I can't recall where I found it and all the information, but when HID headlights began being popular I wondered if they were legal. Specifically my question was about replacing the bulbs in the factory headlight assembly with HID's. I remember it seeing a federal standard that it was illegal to use the wrong bulb in the DOT approved lens/light assembly and somewhere on the lens was a code for the correct bulb. I don't think "illegal" lights are a high priority with LEO's and inspections stations mostly pass any thing. There are also "glaring light' statutes but about in in my town have high wattage driving and replacement parking lights that are blinding to the point they out shine the headlight. There are laws about those light beams extending past a certain point but it's all ignored in my town and on the highways. I make many, many trips to DFW and SA and I amazed at the variety of head and tail light I see. Pink, blue, yellow head lights, blue parking lights, black tail light covers. The latest thing I've been seeing is a wide light bar with to over a hundred LED bulbs array some in the grill some on the spoiler and a couple that were on truck headache racks that must have had a couple of hundred intense LED bulbs. All these things have blindingly intense LED's. In my mind they violate even the simplest rule regarding limiting the number of lights on the front of a vehicle to 8. It's also illegal to have driving lights (KC) turned on above the cab on public roadways. I even seem to remember they were to be covered when not off road. Just not a big deal for DPS and my local PD with bigger fish to fry.
I agree you're not likely to get arrested for that sort of thing. I have searched for the info or a link several times with no success. Sometimes I think I'm getting senile and just imagined it 
. I am extremely sensitive to bright lights at night due to taking my ophthalmologist's recommendation for multi-focus intra-ocular lens implants. I think they were called ReStor. He told me the bullseye appearance and intensification of light issues/problems with the implants had been solved. NOT! I just try to look away but eventually I think my night driving will be kaput! The new LED light bars are impossible to ignore. The lens also affect my shooting because I see multiple images of the sights. I just concentrate on the darkest images among them. He also told me I'd never need glasses again. Another lie!