Colors of retroreflective traffic sign materials when illuminated by high-intensity-discharge headlights.

Abstract

This analytical study evaluated the colorimetric properties of retroreflective traffic signs when illuminated by high-intensity-discharge (HID) headlamps. Two aspects were investigated: (1) colorimetric shifts of individual sign materials when illuminated by HID light sources as opposed to halogen, and (2) colorimetric separations of the red sign material from yellow, orange, and brown sign materials when illuminated by HID light sources. Spectral reluctances of sign materials and spectral power distributions of HID (and halogen) light sources were used to derive the CIE tristimulus values for the sign materials. These values were then transformed into the CIELAB space –a perceptually uniform color space. The results of the analyses indicate that the magnitude of the colorimetric shift increased with increasing correlated color temperature of the light source. The resulting colorimetric separations of red from yellow, orange, and brown for the HID light sources also tended to increase with increasing correlated color temperature, with the highest-temperature HID light source tested yielding greater colorimetric separations than halogen.