"Source lighting is something that the inventors of cinema brought forth as a technique, and it's a good starting point when you're telling a story, but that doesn't mean you have to follow it. If I have an interior daylight scene, I usually struggle to use one light coming in through a window. Inside, I use smaller units and practical lights, and I also figure out how to take light away and create the little separations that provide depth. I can use practical lamps a lot as lighting sources, but will often add to that with additional 'movie' lights. However, you have to make sure that the additional lights you're using on an actor are not also lighting the practical. Finally, I add the proper amount of fill light, which I call room tone, to give the blacks the right tonality. Light bounces off of every surface in a room-- the walls, the floor, the furnature-- and that's what room tone is. I usually hit a white card above the set or directly on the ceiling so that it doesn't cast shadows on the walls. If you were to turn off all the other lights, you'd barely see anything, but everything would still be visible. There's no directionality to it. Room tone is very improtant, and you can use varying amounts of it depending on the speed of your film."
-Conrad Hall, ASC