Blue light and its repercussions on sleep

The monsters that keep you up nights aren’t under the bed, they’re in your hand!

Stress and sleep

Sonia Chartier

02 June 2017

Smartphones are extremely useful for a wide range of tasks, but their role as an alarm clock to wake you up is a little too effective. Allow me to explain. Sleeping near your phone disrupts the quality of your sleep and wrests you from the arms of Morpheus to make you toss and turn all night.

And it’s not just because of the infamous blue light smartphones give off…


Given how smartphones are relative newcomers to our technological world, their impacts on health in general and sleep in particular are poorly understood and have yet to be confirmed scientifically. However, it has been shown that the blue light emitted by backlit screens on tablet computers, phones and laptops significantly affects secretion of the hormone melatonin.

Your body produces melatonin when it gets dark out as a way of preparing you for sleep. Exposed to blue light, your retina sends the brain a signal to keep you awake. In fact, the light given off by smartphone screens is powerful and concentrated, even more so than the light from tablets and laptops. What’s more, the phones are designed to be used within close range of your eyes, which amplifies the light’s impact. The repercussions on sleep are huge: using your smartphone for just two hours can lower your body’s melatonin production by 23%.

So it’s best to avoid using your smartphone or tablet before bed. Researchers have found that teens who use an electronic device in the hour before going to bed take over an hour to fall asleep. Those who use such devices for more than two hours a day are more likely to need over an hour more to fall asleep than people who use them for less than two hours. The figure jumps to 49% in those who use the devices for more than four hours a day. When you realize that teenagers need eight to nine hours of sleep a night and that it takes an hour to fall asleep, evenings can get pretty short on school nights!

Light alert

Surveys have shown that most teens and people aged 18 to 29 who have a smartphone use theirs as an alarm clock or at least sleep next to their phone. If the device is near your face, the slightest light alert, even a flash lasting as little as 0.12 seconds, is enough to put your body into a state of alert. Evolution has given a competitive advantage to people who wake up promptly in times of danger (like when a hungry carnivore starts sniffing around nearby), so the tiny flash of an Instagram or CBC News alert is enough to wake you up. And if you’re thinking “That’s okay, I fall right back asleep again,” you need to know that your sleep cycle has still been disrupted.

  • Sleep involves a cycle consisting of five distinct phases.
  • Each cycle lasts 90 minutes.
  • We need five complete cycles to wake up feeling rested and refreshed.
  • A cycle works like this: you fall asleep in phase 1, move on to phase to 2, and then into phases 3 and 4, which are the deep and restorative sleep phases, before moving onto 5, which is the REM (rapid eye movement) phase.
  • If you get woken up in the middle of a cycle, you go back to square one and start it over, even if you were close to completing it.

Ideally, you have to set your alarm to wake you up 7.5 hours after the time you fall asleep (not your bedtime), or 5 x 90 minutes. For teens, it’s best to calculate six full 90-minute cycles.

And although it’s what people talk about most, blue light isn’t the only culprit. All electronics affect your sleep to some degree depending on whether you use them actively or passively. Because watching TV is a passive activity, it stimulates the brain less than video games, social media, text messaging or chatting. Studies have demonstrated this phenomenon, but have yet to fully explain it.

There are many ways to block out blue light, such as wearing orange glasses or using applications that emit a more subdued light. But if you spend your evenings clinging to your phone and you spend every night tossing and turning, try filling your evenings with other things like taking a walk, spending time with your family or reading a good book—just make sure it’s not too good.


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