The potential benefits offered by high-intensity discharge (HID) sources for vehicle headlamps have raised new issues in the design of headlamp beam patterns. The primary purpose of the present study is to address some of those issues by quantifying the effects of one major aspect of headlamp beam patterns - foreground light - on visual performance. We measured the seeing distance to a dark-clad pedestrian at night on a two-lane road as a function of observer age, foreground luminance, and pavement condition (dry/wet). Observers sat in the driver's seat of a stationary vehicle positioned on the road while a pedestrian walked either toward or away from the vehicle. The observer indicated when the pedestrian just became visible or invisible, depending on the direction of movement. Wet pavement resulted in longer seeing distances under all conditions. The effect of foreground luminance on seeing distance depended on both observer age and pavement wetness. High foreground luminance resulted in shorter seeing distances for older people and longer seeing distances for younger people. High foreground luminance also resulted in shorter seeing distances with dry pavement and longer seeing distances with wet pavement. However, all of the effects of foreground luminance were small, suggesting that although high foreground luminance does decrease seeing distances under some conditions, it is probably not a major problem for drivers. Two major limitations apply to the interpretation of the effects observed in this study. First, the effects of glare from opposing headlamps were not measured. Second, only the effects of pavement wetness itself were measured, not the effects of active precipitation. (Author/publisher)
Samenvatting