I have been using F.lux for a few months now, on both my work and my home displays. It has become a must-have tool for me! You may want to temporarily turn it off (Disable for an hour) if you are processing photos. The warm colors of F.lux at night take a little getting used to in the beginning. Since I am used to it now, my eyes strain when given a normal white-blue display at night! My eyes are no longer strained when I look away from the display to the lit surroundings.
Research is finding strong connections between the light our eyes perceive at night (and day) and our sleep and mood. F.lux is the result of this research for our computer displays. Lights like the Philips Wake-Up Light are appearing on the market now to provide natural transitions from and to sleep in the mornings and at night.
For Linux: I was glad to see that there is a F.Lux version for Linux here. However, it does not seem to work on Ubuntu 14.04. The display does not change no matter what longitude-latitude is set and the Preferences option does not open up at all.