How Light Affects Your Sleep

Light is one of the single most important external factors that affects your sleep.

It’s obvious to most people that it’s harder to fall asleep in an extremely bright room. But this is just the most basic aspect of the relationship between light and sleep. The connection goes much deeper and relates to our body’s sleep-wake cycle and internal biological clock.

If you’re looking to improve your sleep, the light you’re exposed to -- and not just at bedtime -- is a critical consideration. The light you experience throughout the day can affect the quantity and quality of your sleep as well as your mood and overall health.

What Is the Circadian Rhythm?

The circadian rhythm is a part of your body’s biological clock. This clock helps your body adjust as you move through the day. In total, the average circadian rhythm covers a span of 24.5 hours. During this time, you have periods of wakefulness and sleep.

Within these hours, the body will send different signals based on internal and external cues. These form part of the circadian alerting system. This system promotes wakefulness during the day, counteracting the body’s natural “sleep drive.” When this push for wakefulness and alertness drops off, the sleep drive takes over, and the body begins to transition toward a restful state that’s primed for sleep.

Light is one of the strongest influencers of this alerting system. After light is taken in by the retina, signals are sent within the brain and to the body that correspond with wakefulness and activity. When light fades and these signals decrease, the body produces melatonin, which helps prepare the body for sleep.

In ideal circumstances, the sleep-wake cycle is closely synchronized with the day-night cycle where you live and your overall exposure to light. During the day, continued exposure to light, especially sunlight, keeps the circadian alerting system going strong. At night, continued darkness maintains the balance between the alerting system and sleep drive so that you can stay asleep through the night.

What Are Circadian Rhythm Disorders?

Unfortunately, the real world can present a stark contrast with the ideal of a well-synchronized biological clock. Our circadian rhythms can become disrupted by things ranging from travel to social obligations to work schedules to medications. Serious disruptions to your body’s biological clock are known as circadian rhythm disorders.

What Are the Types of Circadian Rhythm Disorders?

One of the most well known circadian rhythm disorders is the travel or jet lag type. Rapidly crossing time zones can cause your biological clock to be at odds with the local time, leading to sleeping problems and fatigue.

Another type of circadian rhythm disorder is the shift work type. This happens when a person’s work schedule runs counter to the local day-night schedule. For example, people who work overnight in graveyard shifts are most likely to suffer from this.

Some night owls have the delayed sleep phase type of circadian rhythm disorder, while other people have the advanced sleep phase type. In each case, a person may be unable to wake up or fall asleep when they want to because their internal clock is not aligned with the time in their area.

A more rare type of circadian rhythm disorder is the non-24 hour sleep-wake type. In people with this type, the circadian rhythm changes daily, making it extremely challenging to align their sleeping schedule with the natural day-night cycle.

What Are the Symptoms of Circadian Rhythm Disorders?

Poor sleep and excessive daytime sleepiness are the primary symptoms of circadian rhythm disorders. Serious physical and mental fatigue can occur, and these symptoms can raise the risk of accidents at work or when driving.

A disruption of the body’s internal clock may have effects on other systems of the body. People with prolonged circadian rhythm disorders may experience depression, nausea, mood changes, and even cardiovascular complications.

How Are Circadian Rhythm Disorders Diagnosed and Treated?

Diagnosing a circadian rhythm disorder typically requires visiting with a doctor to review your sleep habits and problems.

The doctor may recommend that you keep a sleep journal to track when you go to bed and wake up each day, and if you already have a sleep journal, bring it with you to the doctor.

In some cases, the doctor may suggest a sleep study in which you stay overnight in a specialized lab that can use more advanced methods to monitor and analyze your sleep.

Treatments for circadian rhythm disorders often involves improving sleep hygiene. Examples include creating consistency in your daily sleep schedule and optimizing daily light exposure. Medications or supplements may be considered depending on the cause and severity of a circadian rhythm disorder.

The Role of Light in Your Health

Unless you live in a place like Alaska or Antarctica where they experience extremes of both daylight and nighttime depending on the season, it’s easy to take each day’s sunlight for granted. Daily sunlight exposure can seem like little more than a background item: something that’s present but not a focus of attention.

Yet the more research that is conducted about light, and especially sunlight, the more we realize how important it is for our minds and bodies. In addition to promoting healthy sleep, regular light exposure promotes not only a well-adjusted circadian rhythm but also a number of other aspects of our health.

What Are the Benefits of Sunlight Exposure?

Exposure to sunlight is a primary way that the body produces vitamin D, and vitamin D is essential for maintaining proper levels of calcium and phosphate necessary for bone health.

Population studies have found correlations between vitamin D and/or sun exposure and numerous improved health outcomes. Proper exposure to sunlight may be protective in part against depression, some types of cancer, obesity, myopia, neurodegenerative diseases, and metabolic diseases.

Sunlight exposure may help the cardiovascular and immune systems and can contribute to feeling more alert and in a better mood.

Because it promotes the circadian alerting system, regular exposure to sunlight can support a better sleep schedule and deeper, more consistent sleep.

Of course, excessive sun exposure comes with risks. Too much sun, especially exposure that causes even minor sunburns, can harm the skin and increase the risk for skin cancers. While it is possible to get too much sun, research is making clear that too little sun can lead to major health problems.

Does Exposure to Artificial Light Have the Same Effect as Sunlight?

In modern society, levels of artificial light have reached astounding heights. As development has expanded, so have illuminated areas across the world. At the personal level, the proliferation of electronic devices, especially mobile phones, has created billions of new light sources.

Not all light is created equal, and exposure to artificial light is not equivalent to exposure to sunlight. In addition, the abundance of artificial light can disrupt circadian rhythms and complicate sleep hygiene.

How Does Artificial Light Compare to Sunlight?

Though artificial lights can be bright, they provide a low level of luminance relative to the sun, even on a cloudy day.

Lumens measure the total output of a light source, and lux measures the intensity of that light over a square meter. On an average day, the lux from sunlight ranges from 30,000 to over 100,000. The lux level on even an overcast day is 1,075.

In contrast, most indoor spaces have lux of 250 to 1,000 depending on their use. For example, a classroom normally has a lux level of 300, a supermarket closer to 750, and a TV studio closer to 1,000.

As these numbers indicate, though artificial light can be significant, it almost always fails to provide the kind of illumination that comes from sunlight, especially on a bright day.

What Is Light Therapy?

Light therapy uses a high-powered light -- called a light therapy box -- that usually provides close to 10,000 lux, to help counteract problems from decreased exposure to sunlight.

Light therapy is generally prescribed to help with seasonal affective disorder (SAD), which is a type of depression that usually arises during the darker months of the year. It can be used to treat other conditions including circadian rhythm disorders.

To use a light therapy box, a person sits close to the light for between 30 and 60 minutes. Most often, a light therapy box is used soon after waking up.

How Does Artificial Light Affect Sleep?

The complex workings of the body’s internal clock developed over thousands of years during which the primary source of light was the sun. During those millenia, true darkness at night was the rule; now it’s the exception.

Electricity and artificial lighting has become so present in modern society that it is increasingly difficult to avoid light exposure. Fluorescent and LED lighting have heightened indoor illumination. Carrying personal electronic devices including laptops, mobile phones, tablets, and game consoles means that we’re regularly exposed to the light they emit.

All this light poses a serious problem for sleep. We tend to be exposed to artificial light for many hours after the sun has gone down, making it harder to maintain a well-aligned circadian rhythm.

Excess exposure to artificial light makes it harder to fall asleep because we receive more and more signals to stay awake, and our bodies are slower to produce melatonin, which is triggered by darkness and helps us go to bed.

Artificial light in the bedroom can make it harder to stay asleep as well. A brief interruption in sleep may become a full-fledged waking up if a person is quick to turn on their phone to see the time or to check for messages.

What Is Blue Light and How Does it Affect Sleep?

Not all artificial light is the same. Light from different sources has different wavelengths. Blue wavelengths are known for promoting attention and mood, which is a huge plus during the day.

At night, though, studies have found that exposure to blue light has a major effect on melatonin production. Blue light reduces the secretion of melatonin more than other types of light, and that effect is longer-lasting.

Unfortunately, sources of blue light are prevalent and increasing in popularity. Though more energy-efficient, compact-fluorescent and LED light bulbs produce more blue light than traditional incandescent bulbs. Most personal electronics with screens, including mobile phones, are potent sources of blue light.

Some light bulbs have special coatings to reduce the amount of blue light that they emit, and some electronics now have modes that decrease blue light and are designed for nighttime use.

A number of products are on the market to prevent blue light from reaching the retina. Blue-light goggles filter out blue wavelengths but don’t completely eliminate exposure to it. Some research has found that they can help avoid the suppression of melatonin caused by blue light.

Improving The Light in Your Life

There’s no one single recipe for improving sleep, but almost all experts agree that certain steps can improve your chances of getting as much rest as possible. Not surprisingly, many of these are related to light and to avoiding disruption to your circadian rhythm.

  • Strive for consistency: your body’s internal clock benefits from a regular schedule. Going to bed and waking up at the same time each day, including on weekends and holidays, helps in this effort. As much as possible, align these times with appropriate light exposure.
  • Head outside: during the day, you want to get the benefits of sunlight. Even if it’s a cloudy day, you’ll still get this boost. This can improve your mood and energy during the day and help your body know it’s time for bed as you reduce your light exposure closer to bedtime.
  • Limit artificial light in your bedroom: a dark bedroom can increase melatonin production and send the strongest signals to your body that it’s time to sleep. Keep bedside lamps, nightlights, electronic devices, and other light sources to a minimum, and consider using blackout curtains or an eye mask for further darkness.
  • Cut back on blue light before bedtime: most experts suggest creating a 30-60 minute period before bed without blue light exposure. This means avoiding using your phone or being in a brightly-lit room. Goggles that filter blue light may be an option to decrease this exposure as well.
  • Evaluate your sleep hygiene: light exposure is just one aspect of sleep hygiene, which relates to our habits and environment related to sleep. Read our 15 Tips for Better Sleep Hygiene and consider which you can implement.
  • Talk with a doctor: if you have serious, persistent, or worsening sleep problems, it can be useful to talk with your doctor. Your doctor can work with you to diagnose and treat any specific conditions interrupting your sleep.

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