Street lights and car headlights provide visibility to nighttime road users. Street lights are evaluated according to streetlight standards and car headlights by the criteria of designated companies before they are supplied to car buyers. Though standards for evaluation for each of them exist separately, studies of instances when they are used together are currently insufficient. When street lights and car headlights are used together visibility can be decreased. This is because since street lights provide negative contrast when road luminance is higher than obstacle luminance, though road luminance and obstacle luminance may increase their contrast may decrease. Therefore this paper sought to evaluate, compare and analyze the visibility of street lights and car headlights under a variety of road conditions in the country.
A lighting simulation(DIALUX) was used to set up 5 different street light conditions; 9 different street light equipment that fit the national road standards were used for the evaluation of road luminance and obstacle luminance according to road conditions. Real car headlights were used on nighttime roads with no lighting nearby to measure road luminance and obstacle luminance. When street light and car headlight were used together the value was the sum of the two luminance values, and Visibility Level was used to evaluate how visible they were.
Results showed that visibility differed according to lanes, road luminance, obstacle luminance, position of the obstacle, distance of the obstacle, type of light distribution, and type of car headlight. Even if a street light that fit the street light standard was used, visibility of light distribution changed depending on changes in road conditions. Also, car headlights with favorable visibility level when used alone could become disadvantageous when used together with a street light. Therefore further research on mutual evaluation methods of street lights and car headlights is necessary.