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Many individuals believe that yellow headlights are preferable to white headlights when driving at night during a snowfall. Although evidence exists to support the claim that yellow light can be perceived as less “glaring” or “distracting” than white light of equal luminance, it is not clear whether backscattered light of different colors are differentially effective for driver comfort or for driver performance. This study investigates a potential mechanism that could support the supposed benefit of yellow headlamps for reducing the detrimental effects of backscattered light to drivers at night. The results suggest that under low light levels when the visual field is dominated by a dynamic field of visual “noise” (like that caused by backscattered light from falling snow), performance of a tracking task similar to driving is reduced in accordance with the scotopic (rod-stimulating) content of the visual noise.

Flashing emergency and warning lights are critical elements of public safety and traffic control during roadway incidents. These lights should not only alert drivers to their presence, but also should inform them of who and what is present on the scene, and should help to manage the responses of drivers as they navigate past the incident. First responder and driver safety depend upon all three of these functions, yet standards focus almost entirely on alerting drivers. A full-scale outdoor field study was carried out during daytime, during nighttime on dry pavement and during nighttime on wet pavement, using a mock-up roadside scene containing three police vehicles. The lights on the vehicles were adjusted to produce different levels of intensity, flash rate, and synchronization of lights across all three vehicles. In some cases, sequentially flashing lights were present.