I've used this for several years now and have no complaints. The colour change can take a little bit of time to get used to at first in the evenings, but I definitely noticed an improvement in my sleep.
F.lux adjusts your device's display color temperature according to location and time of day. The program is designed to reduce eye strain during night-time use, and to help reduce sleep deprivation because of excessive exposure to blue light before bed.
F.lux is also available for Mac computers.