Forget What You Think You Know About Blue Light and Sleep

It’s become a virtually unchallenged piece of conventional wisdom that exposure to blue light—the type emitted by electronic device screens—is bad for sleep. That thinking has spurred a mini-industry of innovations meant to stop those effects, like warm-toned “night mode” settings on gadgets and glasses that claim to block blue light.

But in December, a group of researchers at the University of Manchester in the U.K. published a paper in Current Biology challenging that notion. After exposing mice to lights that were different in hue but equal brightness and assessing their subsequent activity, the researchers concluded that yellow light actually seems to disturb sleep more than blue. Warm-toned light, they hypothesized, could trick the body into thinking it’s daytime, while cooler blue light more closely mimics twilight.

The study was surprising, given the widespread thinking around blue light, but it wasn’t unprecedented. Some researchers have argued that, while electronics can keep you up because of their bright lights and ability to time-suck, blue light isn’t necessarily the problem. So what’s the best way to get a full eight hours each night? Here’s what experts say about blue light.

Why is blue light thought to disrupt sleep?

Your body is dictated by its circadian rhythms, a set of time-dependent physical, mental and behavioral shifts. The most obvious circadian rhythm is the one that drives you to be tired at night and alert during the day. This process is dependent upon melatonin, a hormone secreted when it’s dark outside. Nighttime light exposure can confuse this process, suppressing melatonin production and keeping you up longer.

Studies have suggested that blue light is an especially powerful melatonin suppressant. Melanopsin, the pigment that helps eye cells assess light brightness, is particularly sensitive to shorter, cooler wavelengths like blue light, which some research says means blue light may affect the body more dramatically than other hues. One highly cited study from 2014 showed that using a blue-light-emitting iPad before bed suppresses melatonin, while reading a traditional book does not. IPad readers started producing melatonin 1.5 hours later than usual the next day, and experienced REM sleep—the phase during which dreams occur and memories are consolidated—once they conked out, the study found.

Does the new study change that theory?

Animal studies should always be taken with a grain of salt, as they often do not translate directly to human behavior. And there are additional caveats to this particular paper, says Dr. Cathy Goldstein, a sleep specialist at Michigan Medicine. The researchers looked specifically at cones in the animals’ eyes, which detect color, instead of melanopsin, which senses light and is central to the issue of melatonin secretion.

They also kept light levels dim, regardless of color, which may not reflect the bright lights of electronics.

And finally, though mice are frequently used in sleep research, Goldstein notes that since the rodents are nocturnal, they may respond differently to light than humans do. Taken together, Goldstein says these conditions mean the study’s results apply only to a very narrow set of circumstances and metrics. “For this to get extrapolated to saying ‘blue light at night isn’t bad for you’ is a little bit of an extension,” Goldstein says.

But that doesn’t mean blue light is evil. “Blue light has become the gluten of the sleep world,” Goldstein says with a laugh. In other words, though it may be a potential trigger for health issues, its impact has been blown way out of proportion.

“We put the cart so far ahead of the horse” with blue light, agrees James Wyatt, who directs sleep disorders and sleep-wake research at Rush University Medical Center. In Wyatt’s view, recommendations around limiting blue light have far outpaced science around its effects. There is a valid scientific basis to the idea that blue light interrupts sleep, since research consistently shows that light of any kind suppresses melatonin and blue light may do so to an especially extreme degree. But Wyatt says most human research done in this field hasn’t been representative of the way the average person is exposed to blue light. That is, most experimental conditions don’t correspond to the average person’s day, and even then they often result in only tiny changes in sleep.

Take that iPad study, for example. While it did show that bedtime exposure to blue light through an iPad can suppress melatonin, Wyatt notes that people who read on their devices for hours took only 10 minutes longer to fall asleep than paper book readers. “In over 20 years of practicing sleep medicine, I have never had a patient come to me and say, ‘Hey, doc, can you help me fall asleep 10 minutes faster?'” Wyatt says.

Goldstein adds that the spectrum of light isn’t the only thing that matters—so do brightness, and duration of exposure. “You can’t just worry about spectrum alone,” she says. “You can’t have your blue light filter on, and then have your phone or your tablet at maximal brightness” and expect to drift right off with no problem.

Should I try to limit blue light exposure?

There are plenty of reasons other than sleeplessness to not spend all your time staring at screens, from possible mental health consequences to their correlation with a sedentary lifestyle. But in terms of eye health, there’s no reason to spend your time and money looking for blue-light-filtering glasses or gadgets, says Dr. Matthew Gardiner, an ophthalmologist at Massachusetts Eye and Ear. While some people report improvements in eye-strain or headaches after using these products, Gardiner says there’s no research to suggest blue light damages your eyes. “If you feel more comfortable, then that’s fine, but it does not do anything for the health of your eyes,” he says.

For sleep, Wyatt says the evidence isn’t strong enough to issue a blanket recommendation on blue light. That doesn’t necessarily mean it’s a good idea to use technology before bed—any bright light right before sleep can mess with circadian rhythms, and firing off last-minute emails is unlikely to lull you to sleep—but blue light may not be as universally bad for slumber as people think. Personal preference plays a role, too. Wyatt notes that some people feel relaxed and sleepy after watching television, while others feel wide-awake after flipping through a page-turning book.

Goldstein agrees that blue light research isn’t as conclusive as it’s often portrayed, but says there’s also no reason not to use night-mode filters on electronics if you find them helpful. Just remember to turn down the brightness and avoid hours of aimless scrolling, she says.

Finally, research is pretty definitive on the fact that a dark room is the best environment for sleep, so it’s smart to block out light sources when it’s actually time for bed. Wyatt suggests keeping your room at a cool 65° to 68° Fahrenheit, limiting intermittent noise and sticking to roughly the same sleep and wake times each day to get quality rest.