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Many circadian rhythm disorders are tied to patterns of light exposure. Circadian Rhythm DisordersĬircadian rhythm sleep-wake disorders occur when a person’s internal clock isn’t functioning properly or becomes misaligned with their environment. Too much light can cause repeated awakenings, interrupting the sleep cycle and reducing time spent in deeper, more restorative sleep stages. Light exposure at night can hinder transitions between sleep cycles, reducing the quality of sleep. Those cycles are made up of multiple stages of sleep, including both rapid eye movement (REM) and non-REM sleep. In a normal sleep period, a person goes through four to six sleep cycles, each of which lasts from 70 to 120 minutes. Not all sleep has the same characteristics. In addition, daily cycles of melatonin production normalize circadian rhythm, reinforcing a stable sleep-wake schedule.įor some people with sleeping problems, including circadian rhythm disorders, synthetic melatonin, available as a dietary supplement, may be prescribed to help regulate sleep timing. In response to darkness, the pineal gland in the brain initiates production of melatonin, but light exposure slows or halts that production.ĭrowsiness increases with rising melatonin levels, which is one way that this hormone facilitates sleep. Melatonin is a hormone that is naturally made by the body, and its production is closely tied to light. Reduced daylight can interfere with circadian rhythm, contributing to mood changes during the winter. For example, seasonal affective disorder is a type of depression that most commonly affects people who live in areas where winter months have very short days. This can throw their sleep out-of-whack and induce other concerning health impacts including worsened metabolism, weight gain, cardiovascular problems, and perhaps even an elevated cancer risk.Ĭircadian rhythms are also related to mood and mental health. While prolonged light tends to be impactful, even short periods of artificial light can affect circadian rhythm.Įxcess or poorly timed artificial light exposure can cause a person’s circadian rhythm to be misaligned with the day-night schedule. Light exposure in the evening pushes the sleep cycle backward toward a later bedtime.Ĭircadian effects vary based on the type of light and the duration of exposure. When light is perceived early in the morning, it pushes the sleep schedule earlier.
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The way light alters circadian rhythm depends on the timing of light exposure. In modern society, though, electricity creates an abundance of light sources that affect the brain’s circadian pacemaker. When exposed to only natural light, a person’s circadian rhythm becomes closely synchronized with sunrise and sunset, staying awake during the day and sleeping when it’s dark. The brain then sends signals throughout the body to control organs and other systems in accordance with that time of day. When light enters the eye, it is sensed by a special group of cells on the retina, which is carried to the brain and interpreted as information about the time of day. This rhythm is controlled by a small part of the brain, known as the circadian pacemaker, that is powerfully influenced by light exposure. Circadian RhythmsĬircadian rhythm is a 24-hour internal clock that coordinates a wide range of processes in the body, including sleep. Light has dramatic effects on sleep, influencing circadian rhythm, melatonin production, and sleep cycles. Learning about the complex links between light and sleep allows you to set up your bedroom to be more conducive to consistent, high-quality sleep. From streetlights to office lighting to cell phones, artificial light is a constant part of modern life, brightening homes and the nighttime sky.ĭaily light exposure, including the type of light we see as well as when and how long we’re exposed to it, has a critical effect on sleep.
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While human biology evolved with sleep following the daily patterns of sunlight and darkness, ubiquitous electricity makes 24/7 illumination possible. Light also affects the production of melatonin, an essential sleep-promoting hormone. Light plays a central role in regulating circadian rhythm, the body’s internal clock that signals when to be alert and when to rest. While most people intuitively know that it’s easier to sleep when it’s dark, the link between light and sleep goes much deeper. Light is the most important external factor affecting sleep.