Visibility Improvement in Expressway Tunnels by Optimizing the Color Temperature and Light Distribution of the Pulse-operated LED Luminaires

Abstract

The presence of obstacles on expressways often results in major traffic accidents. Therefore, ensuring the visibility of obstacles on roads is an important factor for maintaining a safe and comfortable visual driving environment. The visibility of obstacles on road, especially in tunnels, is related to the lighting environment. In this study, we have proposed two lighting-control methods and evaluated the visibility of obstacles under a combination of light-distribution control and lighting-time control and a combination of light-distribution control and color-temperature control. Further, we evaluated the effectiveness of these two lighting-control methods and obtained good visibility by combining the pro-beam lighting operated using direct current (DC) and symmetric lighting operated by pulses having a frequency of 60 Hz and a duty ratio of 50%. The visibility can be effectively improved by increasing the luminous contrast between the background road surface and the object. In addition, when lighting-time control was applied, temporal luminance contrast was achieved, and the perceived luminance was enhanced by the pulse (Broca– Sulzer effect), thereby improving the visibility. Further, the visibility can be improved by changing the color temperature with the light-distribution angle because of the difference in chromaticity between the background road surface and the object.