It's not the Angry Birds, streaming videos, emails from your boss, or your Facebook updates that disturb your sleep when you spend an evening staring at your smartphone or tablet. OK, the apps can keep you glued to your screen until the wee hours, and that doesn't help. But it is the specific type of light from that screen that is throwing off your natural sleep-wake cycles, even after you power down. In a new video from Reactions: Everyday Chemistry, a sleep researcher explains the eerie power of blue light over your brain.

Cells at the back of your eyes pick up particular light wavelengths and, with a light-sensitive protein called melanopsin, signal the brain's master clock, which controls the body's circadian rhythms. Blue light, which in nature is most abundant in the morning, tells you to get up and get moving. Red light is more common at dusk and it slows you down. Now, guess what kind of light is streaming from that little screen in your hand at 11:59 P.M.? "Your iPad, your phone, your computer emit large quantities of blue light," says sleep researcher and chemist Brian Zoltowski of Southern Methodist University

The results of staring at them are tiresomely predictable. Think about that when you are tossing and turning in bed a few hours later. And tomorrow night, try shutting down earlier. Let us know what happens in your comments below, too.