Hi! As a Designer we have the sconces fitting the height of the person that will use it. Generally wall sconces are installed at a height of 66 inches to 72 inches above floor level. This is because you want the light to be eye level, to fill in the sides of your face.

look in the kitchen counter stool dept. standard counter stools are 24", and many are 'dressy' looking suitable for a vanity.

I was told to put them 66" from the floor, but it depends how tall you are, I'm 5'9" and my husband is 6'4" and I had them installed at 72" in my ensuite. You have to be there when the electrician is , he wanted to put the over the mirror light in my husbands bathroom at the standard height, he would have had to bend down to look in the mirror!

It depends the light you choose. You need light that points down. That assumes they will have a glass shade, in most instances. Which means you will be better off with a 42 inch mirror and that is plenty tall enough. It also means you will need TWO HOOKS on the back of the mirror, one on each side and forget wire. You won't have room to lift up and ONTO a hook using wire, even with the shades off in most cases. Two hooks on the back will ensure they hang straight after cleaning the spots off too : ) Must use these . In any casem hard to help without knowing WHICH light and its specs.