Influence of Foreground Illumination from Headlamps on Visibility and Preference

The present design standards for low beam headlamps offer significant flexibility regarding the distribution of light that they generate. Some headlamp systems produce significant amounts of foreground illumination, which increases the apparent brightness of the roadway surface close to the vehicle, and this increased brightness is seen as desirable by many individuals. Some individuals may prefer not only high but uniform foreground illumination. At almost any driving speed, however, any objects located in the visual foreground are too close to avoid with slowing or steering maneuvers. Further, published literature on the mechanisms for disability glare suggests that foreground illumination should have a negative impact in terms of the visibility of objects located well ahead in the visual field. To investigate the role of foreground illumination level and uniformity on driver preference and visual performance, different lighting scenarios were created with different levels of foreground illuminance and uniformity. Study participants were asked to respond to the onset of visual targets located down the road, ahead of the foreground region, and to rate the quality of the headlamp illumination. Subjects preferred high, but not necessarily uniform, light levels in the foreground. In contrast, visual detection of targets down the road was slightly, but not significantly, worse with higher foreground illumination levels. The results suggest that high foreground illumination levels have a negative or at best, a negligible, influence on visual detection of potential hazards, while conveying a sense of improved lighting quality.