Do you mean lights that are legal for riding a bike after dark?
I suppose there'll be some variation by location, but most places mandate a white light up front visible from so many feet away. I don't even remember; maybe 200 feet or something like that. Most places don't even require a light at the rear, just reflectors.
I've never given the matter much thought because I figure that almost any light is going to be visible over the required range. I also double up my lights, front and rear. I do it because I want to be visible much farther than just the legal requirements and in order to have some backup if one light fails.
So I'd just make sure that your lights are better than most bikes you see out there and you ought to be just fine.
Is that what you were getting at?