Visual Search for Safety Colors under Low Illuminance Conditions

This study aims to examine the search efficiency under low illuminance conditions for three safety colors; red, orange and yellow, which are used for danger and caution signs. They are subjected to a visual search task. Images of visual stimuli consisting of an array of colored circles placed on a large visual field (a visual angle of 40 deg.) were displayed on an 80-inch screen through a projector. Illuminance conditions were controlled by decreasing luminous intensity from the light source of the projector using neutral density filters. Three illuminance conditions were set with a linear regression equation corresponding to the luminance of color chips for safety colors and surrounding illuminance in the twilight conditions. Reaction time was measured as functions of the target color, the number of distractors and the illuminance condition. The results showed that the search efficiency for orange decreased with increasing the number of distractors under different illuminance conditions, whereas that of red and yellow scarcely decreased. As illuminance lowers, searching for orange became more difficult than for red and yellow. Consequently, it is implied that as surrounding illuminance lowers in the twilight, orange becomes harder to search compared with red and yellow.