A New Criterion for Road Lighting: Average Visibility Level Uniformity

This study aims to evaluate the effect of the lower uniformity ratios on the visual conditions while keeping adequate average visibility level on the road surface. A computer program has been developed to determine necessary criteria for calculations of the road lighting based on visibility level. Five different arrangements such as left single-sided, opposite, staggered, twin-bracket central and combined twin-bracket central & opposite are examined. The results obtained from the calculations for each arrangement by using one typical cut-off, semi cut-off and non cut-off luminaires are classified in two groups as sufficient and insufficient uniformity. It is seen that there are some invisible area even recommended average visibility levels and luminance uniformity ratios are obtained. Because the visibility levels on the grid points may take values different than the average visibility level of the road, a different lighting criterion is necessary to reduce the excessive variation of them. To prevent all possible negative visual conditions, a new road lighting criterion is defined and called as “Average Visibility Level Uniformity” KEYWORDS: visibility level, overall and longitudinal luminance uniformities, cut-off, semi cut-off and non cutoff luminaries, lighting arrangement, average visibility level uniformity.