Blue light is emitted from our smartphones, computer screens, televisions, the fluorescent lights in the office, and the sun. Blue light is all around us all day long. And sleep experts want you to know that yes, exposure to blue light during the day does affect your sleep.

Blue light is part of the spectrum of light that the human eye can see and has the shortest wavelength and most energy. (Colors on the other end of the light spectrum — red and orange, for example — have longer wavelengths and less energy.)

The biggest source of blue light exposure on earth is the sun, but electronic screens, such as televisions, smartphones, tablets, computers, and e-readers, all emit artificial blue light too. LED (light-emitting diode) lights and fluorescent light bulbs also produce blue light.

People talk about blue light and sleep because it does affect both our alertness during the day and sleepiness at night, explains Colleen Carney, PhD, an associate professor and director of the Sleep and Depression Laboratory at Ryerson University in Toronto.

And while blue light gets a lot of negative press (you’ve likely seen a headline or two telling you to get off your cellphone at night), not all blue light is bad, Dr. Carney says. “It’s a lot more nuanced than that.”

Blue light exposure from the sun throughout the day, for instance, helps set our body clocks and keep our circadian rhythm on schedule day after day, she explains. “It provides the largest confirmation in our environment as to what time it is.”

The problem comes in when we get exposure to too much artificial blue light later in the day and at night. The brain doesn’t distinguish between blue light from the sun and blue light from our cellphones and laptops, so any blue light can signal to the brain that it’s time to be awake.

“It essentially tricks the brain into thinking it’s daytime in the evening and suppresses the mechanisms that promote sleep,” says Phillip Yuhas, PhD an assistant professor at the Ohio State University College of Optometry in Columbus.

So, how can you make sure you’re getting the right amount of exposure to blue light during the day to keep you alert and at night to promote healthy sleep? Here’s everything you need to know.

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Is Blue Light Making My Sleep Worse?

Research from the past decade suggests that more exposure to artificial blue light closer to bedtime tends to indeed make sleep worse.

For instance, past research has found that people who read e-books before bedtime had disrupted sleep patterns and were more tired the next day compared with people who read from traditional books. That research also found that people who looked at e-readers before bedtime even had shorter REM (rapid eye movement) sleep, a deeper state of sleep when key parts of the brain’s memory consolidation processes happen.

Several studies suggest that blue light, more so than other colors of light, disrupts production of melatonin (a hormone naturally produced by the brain that signals it’s time to sleep) in the brain, according to a review published in 2019 in the Journal of Biological and Medical Rhythm Research.

Blue light suppresses secretion of melatonin for twice as long as the immediately longer green wavelength of light, explains Afifa Shamim-Uzzaman, MD, an associate professor in neurology at the University of Michigan and Medical Director at the VA Ann Arbor Healthcare System’s Sleep Disorders Center.

Melatonin levels naturally start to rise in our bodies about two hours before we fall asleep, and remain high while we’re sleeping. But exposure to light — especially blue light — during this time interrupts the natural production of melatonin, making it harder to fall asleep and stay asleep, Dr. Shamim-Uzzaman explains.

But while blue light exposure too close too bedtime isn’t ideal, there’s also no need to panic that a whole night of sleep is going to be ruined if you return a text in the evening, Carney says.

There are some caveats about the research to date on blue light and sleep. Studies on the topic are relatively small and last for short periods of time, Carney says. So it’s difficult to say with certainty if those conclusions apply to everyone all the time. Age of the participants can bear on the outcomes, too. People who are younger tend to be more sensitive to light changes.

What About Exposure to Blue Light Earlier in the Day?

Blue light tells the body to wake up. And in the morning and throughout the day, that’s a good thing.

“Light exposure when you wake up can help you when you have jet lag or need to reset your body’s natural circadian rhythms just like light right before bedtime disrupts that process,” Dr. Yuhas says.

He says blue light tells the hypothalamus, a part of the brain that helps manages biological rhythms based on light exposure, that it's morning. In the same way that at night, blue light signals to the brain it’s time to be awake, in the morning, blue light also helps suppress sleep-inducing hormones, which helps wake you up.

“In a nutshell: Exposure to light shuts off melatonin production in the brain, thereby shutting off the signal from the brain telling the body to be asleep,” says Shamim-Uzzaman.

Research published in the journal Sleep found that blue light “immediately” improved alertness, productivity, and performance in the daytime, in a study that included 32 people in their twenties. The participants exposed to blue light over the course of 6.5 hours in the daytime rated themselves as less sleepy, had quicker reaction times, and reported fewer lapses of attention during performance tests compared with their counterparts exposed to green light for the same amount of time.

Carney encourages her patients who encounter afternoon drowsiness to take a 20-minute walk around the block to reap the benefits of blue light exposure instead of reaching for a cup of coffee.

Blue light affects mood, too, according to a study published in October 2017 in the journal PLoS One. In this case, researchers found that blue light had a stress-busting, relaxing effect on study participants. In a small-scale study, the researchers had 12 healthy volunteers complete a computerized math test designed to induce stress — called the Montreal Imaging Stress Task — before putting the study participants in a color therapy room with either blue light or white light. The researchers monitored the volunteers’ stress levels throughout the study via electroencephalogram (EEG) and electrocardiogram (ECG).

Participants who decompressed in the color therapy rooms with blue light fared better at lowering stress levels measured according to their heart rate and brain activity, and they did so in a shorter amount of time.

The findings build on 2010 research suggesting that blue light taps into parts of the brain that process mood and emotions, which may help explain why some people feel happier on sunny days.

How Does Blue Light Therapy Help With Sleep Disorders?

Blue light is also used therapeutically to treat conditions via exposure to artificial light that resembles sunlight. Patients sit in front of a light therapy box — also called a light therapy lamp — that emits bright light that mimics natural sunlight. You don’t have to sit directly in front of the lamp during these light therapy sessions; typically, patients keep the light box close to them (about 24 inches away) so the light is in their peripheral vision, according to the Sleep Foundation.

Blue light therapy is used to treat a series of sleep-wake disorders brought on by circadian rhythm misalignment, according to Carney. They include delayed sleep phase syndrome, which is when it’s difficult to fall asleep until the early hours of the morning, and advanced sleep phase syndrome, on the other end of the spectrum, making it difficult to stay awake in the early evening while waking up too early in the morning.

Blue light therapy can also be used to help with jet lag and shift-work disorder.

When used consistently, blue light therapy can help with all these circadian rhythm-related sleep issues, by gradually adjusting your sleep schedule, and resetting your circadian rhythm depending on what you need, says Carney. About 20 minutes of light therapy lamps in the evenings can help someone push their bedtime later in the evening, while light exposure — either through natural sunlight or lamps — in the mornings can promote wakefulness earlier, and help someone adjust to an earlier daily bedtime.

What You Can Do to Optimize Blue Light Exposure for Better Sleep

Here’s how and when to exposure yourself to blue light throughout the day to feel more alert, and what to know about shutting things down at night for our best shuteye:

Get your fill of daytime light exposure. Start your day with sunlight — or bright light — to set the tone for the day and help promote wakefulness and alertness. Don’t fret if you’re stuck indoors throughout the day; Yuhas says working on your computer by the window on a sunny day is enough to reap the benefits of blue light in the daytime. If it’s a cloudy day, he says you should still aim to get some outdoor light, which provides more blue light than your computer screen would. Shamim-Uzzaman says some people turn to a light box as an alternative source of light for overcast days or during the winter months. If you’re looking for a light box, she recommends one with a bright broad spectrum of light, between 2,500 to 10,000 lux.
Limit exposure to screens for one hour before bedtime. Yuhas and Shamim-Uzzaman recommend establishing a technology curfew so all electronic devices are stashed away for the evening about one hour before lights out. Turn to other activities that may help with winding down, like reading a book, working on a puzzle, or stretching before bedtime instead.
Alter the settings on your devices. If putting away your smartphone isn’t feasible, check the settings on your electronics and shift them over to “night mode,” “dark mode,” or an option that dims the brightness on your screens, according to Yuhas. This small change can help to reduce blue light exposure.
Avoid devices or specific apps you know to be personal "trouble spots." Most people likely aren’t so sensitive to light that they need to keep their phones under lock-and-key before bedtime, according to Carney. But do be very intentional about how you’re using your devices and for how long. Using a device to use a meditation app or play music, for instance, may require minimal screen time for you and help you relax. TikTok might be another story. “Don’t deprive yourself of something that’s enhancing your wind-down time,” Carney says. But think twice about whether that app or device is actually helping you wind down, she adds.
Seek professional help for sleep troubles if you need it. If you’re having trouble with falling asleep and staying asleep throughout the night, you’re not alone. Insomnia is the most common specific sleep disorder, with short-term issues reported by about 30 percent of adults and chronic insomnia by 10 percent of the population, according to the American Sleep Association. If you have symptoms — such as difficulty falling asleep, feelings of fatigue, or trouble with concentrating and paying attention in the daytime — that occur at least three times a week and linger for at least three months, the Sleep Foundation suggests chronic insomnia may be at play. If your sleep difficulties are bothersome or interfering with your everyday activities, reach out to your primary care doctor or schedule an appointment with a sleep specialist.