Twilight is an app whose main goal is to help you sleep better. It's especially aimed at people with insomnia and based on the theory that exposure to blue light right before going to bed can disturb natural sleep rhythms, causing sleep problems. Again, keep in mind that this is just a theory and is not scientifically proven.
Within the app's options you can set many different parameters to suit your needs. It's possible to adjust the color warmth as well as the intensity of the filter you're using. This filter covers the screen for a period of time that you set so it doesn't disturb your sleep.
Among the app's advanced options are the possibility to automatically open the app when you turn on your Android, allow the app to affect the status bar or not, or even use GPU rendering (this option may consume more battery).
Twilight is an app that looks pretty great on paper. In any case, users with sleep problems have nothing to lose by trying it out for a couple weeks.