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Brightness of colored retroreflective materials


Authors: Josef Schumann, Shinichi Kojima, Hiroshi Hashimoto, Eric C. Traube, Michael J. Flannagan, Michael Sivak

Retroreflective markings can be used effectively to enhance nighttime recognition of pedestrians. Past experimental work concentrated on factors such as retroreflective power, area, and positioning of retroreflective markings. However, the effect of color received less attention, mainly because the use of color reduces the retroreflective power of the material. A nighttime field experiment was performed to address the effects of color. Subjects seated in a car with low beam headlights on, had to rate the brightness of different colors of retroreflective materials. Independent variables included color (blue, green, yellow, orange, red, and white), ambient illumination, age, and sex. Results showed that chromatic stimuli were perceived as brighter than photometrically matched achromatic stimuli. The brightness ratings for the chromatic stimuli followed a U-shaped function of dominant wavelength, with the highest brightness ratings at both extremes of the visual range. Efficiency factors for reach color relative to a whie retroreflective material were calculated.