I'm not 100% sure what you're looking for but the mirror will recieve light. You can test by just aiming a spot light at the mirror and try some test renders with different colors and intensities. You'll see the effect it has.

Not knowing exactly what your scene is composed of, it's hard to say. Once you have a basic mirror setuo it's really just experimenting until you find something you're happy with. There's not really any hard and fast rules, not for me anyway.