When daylight fades: How nighttime, sociodemographics, and urban zones shape safety perceptions of the built environment

Fear of crime restricts use of and access to public spaces, restricting people's economic, educational and socialising opportunities, particularly for vulnerable populations. Although numerous studies and initiatives aim to create safer cities by transforming urban environments, few have measured the causal impact of daytime and nighttime on fear of crime. This study examines how perceptions of safety vary between day and night in the same locations, compares these effects with built environment transformations, and explores the influence of sociodemographic factors, emphasising the critical role of lighting in fostering safer cities. For this, we conduct an image-based randomised controlled trial to explore how perceived safety changes from daytime to nighttime along a 2-km stretch of road in Sheffield, UK, with various functional zones. The findings, based on 3209 image ratings from 160 participants, reveal that moving from day to nighttime decrease perceived safety by 28 %, an effect that is larger than all other environmental variations encountered in the studied area. While a nighttime decrease in perceived safety is consistent for all sociodemographics, significant disparities arise across gender and for those worried about crime at night. Conditions of site illumination affect safety perceptions only at night, while commercial districts are perceived as significantly safer at nighttime than other functional zones. While most studies concentrate on daytime fear of crime, this study highlights the need for nighttime environmental and lighting planning, as this is a time of day when all feel more vulnerable, and fear of crime disparities are at their highest levels. © 2025 Elsevier B.V.