An evaluation of a sustainable contrast-based metric for roadway lighting design

A sustainable road lighting standard should include all the elements drivers need to be able to see including pavements and any obstacles/target on or near the road. In order to improve visibility, roadway lighting standards should take the human visual system into account. Recent studies have focused on utilizing luminous contrast because it has a crucial impact on visibility. The objective of this manuscript is to propose new metrics and to evaluate how they respond to the change in road lighting design variables. Data collection, data analysis, computer simulations, and statistical analysis were applied in this study. In the simulation tool, calculation points were located at various heights along the roadside and longitudinally, based on the possible position of targets. A driver was positioned at a distance equal to the total stopping distance from each target. Luminance of targets and their background were the main test metric used to develop the new metric called "mean contrast". This paper analyses four target heights, five lateral target locations, sixteen longitudinal target locations, and three lumen outputs. Results showed that low-height targets had negative contrast, while targets at 1.0m and above had positive contrast. The positive mean contrast did get affected by lamp lumen output, while the negative mean contrast became more negative as the lamp lumen increased. The positive mean contrast at 1.5m, however, increased with higher lamp lumen output. The positive and negative uniformity dropped with higher lumen intensities. This study concluded that the mean contrast metric has merit and could be used to improve visibility for drivers during the night.