F.lux is an app that mitigates the effect of blue light from your device screens at night by changing the color of your screen. People have been using it on laptops and such for years; blue light is known to stimulate the brain into thinking that it's time to wake up. Its effects can last for hours. (It's the same color light used to treat seasonal affective depression--and boy, does it ever wake you up!) The alternative is to not use devices for a couple of hours before bed, but nowadays, that's not practical for many of us.
A Google search will pull up f.lux's site. I believe the app is still freeware, and can be run on Windows, Macs, and jailbroken iPhones/iPads. For Android, there's apparently an app called "Twilight" that behaves similarly.
