Don't laugh with a webcam we MIGHT JUST BE ABLE TO DO THAT
Ok it would probably require a custom plugin but still.
Probably wouldn't be too hard. The only info you'd really need for something simple is the average brightness of the picture feed. From there, you could adjust the brightness of the room, or create a shadows that responds to the light feed.
For something a bit more complex, factor in webcam position and split the average brightness into smaller sectors.
I'm no programmer however, so I might be making it sound a lot simpler than it is.