Impact of urban daytime and nighttime lighting on drivers’ physiological and psychological states: A driving simulation study

• Reproduce urban lighting in a laboratory using light box and driving simulator. • Conduct driving experiments under simulated daytime and nighttime lighting conditions. • Assess drivers’ physiological and psychological states using HRV, EDA, BR, and KSS. • Find limited or no increases in driver alertness beyond 1500 lx – 4300 K eye exposure. • Suggest design strategies for future in-vehicle lighting to support driver alertness. Lighting influences alertness and fatigue via non-visual pathways, thereby affecting driving safety. Urban lighting conditions vary by season and time of day, potentially altering driver alertness. However, few studies have quantitatively assessed the effects of specific lighting conditions on driver alertness under controlled scenarios. This study investigates urban lighting environments across both day and night, selects five representative lighting levels based on daylight simulation and field measurements, reproduces the corresponding eye exposures using artificial luminaires in a controlled laboratory setting, conducts driving simulation experiments under these conditions, and evaluates drivers’ physiological and psychological states using both objective and subjective indicators. Practical implications for in-vehicle lighting design are also discussed. The main findings are as follows: (1) Heart rate variability (HRV), electrodermal activity (EDA), and blink rate (BR) serve as reliable measures of driver alertness, whereas the subjective Karolinska Sleepiness Scale (KSS) showed weaker correspondence with physiological changes, suggesting limited accuracy in post-session self-assessment. (2) Exposure to brighter light enhances driver alertness; however, further increases beyond 1500 lx – 4300 K do not yield additional improvement. (3) The Circadian Stimulus (CS) model effectively predicts the observed alertness trend across the eye-exposure range of 8 lx – 2600 K to 1500 lx – 4300 K, but may not capture the potential plateau or decline beyond this range. (4) Future in-vehicle lighting should consider drivers’ eye exposure and maintain it within an optimal range that supports alertness without causing overstimulation or visual discomfort, while also accounting for individual variability in light sensitivity.