"Don't bring your iPad to bed with you if you value your sleep.
Researchers at the National Academy of Science published a study on Monday that concludes the "short-wavelength light" (light that's closer to the blue end of the spectrum) messes up the circadian rhythms that govern sleep and suppresses the sleep-inducing hormone melatonin.
The result? People reported feeling less tired, and took longer to fall asleep. They were also more tired the next day."