Rotating warning beacons containing filament light sources have long been used on highway maintenance vehiclesto indicate the presence of the vehicle to other drivers. Flashing warning beacons containing light-emitting diodes(LEDs) are beginning to be used in place of rotating warning beacons, in part because they use considerably lesspower. To help ensure that LED warning beacons will provide a comparable warning signal to drivers approachingvehicles outfitted with them, their photometric and temporal characteristics were measured and compared to humanresponse time data. In addition, several LED warning beacons were compared to a conventional incandescentrotating warning beacon in terms of the distance at which observers could detect that a vehicle had moved closer tothe observer. Pairs of LED warning beacons provided equivalent closure detection distances to a pair ofconventional rotating beacons. While single LED warning light configurations were not tested, the pairs of LEDbeacons tested reliably outperformed a single conventional beacon configuration in terms of both energy use andclosure detection distance. Overall, the results suggest that LED warning beacons provide comparable visualinformation to other drivers, while using substantially less power than conventional rotating beacons.
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