If you mean rear extra bright red lights those are for fog to prevent being rear-ended. If there was no fog it is illegal. Whether or not it is enforced depends on location, agencies, priorities. Example usage would be in Bakersfield, CA there is a location that at times goes from clear to not being able to see lights 2 feet away nearly instantly. Beyond pea-soup fog. It's a very unnerving experience if one is not ready for it.
Those are standard equipment on many big rigs for backing up in the dark. I had the same experience as you when I forgot to dim my brights coming up on a trucker on the interstate at night!
I once came up behind a semi on a rural stretch of I-80 with my brights on. He hit me with a set of rear-mounted flood lights.
Probably illegal, but who's going to stop him? Plus, I got the message.