The Accuracy of Drivers’ Judgments of the Effects of Headlight Glare: Are We
Really Blinded by the Light?

Abstract

Summary: Headlights must balance two conflicting goals: maximizing visibility for the driver and minimizing glare to other drivers. Yet consumer complaints about headlights tend to focus on glare and not on poor visibility -a known casual factor of nighttime roadway crashes. These reactions may help to explain why drivers tend to underuse high beam headlights. This study explored the relationships among objective (impaired visual performance) and subjective (reports of discomfort and participants' judgments of glare-induced visual impairments) consequences of headlight glare. Sixteen participants sat in a vehicle that moved slowly on a closed road and estimated the distance at which they could determine the orientation of a retroreflective Landolt C. Actual recognition distances and reports of glare-induced discomfort were also assessed. Observers' overestimated the extent to which glare degraded their ability to see the target. Participants' estimates of their own acuity decreased significantly when the opposing vehicle used high beams despite the fact that their 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 psychophysical data obtained in a laboratory setting, may help explain drivers' reluctance to use their high beams. The results also underscore the need to collect data on disability glare, not only discomfort glare, when evaluating new lighting technologies.

Observers’ Judgments of the Effects of Glare on Their Visual Acuity for High and Low Contrast Stimuli

“…To assist participants with this task, we gave observers practice viewing both high and low contrast stimuli, and we provided cutouts of the visual stimuli that they could hold while making their judgments. Although making judgments about imagined stimuli is unusual, the methods yielded results that are in agreement with existing data (Balk & Tyrrell, 2011a, 2011b that participants can overestimate the impact of a glare source on their vision.…”

“…Glare was produced by a custom-built ''glare box'' (323 mm high, 325 mm wide, and 42 mm deep; the same glare source used by Balk and Tyrrell, 2011a) positioned 120 cm from the right eye of the participant, between the participant and the computer screen. Participants were asked to use their right eye to look through the center of the circular aperture (72 mm diameter) of the glare box which had been aligned with the center of the computer screen.…”

“…Using both laboratory and field-based methods, we have compared observers' estimates of their acuity in the presence of glare with their actual acuity in glaring conditions. In a psychophysical, lab-based experiment, participants looked through the center of a ring of light toward an acuity stimulus and estimated their own visual acuity as the luminance of the glare ring was manipulated (Balk & Tyrrell, 2011a). The results showed that as the luminance of the glare ring was increased, the participants' estimates of their acuity significantly declined even though the luminance levels used were insufficient to affect observers' actual acuity.…”

“…We measured estimated and actual DGTs for both high and low contrast stimuli. Although many factors (such as the distance from the glare source or angular separation) influence disability glare, this study specifically examined how the contrast and size of the visual stimuli impacted disability glare since previous research (i.e., Balk & Tyrrell 2011a, 2011bStafford Sewall et al, 2014) has shown that contrast is important to the accuracy of observers' visibility judgments in the presence of glare. Additionally, stimulus contrast and size have been shown to be critically important factors in determining drivers' ability to detect and recognize objects at night (i.e., Wood et al, 2005).…”

Drivers’ Beliefs, Habits, and Strategies Regarding High Beam Usage

“…Drivers tend to identify oncoming headlight glare as a serious problem, and identify glare as a contributing factor in their decision not to rely on high beams (Singh & Perel, 2004;NHTSA, 2007;Kingery & Bullough, 2010). Yet other researchers have found that headlamp glare may not always be as visually debilitating as many drivers believe (e.g., Shinar, 1984;Brooks, Tyrrell, & Stephens, 2006;Balk & Tyrrell, 2011a;Balk & Tyrrell, 2011b).…”