Effects of self-selected light-dark cycles and social constraints on sleep timing of people with different chronotypes

Abstract Circadian rhythm is an endogenous rhythmic behavior of organisms which can be entrained by daily light-dark cycles. The timing of human sleep-cycle is regulated by endogenous circadian rhythm and homeostatic processes. Light exposure affects both sleep timing and circadian rhythm. Now humans can extend lighting time by turning on artificial lights and wake up time is usually triggered by alarm clocks to meet social schedules. This modern lifestyle is believed to be related with a temporal mismatch between sleep and circadian rhythmicity (social jet-lag) and insufficient sleep, which lead to ill mental and physical health outcomes. At present, the impacts of self-selection of light exposure and social constrains on sleep timing is far from clear, and there is no quantitative assessment. According to preferred sleep-wake schedule, there are three different chronotypes. In this paper, we apply a mathematical model including circadian rhythm, sleep homeostasis and environmental light to get a quantitative understanding of the effects of modern light consumption and social constrains on sleep timing of people with different chronotypes. The results show that the prolonged day light and evening light exposure both delay preferred sleep timing with the sleep duration almost unchanged. People of evening-type or with longer intrinsic periods are most expected to be vulnerable to evening light. Increasing light exposure can offset the effect of evening light to some extent, but it is most difficult for evening-type people. Social constrains cause the largest social jet-lag in people of evening-type, which increases with evening light intensity or intrinsic periods. Morning-type people's sleep symptoms worsens, while that of evening-type people improves with age. This study provides a theoretical reference for preventing and treating sleep disorder and social jet-lag for individuals with different chronotypes.