Balancing pedestrian cognitive load and vehicle conspicuity with car body lighting

Nighttime traffic environments pose serious safety challenges for pedestrians, making vehicle conspicuity a critical factor for preventing accidents. Decorative car body lighting (CBL) is designed to improve vehicle conspicuity, but it may also impose additional visual-cognitive demand. This study aims to investigate the tradeoff between vehicle conspicuity and pedestrian cognitive load induced by CBL, and provide preliminary CBL luminance guidance for nighttime safety.

Twenty-six participants completed a visual-spatial working memory task while observing a real vehicle with CBL under four logarithmic luminance levels (10^1.5, 10^2.5, 10^3.5, 10^3.75 cd/m²) and three configurations (center, window, grille) across three observation distances (5, 10, 30 m), as well as a control condition without CBL. Cognitive load, vehicle conspicuity, task performance, glare discomfort, and comprehensive assessment were measured.

Higher luminance and the grille-area configuration significantly increased pedestrian cognitive load. Vehicle conspicuity improved as luminance increased, but the benefit diminished at higher levels. Comprehensive assessment was negatively correlated with cognitive load and reaction time, and the hierarchical regression showed that psychological measures explained more variance in overall evaluation than physical light parameters. The multi-response desirability analysis and the comprehensive assessment scores indicated that the center-line configuration at around 10^2.5cd/m² provided the most favorable overall tradeoff among the tested conditions.

Decorative CBL involves a tradeoff between conspicuity benefit and cognitive cost. Increasing luminance does not necessarily improve overall evaluation, because higher luminance can also increase cognitive load and glare discomfort. CBL design should therefore be evaluated using human-centered measures rather than conspicuity alone. These findings provide preliminary evidence for evaluating decorative vehicle lighting from both conspicuity and visual-cognitive perspectives.