There are only so many hours in a day, and you don't want to spend them all sitting in front of a computer. Besides, there are times when you should actively avoid backlit displays like the screen on your laptop, as the blue undertones disrupt the human circadian rhythm. This is in large part because of the way we've evolved. Primitive humans didn't have alarm clocks or curtains, so they rose with the sun, when the light is cooler and has a bluish hint. Moreover, after a yellowy, orange sunset, the evening was spent staring into the amber embers of a fire. Over millennia, and many generations, human brains adapted so that cool light was associated with being more alert and warm light - amber, red and so on - with calming down and getting ready for sleep. That's why daylight-simulation lamps are blue, while evening filters for operating systems give your screen a slightly sepia hue.
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