Why You Should Never Take Your Smartphone to Bed

It’s 11pm and you’re sitting in front of the TV, checking your smartphone for late-night emails, maybe checking in on family and friends’ activities on Facebook and looking up the menu of the restaurant you’re planning to dine at tomorrow evening. You then head to bed, place your smartphone on the side table and try to get some shut-eye.

If this routine sounds familiar, read on. It turns out, using your smartphone, tablet or computer right before bedtime can set you up for an unproductive tomorrow.

Blue Light Blues

Nitun Verma, a physician and co-founder of PeerWell, a company that treats chronic disease via a smartphone app, says smartphones emit blue light that tricks the brain into thinking it’s in the wrong time zone. This effect peaks at the 480-500 nanometer wavelength. (The iPhone 6 produces about 550 nanometers.) Blue light, Verma says, advances the time that melatonin is released. Melatonin is the hormone that tells us when to go to sleep.

“It helps people fall asleep earlier in the evening and it helps them be more alert when they wake up in the morning,” says Verma. Exposure to blue light in the evening tells the body not to secrete melatonin yet, it’s not time to sleep, and throws your circadian rhythm for a loop.

To explain this further, Verma compares city and country lifestyles. Farmers who wake up at dawn and go out to work, Verma explains, are getting lots of bright light in the morning but as soon as the sun goes down, they go to sleep and wake up with the morning sun warming their faces. In the city, by contrast, most of us wake up in a dark room and at night we’re surrounded by bright phones, bright computers and bright TVs that emit a very cool light (blue light). “This causes a lot of problems where people have racing thoughts, difficulty falling asleep and the mornings are quite foggy mentally,” says Verma.

Related: Sleep Deprivation Is Killing You and Your Career

Decreased Mental Alertness

Using a smartphone at night can keep your brain on high alert and prevent you from getting a good night’s rest. “It’s not just a light issue; it’s actually an activity issue,” says Verma. “If the phone is the portal to the world then you’re bringing the world to bed with you if you’re bringing your phone to bed with you,” he says.

With all the notifications and messages from apps, smartphones keep our brains on high alert when they should be shutting down at night. “If you have the phone in your hand, there’s part of your brain that’s always going to be ready to react to the phone,” says Verma. “Just holding the phone in your hand triggers the habit and it’s very hard to relax unless you get rid of those triggers, meaning you’ve got to put the phone away.”

Make Your Devices Sleep-Friendly

If putting away the phone or tablet at night isn’t an option, there’s another way you can help ensure your devices don’t interfere with your sleep. Blue-light screen filters such as Ocushield or Sleep Shield reduce the amount of blue light emitted by your devices. Verma also recommends diming the lights on smartphones, tablets and computers. Apps such as Twilight filter the blue light emitted by your device after sunset, while F.lux allows your screen to run normally during daylight hours but transitions to a warmer color at night. That can also be effective at reducing the amount of blue light you’re exposed to at night, protecting your sleep hours.

Verma also suggests turning off non-essential notifications to avoid interruptions in the evening hours, allowing you to relax just before bedtime.

Related: How Setting an Earlier Alarm Changed My Life