The Dark Side of Light at Night: Biological Effects of Disrupted Circadian Rhythms


Life on Earth has evolved during the past several billion years under relatively bright days and relatively dark night conditions. Biological functions are exquisitely timed for optimal functioning; some processes occur at night and others during the day. The widespread adoption of electric lights during the past century exposed animals, including humans, to significant light at night for the first time in their evolutionary history. Endogenous circadian clocks depend on light to synchronize with the external day-night cycles. Thus, light at night can derange temporal adaptations. Indeed, disruption of naturally evolved responses to light-dark cycles results in several physiological and behavioral changes with potentially serious implications for fitness. The reasons for turning off your devices at night will be discussed.