I'm not saying it wouldn't be useful to have a means of altering a clown's mood by using a spotlight, but it's one of those things that has limited utility. Spotlights are heavy. You'd have to lure someone into the theater, then use the red light to make him enraged! Then he beats you up! Back to the drawing board.

I don't have the rest of the book, but I'm reasonably sure the vilain is defeated by a blind man.