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. Target reflectance was also varied between 20% and 40%. The time of response to target presentation, as well as the number of targets missed, were collected as a measures of performance. Additionally, subjective ratings of discomfort were also collected from the subjects after every test condition.
The results show that illuminance at the eye is the dominant factor in glare produced by an oncoming headlamp under these conditions, both for on- and off-axis visual performance and discomfort. Further, for varying glare illuminances, there was found an interesting interaction between target contrast and discomfort ratings. Light source spectrum did not play a significant role in causing disability glare, but did significantly impact discomfort. Headlamp size had no significant impact on discomfort or disability glare. The impacts of these results on new light sources for vehicle forward lighting, such as HIDs and LEDs are discussed.