Estimation of the Critical Luminance Contrast in Tunnel Interior Lighting

To estimate the total revealing power of tunnel interior lighting for conditions of a specific observation distance and transmittance of the air, we investigated the relationship between road surface luminance and luminance contrast to achieve a correct perception rate of 75% (the critical luminance contrast) with silhouette vision and reversed silhouette vision. First, the relationship between the road surface luminance and the luminance contrast was derived in an experiment that used computer graphics (CG) for the visual angle of a range from 2.8 to 8.9 min under a clean atmosphere. Second, to determine the influence on visibility caused by the decrease in the transmittance of the air by soot and dust, we derived their relationship using a theoretical calculation for more than 50% of the transmittance of the air. These results agreed with those derived in field experiments.