The role of ambient light in shaping public safety: Evidence from daylight saving time

Abstract

Darkness has long been associated with changes in criminal activity. However, evidence on its underlying mechanisms and distributional effects remains limited. This research uses data from 11 densely populated US cities and leverages the discontinuous shift in ambient light caused by daylight saving time to address this knowledge gap. First, it evaluates whether changes in crime reflect deterrence or incapacitation by examining variation in the probability of apprehension. Second, it analyzes the role of routine activity by incorporating ridership and foot traffic data. Third, it studies whether ambient light affects sleep, potentially impairing decision-making and increasing impulsive behavior. The results show that an extra hour of daylight decreases sunset robberies by 28.8%, but increases aggravated assaults by 21.4%. Clearance rates remain stable, suggesting that deterrence rather than incapacitation drives the observed effects. Crimes outside sunset hours and indoor offenses were not affected either, reinforcing the role of natural light exposure. Overall, ambient light operates through multiple, simultaneous mechanisms, causing differential impacts across crime types and neighborhoods. For instrumental crimes, deterrence and enhanced guardianship appear complementary, while alterations in routine activity and cognitive functioning may amplify aggression. Importantly, targeted investments in street lighting, particularly in disadvantaged communities with disproportionate exposure to darkness and situational risks, can help mitigate crime.