How Daylight Controls the Biological Clock, Organises Sleep, and Enhances Mood and Performance

Abstract

The human circadian system drives 24-h rhythms in all aspects of biochemistry, physiology and behaviour. This rhythmicity ensures that the right function occurs at the right time, and separates incompatible functions. Rhythmic synchronisation is key to overall health and wellbeing, and light input from the day-night cycle is the primary ‘zeitgeber’ or entraining agent. Coordination of internal clocks promotes positive mood, optimum alertness and performance, and ensures sleep quality essential for learning and memory. Indoor light intensity is rarely sufficient to stabilise daily entrainment, while even an hour outdoors in the morning can significantly enhance cognitive function, academic achievement, and physical condition.