Spatial Variation of Obstacle Contrast in Roadway Lighting: An On-Site Experimental Investigation

Obstacle contrast is a crucial metric for improving visibility at night. This study investigated how lighting design parameters and obstacle spatial locations affect their contrast along a luminaire cycle, as a quasi-dynamic reconstruction rather than a continuous time-dynamic measurement. Field measurements and computer simulations were conducted on a two-lane road equipped with seven LED luminaires controlled via a Bluetooth solution. Five obstacle models, each model representing obstacles of different heights, were spatially positioned along lateral grids between two streetlights. A vehicle-mounted camera recorded high-dynamic-range (HDR) luminance maps, while the lumen output of streetlights was adjusted for two pole spacing configurations, both with and without headlights. HDR images provided detailed luminance data to evaluate factors influencing contrast. Contrast contour maps illustrated changes under varying lighting conditions, and a simulation model approximating the experimental setup was developed to examine overall trend behavior. Normalized comparisons between experimental and simulated contrast results showed similar relative patterns, indicating trend-level correspondence. Results showed a weak correlation between obstacle luminance and contrast for obstacles 1.0 m or shorter, but a strong correlation for obstacles 1.5 m in height. For very low obstacles, contrast decreased with increased lumen output, whereas for taller obstacles (1.5 m), contrast improved with higher lumen output. While reduced pole spacing increased pavement luminance, it did not increase obstacle contrast. A mixed-effects GLM statistical analysis identified target height, vehicle headlight status, and pole spacing as the dominant factors influencing obstacle contrast. This research offers insights for optimizing lighting design to enhance road safety.