Towards a Darker Sky: The Efficacy of Mitigation Strategies for Artificial Light at Night and Its Impact on Plant Phenology

Abstract

Light pollution, an increasingly recognized environmental hazard, disrupts urban ecosystems, including plant phenology such as leaf-out and senescence. In recent years, municipalities have enacted legislation to reduce artificial light at night (ALAN) at city levels. This study evaluates the effect of ALAN-mitigation policies on changes in intensity and spectrum composition of ALAN and consequent changes in plant phenology in U.S. cities using satellite data for 2022-2023. ALAN declined in cities with ALAN-mitigation measures the following year (New York City: -4.63%, Washington D.C.: -9.44%), with the largest decline in blue band. In contrast, ALAN increased in cities without measures (Newark: 11.78%, Philadelphia: 4.49%). Successful mitigation efforts also corresponded to reduced ALAN-induced shifts of autumn phenology of urban plants. These findings suggest that implementing ALAN-mitigation policies plays a critical role in mitigating the ecological impacts of light pollution and emphasize the need for eco-friendly lighting solutions to support ecosystem functioning.