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.

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reaperducer 7 hours ago | parent [-]

No. Not red lights. Flood lights. Like you'd have to light up your backyard.

	▲	icameron 6 hours ago \| parent [-]
		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!