How Light Exposure Impacts Sleep

Written By Luisa Palloni

Light exposure - whether from natural daylight or electronic devices - has proven impacts on sleep. Some of these impacts can be helpful: exposure to natural light from the sun can help you feel awake during the day and prepare you for a restful sleep at night. However, nighttime exposure to artificial blue light can cause you to feel alert at an inopportune time of day, potentially harming your sleep. When you understand how light impacts your sleep, and why, you can make adjustments to your daily routine to use light to your advantage and prevent it from disrupting your sleep.

What is blue light?

Blue light is a wavelength of light on the visible light spectrum that accounts for about one quarter of the light we see. It’s also considered to have the greatest impact on sleep. It’s produced by many electronic devices and some household lights, but the primary source of blue light is the sun.

When the sun sets, our natural exposure to blue light diminishes, signaling to our brain that bedtime is approaching. Our brain responds by naturally producing melatonin, a hormone that helps us feel drowsy and prepares us for sleep. In contrast, when we are exposed to blue light from the sun or electronic devices, this sends a signal to our brain that suppresses melatonin production and tells us that we should be awake.

Some common sources of blue light:

  • TVs

  • Computers

  • Tablets

  • Smartphones

  • LED lightbulbs

  • Fluorescent lights

  • The sun

Does artificial blue light harm sleep?

With increased access to technology, we are faced with a problem. When the sun goes down, our nighttime world lights up. Lamps, smartphones, TVs, and computers continue to produce blue light long after the sun’s natural light has faded. When you are exposed to blue light late at night, your brain can’t tell the difference between this artificial light and the light from the sun. Consequently, the light from your Netflix binging or late night emailing tricks your brain into thinking the sun is still up and that you should still be awake.

Screens have gained a bad reputation and are commonly cited as being harmful for sleep. This reputation may be well deserved, as there are many studies indicating that blue light can contribute to poor sleep quality and reduced sleep duration. However, some behavioral sleep specialists argue that if you are exposed to enough natural light during the day, a small amount of light from screens won’t make a significant impact on your sleep.

Even if we don’t know the full extent of the effects of nighttime light exposure from screens, it’s a good idea to be cautious, especially if you are already prone to sleep problems. Avoiding electronics before bed can also have other benefits. The habit of scrolling through social media or sending emails at night is probably more likely to keep you awake than the light emitted from your phone or computer screen.

How does natural daylight affect sleep?

Daylight plays an important role in circadian rhythm and sleep. Circadian rhythm (your body’s internal clock) regulates your sleep-wake cycle by sending your brain signals of different intensities over the 24-hour day. The strength and type of the signals you receive depend on a number of things, including the timing and amount of light exposure you get throughout the day. There is strong evidence to support the benefits of blue light from the sun. In a large study of over 5,000 adults in the UK, researchers found that for every hour of daylight exposure, people were less sleepy during the day and had fewer symptoms of insomnia at night.

For many people, getting up in the morning and going outside leaves them feeling refreshed and energized. On bright sunny days, the sun’s blue light sends signals to your brain and your internal clock that it’s time for you to be awake. This process helps people stay alert and focused during the day, improves mood, and even primes us for a good night of sleep.

When daylight exposure is reduced, this can have harmful consequences for some. You may notice that on cloudy or short winter days, you feel tired or have lower energy levels during the day. On these days, your brain may start producing melatonin during daytime hours, causing you to feel sleepier than you otherwise would have. Seasonal Affective Disorder (SAD) is most common in the winter months when there are fewer daylight hours, leading researchers to believe that these symptoms are influenced by the reduced light exposure during this time of year. People with SAD can have symptoms such as moodiness, depression, and fatigue. Those who develop SAD in the summer tend to have difficulty getting to sleep, while those who develop it in the winter tend to produce too much melatonin, which can lead to excessive sleepiness during the day.

To help people diagnosed with SAD and certain circadian rhythm disorders, doctors and therapists sometimes recommend special lamps (also called light boxes) used for bright light therapy. These light boxes simulate daylight by emitting high levels of blue light and help reverse the negative effects of limited daylight.

Tips for managing light and sleep:

When it comes to light, timing is everything! I recommend taking the following steps to increase natural light during the day and reduce blue light exposure in the evening:

  1. Reduce nighttime exposure to artificial blue light from screens.

    While it would be ideal to avoid devices with screens in the two hours before bed, this simply isn’t practical for everyone. If you need to be on your phone, computer, etc. before bed, try turning on the built-in blue light filters for these devices. These filters reduce blue light exposure, mitigating the impact that blue light may have on your sleep.

    Built-in filters tend to give your screen a yellowish tinge. If this bothers you, some devices can be scheduled to turn the filter on only in the hours before bedtime. You can also adjust the color temperature to make your screen appear less yellow, though this will reduce the filter’s effectiveness.

    The graphics to the right give step-by-step instructions for how to turn on these filters for a variety of devices. If your device does not come with a built-in filter, you can purchase an external screen protector that sticks to the screen and filters out blue light.

  2. Reduce nighttime exposure to artificial blue light from lightbulbs.

    If you have fluorescent lights or LED bulbs, you can reduce their effects on sleep by dimming them 2 hours before your typical bedtime. Some people find it useful to set an alarm to help them remember to do this. If your lights are connected to smart plugs, you can also program them to dim at a specific time each night.

  3. Create a dark sleeping environment.

    Use blackout curtains or light blocking shades in your bedroom. If this isn’t an option, wear an eye mask at night to block out light while you sleep. Exposure to light during sleep can disrupt sleep quality even if it doesn’t fully wake you up, so keeping your room dark is important. If you have lights in your room that you can’t (or don’t want to) remove such as a digital clock or night light, check whether you can set the display color to red. Red is the color that is least likely to suppress melatonin and impact your circadian rhythm.

  4. Get plenty of exposure to daylight.

    The sun plays a vital role in helping you naturally maintain a healthy sleep-wake cycle, so try to get at least 1 hour of sunlight in the morning. Get outside on a walk if you can, but even sitting outside or by a sunny window while you drink your coffee or check emails will give you some benefits. If getting sun exposure in the morning isn’t possible, get outside during a lunch break or another time of day. To positively impact your circadian rhythm, consistency is key. If you make this a part of your daily routine you will see greater benefits.

While these recommendations are targeted toward improving sleep, the benefits of getting outside during the day and reducing your use of screens at night are likely to extend beyond better sleep. Making small changes to your daily light exposure can have a profound impact on your overall health and wellbeing.

If you think you might have insomnia, following the steps above may help. However, making changes to light exposure alone won’t cure chronic insomnia. If you are having persistent trouble with sleep that’s negatively impacting your functioning during the day, reach out to your primary care doctor or a sleep specialist for additional support.

Disclaimer: This blog is for informational purposes only and is not intended as a substitute for professional therapy, diagnosis, or treatment. The content provided is meant to offer general information and should not be used as a replacement for individualized care from a licensed mental health professional. If you are in need of support, please seek assistance from a qualified therapist or healthcare provider.

References:

Luisa Palloni
Next

Is Election Stress Keeping You Up at Night?