If you’re like most people, you probably snuggle up to your smartphone, tablet, or e-reader in bed before turning out the lights. This winding-down time is one of the only moments in the day where we have the time to leisurely catch up on our reading, emails, and social media feeds. Unfortunately for years, study after study have shown that using our favorite gadgets right before bed can have detrimental effects on our sleep and, over a long enough period of time, our health.
However, it’s not the mental stimulation from Facebook that is keeping us up. It turns out that our gadgets emit a type of light that can mess with human biology.
"Light has an acute alerting effect when it is transmitted from our eyes directly to our brains," says Dr. Victoria Revell, a senior project manager at the Surrey Clinical Research Centre at the University of Surrey in the U.K. "We know that it is blue wavelength light that is particularly effective at increasing alertness and affecting our body clock, and so we need to minimize the blue/green wavelengths we are exposed to."
Unfortunately, virtually every device we own, from the latest iPad to the Samsung Galaxy Note to Amazon’s Kindle, has light-emitting diodes that give off blue wavelength light. And it’s that blue wavelength light that wreaks havoc on our body’s melatonin production.
"Melatonin is produced by the brain at night and under conditions of darkness," says Dr. Mariana Figueiro, program director at the Lighting Research Center at Rensselaer Polytechnic Institute in Troy, New York. "It is known as the ‘darkness hormone’ because it tells the body that it is nighttime. In diurnal species, like humans, melatonin signals sleep and the body prepares to switch from daytime to nighttime mode."
Figueiro says that blue light suppresses melatonin, which fools the brain into thinking that it is daytime, making us feel more alert when we should be feeling sleepy since we’re lying in bed. Over time, this melatonin disruption can be devastating.
"Disruption of the melatonin cycle resulting from irregular light/dark pattern exposure or exposure to light at the wrong time can lead to circadian disruption, which has been associated with poor sleep and poor performance," she says. If that behavior goes on for years, Figuerio says it can lead to diseases like diabetes, obesity, and even cancer, although she also notes that the disease studies have only used animal models so far. However, Figueiro says "studies in humans have shown that rotating shift workers working at least 20 to 30 years on rotating shifts are at higher risks for breast and colorectal cancer." Also, human research indicates that sleeping only four hours a night can result in more hunger and higher glucose levels.
But while there is no current "fix" for stopping our blue light—emitting devices from messing with our melatonin production—and little hope people will stop using their devices in bed—both Revell and Figueiro say there are steps people can take to limit the negative effects their devices have at night.
Revell says that since our bodies only start to produce melatonin about two hours before our normal bedtime, there is no need to shun our devices just because it’s dark outside. That means if your normal bedtime is midnight, your body will not start producing melatonin before 10 p.m., so even if it’s winter and it’s dark by 5 p.m., there should be no adverse affects on your sleep patterns provided you stop using your devices two hours before going to bed.
To really benefit from this advice, try to limit your gadget use to an hour or less the closer you get to your bedtime, says Figueiro. "Using an iPad for less than one hour—in the evening, before bedtime—has no significant impact on melatonin production. In our study, melatonin suppression levels after one hour of exposure to the iPad were not statistically different than zero; however, this difference reached significance after two hours."
If you do need to use your gadgets to respond to that email in bed, Figueiro says it’s marginally better reaching for your six-inch iPhone than your 10-inch iPad.
"What matters is the amount of light, especially short-wavelength (blue) light reaching the retina. A device that emits more blue light will be more effective at suppressing melatonin," says Figueiro. "An iPad has the potential to impact us more than an iPhone because it is larger and typically emits more light."
She also notes that the closer the device is used to the eye, the more light the eye will take in, so quickly checking a popup notification at arm's length is better than bringing it close up to your face to read it.
Though the quality and resolution of a display matters when you’re shopping around for a device, the pixels per inch of your gadget won’t affect your melatonin production—but the display’s brightness will.
"It is the light being emitted by the device that is important, so the intensity, color, duration, and pattern of the light are all important parameters in determining the response observed, says Revell. "The brightness is important with brighter light having more of an impact, up to a certain level."
The brighter a display is, the more light hits the back of our eye, leading to greater melatonin disruption. Turning the brightness down in bed can reduce the amount of blue light hitting your eye. And while you’re at it, don’t be afraid to engage your device’s "reading mode."
"Some devices have ‘evening’ modes where the light is dimmer and composed of the longer wavelengths, which have less of an impact on our physiology and behavior," says Revell.
Of course, you could always switch to a device without light emitting diodes. And when I say "device," I mean a good old-fashioned paperback book. The very first Kindle also lacked any kind of backlighting. Yet Revell cautions this method isn’t foolproof.
"Exposing yourself to bright light immediately before bedtime will not help your sleep," she says. "This could be with a device or using a bedside lamp or the clip-on light for the Kindle."
That’s where the next bit of advice comes in.
Our gadgets aren’t the only devices that emit blue light. The normal lightbulbs in our lamps do, too. One way to rectify this—and enable you to read that book with a safe amount of light—is to use warm-colored lightbulbs in your lamps at night. Of course, swapping out the bulbs in your lamps night after night would be a pain, but thankfully there’s now a wide array of smart lights—from the Philips Hue line to LIFX bulbs—which make it easy to configure the type of light.
With a smart lighting system you can set the lights to automatically adjust from a brighter blue light to a warmer color a few hours before bed. The best part about these smart lights is you can program your settings into the app once and you never have to worry about remembering to adjust your lighting again.
Speaking of light-altering software, there are several apps for your devices that allow you to adjust the color intensity of the light emanating from your screens. Software like f.lux automatically adjusts the color of your display based on the time of day. The Android app Night Filter does the same thing.
"These are a good idea," says Revell. "It is the blue/green wavelengths that will have the most impact on your alertness and sleep patterns, so using orange/red lights in the evening will help, as these have less of an impact on the body."
iPhone users should take note that Apple doesn’t give developers access to controlling screen color and intensity on a system-wide level, so in order to use an app like f.lux you’ll need a jailbroken iPhone. If you don’t have a jailbroken device, you may want to think of applying a physical filter like the Zzz iPhone Blue-Blocking Filter.
While Figueiro isn’t familiar with the Zzz, she notes her team has "used an orange filter theatrical gel that removes any light below 530 nm. This is very effective at cutting circadian stimulation to close to zero."
Instead of applying a software or physical filter to your devices, you could just choose to wear one on your head. A number of vendors make amber-lensed goggles, which blocks the blue light from your devices and lamps from reaching your retina.
"These need to remove transmission of light below 530 nm," Figueiro says, "so not all of the amber-lensed goggles might be appropriate. Have the manufacturer specify the transmission of the glasses."
It’s worth noting this method is a bit extreme, as your entire world will be cast in an orange hue.
This last bit of advice is my favorite, because it doesn’t involve limiting the use of your devices or using artificial filters. In order to negate the effects of blue light at night from your devices, you need to get outside more during the day, where you can soak up a lot of natural blue light.
This might seem counterintuitive considering the blue light from our devices often gets vilified, but it’s important to remember that blue light itself isn’t bad for you. As a matter of fact, it’s essential for our biological functioning. We need blue light to alert our body that it’s daytime and it’s time to get to work. Blue light only becomes bad for you when you get too much of it at night. Thankfully, the more you get of it in the daytime, the better your body is able to desensitize itself to blue light's effects at bedtime.
"The circadian system is looking for contrast," says Figueiro. "If one is in a dim room all day, the body gets sensitized and will respond to lower levels of light at night. If one is exposed to high light levels during the day, the sensitivity drops and one needs more light to affect the system at night."