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6.1 Introduction

It cannot be stressed too highly how central is natural lighting to memorablearchitecture.Designerswhorelytooheavilyuponelectric lighting for illumination very often produce buildings which are uninteresting and somehow two dimensional. Why is it that a designer produces buildings that people perceive as quality architecturewhentheydesignforgooddaylight? Consider the buildings that you regard as memorable. Ask yourself whetherornotyourresponsetothemdependsupon: i)thewaynaturallightinteractswiththebuildingform, ii)theperceivedtextureofsurfaces, iii)thevistasthroughthebuildingneededfordaylight, iv)thesubtlechangesobservedunderdifferentlighting. A persons response to buildings will depend upon their own experience and sensibilities, but generally people respond positively tothoseaspectsthatadesignerisforcedtoconsiderwhenintroducing natural light. Just by needing to consider natural light a designer is compelled to play with the form of a building, its spatial layout, the opennessofthespacesandthesolidityofthefaade. Thechangingnatureofnaturallightisapartoflife The seasonal rhythms of natural light affect the life cycles of plants andanimals.Bothfloraandfaunarespondtothechanginglengthof day and to the reduced levels of daylight seen in Winter. We as individualsappeartobelesscloselyboundtotheseasonsbecausewe canuseelectriclighttoworkaroundtheclockandimportagricultural produce from around the world. However, there is increasing evidence that we too can be affected by the low levels of light and short days experienced in Winter. One effect that is now widely documentedisreferredtoasSeasonalAffectiveDisorderSADand thisisbelievedtobepartlytheresultofchanginglevelsofmelatonin inthebody. Thediurnalrhythmsofdayandnightaresomuchapartofourdaily life that they are taken for granted. Daylight resets our body clock each day and our state of arousal is partly determined by our exposuretohighlightlevelsexperiencedduringtheday.Depriving peopleofexposuretodaylightwithoutpropercompensationforthat losscandisturbthephysiologyofthehumanbody.Thepsychological need for daylight and its rhythms is even less well understood, althoughitsneediswidelyrecognisedinthewordsofpoets.

Building Environment 1

It is worthwhile considering that we increasingly spend the greater partofourdayindoors.Indoorswemightbeexposedtolightlevels oftheorderofa500lx,whereas,eveninmidwinter,anovercastsky might provide about 5000 lx 10 times as much. Given this information,ifwearereceivingtoolittlelightduringthedaythenthe solutionistogooutsideforawhileratherthantoincreasethelevelof electriclightindoors.Anyincreasewouldbebyonlyasmallfraction andthissimplywouldnotfullymakeupforthedifference. The colour of daylight can vary widely from the warm rosy hues of thesettingsuntothecoolblueofaclearsky.Althoughplantsreactto different hues in the spectrum of light there is little direct evidence that humans respond to different colours. However there are those whobelievethatthecolouroflightdoesaffectourmoodandhealth and that the range of colours provided by daylight promotes health. Certainly, daylight is a continuous broad spectrum light source and thereforecoloursandmaterialsappearwellunderit.Forthisreason natural light is often the preferred light source in art galleries and museums. Recent evidence from surveys undertaken in the USA indicate that good levels of daylight in classrooms can materially improve the performance of students. The exact mechanisms through which this occurs is unknown, but the effect is significant and unlikely to have arisenbychance.


Introducing natural light forces designers to think in 3 dimensions. Lightmustenterthroughthebuildingenvelope,beiteitherthewall ortheroof.Thesupportingstructuremaytakeanumberofroles; i) it can be minimised in order to aid the passage of light to an internalarea, ii) itmaybeutilizedasascreentofilterthelight, iii) itmaybepositionedtointerceptthelightinordertocreatevisual interestinitselfandreflectlighttootherareas. Asmalllightsourcesuchasalampcanbefocusedandredirectedby lenses and mirrors and this is also possible with sunlight because it too is a relatively small source of light. However, the diffuse light from cloudy skies is an extended light source and can not be refocused. If the light from an extended light source is to be redirected by using a mirror, then it will be found that the mirror obscures the same amount of light as it reflects. If it is desired to accentuatethedaylightlevelinoneareathenitisgenerallynecessary to reduce it in another area. Thus obscuration or shading is an important means of controlling the light from diffuse skies. This applies at all scales of detail within the building, from the design of smalllouvreswithinawindow,throughthedesignofroofprofilesto thearrangementofgrossbuildingforms.


Chapter 6 Natural Light and Sunlighting

Becausethemainmethodsofcontrollingandredirectingdiffuselight are those of obscuration and plane reflection, it is the architectural elements themselves which create the patterns of light. Thinking about lighting automatically ensures consideration of architectural form. Thedramaofspaceismediatedthroughtheflowoflight Lightmaycomefromanydirectionoftheenvelope.Decisionsasto where openings in the envelope are positioned will determine the direction from which light arrives in the interior. This flow of light will naturally lead to a particular grading of light level through the room, it may be great or small depending upon the relative position and areas of the windows. Not only will the flow of light affect the appearance of the rooms surfaces, but objects within the room will respond to the different directions and strengths of modelling throughouttheroom. The flow of light may be clearly defined. A single window will produce a simple and consistent flow of light where the observer is consciousofhowlightischangingthroughoutthespace.Theindirect daylightingofbaroquechurchesproducesamuchlessdistinctflowof light and this can lead to a lighting effect which is almost ethereal. Such effects are quite appropriate to reverie and religious buildings butmaybeperceivedassoporificinaworkinginterior. A room of white surfaces will reflect the light all around so that no matter from where the light originated the resulting light will be uniform.Thiswillsoftenifnotcompletelyeliminateshadowscreated by the original flow of light into the room. When considering the interior decor it therefore needs to be remembered that surface reflectance not only determines the appearance of a surface but also changesthenatureoflightinaroom. Thesenseofenclosureisinseparablylinkedwithwindows. Awindowisanopeningouttotheworldbeyondanditincreasesthe senseofspaciousnessthatweexperiencewithininteriors.Thisisnot only the result of the window physically allowing the eye to gaze beyond the confining surfaces of a room, but it is also in part the result of a perceived link with outside world. This link does not depend upon the actual view seen through an opening, although its qualitycanaffectourresponsetoaspectssuchasdiscomfortglare. OneaspectoftheexperienceofArchitectureisthesenseofenclosure and therefore it is essential that building designers appreciate the waysinwhichwindowsmodulatetheperceptionofspace.


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Solidorlight,texturedorplain,thewindowscreatethefaade. Windows are a major element in the pattern of the faade. If it is desiredtobringordertothefaade,thenitmaybenecessarytoadd oromitwindows,perhapsevenchangetheproportionsofwindows. In doing this it may be that other design considerations are compromised. The particular type of glass used and the number of layers of glass may considerably alter the appearance of the glazing and hence the faade. Similarly the apparent transparency of the windowwillbeaffectedbythelightlevelsbeyondthefaadeandthe anglesfromwhichthebuildingistobeviewed.

6.2 Simplification of Natural Lighting

Real skies change continuously. The sky becomes brighter towards noonasthesunrisesinaltitudeanditslightdistributionchangesas cloudsgather,thickenanddisperse.Thesechangesindaylightoccur inresponsetothepredictablemovementofthesunacrosstheskyand theratherlesspredictablecloudcover.Thealmostcontinuouschange that occurs in natural lighting provides good reasons to try and simplify matters. Designers need to appreciate how their buildings willrespondtodifferentlightingconditions,butifthereisnofocuson particular aspects of natural light, then it is difficult to make an assessmentoftheimportanceofanychangesmadetothedesignofa building. The basic simplification adopted by designers is to initially consider onlythetwoextremesofnaturalskies; a) sunlightwithaclearbluesky, b) acompletelyovercastsky. Inthesenotes,thetermnaturalwillbeusedtodescribethelighting under real skies and encompasses all the many unpredictable variationsthatoccurinreality,sunlightwillbeusedtodescribethe combined effects of sunlight and a clear blue sky, and daylight will beusedtodescribethelightunderacompletelycloudysky. Therationalefortakingthesetwoextremesisthatthebuildingneeds to accommodate them. In summera sunlit building may need to be shadedinordertolimittheuppertemperatureexperiencedwithinthe buildingand also to control the experience of glare such that itdoes not hinder visual performance and comfort. In winter the building needstoprovidesufficientdaylightonfullyovercastdaysinorderto allowoccupantstocontinueworkingeffectively.Byconsideringboth cases the designer ensures that the building will perform at the extremes, and it is assumed that it is also likely to work during intermediatestatesofnaturallightingthroughouttherestoftheyear.


Chapter 6 Natural Light and Sunlighting

6.3 Sunlighting
Sunlight can contribute to the working light within a room but it is difficult both to control the light and to estimate the extent of its contribution. For these and other reasons it is only recently that techniques of prediction and analysis have progressed sufficiently to incorporate sunlight illuminances into calculations of usable light withinaroom.Initially,sunlightwillnotbepromotedasaworking illuminant, but as a means of enhancing the quality of a rooms environmentandimprovingtheoutsideareasaroundbuildings. From evidence available even the most primitive civilizations recognisedtheimportanceofthesunasasourceoflighttotheworld. Indeed,insomeculturesthesunwasseenasbeingsuchanimportant part in life that it became a symbol that was synonymous with life itself.Unfortunatelyintheworldoftodayitisalltooeasytoforget abouthownecessaryissunlighttoourwellbeingbecausethesunis nolongertheonlypracticalsourceoflight. To those sensitive to the world about them the fundamental importanceofsunlightisaselfevidenttruth,however,intuitionsdo not necessarily provide firm foundations for design. Fortunately, thereismuchevidencethatsunlighthasbothbeneficialphysiological andpsychologicaleffectswhichhaveadirectimpactuponthequality of our lives. It is also true that utilizing natural light as a working illuminantisoneofthemosteffectivewaysofmakinguseofnatural resources and the provision of natural lighting has been an essential aspect of planning buildings in the past. For these reasons it is worthwhileknowinghowconsiderationsofsunlightingcontributeto thedesignofbuildings.

6.3.1 Initial aspects of designing for sunlight

Considerations of sun lighting can be a great help in planning a building. They have the advantage that they can be both used effectively by the designer and appreciated by those using and viewing a building. A further advantage of using sun lighting as a primary design criteria is that the basic facts needed for design are simple and have probably been known to readers from their schooldays,i.e.: i) thesunisalmostduesouthatnoon, ii) thesunrisesintheeastandsetsinthewest, iii) thesunishigherintheskyinsummerthanitisinwinter. Although simple, when they are considered in relation to the particular requirements of a design, these facts can be invaluable in helping to sort out the overall planning of a building. Consider the exampleofahousethatistobebuiltinthetemperateBritishclimate.


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Becauseofaperceiveddeficiencyinthehoursofsunlight,peoplewill generally wish to make the most of whatever sunlight there is and underthesecircumstancesthefollowingpointsmightbeconsidered; (i) it is pleasant to awake in the morning with sunlight streaming through the window andthereforeas the sun risesin the east it might be worthwhile placing bedroom windows on an easterly aspect, (ii) kitchens can be rather warm because of all the heat generated when cooking and therefore one should consider placing a kitchen or pantry on a northern facade in order to prevent sunlightfurtherraisingtheroomtemperature.Alsoinaworking roomwhereonewillbeusingsharpknivesitispreferabletohave anevenlightfreefromhardshadowsacrosstheworkingsurface, (iii) lounges are mostly used in the afternoon and evening and because they are places of relaxation the presence of sunlight is generally welcomed. By placing the lounge on a southern or western aspect the most can be made of the afternoon and eveningsun. (iv) the low altitude of the sun in winter makes northern slopes less favourable than southern slopes, and therefore southern slopes willnormallybedevelopedbeforenorthernslopes. (v) obstructionstothesoutharethatmuchmorecriticalandwhereit isintendedtoplanttreesontheboundaryitisbetterthattheyare deciduous so that they loose their foliage in winter and thus admitsunlightontothesite. These points make it quite clear that considerations of sunlight can, andindeed should playan important role in helping to generate the formofanarchitecturaldesign. Of course the above suggestions cover only a single aspect of the design and they should not necessarily override all other considerations. Also, the way in which the design is affected by considerations of sunlight will vary depending on the priority given todifferentenvironmentalfactorsbytheclient.Forexample,itmight wellbethataclientprefersasplendidviewfromthekitchenandthis mightonlybeavailableonawesternaspect,oraclientmightbekeen on watching television throughout the day and therefore the penetrationofsunlightmightneedtoberestrictedinordertoreduce glareonthetelevisionscreen. Theselasttwoexamplesillustratethefactthateventhoughthebasic facts about sunlight are easily appreciated there is no simple recipe thatcanensureadesignwillsatisfyaclientswishes.


Chapter 6 Natural Light and Sunlighting

6.3.2 The need for more detailed design

Although these simple facts may help when planning a building, there is merit in knowing how to predict with a little more accuracy thesunspositionatdifferenttimesofdayandyear. This is because there are buildings such as museums, art galleries, sports halls and libraries where it is necessary to closely control the sunlight entering the building in order that critical visual tasks are performedundergoodlightingconditions. Also,theincreaseduseofVisualDisplayUnitshasalsoincreasedthe disruption to working caused by sunlight. The screens of VDUs are not very bright and the extremely high brightness of the sun and sunlitsurfacescanconsiderablyreducethevisibilityofthedisplay. Additionally, shading devices might be crucial to achieving a comfortablethermalenvironmentduringthesummerandinorderto properly control the transmission of sunlight they may need to be designedtoquiteclosetolerances. Thereareanumberoftechniquesthatcanbeusedtoinvestigatethe position of the sun. Although in architectural applications the accuracy required is less than that expected in astronomical or navigational work, there is a need for information to be readily understoodbythedesignersandclients,andeasilyappliedtodesign problems.Theseneedsmeanthatthereisnosinglemethodthatcan be recommended above all others and particular techniques will be appropriatefordifferentcircumstances.Onemethodwillbetterallow aclienttoappreciateaproblemwhilstanothermightproveeasierasa designtoolthatwillensuretheshadingofsunlightatdefinedtimes. Anabilitytousethemoreinvolvedtechniqueswillnotonlyfacilitate thedetailedconsiderationofsunlightingonthemorecriticalprojects, but it also enables designers to predict the position of the sun at latitudeswheretheyhavenoexperiencetoguidetheirjudgment. Knowledge of the basic astronomical facts is not essential for the successful application of the prediction techniques, but they are briefly described later in order to help with understanding some technicalterms.

6.3.3 Additional factors in sun lighting design

Onefeelsintuitivelythatsunlightisanimportantelementinpeoples livesandtherehavebeenattemptstoestablishjusthowimportantby surveying peoples responses to sunlight in buildings. However, because of the complexity of our interactions with the environment, thesesurveysrarelydomorethanconfirmthatsunlightisindeedan important factor. In many ways this absence of a clear hierarchy in the priorities of various environmental factors is heartening to


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designers, for it presents them with the freedom to make decisions according to the circumstances. However in order to utilise this freedom the designer must be aware of the benefits and problems associatedwiththedifferentaspectsoftheenvironment. BenefitsofSunlight a) thesheerintensityofsunlightprovidesasparkleandbrilliance thatcantransformwhatmightotherwisebeadullscene, b) the directionality of sunlight means that there is often the addedfeatureofheightenedcontrastsbetweenareasinsunlight andthoseinshadow, c) that same directionality of light will reveal the texture of buildingsurfacesandtheformofacomposition, d) themovementofthesunacrosstheheavensensuresthatitwill reveal different aspects of building form at different times of day, e) theregularnatureofitscourseacrosstheskymeansthatitcan actasatimekeeper, f) the changing nature of sunlight through clouds provides a variety of appearance which gives life to a perhaps otherwise staticscene, g) a shaft of sunlight piercing through a window can provide a tangible link to the outside world for those cocooned within a building, h) the sun also has non visual effects which are of benefit to humans, it is a bactericidal agent against pathogens, is necessaryforthesynthesisofvitaminDandpossiblyhasother directphysiologicaleffectsuponthebody, i) thereisawarmthtothesunwhichcanbeutilizedtohelpheata building and ensure that external areas do not become dank andmouldy. Possibleproblems: a) direct sunlight generally makes written material too bright to read, b) sunlight can cause excessive direct glare and even when reflectedfromglassitcanbeuncomfortablybright, c) shadows cast by sunlight can cause misperceptions of form andshape,


Chapter 6 Natural Light and Sunlighting

d) e) f) g) h)

materialinshadowmaybedifficultifnotimpossibletosee, excessiveinsolationwillresultinbuildingsoverheating, itisuncomfortablyhottoworkinsunlightifthereislittleorno breezetocoolonedown, the heat and UV in sunlight can be harmful to materials and causeadeteriorationoftheirphysicalproperties, excessiveUVcanharmlivingorganisms.

6.4 Simple guidance for sun lighting

In the past guidance was provided in codes of practice for certain building types, such as houses and schools, but these were not enforceablebylawandarenolongercurrent.Howevertheyarelisted hereasguidance. BSCP31bSunlight a) Domesticbuildings Livingrooms:1hour/dayfor10monthsfromFeb.toNov. Kitchenandbedrooms:someinsolationifpossible b) Teachingspaces Twohoursadaythroughouttheyear. ThecodesofpracticehavebeensupersededbyaBREreport, Site layout planning for daylight and sunlight a guide to good practicebyPJLittlefair. Hereitissuggestedthatabuildingwillreceivereasonablesunlightif; i) Atleastonemainwindowfaceswithin90ofduesouth, ii) on this wall, all points on a line 2m above ground level are within4msidewaysofapointwhichreceivesatleastaquarter ofannualprobablesunlighthours,includingatleast5%during thewintermonthsbetween21Septemberand21March; andagardenwillappearadequatelysunlitthroughouttheyearif; i) less than 40% and preferable no more 25% of the garden is shadedon21March.