Actually, film editors often have to insert a quick shot of a character's expression/reaction or a Point-Of-View shot to cover just such a real-world mis-match of lighting or whatever between different "takes" of a scene. It's really educational to watch films without the sound, so you focus on that sort of thing. A skillful editor can keep you from noticing inadequacies in footage that cannot be re-shot. Even so, you'll be amazed at some substandard stuff that ends up films. At least we can archive our actors and sets and rerender!