Sleep timing in industrial and pre-industrial societies syncs to the light/dark cycle

Abstract

Did artificial light reshape human sleep/wake cycle? Most likely the answer is yes.\n\nDid artificial light misalign the sleep/wake cycle in industrialized societies relative to the natural cycle of light and dark? For the average person --that is, obviating the tail of the distributions-- the answer is probably not.\n\nSleep timing in industrial (data from eight national time use surveys) and pre-industrial, hunter-gatherer/horticulturalist societies (seven data from three previous reports) with and without access to artificial light across a wide range of angular distance to the Equator (0{degrees} to 55{degrees}) finds a remarkable accommodation in trends dominated by the light/dark cycle.\n\nDaylight saving time (DST) in modern societies helps swinging synchronization through seasons. During standard time, winter sunrise synchronizes sleep timing in the observed range of angular distance to the Equator. That means sleep timing delays with increasing distance to the Equator. DST mitigates this delay and makes summer sleep timing is less influenced by distance to the Equator.