Effects of snow-reflected light levels on humanvisual comfort

Hasan Yilmaz & Nalan Demircioglu Yildiz &

Sevgi Yilmaz

Received: 15 March 2007 /Accepted: 19 September 2007 /Published online: 8 November 2007# Springer Science + Business Media B.V. 2007

Abstract The intensity of the sunlight reflected bythe snow-covered surfaces is so high that it maydisturb humans many times. This study aims todetermine the reflected sunlight intensities from snowcovered areas at points near (at a distance of 2 m) andunder an individual tree and among trees (in the forestarea) by accepting the open area as control; thereducing effects of the plant materials on reflectedsunlight in percentage by comparing with the valuesof the open (control) area; and critical reflectedsunlight threshold values for human visual comfort.The study was carried out over 22 clear and calm, i.e.sky was cloudless and wind was calm, days betweenthe 1st and 31st days of January 2004, at 8:30 in themorning, at 12:30 at noon and at 14:30 in the afternoonin Erzurum. In order to determine the discomfortinglight intensity levels, 25 females and 26 male (totally51) student subjects whose mean age was 20 and whohad no visual disorders were selected. Considering theopen area as control, mean reflected sunlight reducingeffects were found to be 19.0, 66.0 and 82.7% for the2 m near a tree, under a tree, and forest area, respectively.According to the responses of 51 subjects in the study,visually “very comfortable” range is between 5,000 and

8,000 lx; “comfortable” range is between 11,000 and75,000 lx (mostly at 12,000 lx); “uncomfortable”condition is above the light intensity value of 43,000 lxand “very uncomfortable” condition is above theintensity of 80,000 lx. Great majority of the subjects(91%) found the value of 103,000 lx to be “veryuncomfortable.” As it is not an applicable way to usethe great and dense tree masses in the cities, at leastindividual trees should be used along themain pedestrianaxels in the cities having the same features with Erzurumto prevent the natural light pollution and discomfortingeffects of the snow-reflected sunlight.

Keywords Snow reflected sunlight pollution .

Human visual comfort . Urban forest . Erzurum

Introduction

Consistent increase in the human population growthand technological development add new pollutiontypes on present ones. One of them may be the naturalsunlight pollution reflected from the snow-coverremaining on the ground surface for a very longperiod in mid-latitudes and at relatively higheraltitudes. When mentioned about the light pollution,unfavourable effects of artificial light sources areconsidered and for this, there are many studies in theliterature about the artificial light pollution. However,discomforting natural light reflections from both freshand old snow-covered surfaces can complicate human

Environ Monit Assess (2008) 144:367–375DOI 10.1007/s10661-007-9999-1

H. Yilmaz (*) :N. Demircioglu Yildiz : S. YilmazDepartment of Landscape Architecture,Faculty of Agriculture, Ataturk University,25240 Erzurum, Turkeye-mail: hyilmaz@atauni.edu.tr

life many times and this event from natural sunlightreflection in the settlements where the number of dayswhen the ground is covered with snow is relativelylarge may be considered to be a kind of pollution.

Intensive sun light reflection causing many healthproblems has especially negative effects on the humanskin, eyes and on children. In the mountainous areas,where snow surface is large and consistent, theseproblems can be seen more apparently because theamount of the ultraviolet sunlight is 80% more inthese areas (Amato 2007). Light intensity reflected bythe snow cover can also affect the human sight(visual) comfort.

Because the study of the effects of the sunlightreflected by the snow covered surfaces is a very newsubject and relatively less people are affected by thiskind of natural event when compared with the otherenvironmental matters, such as global warming, humanthermal comfort or urban heat island etc., no relatedstudy could be found in the literature in spite of thedetailed literal searching. However, the results of theliteral scanning showed that the related studies withthe subject of the present study are on the artificial lightpollution rather than natural (sun) light reflection.

Light pollution has become a common problem ofall countries. Light pollution, which initially had noimportant place among the environmental problems,has begun to pull attraction in the last a few decadesand it has been accepted as one of the pollutionelements (Demircioglu and Yılmaz 2005). For thatreason, in many countries, campaigns against the lightpollution such as IDA (International Dark-Sky Asso-ciation), CfDS (Campaign for Dark Skies), CIE(International Commission on Illumination), TC(Technical Committee) and MIRA (The MontereyInstitute for Research in Astronomy) have beenestablished and national committees have been shaped(Hermann 2001; Remande 2001 and Vandewalle et al.2001). The first map of light was formed in 1973 inItaly and the fourth day of October was announced asthe “National Day of Light Pollution” (Aslan 2001).However, people are not informed about the reasons,negative effects, and solution process of light pollution(Percy 1996; Green 1997; Murdin 1997; Olgyay andOlgyay 1976 and Hanel 2001).

There are many studies about the light pollution inmany countries. Researchers such as Smith (2001) inChile, Osman et al. (2001) in Cairo, Di Sora (2001)in Frosinone, Italy, Dutil (2001) in Quebec, Hanel

(2001) in Germany, Isobe and Aslan (2001) inTurkey, Cinzano et al. (2001) in North America,Isobe and Hamamura (2000) in Japan carried out theirstudies to determine the light pollution and findsolution processes for it. But all of these studies areon the pollution from artificial light sources ratherthan from natural.

As the result of the reflection of the sunlight from thesnow covered surfaces people are mostly exposed tohigher sunlight intensities and because of this eventhuman visual comfort is affected unfavourably. Naturallight pollution has unfavourable effects on all livingthings. Exposure to intensive light may cause skincancer, and physiological illnesses in humans; diapose,polymorphism, genital disorders and migration ininsects (Kansu 1988); changes in the larva period andreduction in larva quality in fish (Akyurt 1993; Yanıkand Atamanalp 2001; Simenson et al. 2000; Leonardiand Klempau 2003 and Ebbesson et al. 2003);cannibalism and feather striping in chickens (Akbay1982 and Emsen 1997); stem thickening, shortenedinternodes, increased branching, thickened cuticle andcell membranes, elongation in the roots, reduction inthe amount of chlorophyll, increased respiration andtranspiration, high salt rate and osmotic pressure,unexpected bloom and etc. in plants (Barbour et al.1987; Andic 1993; Agaoglu et al. 1995; Bedunah andSosebee 1995 and Taiz and Zeiger 1998); and birds tocrash into the buildings (McCarthy 2000).

Since the natural sunlight reflection by snowcovered surfaces is not considered to be the artificiallight, it may not be evaluated as the light pollutionsource. However, the level of the sunlight reflected bythis surface is of so high intensity that it may disturbhumans many times. For this reason, this study aims todetermine the reflected sunlight intensities from snowcovered areas at points near (at a distance of 2 m) andunder an individual tree and among trees (in the forestarea) by accepting the open area as control; thereducing effects of the plant materials on reflectedsunlight in percentage by comparing with the values ofthe open area; and critical reflected sunlight thresholdvalues for human visual comfort.

Materials and methodology

This study was carried out in Erzurum, located in thenorth-eastern part of Turkey, (39° 55`N and 41° 16`E)

368 Environ Monit Assess (2008) 144:367–375

(Fig. 1). The city, where a typical continental climatecharacteristic is prevalent, is one of the coldest cities ofTurkey. Long-term annual mean temperature in the cityis 5.2°C. According to mean meteorological valuesbetween 1988 and 2002; the number of the days whenthe snowyweather is prevalent and the ground is coveredwith the snow-cover is 53.9 and 94.7 days, respectively(Anonymous 2002). For this reason, the reflection ofsunlight due to the snow cover is expected to be large.

Study area encompasses both forested and openareas on the Ataturk University campus in the west ofthe city. This area of 388 ha is at the access point ofthe city and on the E-80 state highway (Fig. 1). In thestudy area, there are approximately 50-year-old trees,dominantly pines (Pinus sylvestris L.; Fig. 2).

The study was carried out over 22 clear and calm,i.e. sky was cloudless and wind was calm, daysbetween the 1st and 31st days of January 2004. Oneach observational day, measurements were per-formed at 8:30 in the morning, at 12:30 at noon andat 14:30 in the afternoon, considering the workingactivities of people, because at these hours, people aremostly in outdoor areas, on the way to work or schoolor break times. Selected measurement points wereopen area as control and points 2 m near and under anindividual tree and urban forest area (Fig. 3) andmeasurements were performed with 2 replicationsusing a Light Meter, LT Lutron LX 105, a devicecapable of measuring the intensity values between20,000 and 200,000 lx. In order to determine thediscomforting light intensity levels, 25 females and 26

male (totally 51) student subjects whose mean agewas 20 and who had no visual disorders were selectedamong the Landscape Architecture Department studentsand exposed to various reflected sunlight intensities inthe same period. Mean body length of the subjects is160 cm and only 6 subjects had coloured eyes.

The ANOVA test was used to determine the differ-ences in the sunlight intensities between the locationsand the means were compared by the Duncan’s multiplecomparison tests using the SPSS Software Package.According to the responses of the subjects to thereflected sunlight intensities, comfort conditions weredivided into the ranges as “very uncomfortable” (1),“uncomfortable” (2), “comfortable” (3), and “verycomfortable” (4).

Results and discussion

Effects of the snow reflected sunlight on people

Unfavourable effects of reflected sunlight on peoplemay vary depending on the age, sex, diet, and climateof the habitat and the inclination of sunlight.However, there are no sufficient studies determiningthe intensity values of sunlight which may disturbpeople physically, psychologically and especiallyvisually. For this, in order to determine the snow-reflected natural sunlight intensities, above whichpeople can be in an uncomfortable condition visually,responses of 51 subjects were evaluated.

Fig. 1 Location of studyarea in Turkey

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The results of ANOVA indicated that there werestatistically significant differences among the reflectedsunlight intensities for human visual comfort (Tables 1and 2).

According to the results taken from the responsesof the 51 subjects to the light intensity values, whichare also presented in Tables 1 and 2, the mostdiscomforting sunlight intensity reflected from thesnow is 103,000 lx, which was found to be “veryuncomfortable” by 91% of the subjects and followedby 90,000, 83,000 and 80,000 lx, which were foundto be “very uncomfortable” by 59, 65 and 65% of thesubjects, respectively. As the intensity value increasesfrom 11,000 lx, visual comfort conditions of thesubjects decrease. For the “uncomfortable” lightintensity level, 51% of the subjects found the reflectedsunlight light level of 90,000 lx to be “uncomfortable”

which was interestingly followed by 43,000, 54,000 and75,000 and 80,000 lx, which were found to “uncom-fortable by 49, 46, 41% of the subjects, respectively. Ascan be seen again from Table 1, “comfortable” reflectedlight intensity level is 12,000 lx, which was found tobe “comfortable” by 70% of the subjects. This valuewas followed by the light intensity values of 15,000,25,000 and 11,000 and 45,000 lx, which were found tobe “comfortable” by 59, 56 and 45% of the subjects.For the “very comfortable” visual range, the reflectedsunlight intensities of 5,000 and 8,000 lx were bothfound to be “very comfortable” by 82% of the subjects.These values were followed by 11,000 and 15,000 lx,which were found to be “very comfortable” by 55 and27% of the subjects, respectively.

From the results mentioned above, it might bestated that visually “very uncomfortable” conditions

Fig. 3 Representatives ofmeasurement points

Fig. 2 A view from themeasurement area

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range from the reflected sunlight intensity of 80,000to 103,000 lx and above while “uncomfortable”conditions for the human eyes are in a range between43,000 and 90,000 lx. From this point of view, thelower limit (or critical threshold) of the human visual“uncomfortable” conditions might be thought as thevalue of 43,000 lx. For the “comfortable” conditions,the upper limit value is 75,000 lx, while “verycomfortable” conditions are provided under the intensi-ties of 5,000 and 8,000 lx mostly and 11,000 lx partially.In a very rough perspective, human visual comfort maybe provided within reflected sunlight intensity valuesranging from 5,000 to 43,000 lx (Table 1).

Evaluation of the snow-reflected sunlight intensitiesobtained from the measurement points

Snow-reflected light intensity values obtained from themeasurements carried out at four different locations

and three times a day are shown on Table 3 andfollowing results were found.

For the morning measurements, the highest meansunlight intensity value was taken from the open(control) area with 36,366.5 lx, followed by the point 2m near a tree with 28,175.4 lx, under tree with 10,961.9lx and forest area with 5,971.1 lx. At noon measure-ments, the light intensity values were expectedly higherthan the other times because of the inclination of thesunlight. For this measurement time, the highest meanreflected sunlight intensity was observed in the open(control) area with a value of 71,260.9 lx, followed bythe points 2 m near a tree with 54,922.5 lx, under treewith 15,998.4 lx and forest area with 9,179.3 lx. In theafternoon, mean reflected sunlight intensity was thehighest in the open (control) area again with the value of29,077.9 lx, which was followed by the point 2 m near atree with 25,711.4 lx, under tree with 14,747.0 lx andforest area with 7,079.1 lx (Table 3).

Table 2 ANOVA for the effects of natural light on people

Intensity of illumination N Mean Std. deviation Std. error 55 Confidence interval for mean Minimum Maximum

Lower bound Upper bound

5,000 51 3.7451a .48345 .06770 3.6091 3.8811 2 48,000 22 3.8636a .35125 .07489 3.7079 4.0194 3 411,000 22 3.5455ab .50965 .10866 3.3195 3.7714 3 412,000 29 3.0000cde .65465 .12157 2.7510 3.2490 1 415,000 22 3.0909cd .75018 .15994 2.7583 3.4235 1 425,000 51 2.6863ef .58276 .08160 2.5224 2.8502 2 443,000 29 2.5517f .73612 .13669 2.2717 2.8317 1 445,000 22 2.6364ef .78954 .16833 2.2863 2.9864 1 454,000 29 2.7931def .94034 .17462 2.4354 3.1508 1 475,000 51 2.1961g .69339 .09709 2.0011 2.3911 1 480,000 22 1.5000h .59761 .12741 1.2350 1.7650 1 383,000 29 1.4828h .82897 .15394 1.1674 1.7981 1 490,000 22 1.4091hi .50324 .10729 1.1860 1.6322 1 2103,000 22 1.0909i .29424 .06273 .9604 1.2214 1 2Total 481 2.6840 1.03679 .04727 2.5911 2.7769 1 4

F=45.688 P≤0.01Different letters reveal the different means

Table 1 Responses of the subjects to the different reflected sunlight intensities

Comfort levels Reflected sunlight intensities (lx)

5,000 8,000 11,000 12,000 15,000 25,000 43,000 45,000 54,000 75,000 80,000 83,000 90,000 103,000

Very uncomfortable – – – 3 3 – 3 5 7 14 54 65 59 91Uncomfortable 4 – – 10 11 34 49 36 46 41 41 35 51 9Comfortable 14 18 45 70 59 56 38 45 32 45 5 – – –Very comfortable 82 82 55 17 27 10 10 14 15 – – – – –

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In the measurement period, maximum reflectedsunlight intensity was found to be 95,700 lx in theopen area in the morning, it reached 122,900 lx atnoon, increasing by of 23% and decreased to 82,150lx in the afternoon on the 21st day of the period.Approximately the same increase was seen at otherpoints on the same day (Table 3). In the wholemeasurement period, on 77% of all measurementdays, the light intensity values at noon exceeded43,000 lx in the open area while at the point 2 m neartree, 63% of the observed light intensities at the samemeasurement time again were found to be uncom-fortable, exceeding 43,000 lx. However, at the sameobservation time, the light intensity levels eitherunder tree or in the forest area were stated to be inthe “very comfortable” or “comfortable” range by thesubjects because the values taken from these areaswere not above the upper limit of 43,000 lx, exceptfor the value of 56,900 lx measured under tree at noonon the 4th day of the period.

Based upon the measured reflected sunlight inten-sities, the morning and afternoon values were found tobe in the “comfortable” and “very comfortable” ranges,in spite of the presence of a few extreme values.

After the subjection of the mean reflected sunlightvalues to ANOVA test (Table 4), statistically signif-icant differences were found to exist between both theareas and measurement times (P≤0.01) and it wasseen again that the intensity of the reflected sunlightwas reduced from open area to the forest area.

When considered the snow reflected sunlightintensity values of the measurement days and openarea as control, mean reflected sunlight reducingeffects were found to be 19.0, 66.0 and 82.7% forthe 2 m near a tree, under a tree, and forest area,respectively (Table 5). The highest reducing effectswere seen at noon measurement for all of themeasurement areas and the most effective area forthe reduction of the light intensity, in terms of bothdistinct measurement times and mean reduction

Table 3 Sunlight intensity values for the different measurement times and points

Times Morning Noon Afternoon

Days Openarea

2 m near atree

Undertree

Forestarea

Openarea

2 m neara tree

Undertree

Forestarea

Openarea

2 m neara tree

Undertree

Forestarea

1 18,300 9,675 1,516 2,150 67,100 31,550 22,400 9,715 33,650 23,450 14,006 7,2002 16,750 9,980 2,480 5,960 97,050 88,050 23,450 12,717 9,915 6,750 5,705 2,4853 15,615 12,125 4,050 3,885 23,400 14,095 3,200 4,020 31,000 1,865 669 8784 15,540 12,565 4,275 3,930 104,000 71,550 56,900 8,070 42,955 35,000 15,850 8,2755 23,650 14,205 2,685 3,905 35,950 24,000 4,310 6,375 3,140 1,550 353 5306 14,710 8,000 1,980 3,110 101,350 65,650 24,900 12,710 37,750 27,300 7,030 5,8657 23,500 14,250 4,050 3,185 35,350 28,000 9,290 8,710 7,265 6,280 3,445 4,3358 56,100 41,400 37,250 10,380 27,950 23,750 9,890 6,175 11,895 11,200 7,200 5,8559 53,350 42,850 13,050 9,605 88,000 68,200 19,500 15,200 41,450 35,800 27,650 16,02010 49,100 38,750 8,380 5,290 59,050 40,400 10,185 7,550 27,650 22,950 17,115 9,13511 15,905 11,830 3,045 2,770 45,000 36,150 12,250 7,240 12,195 11,185 7,475 8,12012 25,700 18,950 3,585 3,780 85,850 81,900 13,360 10,585 27,400 20,300 16,000 7,78513 23,500 23,250 5,765 4,200 94,100 78,050 20,400 11,005 26,350 22,500 14,305 7,93514 49,350 42,000 10,820 4,770 80,450 71,450 17,170 9,145 26,350 21,200 12,750 5,92515 55,100 46,350 12,350 9,525 72,500 68,000 17,900 12,960 31,500 26,850 15,040 7,37516 21,350 14,240 3,375 3,665 81,390 65,700 7,720 4,715 25,850 20,590 14,800 8,35017 55,100 43,750 13,960 8,955 78,000 58,200 12,050 9,050 39,950 35,650 25,650 15,00018 76,850 63,000 17,210 8,085 34,950 23,000 4,800 3,040 4,230 1,900 370 27819 24,150 15,765 4,535 4,580 67,950 43,400 12,165 9,395 4,595 3,330 1,300 78220 18,395 13,675 2,700 3,485 83,300 57,750 10,265 4,815 30,350 18,950 10,040 8,08021 95,700 74,600 23,100 13,055 122,900 97,750 19,950 17,950 82,150 76,050 22,350 12,75022 52,350 48,850 25,000 16,250 82,050 67,950 15,385 10,800 82,050 67,950 15,385 10,800Mean 36,366.5 28,175.4 10,961.9 5,971.1 71,260.9 54,922.5 15,998.4 9,179.3 29,077.9 25,711.4 14,747.0 7,079.1

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values, was found to be the forest area, followed byunder and 2 m near a tree (Table 5).

It is a well known and well documented fact thattrees have canopy effects and protect the areas onwhich they are present from the excessive sunlight,which shows again the importance of green areas inthe urban areas (Akbari 2002; Heisler and Grant2000; Novak et al. 2000 and Novak and Craine 2002).Plant materials create local microclimates by blockingthe solar radiation (Heisler 1986; Simpson 2002;Bouchair 2004 and Picot 2004); are regulatory factorson urban climates and moderate the extreme temper-ature values to the normal due to humidity theyrelease to environment and their canopy effects(Bernatzky 1982; Wilmers 1988). Tree transpirationand tree canopies affect air temperature, radiationabsorption and heat storage, wind speed, relativehumidity, turbulence, surface albedo, surface rough-ness and consequently the evolution of the mixing-layer height (Novak et al 1998). In areas with scatteredtree canopies, radiation can reach and heat groundsurfaces (Heisler et al. 1995). This is supported by

Robinette and Mcclenon (1977), who determined thattrees absorbed 60–90% of received light and thisamount of absorption depends upon the density andthe developmental conditions of leaves of trees.Robinette and Mcclenon (1977) also determined thatwhile in an environment with dense coniferous andbroadleaf trees, 75–90% of sun radiation was absorbedby trees, small crown coniferous trees in loose position60% of it is absorbed and absorption rate by anindividual leaf is 25%. Aslanboga (2002) focused thatin a forest area, while 10–20% of the sunlight turnsback to the sky by reflection, 30–60% was absorbedduring transpiration and 50–80% was lost by absorp-tion, only 10–30% of the sunlight can penetrate in theforest. Similarly, Rainer et al. (2001) reported thatplants reflected about 40–50% of natural light.

Similar statements can be said for the present studyand while the highest amount of reflected sun lightwas found to be in the open area, considerably lowervalues were found near, under and among trees.Results found in the present study are within therange found in the studies mentioned, with thereduction values of 19.0% 2 m near a tree, 66.0%under a tree (scattered canopy) and 82.7% underdense canopy layer (forest area) compared to thecontrol in terms of mean values.

Conclusion

In the mid-latitude and high altitude cities, likeErzurum, the number of clear (sunny) days when theground is covered with snow is so large that the snowcover may remain on the ground as long as sixmonths, in a period beginning with the late Octoberand lasting until early April. In this kind of areas, the

Table 5 Reflected sunlight reducing effects of trees for themeasurement areas compared to the open (control) area

Measurement times Location types

Openarea (%)

2 m neartree (%)

Undertree (%)

Forestarea (%)

Morning 100 22.0 70.0 84.0Noon 100 23.0 78.0 88.0Afternoon 100 12.0 50.0 76.0Mean 100 19.0 66.0 82.7

Table 4 Mean light intensity values for the observation times

Location types Mean

Open area 2 m near tree Under tree Forest area

Morning 36,366.5 28,175.4 10,961.9 5,971.1 20,368.7bNoon 71,260.9 54,922.5 15,998.4 9,179.3 37,840.2aAfternoon 29,077.9 25,711.4 14,747.0 7,079.1 19,153.8bMean 45,568.4a 36,269.7b 13,902.4c 7,409.8d 25,787.6

LSD (%): Mean: 9,050.1, Application: 5,632.9, Mean × Application: 9,756.5

F Values: Mean: 19.518, Application: 141.4, Mean × Application: 16.5

Different letters reveal the different means

Environ Monit Assess (2008) 144:367–375 373

natural sunlight reflection from snow cover has sodiscomforting effects on humans that people mayhave to wear sunglasses in winter and get suntannedmore than in summer months. Although it is a naturalevent and considered not be a light pollution, somecares should be taken to prevent it.

Perhaps the most important outcome of the study isthe determination of the critical sunlight intensityvalues for the human visual comfort. According to theresponses of 51 subjects in the study, visually “verycomfortable” range is between 5,000 and 8,000 lx;“comfortable” range is between 11,000 lx and 75,000lx (mostly at 12,000 lx); “uncomfortable” condition isabove the light intensity value of 43,000 lx and “veryuncomfortable” condition is above the intensity of80,000 lx. Great majority of the subjects (91%) foundthe value of 103,000 lx to be very uncomfortable.

Another important aspect of the study is thedetermination of the reducing effects of the trees onthe snow-reflected sunlight intensity. In this respect, itmight be said considering the open area as controlthat trees reduced the sunlight reflection from snowby 19.0% 2 m around them, by 66.0% under them and82.7% in the forest (when used in group) in terms ofmean values. From this respect, the study re-empha-sizes the importance of the urban forest areas.

As a consequence, green area planning has nowundertaken a vital role for the solutions of theproblems faced in the urban areas for not only theesthetical considerations but also the functional uses.In this study, an additional necessity for the use oftrees in the cities, especially those having the samefeatures with Erzurum was determined. As it is not anapplicable way to use the great and dense tree massesin the cities, at least individual trees should be usedalong the main pedestrian axels in this kind of citiesto prevent the natural light pollution and discomfort-ing effects of the snow-reflected sunlight. In thisrespect, the species to be used should be evergreen;existent plant masses should be preserved and thelocal administrators should be informed about thisnew kind of environmental matter. As this kind oflight pollution (snow-reflected natural sunlight) is anewly introduced matter, supporting and detailedfurther studies, which may involve the situationsunder the broad-leaved trees and may have largersampling population for the determination of thevisual comfort ranges, are needed.

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