Can you please tell me if there is a standard height for a vanity light fixture or distance from vanity mirror or combination of both? Thank you Bob

There is no standard, as there are no standard light fixtures.

Placement will depend on the fixtures, and esthetics of how the fixture will look in the space.

What do you have for fixtures and size of vanity?

If its unknown, 80" to the center works many times, width can vary widley due to various vanity widths.