Rated Discomfort Glare from High-Beam Headlamp Reflection in Rear-View Mirrors

This study compared the rated discomfort glare from vehicle headlamps for different candidate rear-view mirror types in a situation very much like that encountered while driving. The tests were performed using an actual automobile with ten different rear-view mirrors, including the interior center mirror. The test was conducted on a private road, out of traffic, in nighttime conditions. In this experiment the confederate vehicle (large pick-up truck), with its headlamps set on high beam, moved to different positions behind the static subject vehicle. All subjects rated the glare at each position using the glare scale. The results provide a direct within-subject comparison of the various types of mirrors and are consistent with previous analyses. Flat mirrors proved to produce the highest ratings of reflected glare. The aspheric and convex mirrors having a 1,400 mm radius of curvature produced lower glare ratings than other outside rear-view mirrors tested. However the glare ratings of 1400 mm radius of curvature mirrors averaged about one rating value higher in glare than the inside rear-view mirror in the nighttime setting. Compared to an interior mirror that is adjusted to manual nighttime setting the outside mirrors produced higher glare ratings. The findings of this research also indicate, surprisingly, that older drivers provided lower glare ratings than younger drivers at distances beyond 30 ft. Examination of the data by subject showed no outlier effects, suggesting that the current results are very likely to be repeatable and are therefore considered to be reliable.