Headlight Glare Exposure and Recovery

There is concern that the greater light output and increased beam pattern widths of some headlamp systems may be resulting in higher glare exposures to drivers for longer times. A set of experiments is described that examines how headlamp glare exposure affects recovery time and ratings of discomfort. Theoretical glare exposures were examined to study different aspects of glare, namely peak glare illuminance and total glare dosage. Glare exposures corresponding to representative tungsten halogen (TH) and high intensity discharge (HID) systems were also examined.

It was found that the shape of the glare profile had a significant effect on recovery time. A larger dose of glare (product of illuminance and exposure time) results in a longer recovery time. It was also found that discomfort ratings are dependent on glare profile, with greater discomfort being proportional to larger peak illuminances. Surprisingly, no effect of glare duration or dosage was found on discomfort. It was also found that under nominal aiming conditions the glare exposures representing TH and HID systems produced similar recovery times. However, with 1° of misaim upwards, the HID exposure produced significantly longer recovery times.