The expression “as clear as daylight” did not come into existence by chance. We associate daylight with clarity and brightness, and for most aspects of our life both of these are desirable qualities.
But not when we are trying to sleep. We naturally seek out dark corners and shady places to rest, if we want a snooze during the day. And our main sleep is taken after sunset. This is not an accident, either, because we are programmed by our body clocks to feel sleepy when it grows dark. The process involves the release of melatonin, which is the hormone that prepares our body and mind for sleep.
If our eyes are exposed to bright blue light of the wavelengths we normally associate with daytime, our brain will delay the release of melatonin, even though our body clock says that it should now be getting dark. This delay is a problem. Not only does it delay the onset of sleep, it particularly delays the onset of the deep sleep we need to stay healthy.
Because of this, we are now advised by scientists to avoid evening or night time exposure to blue light of the sort that LED screens produce. Achieving this can be difficult for anyone who uses their smartphone after dark, since smartphone screens produce this blue light at a high intensity.
A blue light screen protector filters out the blue light wavelengths in question, making it safe to use your smartphone at all hours.