Abstract
Eight different configurations and color combinations of rotating-beam emergency vehicle lights were evaluated in terms of information conveyed about rate and direction of travel when viewed at night. The lights were viewed moving toward or away from stationary observers at rates of 0, 5, and 10 m/s at overall ranges of 300 to 450 m.
Differences were found between individual lights in terms of illusions of motion, signal-to-noise ratios, and overall error scores. All-red lights conveyed more information than combinations of red and blue lenses in the same light. Twin lights were superior to single beacons, and twin models with a sequential mirror-generated flash pattern were superior to plain ones.
Several of the lights created an illusion of receding motion when actually at rest. This was most severe for a side-to-side alternate flash pattern using red signals. Lights considered to be highly conspicuous were not necessarily those with the best information transfer characteristics. The cues relevant to this perceptual task appeared to be provided by changes in light intensity with distance, rather than changes in angular displacement.
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