The visibility of small objects is affected more by the contrastbetween the outline of the object and the background than by the adaptation level produced by the pavement luminance. Because the object luminance is likely to be produced by a different luminaire than most pavement luminances, the contrast can be controlled by the lighting system designer. Both the pavement and the object have distinct directional light reflectance properties; hence, the luminaire arrangement is one of the major factors used in determining the directionfrom which light reaches both the object and its background. The substantial changes in visibility that occur as the result of the choices made in luminaire arrangement and light distribution are explored. These explorations are made by studying the visibility of a smallstandard target placed on a grid overlay on the pavement. The resulting small target visibility can be calculated and summarized to serve as a criterion for the quality of the roadway lighting system. This paper appears in transportation research record no. 1247, Visibility criteria for signs, signals, and roadway lighting.
Abstract