Light and Sleep

How Does Light Affect Sleep?

While human biology evolved with sleep following the daily patterns of sunlight and darkness, ubiquitous electricity makes 24/7 illumination possible. From streetlights to office lighting to cell phones, artificial light is a constant part of modern life and has dramatic effects on sleep, influencing circadian rhythm, melatonin production, and sleep cycles.

Circadian Rhythms

Circadian rhythm is a 24-hour internal clock that coordinates a wide range of processes in the body, including sleep. This rhythm is controlled by a small part of the brain, known as the circadian pacemaker, that is powerfully influenced by light exposure.

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. The brain then sends signals throughout the body Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source to control organs and other systems in accordance with that time of day.

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. In modern society, though, electricity creates an abundance of light sources that affect the brain’s circadian pacemaker.

Excess or poorly timed artificial light exposure can cause a person’s circadian rhythm to be misaligned with the day-night schedule. 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 Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . Circadian rhythms are also strongly correlated to mood, mental health, and seasonal affective disorder.

Melatonin

Melatonin is a hormone that is naturally made by the body, and its production is closely tied to light. In response to darkness, the pineal gland in the brain initiates production of melatonin Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , but light exposure slows or halts that production.

Drowsiness increases with rising melatonin levels, which is one way that this hormone facilitates sleep. In addition, daily cycles of melatonin production normalize circadian rhythm, reinforcing a stable sleep-wake schedule. For some people with sleeping problems supplemental melatonin may be prescribed to help regulate sleep timing.

Sleep Cycles

Not all sleep has the same characteristics. In a normal sleep period, a person goes through four to six sleep cycles, each of which lasts from 70 to 120 minutes. Those cycles are made up of multiple stages of sleep, including both rapid eye movement (REM) and non-REM sleep.

Light exposure at night can hinder transitions between sleep cycles, reducing the quality of sleep. Too much light can cause repeated awakenings, interrupting the sleep cycle and reducing time spent in deeper, more restorative sleep stages.

Circadian Rhythm Disorders

Circadian rhythm sleep-wake disorders occur when a person’s internal clock isn’t functioning properly or becomes misaligned with their environment. Many circadian rhythm disorders are tied to patterns of light exposure.

Jet Lag

Jet lag is a circadian disorder that arises after long-distance plane travel. When confronted with the distinct day-night cycle in the arrival city’s time zone, circadian rhythm can get thrown off-kilter. As a result, a person may struggle to fall asleep, wake up earlier than they want to, or experience excessive daytime sleepiness.

Addressing jet lag usually means acclimating to the new time zone, such as by getting daylight exposure at specific times and avoiding light at certain times to realign circadian rhythm. This process can take several days and up to two weeks.

Shift Work Disorder

Some work schedules, known as shift work, require working into the evening or overnight. Night shifts may be an everyday part of a job or part of a rotating schedule. The Bureau of Labor and Statistics estimates that around 16% of workers Trusted Source U.S. Bureau of Labor Statistics The Bureau of Labor Statistics measures labor market activity, working conditions, price changes, and productivity in the U.S. economy to support public and private decision making. View Source in America have evening or overnight shifts.

Shift workers typically have to sleep during the daytime, putting them at high risk of a misaligned circadian rhythm and the development of shift work disorder. This circadian rhythm disorder can cause insufficient sleep, excessive sleepiness at inopportune times, mood problems, and elevated risk of workplace accidents.

Other Circadian Sleep-Wake Disorders

Circadian rhythm disorders can happen when a person’s internal clock gets shifted too far forward or back or if it fails to follow a stable 24-hour schedule. These problems are frequently connected to a person’s daily behavior and light exposure.

One treatment for many circadian disorders is light therapy Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , which uses sitting close to a high-powered lamp at scheduled times to retrain the body’s internal clock. The strong lamp is meant to mimic daylight and is often used in the morning to normalize circadian timing.

What Types of Light Affect Sleep?

Virtually all light can affect sleep, but not all types of light have the same impact. Daylight, which in direct sunlight has up to 10,000 lux, a unit to measure illuminance Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , is far more intense than even bright office lighting, which rarely reaches about 500 lux. For this reason, daylight is a profound influence on sleep and circadian timing.

There can be important differences between types of artificial light as well. Some types have more illuminance and brightness. That said, even light that appears to have the same brightness may, in reality, have a different wavelength, changing how it’s perceived by the eye and brain.

For example, blue light has a short wavelength and is emitted by many LEDs. Studies have found that it has a significantly larger effect on melatonin and circadian rhythm Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source than light with a longer wavelength. Many electronic devices, including cell phones, tablets, and laptops, emit blue light, and their extensive evening use can contribute to sleep problems Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source .

Is It Best to Sleep in Pitch Darkness?

As a general rule, it is best to sleep in as much darkness as possible. Pitch darkness reduces potential distractions and disruptions to sleep. Sleeping with a light on interferes with sleep cycles and causes more fragmented sleep, and these downsides may be greatest in the few hours before waking up.

Research demonstrates that closing your eyes isn’t enough Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source ; your eyelids can’t block sufficient light. The effects on circadian rhythm can occur even with low levels of indoor light and closed eyes.

In addition to sleep quality, there are other reasons why research indicates that it’s best to sleep in pitch darkness:

• Eye strain: Even low levels of ambient light during sleep have been associated with eye strain Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , resulting in soreness, tiredness, and discomfort in the eyes, as well as greater difficulty focusing.
• Weight gain: Keeping lights on during sleep appears to affect circadian regulation of metabolism, increasing the risk of weight gain even if sleep itself is not disrupted. In one study over a five year period, women who slept with a light or TV on were considerably more likely to gain 10 pounds or more Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , even after controlling for factors relating to their diet and exercise habits.
• Cancer risk: One observational study found an association Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source between people whose homes had high levels of artificial light at night and their risk of breast and prostate cancers. This study did not demonstrate causation, and further research is necessary to understand this correlation.

The diverse potential consequences of excess artificial light in your bedroom reflect that light exposure may throw off circadian rhythm and its vital role in promoting numerous elements of physical and mental health.

How Can You Adjust Your Bedroom Environment to Get the Best Sleep?

A first step in setting up your bedroom to promote sleep is to make it as dark as possible. Blackout curtains block the majority of external light to foster a darker environment.

When preparing for bed, keep your lights dim. Using a small, low-power lamp can help transition to bedtime and pitch darkness. Low illuminance and warm color temperature may help with relaxation and getting into the right mindset for sleep.

Another step is to reduce or eliminate technology in your bedroom. Screen time can keep your mind stimulated, delaying bedtime, and, at the same time, the light can disrupt circadian timing, melatonin production, and overall sleep. If you can’t get electronics completely out of your bedroom, turn their brightness down as far as possible, try not to use them before bedtime, and keep them silenced during the night.

Lighting a Path to the Bathroom

For many adults, especially older adults at risk of falls, it’s important to be able to see where they are walking when going to the bathroom at night.

To address this, first ensure that the floor is free of tripping hazards like rugs or cords. Motion-activated lights for hallways or the bathroom can deliver low levels of light only when it’s necessary rather than throughout the night.

Wearing an Eye Mask

Sometimes another person wants to keep the TV or a light on, preventing you from sleeping in the dark. Having a conversation about keeping the bedroom dark may or, if they insist on having a light or the TV on, it should be kept at the lowest brightness setting.

If the light is still bothersome, you may get relief by wearing a close-fitting eye mask. Some evidence indicates that an eye covering can contribute to improved sleep quality Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source .

Changing the Settings on Your Electronics

If you doze off with the TV on, it continues generating artificial light in your bedroom during the night. The most sure-fire way to resolve this is to remove the TV from your bedroom. If that’s not practical, check if your TV has a sleep timer to automatically turn off after a period of time. If not, schedule a “lights out” time to shut off the TV each night, and use that as a way to establish a consistent bedtime.

Staring at a cellphone screen before bed has also become more commonplace. Make it a routine to minimize electronic use two to three hours before bedtime. Special glasses can filter blue light to keep it from reaching your eye, which may cut down on the effect of blue light on your sleep Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . Many phones and tablets have a “night mode” to reduce blue light, although the stimulation from screen time may still affect sleep. If you need to use devices before bed, try out one of several smartphone and computer applications that can help reduce blue light emission.