switch from screen to printing books - for better sleep. Why?

Screen of computer/cell phone, emits blue light, disrupting the release of melatonin, hormone promoting sleep.

Don't lie down on bed, reading your cell phone or iPad - bad habit! The closer to your eyes, the more exposure to blue light you got, the worse effect on your asleep.

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Don't use "blue color" as blue is color, redundant.  You can say blue light, blue flag, blue cloth.