anevolutionary point of view, is the one in-volving the rods. The special features of thissystem are a high level of light-sensitivityand a l

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