High-contrast brake lamps are lamps that appear black or body color when they are not energized. In addition to stylistic advantages, there may be some behavioral benefits from using high-contrast brake lamps, such as a reduction in driver reaction times to brake signals during high levels of ambient illumination. There are two possible mechanisms for such an effect. The first mechanism is based on the increased brightness difference between the off and on states. The second mechanism involves the increased color difference between the two states. While the standard brake lamp goes from darker red to brighter red, the high-contrast lamp appears to change from black or body color to red.
The present study was designed to evaluate the potential reaction-time benefits of high-contrast brake lamps. The study, performed in a laboratory, simulated a daytime driving condition with illumination from the sun being reflected by the lenses of the brake lamps. The subject's task was to respond as quickly as possible to the onset of one of two brake lamps (a standard lamp and a high-contrast lamp of the same luminous intensity) in the near visual periphery, while engaged in a central tracking task.
The results showed that reaction times were shorter to the high-contrast lamp than to the standard lamp. The difference in reaction time was highly significant statistically, but not large. On average, this difference was 19 msec, which corresponds to a saving of 0.5 m of stopping distance from an initial speed of 100 km/hr. This finding indicates that high-contrast brake lamps might have a positive effect on the performance of following drivers.