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The impact of lighting on mood

C L B McCloughan† BSc PhD, P A Aspinall† MSc PhD and R S Webb‡ BEng MSc CEng FCIBSE† Environmental Studies Faculty, Edinburgh College of Art, Edinburgh, UK‡ Department of Building Engineering and Surveying, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK

Summary Reports of the effects of lighting on mood are mainly at an anecdotal level There is littleby way of empirical support and the existing evidence is problematic and contradictory. Thisexperimental study shows that there are systematic influences of lighting on mood from lightingparameters within the range of those encountered in everyday interior conditions. The nature of thelighting effects is complex and is best summarised as initial effects and longer-term effects. Initialeffects link illuminance with sensation seeking and correlated colour temperature (ccr) with hostility.Longer-term effects involve complex interactions between gender, illuminance and CCT. The results areconsistent with Küller’s proposal for short-term and long-term lighting effects.

1 Introduction

Apart from anecdotal reports of the influences of lighting onmood, there has been relatively little by way of empiricalsupport. These anecdotal reports form part of a broad set ofassumptions about lighting that inform daily practice forlighting installations varying from domestic conditions torestaurants and offices. There is an acknowledged need formore work in this area(1). The study reported here is part of awider investigation to establish whether artificial interiorlighting influences mood and behaviour. Within the scientificcommunity, nonvisual of lighting have been viewedwith a degree of scepticism. Reported effects of either illumi-nance or spectral composition on mood have been dismissedby some<2,3) and viewed as problematic by others(1,4) as a conse-quence of habituation effects or complex interactions withother variables. At an empirical level, the prevailing literaturecontains a mix of contradictory evidence of effects on moodfrom lighting. This paper attempts to structure and to providea framework for some of these contradictions on the basis ofrecent experimental studies.For the purpose of this paper, mood or affect is defined as ’thecore feelings of a person’s subjective state at any givenmomene and is not necessarily ’about anything’(5). It can bedistinguished from emotion, which may have identifiablecauses and is more variable, less intense and less transientthan mood

2 Background

Zi Positi1le or negative i;6~iaVeitch(4) a summary of many attempts to mampulateilluminance level or correlated colour temperature (ccr) toinvestigate positive affect (good mood) or negative affect (bandmood). Any of lighting upon mood are more likely tobe due to illuminance than lamp type, but the combined find-are far from clear. Becher and Kluczny (6) found aninverse relationship between illuminance level and positiveaffect Further analysis of mood change under either 215 Ix or2175 Ix showed a gender difference in which women’s positivemood decreased in the higher illuminance condition yetstayed the same in the lower illuminance condition, whereasmen ’reacted in the opposite direction’. On the other hand,Baron and colleagues(7) found no sex difference in reactions tolighting. In their study there was an interaction between

correlated colour temperature and illuminance such thatunder warmer ccr (3000 K) subjects had a tendency to beboth ’calmer and more awake’ under 150 than under 1500 Ix.In Barents study, mood was measured at one instant duringthe experiment. More complex findings have resulted fromstudies by Kne£8>, who mood twice and could there-fore measure mood change across the course of his experi-ment. When subjects were exposed to high (95) CRI (colourrendering index) lamps, women’s negative mood decreasedunder warm ccr (2950 K), but men’s negative mooddecreased most under the cool ccr condition. At low (51-58)CN, an interaction effect between illuminance and correlatedcolour temperature was found. Good mood was preservedbest under conditions of low illuminance (300 Ix) combinedwith a cool correlated colour temperature (4000 K) or inthe higher illuminance level (1500 Ix) combined with thewarmer CCT (2950 K).At the same time, other studies have found no difference inmood between different illuminance levels or lamp types(9).One contributory factor to these contradictory reports is thevariety of experimental procedures used, differences in inde-pendent variables manipulated and differences in mood-measuring instruments used,

Z2 ~MM~~

In many theories of emotion, arousal with affect as acomponent of mood(&dquo;),&dquo;). Arousal is defined as a continuum ofof alertness ranging from a comatose state to one ofexcitement. Evans(l2) three types of arousal asbehavioural (measured by behaviour or self-report), auto-nomic (measured by indices such as an electrocardiogram)and cortical activity in the brain), of bothand lamp type have been on two of thesetypes of arousal: cortical and behaviouraL For example, whilemeasuring the of illuminance and correlated colourtemperature upon cortical arousal, Kuller and WetterbergP)found that 700 Ix had a waking on the central nervoussytem when compared to 450 Ix and that a cool colour temper-ature (5500 K) at low illuminances is more restful than at highilluminance. Various effects of lighting upon behaviouralarousal have also been found, mostly through observationstudies. Gifford<13) reported that communication exchanges(interpreted as an index of arousal) were lower at 60 Ix than90 Ix. A similar inference may be drawn from the findings ofNelson(14). who reports a tendency for individuals to be lessfatigued under 300 Ix than 100 Ix. Fatigue has also been

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measured with respect to lamp colour. et alPS) found thatsubjects were ’less lively* after being exposed to cool whitelights as opposed to Vitalite lamps (no objective values aregiven). In summary, although there are few studies on corre-lated colour temperature, it does appear that higher illumi-nances are more arousing both cortically and behaviourallythan lower illuminances. In addition to the possible effect oflighting on hedonic tone (erg. from low positive affect to highpositive a~’ect), lighting may shift already positive states thatcan be described as calm or relaxed to more excited states orvice versa.

2.3 ~’u.~j~ct~ a~a~r~;rs~~sA number of investigators have suggested (implicitly orexplicitly) that subjective responses to the environment areindicative of states of mood even though overt measurementsof mood response have not detected this. For example,’preference judgements are sometimes taken as a proxy formood’(8). This type of subjective response can be described asan ’affective appraisal’(5), which is a judgement of somethingas pleasant attractive, likeable~ etc. Baron et al.~ found thatobservers were more likely to ascribe terms like relaxing orpleasing to an ental room when under warm ratherthan cool ccr conditions or under low rather than high illu-minance. However, Boyce and Cuttle<16) found no e ofcorrelated colour temperature upon subjective impressions,but (within the range 30-600 Ix) found higher illuminancesrated as more pleasant and comfortable, whereas the lowerilluminances were described as hostile. The authors warn thatsubjective impressions of correlated colour temperature maybe affcted by incomplete adaptation, depending on the condi-tions from which the observer is adapting. Again the issue ofexposure to lighting appears critical. UTfle Baron et ~l*~found more positive appraisals at lower i~ an Boyceand Cuttle(l6) found this occurring at higher illuminances. Acomparison of illuminance levels in the two experimentsshowed that it was the mid-range illuminances that elicitedmost positive appraisals. This mid range may be the familiarrange for pen-and-paper tasks, resulting in the ’mere exposureeffect’ - ’the more you see it, the more you like if.

Other hectors have been found to influence lighting effects onaffective appraisals. Perhaps not surprisingly, the activitybeing performed influences appraisal(l7), with participantspreferring higher illuminances for reading tasks than forlistening tasks. Gender also influences prefer~n althoughthe direction of tb.e ~‘~t is not cl~r. Leslie and Hartleb(IO)state that males prefer higher levels of illuminance thanf~ es, while Buder and BineF1° found the opposite.

this confused background there are f~rr moreresearch in the area. As Baron(1) put it: Turther research isnecessary top ... determine the relative contribution of f=A-iarity... of various conditions themselves to affectivereactions to indoor illumination*. There is also a need toinvestigate mood effects under less extreme illuminanceslevels, those that are commonly encountered in the range ofpractical artificial lighting conditions.

3 Method

3.1 .~x ~rac~rztal COH<&MKy

-fc~ur participants (38 male and 26 female) from theuniversity population were used, in the study including post-graduate students, lecturers, administrators, librarians,students, and ancillary s The age range was from 24 to 65

years with an estimated mean of 37 years. The experimentallaboratory contained two identical rooms that were mirrorimages of each other. Two subjects were tested simultane-ously, one in each room. Each room measured 6.25 X 4.1 mwith a 2.2 m high ceiling. The walls and ceiling were paintedwhite and the windows were covered by shutters. Each roomcontained two desks, three chairs and posters and p t~ inidentical positions in each room. The luminaires used werePhilips TLD surface luminaires with p3 standard prismaticcontrollers, six in each room. The lamps used were PhilipsTLD 58w/colour 84 (cooler colour temperature) and PhilipsTLD 58w/colour 83 (warm colour temperature). The illumi-nance, colour temperature and uniformity measures are givenin Table 1. All lamps were new and were operated for 30 minprior to the start of each experimental session to stabilise illu-minance levels. illuminance was varied by removing lampsfrom the luminaires, while correlated colour temperature wasvaried by changing the lamps. The lamp ballasts were of theconventional type.

3.2 procedure

The experiment employed a mlly randomised factorial designwith repeated between-subjects measures across two illumi-nance levels, two ccr levels and two experimenters. The fullsequence of experimental conditions was determined by aseries of Latin squares across the ind dent ~ l~*Mood was assessed using the Multiple A;de‘ect AdjectiveChecklist - RevisecL(19) The ~~°t.-~ scale (which contained132 items) assesses five major components of mood: anxiety,depression, hostility, positive affect and sensation seeking.The MAACL-R has been shown to be a sensitive indicator of theeffect of experimental or natural conditions upon mood(19) andhas psychometric properties such as reliability and validityequivalent to other similar tests(2l). In addition, subjects eval-uated the lighting and the room on a series of five bipolarpoint scales for g, ca ar~, pleasantness, brightnessattractiveness, clarity and warmth.

Participants were randomly assigned to one of the fourlighting conditions and were tested on their own. The exper-imenters were unaware of which lighting condition was beingtested and the subjects were unaware that the effects oflighting were being assessed at all. The reason given tosubjects for carrying out the experiment was to gather data ona new computerised vision test and it was stated that as a breakbetween tests some si~np3~ pen-and-paper psychological ques-tions would be asked. This was done to reduce tioneffects, which are common in psychological testing and arereported to occur in lighting r ch~~°~. Taking the focus offthe main of interest reduces the chance of subjects givinganswers they think the experimenter wants. The experimentalorder was as follows:

(1) A test on contrast sensitivityc2O)

(2) Mood assessment 1 (at 5 min)

(3) Simple decision tasks

Table 1 Summary of lighting conditions

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(4) Room appraisals

(5) Mood assessment 2 (at 40 min)

(6) Computer vision test (at different spatial frequencies from(1»

The time between the first and second mood assessments was

approximately 35 min. The computer vision test took 5 minand the whole experiment 45 main. At the end of the experi-ment subjects were given a £4 book token and thanked fortheir efforts. The reward was advertised as part of the recruit-ment of subjects.

4 Results

The data were analysed by multivariate analysis (MANOVA)and univariate analysis (ANOVA) on each variable separately.As the psychometric properties of the MAACL-R mood assess-ment test have been assessed independently(&dquo;), the establishedsubscales of the test (i.e. Anxiety, Depression, Hostility,Positive affect and Sensation seeking) and their simphfiedgeneral combinations Dysphoria (an additive combination ofAnxiety, Depression and Hostility) and PASS (an additivecombination of Positive affect and Sensation seeking) werechosen as the dependent variables. Mean t scores on thesescales for the experimental subjects showed the results werewell within the normal range on the test. As a further check,a principal-component analysis followed by varimax rotationon mood assessment at time 1 confirmed the overall MAACL-Rtest structure in the current data. Two main factors emergedthat accounted for 73.90/o of the total variance, these beingDysphoria (Anxiety, Depression and Hostility, whichaccounted for 52.7%) and PASS (Positive affect and Sensationseeking, which accounted for 21.2% of total variance). (Factorswith eigenvalues < 1.0 were selected for inclusion and vari-ables with loadings >0.7 were included for factor description.)The present data therefore compare favourably with the asser-tion of the creators of MAACL-R that Anxiety, Depression andHostility correlate significantly and may represent sub&ctorsof a larger Dysphoria (negative mood) factors and that Positiveaffect and Sensation seeking also correlate to warrant an addi-tive scale of PASS.

Prior to the main analysis, a logarithmic transformation wasperformed to normalise the data. A multivariate analysis ofvariance that assessed all the mood variables simultaneouslyacross all experimental conditions was carried out- Resultsshowed that the only significant effect was the complextriple interaction term sex X illumination X ccr (F = 2.32, df= 7,50p<0.05).A univariate analysis assessing each of the dependent moodseparately under each experimental combinationwas This was out on mood data at time 1and on the differences in mood data between time 1 and time2. Results are given in Tables 2 to 7.

First, in Table 2 each of the five mood variables andtheir two combined were assessed the inde-pendent variables. For all measures at time I (i.e. 5 min intothe experiment) there were main order effects, which aresummarised in Table 3, but no significant interaction effects.

For example, Table 2 shows a highly significant gender effect(on Positive and its correlate PASS); a significant rela-tionship between illuminance and Sensation seeking; and asignificant relationship between ccr and negative mood, i.e.Hostility.

The directions of the influences as shown by the means inTable 4 were as follows.

(a) Females were si~nific~z~~Iy higher in positive affect thanmales.

(b) Sensastion seeking was significantly higher under lowthan under high illuminance.

(c) Hostility was significantly greater under the warm ratherthan under the cool ccr.

(fl Females had significantly higher Postive affect andSensation seeking (PASS) than did males

In Table 5, representing change in mood between time I (after5 min) and time 2 (after 40 mkX there are both main orderand interaction effecs. These are summarised in Table 6 andthe means of the differences values given in Table 7.

It is apparent that, while main order effects characterise themood at time 1, the changes taking place in mood after 40 minin a room were more complex and involved mostly interaction~e~. Furthermore, the significant changes in mood were allassociated with negative mood and its elements. These areshown graphically below and are derived from the table ofmeans in Tables 4 and 6.

The first two graphs (Figures 1 and 2) show a similar trend forboth anxiety and hostility mood changes across illuminanceand ccr. The measure of mood change on the vertical axis ismood at time 1 minus mood at time 2. Positive values of

change therefore indicate a reduction in, say, hostility, whilenegative values of change indicate its increase. The results

Figure 1 The effects of the interaction between illuminance and sex uponchange in dyspho~ scares

Ftgme 2 The effects of the interaction between sex and ccr upon change inhostility scores

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Table 2 Uiuvanate analysis of mood at time 1

TaMe 3 S~ ’ ~~ levels for mood at time 1 Table 4 TaMe of mean mood (taw to logarithmicvalues)

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Table 5 LTz~ivariate analysis of mood ~er~c~s between time 1 and time 21

show an increase in and hostility at high illuminancesfor ccr lamps. At the same the levels of anxiety andhostility are reduced for warm ccr lamps at high illuminance.Figure 3 shows a significant interaction between colourtemperature and Females’ negative mood (i.e. hos-tility) decreased in and increased in the cool white lightsource, while the response is similar under both lightsources. The result for females is similar to that found byKneztJ3), while the similar response by males contrasts with hisfindings of an in males’ negative mood under thewarm CCT condition. Finally, Figure 4 shows a reduction ingeneral negative mood (i.e. dysphoria) at high illuminancelevels for females but an increase in negative mood for malesunder higher illuminance.

AN assessed the mom on first it on a set of5-point bipolar semantic scales for hEng pleasantness, attrac-tiveness, comfort, brightness, clarity, warmth. t-Testsshowed no significant differences any of the scales witheither illuminance or ccr. The only exception was the ratingof brightness with illuminance (F = 7.68, df = 1,63,p<0.01).A fàctor analysis (with vartmax rotation) of the room andlighting appraisals produced just two factors accounting for66% of the variance (see Table 8). Factor 1 appears to be ageneral evaluation factors including judgements such as attrac-tiveness, comfort, liking, and warmth whilefactors 2 is a brightness and clarity factor. Of interest is theobservation that the aesthetic judgement of attractiveness isindependent of appraisals of brightness, whereas pleasantness

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Fi 3 The effects of the interaction between illuminance and ccr uponchange in hostility scores

~’ 4 The effects of the interaction between illuminance and ccr uponchange in anxiety scores

Table 6 Significance lev~ls for mood di ~e (Tt - T1)

Table 7 Mean mood scores for difference in mood for (T~ - T2)

Table 8 Factor structure of room appraisals fc~ll vanmax rotation

and liking are moderately loaded on the second factors (0.36and 0.35, respectively).

5 Discussion

The experimental work reported in this paper has demon-strated that there are systematic influences of lighting onmood from lighting parameters within the range of those

encountered in everyday interior conditions. The nature ofthe lighting effect is complex and is best summarised undertwo separate headings, initial effects and longer-term effects.

5.1 jMa~~eeWhen assessments of mood are made within 5 min of firsta room, are two main order and no inter-The main of its on the moodvariable of Sensation Sensation is signifi-cantly higher under lower than under higher illuminance.That Sensation seeking would be influenced by an illumi-nance change from 280 to 770 Ix was not hypothesÎ8ed and isa novel finding. The described shut is, however, in the direc-tion anticipated from previous work on arousal(2). The maineffect of ccr relates to the negative mood of hostility, whichwas significantly higher under the warm than under thecool ccr condition. Finally, there were gender differ-ences in Positive affect, with females being significantlyhigher in positive aspect than males, and in the general posi-tive mood assessment of PASS Positive affect and Sensationseeking).

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When mood assessments were made after a period of over30 min in the room, complex interactions between the

lighting parameters and the mood subscales were present. Theoverall characteristic of the change that had taken place wasthat it was confined to negative aspects of mood only. The hctthat there were no differences in mood assessment betweentime 1 and time 2 on Positive affect or Sensation seekingmeant that the effects recorded at time 1 were still in place.However, measures of Anxiety and Hostility and the com-posite negative mood measure Dysphoria showed complexinteractions with gender, illuminance and ccr as can be seenfrom Figures 1 to 4. Lighting effects on Sensation seekingtherefore appear more stable across a 45 min period, whilenegative mood changes appear to be more complex andvolatile.

The overall picture presented here of a two-stage influence oflighting on mood is consistent with an explanation of envi-ronmental effects put forward by Kuller(22). Kuller suggestedtwo mechanisms for mood change linked to notions of phasicand tonic arousal. Phasic arousal is an initial response to anenvironmental setting, while tonic arousal is a longer-termhabituation eSect. There is; of course, no way of knowingwhether the structure of the interaction effects within theexperimental period of 45 min subsequently changes overlonger periods; only longitudinal studies would determinethis. Secondly, with regard to the initial effects, there is ageneral explanation of mood effects due to discrepanciesbetween stored expectations in memory and current inform-tion inpuf23~ Purcell(,23) hypothesised (and subsequentlyprovided supportive evidence) that there is an emotionalcomponent directly linked to these discrepancies. When thediscrepancy is minor, there is a positive hedonic response; butas the discrepancy increases, there is an increasingly negativeemotional response. It is interesting to note that the experi-mental subjects were taken to the laboratory via an externalwalk during the period between 12.00 and 14.00 during theworking day. Whatever the weather conditions, the sky illu-minance and CCT, the results show that it is the greater differ-ence from the exposure conditions (I.e daylight) that resultedin greater sensation our greater negative mood.PurceWs hypothesis is closely linked with prior expectationsand these are of course unknown for the experimentalsubjects. None the less, the subjects were told they would betaken to an ’office-like room. Furthermore, the higher experi-mental values of illuminance and ccr were closer to the normfor than the lower illuminance, which was deliberatelyset at the lower limit of acceptability. On these grounds, there-fore, the lower settings by the pre-exposureconditions would be the more deviant office settings fromnormal expectations-

As mentioned it is the lower illuminance thatsensation seeking (a correlate of arousal) is highest. For theMAACL-R many items used to measure sensation seeking mightbe interpreted as arousal. The behavioural consequence of thisis that risk-taking with arousal) may be increasedunder lower illuminances. While sensation its not thesame as positive mood, the creators of the MAACL-R report thatthe two mood types correlate significantly<20), and this is borneout by the factor structure in which Positive andSensation load on the factor. Therefore,although direct measures of Positive affect were not affectedby illuminance, correlates of Positive affect were affected. Thisis in keeping with the finding of other studies that lower illu-minance leads to more positive hedonic tone<6,7).

Following the work of Knee8), it was hypothesised that ccrmay be implicated in mood differences. In Knez’s study therewere interactive effects of ccr with illuminance and sex ofsubject to influence negative mood. In the present study, thereare again similar interactive e~ between illuminance, ccrand gender to influence negative mooch This replication ofgeneral negative mood shifts with lighting is worth noting.The direction of the hostility shifts for females is exactly thatreported by Knez(’). However, the present study did notconfirm the increase in negative mood for males. Behaviouralconsequences from increased negative mood are difficult toassess. In particular because of the ~thiee~l problems inherentin inducing unpleasant moods, experimentally there is verylittle literature regarding the consequences of temporaryincreases in negative mood state. However, where negativemoods have been assessed, they have been shown to inducemore stereotypic thinking in social judgements<24) and toinfluence confidence and self esteem(25), risk estimations forunpleasant events(--6) and even willingness to pay for insur-ance<21). Of course, the degree of negative mood induced is crit-ical to whether any of these behaviours would be ~~t~d.

It is important to emphasise that the mood effects pr inthis study occurred under moderate c~.s in illumi-nance and that were well within the ranges normallyencountered in artificially lit environments. Direct effects ofilluminance or CCT on positive mood that have been reportedin other studies, but that were only indirectly supported her~may depend on greater illuminance and ccr differences.Indeed, most experiments ~~.~. Baron<2» in which a shift in

positive mood occurred had similar low illuminance levels butemployed high illuminances in of 1500 Ix. The initialimpact of an environment and the pre-exposed conditionsrequires further investigation. In addition, the role of expec-tations at the initial stage needs to be considered The second-stage mood changes, with their complex interactions, point tothe need for new longitudinal studies in which mood is moni-tored over considerably longer time intervals.

Finally, the results from the experiment did not support thenotion that an affective appraisal must occur as a precursor tolighting-induced mood effects. No differences in ’aesthetic’ rat-ings (i.e. attractiveness) were observed between any of the light-ing conditions despite the occurrence of mood ~~~. This isrelevant for further research in the area, as appraisal studieshave routinely been used as a proxy for mood measurement.

Acknowledgements

This research was funded by the Science and EngineeringResearch Council, grant no. GRlH15936, and the wascarried out in the Department of Building Engineering andSurveying, Heriot-Watt University.The authors thank Bill Adams of the Medical Statistics Unitat Edinburgh University for help with the analysis.

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