Screen time at night keeps adults from falling asleep and sleeping well due to cognitive stimulation and sleep deprivation. Your brain's electrical activity increases, neurons race and divert you from calming down into a peaceful state of mind for sleep.
In addition the physical act of responding to an email, text, or video increases the tension in your body which results in stress. Your body then produces the stress hormone cortisol released by the adrenal gland aversive to sleep.
Fuethermore, the brain naturally creates the hormone, melatonin, that regulates the sleep-wake cycle. Too much light from video screens at bedtime affect the melatonin production giving the body the impression you aren't ready for sleep. In addition the screen emits light that suggests to the brain that it is still daytime which contributes to insomnia and sleep deprivation. Holding a device such as a smartphone close to one's face increases this effect giving the brain the wrong signal as if it's not time to go to sleep. The best advice is to stop watching TV or using smartphones and other screen devices an hour or two before bedtime to give your brain a rest and the correct signal that it is time for sleep.
Harvard Medical School scientists concur that specific wavelengths of light suppress the sleep-inducing hormone melatonin in the brain. The National Sleep Foundation in Arlington, Va surveyed 1500 randomly selected adults in the U.S., Canada, Mexico, Germany, Britain, and Japan showing that at least two-thirds of those people who watched TV in the hour before bed didn't get a good night's sleep on work nights. The circadian clock, the body's biological time keeper that is synchronized to the 24-hour day is thrown off by this interference with the light -dark cycle. This light exposure delays the melatonin that should surge forward.
So limit your screen time and get a good night's rest. You'll be happy in the morning!