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New headlamp sources and optical designs are creating new glare scenarios on today's roadways. Recent evidence suggests that the spectral content of vehicle forward lighting may play a role in the glare that it produces. Additionally, there is concern that the decreasing size of some headlamp systems may be contributing to glare. This paper describes a field experiment designed to take a fresh look at headlamp glare, both disability and discomfort, by exploring the role of illuminance, spectrum, and size and determining the relative magnitude of each as it affects oncoming glare. Subjects seated in a test vehicle were exposed to small targets at various angles. Test glare headlamps were positioned 50 m in front of the subject at an angle of 5°, simulating oncoming traffic. The glare intensity at the subject's eye, the spectrum of the glare source (among high intensity discharge, halogen, and blue filtered), and the glare source size were systematically varied.

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.