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One of the widely known secrets in automotive lighting is the problem of detecting low reflectance roadway obstacles. At speeds beyond 40 mph, most drivers cannot see dark-colored obstacles (such as dark-clad pedestrians) in time to bring their vehicle to controlled stop in time to avoid a collision. For pedestrians crossing the roadway, the vehicle does not actually have to stop, only slow - slow enough to allow the pedestrian to walk beyond the vehicle path before the vehicle arrives. There are rational means of estimating the extent and the implications of the temporal bonus attributable to early detection of crossing pedestrians. This study suggests potential lighting standard modifications to address these needs.

The Uniform Detection Characteristic (UDC) locus circumscribes a region in front of a vehicle at which the luminance requirement for detecting a roadway obstacle is met by the vehicle's headlamp system. Algorithms take into account variables that are not typically addressed by traditional (isolux) roadway illumination methods. The variables that can be treated include: obstacle size, coloration or reflectance characteristics; a driver's state of expectancy, age-related changes in visual sensitivity, and adaptation levels elevated by ambient light. The discernibility locus defines the distance at which a detection criterion, the luminance sensitivity threshold, is satisfied for moving or stationary obstacles. The locus protocol can be used for grading the effectiveness of lighting systems on specific vehicles, or for forensic investigation of nighttime automobile accidents

Models using contrast as the measure of discernibility or detection of roadway obstacle on non-lighted roadways have not recognized the lighting effects caused by the lateral spacing of headlamps on the vehicle. When the only significant sources of roadway light are a vehicle's headlamps, shadows on the roadway behind and to the left and right of the obstacle are viewed simultaneously with the obstacle itself. It can be shown that in certain obstacle-sighting situations, where there is little or no significant background light from sources other than the headlamps themselves, sufficient contrast is provided by the shadow outlines. Shadows created by the lateral spacing of the headlamp light sources and the driver's eyepoint, framing one or both sides of the obstacle, serve to outline the illuminated obstacle on the roadway in front of a vehicle.