The (In)Accuracy of Estimations of Our Own Visual Acuity in the Presence of Glare

Headlights must balance two conflicting goals: maximizing visibility for the driver and minimizing glare to other drivers. Yet, recent increases in the number of complaints about headlights indicate a consumer focus on glare discomfort and not on poor visibility – a known causal factor of nighttime crashes. This study, as part of a series of experiments, explored the relationship between subjective and objective consequences of glare. Twenty-four participants used a psychophysically based technique to estimate their visual acuity in the presence of three different glare intensities. Actual acuity and subjective reports of discomfort were also assessed. Observers’ estimates of acuity significantly worsened as glare intensity increased, yet actual acuity was unaffected. Overall, estimates of the disabling effects of glare were more tightly correlated with subjective reports of glare-induced discomfort than with actual visual performance. These results, which are consistent with data obtained in the field – using vehicle headlights as the glare source – may help explain drivers’ reluctance to use their high beams. The results also underscore the need to collect data on disability glare, not just discomfort glare, when evaluating new lighting technologies.