Artificial light at night disrupts the behavior, physiology, and survival of nocturnal animals across virtually every ecosystem on Earth.
Artificial light at night constitutes a form of habitat modification that affects billions of individual animals — disrupting circadian rhythms, navigation, predator-prey relationships, and reproductive behavior. The welfare harms are widespread: seabird chicks that starve because parents cannot navigate home by moonlight, sea turtle hatchlings that die turning inland toward road lights, nocturnal mammals that cannot forage safely in artificially illuminated landscapes. Many of these harms can be reduced at low cost through downward-directed, motion-sensitive, amber-spectrum lighting.