Twilight is a piece of software which has the purpose of making sure you're going to sleep well after you've used your Android tablet or smartphone during the night. It manages to do so by making the screen of your device tinted with a certain color. If you have the habit of using your Android machine at night, you should check out this app to see if it works for your eyes.
A big aspect is the friendly and simplistic user interface where you have the power of adjusting various parameters, like color temperature, screen dim, intensity, and more. Another nice thing is that you can configure when the filter becomes active and inactive. When the app is activated, you will easily notice how the screen of your smartphone/tablet gets more reddish and it might be easier for you to use your device.
This happens because Twilight seeks to remove the blue light in order to prevent it from disturbing your circadian rhythm and cause inability to fall asleep. It even comes with a built-in widget which lets you play with a couple of settings directly from the home screen.