Discomfort glare is task dependent.

Abstract

This laboratory study evaluated the effect of task difficulty on discomfort glare. Two tasks were performed on each trial. The first was a gap-detection task, in which the subject indicated whether the gap had appeared on the top or the bottom edge of the outline of a briefly projected square. The difficulty of this task was manipulated by changing the size of the gap in the square. The second task was a discomfort-glare rating, in which the subject gave a numerical rating of the discomfort experienced from a glare sources that was presented simultaneously with the gap-detection stimulus. The hypothesis was that the resulting changed in the difficulty of the gap-detection task would influence discomfort glare. The results indicate that (1) as expected, discomfort glare was strongly influenced by glare illuminance, (2) an increase in the difficulty of the gap-detection task resulted in an increase in discomfort glare, and (3) the subjects with poorer overall gap-detection performance tended to assign more discomfort to the glare stimuli than subjects with better overall gap-detection performance. These results are consistent with the hypothesis that discomfort glare is related to task difficulty. Consequently, a valid evaluation of discomfort glare in a give situation requires the presence of the relevant concurrent visual task. One possible interpretation of these findings is that task difficulty influences discomfort glare by modifying an observer’s perceived level of visual impairment (perceived disability glare).