As we know (if we’ve learned our high school physics), any warm body emits energy in the form of electromagnetic waves. Depending on its temperature, longer or shorter waves prevail. And if the body is very hot, it emits enough energy in the visible light spectrum, so we can see it heating up to red and then to white. That’s why the sun shines – because it’s pretty hot over there!
I am telling you these physics tales in order to explain how the various human-designed lighting sources – fire, candles, standard light bulbs – are different from the sun. All these things glow because they are hot. But they are not nearly as hot as the sun. Therefore they emit lightwaves with a lower frequency, which we see as a slightly yellowish light. In contrast, daylight contains more blue in it – look to the sky and see how much that blue is…
And it appears that blue light is the main factor by which animals synchronize their watches. And since we’re animals too, our body relies on blue color to distinguish day from night. When the blue disappears, we begin to produce various “sleepy” hormones. When the blue appears, we awaken.
The thing is that the screens of modern computers, phones, TVs and tablets emit light that’s similar to sunlight. When you use them at night, you can see their bluish glow. The color of these screens doesn’t let the body prepare for sleep properly. That’s why it’s not a good idea to surf the web right before bed – you then run the risk of twisting and turning for about an hour before finally falling asleep.
A simple and ingenious app called f.lux comes to help here. After sunset it automatically adjusts your computer screen colors to a more normal “evening” yellowish tinge. In the first 1-2 minutes it seems a bit strange, but the eye soon gets used to the new color, and you stop noticing it.
Sweet dreams! =)