The Effect of Mirror Color on Driver Performance

When the brightness of a test stimulus which is colored is matched in luminance to a fixed white reference, it is usually found that the colored stimulus will appear brighter than the white stimulus. Reflectivity is determined by measuring the luminance of reflected light. Therefore, although a white object reflected from both a colored mirror and a neutral mirror with the same reflectivity will have the same luminance, the object reflected from the colored mirror will look brighter because color has been imparted to it by the mirror. This study examined the effect of this added brightness on driver performance.

Three colors were studied; blue, green and amber, each at three purity levels; 0.0, 0.3, and 0.6. Brightness was measured as the luminance of a neutral stimulus which appeared equal in brightness to the colored stimulus. Performance was measured as the ability to detect the presence of a vehicle in a roadway scene typical of those viewed in a rearview mirror. Performance was found to be not only a function of the image luminance, but also of the dominant wavelength and purity of the color.