I am confused by the wording of your post. What do you mean by "microwave shelf"? Do you mean you have an over-the-range microwave installed? Or, do you mean that you have a shelf that holds a microwave? If it is a shelf, that is very dangerous. You should not have a combustible material over a rangetop. It is, of course, against Building Code, and for good reason. If you meant that you have an over-the-range microwave, they have lights.

"You should not have a combustible material over a rangetop."

That depends on how high up the flammable material is.

Brickeyee - I would assume the shelf is not that high, because you would need access to pull dishes out of the MW, and be able to see the controls and see inside it. Is there a specific distance from a cooktop that a combustible material is allowed?