Discomfort glare from high-intensity discharge headlamps: Effects of context and experience.

Abstract

This study was designed to investigate further a difference in discomfort glare produced by tungsten-halogen (TH) and high-intensity discharge (HID) headlamps that we had found in a previous experiment. In a static field setup, 36 subjects, 24 in a younger group and 12 in an older group, made de Boer ratings of discomfort glare for TH and HID lamps. The lighting conditions were similar to those seen while driving on a dark, two-lane road when glare from an oncoming car is encountered. The results replicated the difference between TH and HID lamps that we observed in the earlier study, and indicated that the difference is not reduced by several manipulations of context and experience that we introduced in the present study. Analysis of subjects’ discomfort ratings indicated that when TH and HID lamps produce equal discomfort glare, the tungsten-halogen lamps produce more photopic lux at the eye of the observer. The magnitude of this difference was not affected by the type of headlamp (TH or HID) used on the car in which observers sat while viewing the glare stimuli, nor by whether the TH and HID lamps were presented in the context of headlamps that had been filtered to produce strongly saturated colors. For younger subjects, the magnitude of the difference did not change over the course of the experimental session, but for older subjects the difference became larger. During the early part of the experiment, in which the magnitude of the difference was the same for younger and older subjects, the average difference between TH and HID lamps in photopic lux corresponding to a criterion level on the de Boer scale was 0.165 log units (meaning that photopic lux for TH lamps would be 1.46 times greater than for HID lamps when discomfort glare was equal). The significance of these findings for possible effects of HID lamps in actual driving is discussed.