Do you have trouble getting to sleep because you mess around on your phone right up to the minute you go to sleep?
If so, that may be due to over exposure to blue light from your device. "The cause is the photoreceptor in your eyes, called Melanopsin. This receptor is sensitive to a narrow band of blue light in the 460-480nm range which may suppress Melatonin production - a hormone responsible for your healthy sleep-wake cycles. In experimental scientific studies it has been shown an average person reading on a tablet or smart phone for a couple of hours before bed time may find their sleep delayed by about an hour."
Twilight is one of the best (non root) options for managing this problem (if you are a root user you should check out CF.Lumen) and at 10p for the pro version, it's a no-brainer purchase right now.
The app makes applies a filter to your device screen appropriate to the time of the day. It filters the flux of blue light emitted by your phone or tablet between sunrise and sunset to protect your eyes. The filter intensity is smoothly adjusted to the sun cycle based on your local sunset and sunrise times.
The newly updated release also includes support for Android TV and Android Wear as well as auto-pause for specific apps.
Interested? Head on over to the Play Store to download (and upgrade via the in app purchase).