Driver decision making in response to peripheral moving targets under mesopic light levels

A field study was conducted to extend fundamental findings about visual performance at mesopic light levels to a driving context. Subjects participating in this field study drove a vehicle along a lighted street while performing a high-order decision-making task. Subjects identified the direction of an off-axis target, toward or away from the street, and braked or accelerated, accordingly. Two sets of light sources were compared: a set of ceramic metal halide light sources and a set of high-pressure sodium light sources. The same study was also performed during the day-time. The results demonstrated that both braking and acceleration response times decreased monotonically as unified luminance increased, suggesting that unified luminance is a suitable rectifying variable for characterizing light levels for different light sources with respect to a complex visual task.