Underglow lights, often referred to as neon lights, are colored neon or LED lights attached to the undercarriage of a car, truck or motocycle. These lights emit a glow that makes the vehicle appear as if it is floating. This is a popular feature to install aftermarket on customized cars, particularly in California, where use of underglow lights is permitted by law.
In California, underglow lights must emit a diffused light in order to comply with state law. More specifically, under Division 12, Chapter 2, Article 10 Section 25400(a) of the California Vehicle Code, aftermarket exterior lights attached to vehicles must emit a nonglaring light of 0.05 candelas per square inch of area or less.
Under under Division 12, Chapter 2, Article 10 Section 25400(b) of the California Vehicle Code, aftermarket exterior lights, including underglow lights, attached to the front of a vehicle cannot be red in color, but all other colors are permitted. Aftermarket exterior lights must also not be place in a position where they might interfere with the effectiveness of visibility or required lights such as break lights, tail lights, turn signals and headlights.
All aftermarket underglow lights must be 720 square inches or less if the vehicle is leased or rented or it will be primarily driven in residential districts and nearby municipalities. However, show cars are not subject to this limitation in Division 12, Chapter 2, Article 10 Section 25400(c) of the California Vehicle Code aftermarket exterior lights attached to vehicles