When you go to a movie theater, you get your first indication that the movie is about to begin when the lights turn off. So what's the big deal over lighting systems if we only plan to watch movies in the dark?
A good lighting system enhances your theater room in a couple of ways. From a performance point of view, the system needs to provide light so that people can safely move around the room. You should also arrange the light sources so that they don't cast any glare or light on the image, which would wash out the picture. If you have a direct-view or rear-projection display, the folks at the Imaging Science Foundation (ISF) recommend that you place a bias light behind the display. This reduces eye fatigue by providing a constant light source, and it doesn't compromise image performance.
Beyond the performance issue, lighting provides an aesthetic benefit. The theater room should be an inviting, comfortable space, and a lighting system that sets the right mood is invaluable. For added wow factor, you could integrate a lighting-control system into your theater's remote system.
A theater system that's integrated into a family room brings a whole bevy of lighting needs along with it. In this situation, you'd need a lighting system that's artistic, good for video performance, and functional enough for playing games, doing homework, reading, and entertaining friends.