SINGLE FIXTURE ABOVE MIRROR
In a smaller bathroom or powder room where you might not have as much wall width to work with, you can position a sconce above the mirror instead of squeezing one in on each side.
An overhead fixture will keep things symmetrical, but might cause some shadows on your face.
For more even light, you can opt for side-by-side sconces or twin-light fixtures that will illuminate down from both sides for better coverage. Keep in mind: If your mirror is more than 60 inches wide (often the case with a double vanity), sconces on each side might be spaced too far apart to provide adequate light, so consider an over-mirror fixture in this situation.
According to the American Lighting Association, the ideal height for installing fixtures above a mirror is about 78 inches from the floor.
Choose a single fixture above the mirror if:
You don’t have room on one or both sides of the mirror to fit a pair of sconces.
You have a very wide mirror with no breaks in between.
You have a tall ceiling and want to dramatically accentuate the height by adding a focal point up high.