The legality of installing underbody, or undercar, lights depends upon the state in which you reside. Several states, such as Michigan, have made underbody lights illegal if they can be openly observed while the car is driven. “If equipped, the lights must be unlit and covered while on a highway, which includes all public roads and the adjacent rights-of-way,” states the Michigan State Police website.
Because even state laws may vary, ask a representative from your local precinct about undercar-light installation to prevent any potential hassles. In addition, obtain a copy of the applicable laws and keep it in your glove compartment.
States like Illinois allow the display of underbody lights. State statute Sec. 12 209 on "Additional Lighting Equipment" states that “any motor vehicle may be equipped with not more than 2 side cowl or fender lamps which shall emit an amber or white light without glare.”
Many states prohibit the use of neon lights that flash, rotate or alternate between blue and red. Florida car-lighting statues prohibit any lights that change the intended original design or performance. “This includes neon lights under the vehicle and around the license plate," according to the Orlando Police Department website.
