Just Noticeable Differences for Low-Beam Headlamp Intensities

摘要

A recent study by Huey, Dekker, and Lyons (1994) concluded that a differencebetween two signal lamp intensities of less than 25 percent cannot be detected reliably by most drivers. Consequently, Huey et al. recommended that an intensity difference of 25 percent be used as a criterion for inconsequential noncompliance with federal regulations for signal lamps. The present study was designed to evaluate just noticeable differences for glare intensities of oncoming low-beam headlamps. The results of this study indicate that, under controlled conditions, just noticeable differences in the low-beam headlighting context are between 11 percent and 19 percent. In real-world conditions, just noticeable differences would probably be somewhat larger. Therefore, the recommendation by Huey et al. if using 25 percent as a criterion for inconsequential noncompliance of themselves are perceived by other drivers (such as discomfort glare). The 25 percent value may also apply with respect to how headlamps affect the ability of drivers to see illuminated objects, but further research on that issue would be desirable.