It’s a common impulse: wake up in the middle night, and immediately reach for the smartphone/tablet/fill-in-the device-of-your-choosing here. But as researchers have uncovered over the past decade, it’s a harmful one. Multiple studies have shown that the blue light emitted by smartphones, laptops, and tablets doesn’t just make it harder to get back to sleep, it also makes it more difficult to achieve "deep sleep," and thus get the rest required to function optimally the next day. 

The science behind screens' effect on sleep is fairly straightforward: the blue light emitted by LED screens (those on your smartphone, computer, tablet, or flat-screen TV) tricks the brain into wakefulness, delaying the production of melatonin, a hormone secreted by the pineal gland that helps prep your body and brain for sleep, altering its natural circadian clock. 

So if you are having trouble sleeping and can’t figure out why, take a cold, hard look at your bed. Does it contain an electronic screen of any kind?

Any artificial light is bad before bed

Any artificial light after dusk has an impact on our bodies’ internal clock, which means that to some degree, the vast majority of us are tampering with our circadian rhythms. Before the advent of artificial lighting, our internal clocks were dictated by the sun’s progression across the sky. Now, as we artificially inflate our days to fit our lifestyles, “we are extending our body clock,” says Dr. Shadab Rahman, a researcher in Brigham Woman’s Hospital division of sleep and circadian disorders. Light exposure at night suppresses the secretion of melatonin, delaying feelings of sleepiness and causing us to rise (without an alarm) later than we would if we maintained a natural sleep cycle. 

But blue light is the worst light 

While artificial light of any kind can tamper with our circadian rhythms, a 2002 study revealed that the photoreceptors in our eyes, which absorb light signals and converts them into neural signals, are most sensitive to shortwave length light, i.e. blue light. Compared with green, red, or yellow light sources, blue light has an outsized impact on the “shortening of the body clock as well as the reduction of the sleep drive,” Rahman told ATTN:.

Unfortunately, most of the screens we take to bed with us are LED-lit, and therefore blue-enriched. The cool glow from our collective screens has the power, Rahman says, to “activate the arousal centers in your brain and shift your sleep cycle far more than an incandescent source.”

Simply put, “you don’t want to be exposed to that blue light in the evening,” says Dr. Steven Lockley, an associate professor of medicine at Harvard Medical School’s division of sleep and circadian disorders. “Because electronic devices have a very blue source, they are an increasing concern, especially just before bed.”

The length of one’s light exposure matters, but short bursts have a maximum impact

While a 2012 study found that two hours of using an iPad at maximum brightness suppressed the release of melatonin in study subjects significantly more than one hour, short bursts of light exposure can have an outsized impact on one’s body clock, says Rahman. For instance, a six-and-a-half-hour period of bright light exposure in the middle of the night has been shown to result in a three-hour phase shift. Meanwhile, 12 minutes of light exposure can shift the body clock by one hour, a clearly disproportionate response.

“Yes, duration matters,” says Mariana Figueiro, program director of the Lighting Research Center at Rensselaer Polytechnic Institute. “The best would be to reduce the use of screens starting about two hours prior to your desired bedtime. Our studies have shown that the dose -- time versus intensity -- is important, so two hours is more effective than one hour.”

Steps to achieving better sleep

For a blissfully unadulterated sleep, avoid all artificial light and allow your body to take its cues solely from the sun. “Obviously, this is an unrealistic option for most people,” acknowledges Lockley. Still, he wishes more of us would at least recognize that “any light after dusk is not natural” and, whenever possible, attempt to “reduce exposure to light, particularly blue light, at night.”

Sadly, for many of us -- with work, family, and social obligations -- artificial light, not to mention light from screens, is a nightly ritual. That said, there are strategies for minimizing its detrimental affect on sleep. 

“If you can’t turn off your devices two hours prior to your desired sleep time, reduce the brightness to the lowest setting and reverse the polarity of the screen,” says Figueiro (i.e. white font on a black background instead of the standard black on white). Small adjustments, such as holding the device away from the eyes to minimize the amount of light to which the retina is exposed, can also have an impact. 

For those reading, working or watching content on devices before bed, Lockey recommends applying an orange screen filter or downloading software that alters the emitted light from blue to a warmer, longer wavelength variety. There are also available apps that sync with the sun’s descent, and “will start to dim the blue content on your screen after dusk.” 

But his favorite, if distinctly low-tech, piece of advice is simple: “no electronic devices in the bedroom,” he says. “Leave your phone in the kitchen. It’s that easy.”

Additional expert-approved methods to help you sleep better include sticking to a strict sleep schedule (even on weekends), keeping your room dark and cool at night, avoiding daytime naps (they'll only make it harder to fall asleep at night), exercising regularly, and avoiding stimulants like alcohol, caffeine, and nicotine, as well as heavy meals, in the hours before bedtime.

The reality is that we are all sleep-deprived

 “All of us use light after dusk,” says Lockey. “None of us are sleeping enough.” He cites a recent study in which researchers at the University of Colorado Boulder examined eight adult participants' internal clocks before and after they went camping without electric light; they found that, on average, the campers’ internal clocks shifted so that they went to bed at least an hour earlier, woke up an hour earlier and that their peak melatonin production shifted to occur around midnight. As their internal clocks adjusted to sync up with natural daylight hours, they reported feeling less groggy and tired.

The same would be true for the majority of us, he says. Our rampant use of artificial light -- combined with the fact that a large percentage of the population adheres to work schedules that misalign with their natural sleep cycles – means that we are a chronically tired nation. “Virtually everyone is sleep-deprived,” he says.

And that’s a real problem. In case the sheer bliss of getting seven to eight hours each night isn't enough to convince you of the intrinsic value of sleep, consider that sleep deprivation has been linked in past studies to a higher risk of obesity and heart disease, as well as (surprise, surprise) reduced alertness, a diminished capacity to form memories, and lower academic and cognitive performance — short-term effects that may accumulate if the sleep deficit is left uncorrected.

So don’t compound the deprivation: the next time you wake up in the middle of the night, resist the urge to reach for your smartphone and try counting sheep instead.