If you frequently lie awake in bed at night — tossing and turning but unable to sleep — you may think you have a sleep problem. But odds are you probably have what could more accurately be described as a light problem.
Many people don’t realize how much using artificial lights at night can disrupt sleep. And did you know that sleeping with the lights on is even more problematic? Well, consider this your lightbulb moment: Restful sleep requires darkness, so turn off that night light.
Each of us has an internal body clock that regulates different biological processes based on cues from the environment. Light is one of the most powerful cues we have to stay awake and fall asleep, and we need darkness to get the sleep our bodies need.
In this article, we’ll discuss the following:
Your circadian rhythm is an internal body clock that uses internal and environmental cues to regulate the energetic peaks and dips you experience in roughly 24-hour periods. This biological clock is heavily influenced by the rising and setting of the sun. And using artificial lighting in your home late into the night and when you go to bed suppresses your brain’s production of the sleep-inducing hormone melatonin.
Your circadian rhythm is actually not one clock but a network of peripheral clocks distributed across a number of your organ systems and cells. But inside your brain’s hypothalamus, there is a master circadian clock. Called the suprachiasmatic nucleus (SCN), it’s a special group of neurons attuned to the roughly 24-hour cycle of changing light caused by the Earth’s orbit around the sun.
The SCN is an information hub that serves as command central. It receives and transmits internal and external circadian cues that help start and stop various biological processes that allow your body to function. Chief among these processes is your sleep-wake cycle.
Although certainly not the only circadian cue, light is the most powerful external influence on the SCN. In the morning, when the SCN senses daylight via the optic nerve, it releases serotonin, cortisol, and norepinephrine. These hormones then send out chemical signals that make you feel alert and awake.
At night, about 2–3 hours before your biological bedtime, darkness signals the SCN to prompt the brain’s pineal gland to ramp up production of melatonin. This circadian phase marker is called the dim light melatonin onset (DLMO), and it signals the beginning of your daily Melatonin Window in the RISE app.
You’ll find it easier to fall asleep and stay asleep if you go to bed during your Melatonin Window, because this is when your body is generating peak levels of melatonin. If you leave the lights on when you go to bed, your brain, which is trying to keep your melatonin levels up to help you sleep, is fighting a losing battle — all night long.
Any light can inhibit melatonin production, but blue light is especially disruptive, thanks to a special group of neurons in your retina called intrinsically photosensitive retinal ganglion cells (ipRGCs). These ipRGCs are especially sensitive to blue light’s short wavelengths, which have a higher frequency and carry more energy than the longer wavelengths of red light. In addition, ipRGCs express the photopigment melanopsin. In the presence of blue light, melanopsin suppresses melatonin production.
Without melatonin and the sleepiness that comes with it, it will be harder to fall asleep and stay asleep, and this will cut into your sleep time. Exposure to blue light also disrupts normal sleep cycles because it reduces REM sleep (which is important for emotional health) and suppresses deep sleep (which is important for brain restoration and recovery).
In a modern world where most people reading this have access to unlimited artificial illumination at any time of the day or night, it’s easy to see how your circadian rhythm can get thrown off track by the flip of a switch. And the hazards of sleeping with the lights on are especially pronounced in certain medical and institutional facilities where patients are exposed to constant artificial light.
Older adults and patients in nursing homes and long-term-care facilities are particularly vulnerable to circadian misalignment. Not only are they subject to constant or intermittent exposure to room-level light during the night, but also many are seldom taken outdoors and therefore get very little exposure to bright sunlight during the day. Lack of bright light during the day can also lead to circadian destabilization (more on that later).
Some hospitals are looking to make light changes for the better, exploring the feasibility of designing facilities with lighting that’s supportive of and not disruptive to circadian alignment and natural sleep. But patients at medical facilities are not the only people at risk.
In 2007, the International Agency for Research on Cancer declared persistent night-shift work as a probable human carcinogen. A 2021 report by the National Toxicology Program showed that the circadian disruption caused by shift workers’ frequent exposure to artificial light at night increased their risk for breast cancer and prostate cancer.
But you don’t have to have excessive exposure to artificial light at night to experience the most common and immediate effect of nighttime light disruptions: lost sleep. The hours of sleep you lose can quickly add up to high sleep debt that can prevent you from feeling and functioning at your best during the day.
Sleep debt is the running total of the sleep you’ve missed (as compared to the sleep your body needed) over the past 14 days. It’s the number that best predicts how you feel and function during the day. Keeping your sleep debt below 5 hours will help you feel and perform at your best. Past that point, if your sleep debt gets higher and higher, you’ll feel and function worse and worse.
Short-term sleep debt can also increase your risk of accidents and negatively impact your immune system, metabolism, cognitive abilities, and attention span. The longer you live with high sleep debt, the more it can impact your health. Chronic sleep debt is associated with increased risk for weight gain, obesity, type 2 diabetes, high blood pressure, heart disease, and certain cancers.
When you take into account the health impacts of sleep debt, it’s hard to look at sleeping with the lights on as an isolated or insignificant choice. The follow-on effects of nighttime light exposure can be quite serious.
Low sleep debt depends on good sleep hygiene, which is the upkeep of behaviors that influence your sleep. One of the most important aspects of sleep hygiene is light exposure, and sleeping with lights on in your bedroom is definitely a no-no. Beyond the bedroom, being strategic about the timing of your light exposure throughout the day can help you get enough sleep to give you the energy you need during the day.
Even if you don’t wake up in time to see the sun rising, you can help regulate your circadian rhythm with morning sunlight. After you get up, expose your skin and eyes to natural light as soon as you can. The light serves as a signal to your brain to stop producing melatonin and increase production of serotonin. In about 12 hours or so, that serotonin will be converted into melatonin to help you sleep that night.
Morning sun exposure is best outdoors and without sunglasses. Getting the light through a window or a lens won’t be as effective. If you live someplace with very minimal light, consider using an artificial daytime simulator source.
Getting some light in the daytime will help you sleep at night. Studies show that exposure to white light during the day can help you feel sleepy as bedtime approaches, fall asleep faster, and get more restorative slow-wave or deep sleep.
Avoiding all artificial light after sunset might be one way to support your circadian rhythm, but it’s not exactly practical. And interestingly, if you want to reduce the negative effects of late evening light exposure (especially on nights when you cannot avoid it), you might want to turn those lights up early in the evening. A 2019 study found that exposing yourself to bright light in the early evening helped mitigate the effects of additional light exposure later in the evening closer to bedtime.
As a broader recommendation, it’s best to avoid light as much as possible in the 90 minutes before bed. In the words of Dr. Andrew Huberman of Stanford University, “Here is a simple rule: only use as much artificial lighting as is necessary for you to remain and move about safely at night.”
Candlelight and moonlight are ok, but turn off bright lights, especially overhead light sources, in favor of dim light from lamps and ground-level sources. To keep the blue light out of sight, you can use red or amber light bulbs. Wearing blue-light blocking glasses is highly recommended, especially if you use blue-light emitting electronic devices at night.
Not sleeping with the lights on is a good start, but you may need to take it a step further to create a truly pitch-black bedroom. Wear a sleep mask and use blackout curtains or blinds to prevent light from street lights (or other light sources around your house) from seeping into your bedroom.
Although it’s not ideal, if you absolutely need a small night light for anxiety reasons, keep the light low to the ground and consider putting it on a timer. Avoid bright and blue or cool-toned light in favor of a dim night light with a warm red or orange glow. And try to make it a temporary intervention, so that you can get back to a melatonin-friendly bedroom.
Even for someone who’s afraid of the dark, the side effects of sleeping with the lights on are scarier still. From low energy to serious health risks, the negative impacts of high sleep debt from nighttime light exposure should not be overlooked.
Ready to trade in that night light for a good sleep app? The RISE app will help you develop healthy sleep habits and keep your sleep debt low, for better sleep, better days, and better health.
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