A meta-analysis of biological impacts of artificial light at night

Abstract

Natural light cycles are being eroded over large areas of the globe by the direct emissions and the sky brightening that result from sources of artificial nighttime light. This is predicted to affect wild organisms, particularly because of the central role that light regimes play in determining the timing of biological activity. Although numerous empirical studies have reported such effects, these have focussed on particular species or local communities and have thus been unable to provide a general evaluation of the overall frequency and strength of these impacts. Using a new database of published studies, we show that exposure to artificial light at night induces strong responses for physiological measures, daily activity patterns and life-history traits. We found particularly strong responses for hormone levels, the onset of daily activity in diurnal species, and life-history traits such as offspring number, predation, cognition and sea-finding (in turtles). There have been few studies so far on the impact of artificial light at night on ecosystem functions. The breadth and often strength of biological impacts we reveal highlights the need for outdoor artificial nighttime lighting to be limited to the places and forms (such as timing, intensity, spectrum) in which it is genuinely required by the people using it to minimise ecological impacts.