At least in my state, there is a law that restricts the location of headlights to between 22 and 54 inches from the ground. 54 inches is quite tall, though, I think that a lot of cars have roofs that are shorter than 4.5 feet. I'd love to see a much lower upper limit.

I don't think there's a limit to how bright they can be. The law limits the lights to "70 watts", which I believe is intended to limit brightness but misses the mark. I bet the law was passed back when headlights were incandescent.