Effects of snow-reflected light levels on human visual comfort

The intensity of the sunlight reflected by the snow-covered surfaces is so high that it may disturb humans many times. This study aims to determine the reflected sunlight intensities from snow covered areas at points near (at a distance of 2 m) and under an individual tree and among trees (in the forest area) by accepting the open area as control; the reducing effects of the plant materials on reflected sunlight in percentage by comparing with the values of the open (control) area; and critical reflected sunlight 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 between the 1st and 31st days of January 2004, at 8:30 in the morning, at 12:30 at noon and at 14:30 in the afternoon in Erzurum. In order to determine the discomforting light intensity levels, 25 females and 26 male (totally 51) student subjects whose mean age was 20 and who had no visual disorders were selected. Considering the open area as control, mean reflected sunlight reducing effects were found to be 19.0, 66.0 and 82.7% for the 2 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 and 75,000 lx (mostly at 12,000 lx); "uncomfortable" condition is above the light intensity value of 43,000 lx and "very uncomfortable" condition is above the intensity of 80,000 lx. Great majority of the subjects (91%) found the value of 103,000 lx to be "very uncomfortable." As it is not an applicable way to use the great and dense tree masses in the cities, at least individual trees should be used along the main pedestrian axels in the cities having the same features with Erzurum to prevent the natural light pollution and discomforting effects of the snow-reflected sunlight.