A Systematic Study of Pedestrian Contrast and Detection From Vehicle Headlights

An important factor in evaluating the visibility of pedestrians at night is the contrast they offer an observer. This paper investigates and quantifies the influence of various parameters on contrast. An experiment was conducted using pedestrians and surrogate human models positioned along a grid in relation to the illuminated headlights of vehicles positioned on a dry asphalt roadway with no additional overhead lighting. As part of this experiment, headlight illuminance was mapped, and pedestrian luminance data were comprehensively collected to provide parametric data necessary to evaluate patterns affecting contrast. Luminance and illuminance data are presented in the form of three-dimensional plots and further related to visibility levels using the Adrian model. The results of this study highlight and quantify important factors present in night visibility of pedestrians. These include position of the pedestrian both longitudinally and laterally, reflectivity of the clothing, vertical variations in luminance and illuminance, the background, and headlamp characteristics. They emphasize that three-dimensional modeling of headlight illuminance and pedestrian luminance enhances the understanding of pedestrian contrast and visibility.