ABSTRACT
While a variety of visual factors can affect perception, luminance contrast is the principal visual cue at night since colors, surface textures, surface details, and contours are not discernible at low luminance levels. Luminance contrast is the contrast between the brightness of an object and that of its background. It can be positive (bright object on dark background), negative (dark object on bright background) or null. All three types are possible under normal roadway lighting conditions. It is generally preferred to provide positive contrast in busy urban environments as this type of contrast facilitates object recognition.
