Assuming your talking about the front bumper/plate area?
The front bumper, the plate is held in with threaded screws into the plastic bumper. I would NEVER hang anything with a great deal of weight (if anything significant) at all as you'll eventually rip the screws through the bumper cover. The front plate is only held on via the bumper cover, not any sort of metal support behind there.
The back bumper is different but I don't know what kind of lights you would ever want back there.
As well there might be 'legal' issues with that as there are laws that are against obstructing the view of a license plate, especially the rear one.