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Flashing emergency lights on police cars, fire trucks, and ambulances need to be bright enough to alert otherwise unaware drivers about their presence on and near the roadway. Anecdotal evidence suggests that public safety agencies select emergency lighting systems with red or blue flashing lights based on their apparent brightness, with brighter lights judged as "better." With the advent of light emitting diodes (LEDs), emergency flashing lights are brighter and produce more highly saturated colors, thereby causing greater discomfort and disability glare. As a result, first response workers are at higher risk for being injured or killed in vehicle crashes because approaching drivers cannot see them. In the present study, participants viewed red and blue flashing lights on a scale model police vehicle, conforming to present recommended practices for emergency lights. Lights varied in intensity and optical power (intensity × duration).

Flashing lights on emergency and maintenance vehicles should be critical components to alerting, informing and managing drivers as they navigate around work zones, vehicle accidents and other roadway emergency incident scenes. These vehicles often also use distinctive colors and markings to identify the type of vehicle and potentially provide drivers with information about the nature of the incident they are approaching. In order to begin to understand how these elements (flashing lights and vehicle/marking colors) contribute to perception, a study was carried out in which participants viewed pairs of roadway scenes using scale model vehicles and lights adjusted to produce similar apparent intensities as full-scale lighting systems. In some cases the colors of the flashing lights were coordinated with those of the vehicle and its reflective markings, and in other cases the colors were not coordinated.