f.lux adjusts the colour temperature of a computer screen based on location and time of day. Tell it where you live and it will automatically adjust both the brightness and tint match the ambient light of the room. It is a free utility available for Windows, Mac and Linux.
The interface is on the small side, but easy to use and f.lux is free. It has a preview option that runs through the dimming to show you what it looks like, it be disabled for an hour or until sunrise when you don’t want to use it and it has a movie mode.
The theory behind f.lux is that adjusting the colour temperature of the display can help reduce insomnia for anyone who uses a screen in the evening and if you are an insomniac, being able to turn on your device in the middle of the night without being hit with a ton of bright light is fantastic. I find that it also reduces eye strain and related tension headaches.