OBSERVERS ’ JUDGMENTS OF THE EFFECTS OF GLARE ON VISUAL ACUITY

ii Traffic collisions and pedestrian fatalities increase significantly when driving at night. There is a need for greater roadway visibility when driving at night and the use of high beam headlights can significantly improve the distance at which drivers recognize objects along the roadway. However, research suggests that drivers underuse their high beams. It is possible that drivers do not use their high beam headlights in an effort to minimize glare to oncoming vehicles. The purposes of this experiment were to extend earlier research indicating that the visually impairing effects of glare may often be exaggerated and to investigate the role of stimulus contrast and size in observers’ judgments of the effects of glare. Participants were asked to judge the luminance of a glare source sufficient to impair their visual acuity of a target viewed through this glare source; these estimated glare thresholds were compared to the participant’s actual glare thresholds. Participants overestimated the intensity of glare required to produce a decline in their visual performance. On average, estimates of glare threshold were 88 % lowe