Daytime Artificial Light: Better Sleep Ahead?

Light is the most important external factor affecting sleep. While it is intuitive that darkness makes it easier to sleep, the link between light and sleep goes deeper. Light plays a central role in regulating the circadian rhythm, the body's internal clock that signals when to be alert and when to rest. Circadian rhythm is a 24-hour internal clock that coordinates a wide range of processes in the body, including sleep.

Daily light exposure, including the type of light we see, when and how long we are exposed to it, has a critical effect on sleep. Excess or poorly timed artificial light exposure can cause a person's circadian rhythm to be misaligned with the day-night schedule, throwing their sleep out of whack and inducing other concerning health impacts.

Not all colours of light have the same effect. Blue wavelengths, which are beneficial during the day, boosting attention, reaction times and mood, seem to be the most disruptive at night. The proliferation of electronics with screens, as well as energy-efficient lighting, is increasing our exposure to blue wavelengths, especially after sundown.

Harvard researchers and their colleagues conducted an experiment comparing the effects of 6.5 hours of exposure to blue light to green light of comparable brightness. The blue light suppressed melatonin for twice as long and shifted circadian rhythms by twice as much (3 hours vs 1.5 hours).

In another study, researchers at the University of Toronto compared the melatonin levels of people exposed to bright indoor light wearing blue-light-blocking goggles, to people exposed to regular dim light without goggles. The fact that the levels of the hormone were about the same in the two groups strengthens the hypothesis that blue light is a potent suppressor of melatonin.

Blue light exposure at night

Blue light is a type of high-intensity light that comes from the sun. It can boost alertness and mental sharpness, but too much of it may keep people awake when their bodies need to wind down. Blue light, whether from the sun or a laptop, is very effective at inhibiting melatonin production, thus reducing both the quantity and quality of sleep.

There are several ways to reduce exposure to blue light at night. These include:

• Using blue light-blocking glasses or installing an app that filters the blue/green wavelength.
• Avoiding looking at bright screens beginning two to three hours before bed.
• Exposing yourself to lots of bright light during the day, which will boost your ability to sleep at night.
• Using dim red lights for night lights as red light is less likely to shift the circadian rhythm and suppress melatonin.

Circadian rhythm and melatonin suppression

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

The pineal gland in the brain initiates the production of melatonin in response to darkness. Melatonin is a hormone that plays a role in managing your sleep-wake cycle and circadian rhythm.

Melatonin production is closely tied to light. When exposed to light, the production of melatonin slows or stops. Drowsiness increases with rising melatonin levels, which is one way that this hormone facilitates sleep.

Daily light exposure, including the type of light, when and how long one is exposed to it, has a critical effect on sleep. Excess or poorly timed artificial light exposure can cause a person’s circadian rhythm to be misaligned with the day-night schedule. This can induce other concerning health impacts including worsened metabolism, weight gain, cardiovascular problems, and perhaps even an elevated cancer risk.

The effects of light on the phase of the circadian clock depend on the timing of light exposure. Generally, morning light advances the clock, while evening and night light delays the clock. The human circadian system integrates across multiple light exposures as short as five minutes.

Evening use of light-emitting e-readers negatively affects sleep onset latency, reduces evening sleepiness, melatonin secretion, and next-morning alertness, and delays the timing of the biological clock.

Circadian rhythm sleep-wake disorders occur when a person’s internal clock isn’t functioning properly or becomes misaligned with their environment. Jet lag and shift work are circadian rhythm sleep-wake disorders.

Light can also be used as an effective and non-invasive therapeutic option with little to no side effects, to improve sleep, mood and general well-being.

Health risks: heart disease, diabetes, obesity, and cancer

Excessive exposure to artificial light during the day can have a detrimental impact on health, increasing the risk of heart disease, diabetes, obesity, and cancer.

Heart Disease

Artificial light during sleep has been linked to an increased risk of heart disease. A study by Northwestern Medicine found that even moderate light exposure during sleep can harm heart health. The study reported that exposure to artificial light during sleep can cause an increase in heart rate and heighten alertness, which is detrimental to getting a good night's rest. This finding was supported by another study that found that exposure to light during the daytime increases heart rate.

Diabetes

Research has also found a correlation between exposure to artificial light at night and an increased risk of diabetes. A study by researchers at Shanghai Jiaotong University School of Medicine in China found that people in the highest artificial light at night exposure group had a 28% increased risk of diabetes compared to those in the lowest exposure group. The study also found that people in the higher exposure groups had a higher BMI, which is a risk factor for diabetes.

Obesity

Artificial light during sleep has also been linked to obesity. A study by the National Institutes of Health found that women who slept with a television or light on were more likely to gain weight and become obese. The study suggested that turning off lights at bedtime could reduce the risk of obesity. Another study found that exposure to artificial light at night can affect the body's natural production of melatonin, which can lead to changes in circadian rhythms and weight gain from altered eating patterns.

Cancer

Artificial light at night has been linked to an increased risk of certain types of cancer, including breast, prostate, lung, and colorectal cancer. A global study found a positive correlation between artificial light at night and all forms of cancer, with the variation in cancer incidence explained by artificial light exposure ranging from 3.3% to 35.5%. Another observational study found an association between high levels of artificial light at night in people's homes and their risk of breast and prostate cancers. However, more research is needed to establish a direct causal relationship.

Light exposure and sleep quality

Light is the most important external factor affecting sleep. While it is easier to sleep in darkness, the link between light and sleep goes deeper. Light plays a central role in regulating the circadian rhythm, the body's internal clock that signals when to be alert and when to rest. Light also affects the production of melatonin, a sleep-promoting hormone.

Circadian Rhythm

Daily light exposure, including the type of light we see, when we see it, and for how long, has a critical effect on sleep. The 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, which is powerfully influenced by light exposure.

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. However, artificial light from sources such as streetlights, office lighting, and electronic devices can affect the brain's circadian pacemaker, causing a misalignment with the day-night schedule and leading to sleep issues and other health concerns.

Melatonin

Melatonin is a hormone produced by the body in response to darkness. Light exposure, especially blue light, slows or halts melatonin production, leading to increased drowsiness. Daily cycles of melatonin production normalize the circadian rhythm, reinforcing a stable sleep-wake schedule.

Impact of Artificial Light During the Day

Artificial light during the day can improve sleep quality by boosting one's ability to sleep at night and enhancing mood and alertness during the day. Exposure to natural daylight at high intensities has been shown to advance sleep timing, improve sleep quality, and increase sleep duration.

Impact of Artificial Light at Night

Exposure to artificial light at night, especially blue light, can suppress melatonin production and disrupt sleep cycles, leading to reduced sleep quality. Blue light, found in energy-saving lightbulbs, LED lights, and electronic device screens, is particularly powerful in reducing melatonin production. This can result in repeated awakenings and reduced time spent in deeper, more restorative sleep stages.

Strategies to Improve Sleep

To enhance sleep quality, it is recommended to reduce exposure to artificial light, especially blue light, close to bedtime. Using dim red lights, avoiding bright screens, and wearing blue-light-blocking glasses or installing blue light filters on devices can help minimize light's impact on sleep. Additionally, increasing exposure to bright light during the day can improve sleep at night.

Reducing light exposure at night

• Install window curtains or blackout blinds: Achieving complete darkness in the bedroom by using thick curtains or blackout blinds can significantly improve sleep quality. These measures block external light sources, creating an ideal environment for sleep.
• Use eye masks: Eye masks are a simple, inexpensive solution to block out light during sleep. They can be especially useful when you have no control over the lighting in your room or when travelling.
• Dim lights before sleep: Reducing the lighting in your room before bedtime can help protect you from the adverse effects of bright light on sleep and your body's internal clock, known as the circadian rhythm. Using a small, low-power lamp with warm-coloured lighting can aid in relaxation and prepare your body for sleep.
• Remove or limit electronic devices in the bedroom: The light emitted by electronic devices like computers, TVs, phones, and tablets can disrupt your sleep. It is best to keep these devices out of the bedroom or, if not possible, turn down their brightness and avoid using them right before bedtime.
• Get sunlight during the day: Exposing yourself to natural daylight during the day helps strengthen your sleep-wake cycles and promote better sleep. Try to get sunlight, especially in the first hour or two after waking up, to support your body's circadian rhythm.
• Wear blue-light-blocking glasses: If you must work with electronic devices that emit blue light in the evening, consider investing in a pair of blue-light-blocking glasses. These glasses limit the amount of blue light reaching your eyes and have been shown to improve sleep quality and duration.
• Limit screen time: Reducing screen time on computers, phones, and other electronic devices before bed can improve your sleep. You can cut down on screen time by blocking or deleting frequently used apps, turning off notifications, or putting your phone in grayscale mode to make it less appealing.
• Use night mode on devices: Many phones and tablets have a "night mode" feature that reduces the amount of blue light emitted. While this may help to some extent, it is important to remember that the stimulating nature of screen time itself can still affect your sleep.
• Change settings on electronics: If you fall asleep with the TV on, consider removing it from your bedroom or using a sleep timer to automatically turn it off. Similarly, establish a consistent bedtime routine by minimising electronic use two to three hours before bedtime.
• Address lighting concerns with others: If someone else in your household prefers to keep the lights or TV on while you sleep, try having a conversation about the importance of a dark bedroom for your sleep quality. Suggest keeping the lighting at the lowest brightness setting or using a timer to turn off the lights or TV after a certain time.

By implementing these strategies, you can effectively reduce light exposure at night, supporting your body's natural sleep-wake cycles and promoting overall health.

Frequently asked questions