Body-color brake lamps are lamps that in their off state match the body color of the car. When energized, all body-color lamps, as well as conventional lamps, appear bright red. The speed of response to a body-color brake lamp may differ from the speed of response to a conventional lamp for two reasons. The first is that the difference between off-and on-state luminances varies primarily with off-state luminance. When the difference is larger than for the conventional lamp, the increased luminance contrast may speed reaction time. The other reason that responses for the two types of lamps may differ is the greater chromaticity contrast that body-color lamps have between their on and off states.
This study separately evaluated the effects of luminance contrast and chromaticity contrast for body-color brake lamps. One set of chromatically neutral lamps of varying lightness (from black to white) was tested, along with a set of chromatically varied lamps of equal lightness, and a conventional lamp. The lamps were tested pair-wise in a dual-task paradigm where one task involved simple compensatory tracking, and the other task was to respond to the onset of either of the two brake lamps. Reaction times were recorded.
The primary findings are statistically significant effects of both luminance contrast and chromaticity contrast on reaction time to brake lamps. Neither of these effects is large; the difference between fastest and slowest mean reaction times was 33 msec. The effect of luminance contrast is such that lamps that are light in their off state yield slower reaction times. Performance with the lightest lamp in this study was slightly worse than performance with the conventional lamp. None of the chromatic lamps degraded performance relative to the conventional lamp. The pattern of responses to the chromatic lamps suggests that for all lamps that are different from red in their off state, the effect of chromaticity contrast will be to speed up reaction time slightly compared to the conventional lamp.