Want to Sleep Better? Turn Off That Screen! Smartphone, tablet, and laptop screens all emit blue light, which mimics daylight, increasing alertness and suppressing melatonin. A recent study by Anne-Marie Chang and her colleagues (2015) compared the effects of reading a print book with reading a light-emitting e-book two hours before bedtime. They found that the e-book readers took longer to fall asleep, had disrupted sleep patterns, and were less alert the next day than the print book readers. Melatonin production was also lower in the e-book users.

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