Large area glare sources and their effect on visual discomfort and visual performance at computer workstations

The authors studied the effect of a large area light source of variable but uniform luminance surrounding a video display terminal on the perceived glare discomfort and visual performance of computer operators. A set of criteria was established for rating the discomfort. Source luminance adjustments by means of a variable transformer to match the subjective glare criteria, as well as ratings of preselected lighting conditions on a visual analog scale with the same criteria, were used to determine comfortable lighting conditions. Results from the experiment indicate that subjects reliably selected a preferred lighting condition at any time when asked to adjust the luminance to produce optimum visual comfort. Subjects preferred higher luminances following high initial presentation luminances. Performance speed at a difficult letter-counting task suggest that visual performance was slightly impaired by the presence of glare discomfort. Counting errors also occurred slightly more frequently under higher surround source luminances. There was a tendency for subject to become more susceptible to glare over the course of the experiment