Impacts of flashing emergency lights and vehicle-mounted illumination on driver visibility and glare

John Bullough, Nicholas Skinner, Mark Rea

Research output: Contribution to journalConference articlepeer-review

2 Scopus citations


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). Participants were asked to view the scale model police vehicle and identify whether a police officer figure was standing beside the vehicle. In some trials, white LED sources were energized, providing low-level illumination on both sides of the vehicle, near the possible locations of the police officer figure. In some trials, no police officer figure was present. Participants identified the location of the police officer figure, if any, as quickly as possible. The blue flashing lights were always perceived as brighter and as more glaring than the red flashing lights at the same intensity. While the probability of correctly detecting the police officer figure was affected by intensity, the color of the flashing lights did not matter. Importantly, the presence of low-level white illumination at the side of model vehicle significantly improved detection accuracy.

Original languageEnglish
JournalSAE Technical Papers
Issue numberApril
StatePublished - 2 Apr 2019
Externally publishedYes
EventSAE World Congress Experience, WCX 2019 - Detroit, United States
Duration: 9 Apr 201911 Apr 2019


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