Method of calculating the required luminances in tunnel entrances

Abstract

Controversial results from different studies of the luminance required in the entrance zone of vehicular tunnels lead to the development of the method described to obtain the actual adaptation luminance of the observer in approaching the tunnel. The equivalent veiling luminance following from the luminances occurring in the visual field can be computed for different fixation points and distances to the tunnel. (Ls)eq superimposes on the luminance of the area around the fixation point and has the etfect of decreasing the contrast of a small target to be perceived in its centre. Since its contrast reduced in such a way has always to be 0.2 to ensure visibility under practical conditions the required entrance luminances for different (Ls)eq levels and target contrasts can be derived by calculation.