All states require that vehicles have headlights and taillights and that they meet certain standards. But not all aftermarket products meet these requirements. Installing products that aren't consistent with the legal standards can lead to a ticket. The laws of each state are different, but this article outlines some of the aftermarket lighting options that may be unlawful.
Most regulations on headlights and taillights set limits on color and brightness.
In compliance with federal recommendations, all states require headlights to be white or amber. It's usually illegal if any other color of light can be seen from the front of the vehicle. This restriction applies to roof lights, under-glow, and lighting in the engine compartment. The idea behind lighting restrictions related to color is to prevent confusion with emergency vehicles. The safest option is to use only headlights and taillights with a "DOT-approved" sticker.
You may see advertisements for "blue" headlights that are DOT-approved. However, these lights aren't truly blue. In reality, these bulbs produce such a pure white light that they just appear slightly blue. As long as these aftermarket headlights don't exceed brightness laws, they are legal to use.
As a general rule, the color of taillights should not be modified. Vehicles must have only two brake lights and the brake lights must be red. Any color customization is generally prohibited. Overhead brake lights, backup lights, or truck-bed lights are generally permitted but optional.
Headlight brightness is primarily governed by federal rules. Pursuant to the Code of Federal Regulations (CFR) luminous intensity of headlights must be between 500 and 3,000 candelas. The DOT and SAE certify headlights that are legal in the United States. As long as the headlight is labeled as DOT or SAE approved, it is legal to operate in all 50 states.
Taillights are also subject to brightness limitations, but as they must be red in color, taillights rarely violate these limits. Just ensure that any custom, aftermarket taillights are DOT or SAE approved.
Some design trends include adding lights to the roof, chassis, or interior of the vehicle. In some cases, these modifications can violate the general federal regulations as well as some state-specific laws.
Most states prohibit the use of any flashing or strobe lights on non-emergency vehicles. This restriction includes any lights visible from the exterior, including roof lights, under-glow, and even interior lighting.
Since lights visible from the front of a vehicle can only be amber or white, off-color underbody lights generally aren't allowed. Many states also limit the brightness of under-glow, the distance from which it can be visible, and even the times when they can be used. Again, the primary purpose of the limitations is to prevent confusion with emergency vehicles.
Few state laws specifically address interior lighting. However, an interior light that is off-color and visible from the front of the car can result in a ticket. Some state-specific laws permit non-red diffused lighting on the passenger windows.
Lighting-related offenses are typically non-moving traffic violations and carry a fine. While removing lighting effects may seem like a waste of money, continuing to drive with illegal lighting can result in increased penalties and possible registration revocation.
Lighting regulations generally apply to all vehicles on public roads and roadways open to the public. So exhibiting light effects while parked in a showroom or private car show isn't illegal.