Brightness Evaluation of Colored LEDs in Dense Fog —Nighttime Situation—

In the present condition, traffic sign and traffic information board is continue to be an area in which LED light source are being used widely and successfully. In order to design suitable road or vehicle solutions compensating for the loss of visual information, its understanding on how fog reduces visibility is necessary. The characteristics of color LED in nighttime fog are affected by various densities and droplet size distribution, because different fog density and droplet size can cause color LED become fainter and reducing contrast. To prevent this problem, in this research we used 12 kinds of colored LED light as a test stimulus. Subject observed brightness of all the test stimuli with reference white light adjusted to 30 cd/m² in luminance. They then evaluated the apparent brightness of the test stimuli in dense fog and no fog condition with level estimation of 11 grades, as a result it was found that RY (Reddish Yellow) is the brightest and B (Blue) is the faintest in nighttime fog.