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One claim I come across again and again and again in some form is this:

Blue light from screens before sleep affects the production of melatonin in your body therefore it's harder to fall asleep (or your sleep isn't so good).

Googling for this reveals it regurgitated again and again. There are even products like "blue light blocking glasses" that are supposed to help with this (because of course there are). However... I'm doubtful. Here's why:

  • The light from devices pales in comparison to all the other light you're getting from simply the lighting in your room. Even if you're in bed in a dark room with your phone, there's... just not that much light coming from it.
  • The light from the screens isn't predominantly blue. It's all kinds of colors, depending on what you're viewing.
  • I seem to recall that the original research on this topic was inconclusive, and there was more research that actually didn't find any correlation... but I don't know where to find either.

And it also seems to me like there are other related factors that would have a much stronger influence on your sleep:

  • The overall amount of light is important. Darkness helps sleep, light keeps it away. If you're watching TV in a brightly lit room, obviously you're not going to be very sleepy. And the same goes about playing with your phone or computer.
  • When you're actively using a device, that in and of itself drives sleep away since you're focusing on it. From my own anecdotal experience, computer games are VERY efficient at keeping sleepiness at bay; and when I awake, the quickest way to get rid of sleepiness is also to start using my phone - but that's because I focus on it and find it interesting and engaging.

So... while the advice to lower the light levels and put away your devices before sleep is probably a good one, is it really some mystical "blue light" that is the issue, or is that just another myth?

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    I'm thinking this question is a dupe. – Daniel R Hicks Mar 25 '19 at 1:56
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    Other very similar question: Does using the computer before sleeping affect sleep patterns – Oddthinking Mar 25 '19 at 6:15
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    "The light from the screens isn't predominantly blue" - Blue here doesn't really mean the light being visibly blue in color. It means light in HEV range - 400 to 450 nm wavelength. It is also called "cold light" sometimes. Whether computer/smarthone screens emit light in that wavelength in any significant amount, I don't know. – Danila Smirnov Mar 25 '19 at 6:27

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