Does this scenario sound familiar? You’re browsing Facebook and come across a post from a friend complaining that they can’t sleep. You notice they posted it at 1 a.m. “Maybe stop staring at a screen, dummy,” you think.

Then you realize it’s 2 a.m., you’re reading Facebook from a smartphone in bed, and you’ve never been more awake.

It’s an inconvenient truth for an increasingly connected (and addicted) world, but LED screens are the enemies of sleep. A steady trickle of studies confirm this, the latest being a survey of 9,846 teenagers aged 16 to 19 in Norway, two years in the making and published Monday in the medical journal BMJ Open.

The teens recorded their sleep patterns as well as their technology usage throughout the day, with a focus on the hour before bedtime. The result? What researchers call a “dose-response relationship” — the more you dose yourself with devices, the higher your risk of sleeplessness.

“Almost all adolescents reported using one or more electronic devices during the last hour before bedtime,” the Norwegian scientists wrote. “Extensive use of these devices was significantly and positively associated with SOL [sleep onset latency, or the amount of time it takes to nod off] and sleep deficiency, with an inverse dose–response relationship between sleep duration and media use.”

Rationalize it all you want — a quick game of Candy Crush will relax me! — but the numbers don’t lie.

What exactly is the big problem with screens? Previous studies have pointed the finger at the blue light emitted by all LED screens, which has been found to interfere with production of the sleep hormone melatonin in the brain.

That would explain the popularity of apps such as Twilight for Android, which promises to “harmonize your screen with the sun cycle” — automatically lowering brightness at night, basically. Twilight has more than 74,000 positive reviews in the Google Play store. (Sadly, there is no iOS equivalent unless you jailbreak your iPhone.)

But that’s only the start of the story, the Norwegian researchers suggest; they also raise the disturbing possibility that electromagnetic radiation may be one of the factors stopping us from getting a good night’s rest. The hunched-over posture that tends to come with screen usage can lead to headaches and muscular pain. And that’s not even counting all the ways the Internet jolts our tired brains.

“There are probably multiple pathways explaining the associations between sleep and electronic devices,” the study says. “Media use may directly affect sleep by replacing it due to its time-consuming nature, or may interfere with sleep through increased psychophysiological arousal.”

In other words, it isn’t just the fact that you’re using your smartphone, it’s what you’re doing on it. All that important-looking news and social media may be overstimulating your brain; even a simple game like Candy Crush can raise your heart rate and induce the fight-or-flight response.

More study is needed; that’s the loud-and-clear message from these researchers and others. These devices and the behavior they engender are so new that science doesn’t have a full answer to smartphone sleeplessness yet.

But in the meantime, there are a number of common-sense steps you can take. The ideal nodding-off activity? Read a slow-paced book. If you must read it on a screen and don’t trust yourself to stick to the Kindle or iBooks app, get a dedicated Kindle device (although even the lowest brightness setting on the Kindle Paperwhite can be a little on the bright side).

Reading on a phone or tablet probably isn’t the best idea, since your brain may associate these devices with more stimulating activities. But if you can handle it, try getting a good privacy screen for the mobile device that reduces glare. Fire up Kindle or iBooks in night mode, then turn the brightness all the way down.

(You can also try this bizarre experiment with blue light-blocking sunglasses if you’re willing to look a little silly in the sack.)

Resist the urge to check Facebook, and you may be well on your way to a slumber that should enhance your social life the following day.

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