When you have to visit the bathroom at night, you don't want to have the full power of your bathroom light. So why don't you install a hidden diffused light behind your mirror?

You have to open (in this case crack open) the transformer of the LED light strip. Attach it to power using an insulating screw joint. As always: Don't electrocute yourself!

Put the mirror on the wall, put the LED light strip behind your mirror and you're done.