Visual Acuity in a Condition of Traffic Sign Viewing: The Effects of Luminance Changes

Landolt C visual acuity of eight subjects was measured as a function of stimulus luminance. To simulate traffic sign viewing, a stimulus field width of 0.7° with a surround field of 60° was used. The surround luminance was changed in steps of a factor of 10 from 0.5 to about 5000 cd/m 2 . Both dark symbols on a light background and light symbols on a dark background were considered. The presentation time was either unlimited or 200 msec. For surround luminances up to 5 cd/m 2 , the relation between acuity and stimulus luminance can be described by a function of the same shape. For all surround luminances higher than 50 cd/m 2 a second function is needed. In all conditions with long presentation times, the results were identical for light symbols on a dark background and dark symbols on a light background. With a stimulus time of 200 msec the acuity is, on the average, 0.7 times the acuity with long presentation time.