Lighting control is one of the most important but often overlooked elements of a home theater system. For the best video performance, you want the room to be as dark as possible, so that you can get the highest level of contrast. Window treatments, special doors and/or dedicated rooms with no access to sunlight whatsoever are all considers ways to get your room as dark as possible for video.
For audio, music sounds better to you when the lights aren't on full blast. Your brain is more receptive to sound and you focus less on your environment and more on the music.
Lighting control systems range from simple dimmers to complete lighting computer systems that have multi-zone control over bank after bank of lights. Lutron's Grafix Eye is a popular choice for home builders and home theater designers alike.
Lighting control is just the beginning of home automation, that can also incorporate HVAC and control over every aspect of your home theater system.