Pennsylvania regulates neon underglow through Pennsylvania Vehicle Code, Title 67: Transportation, Chapter 175: Vehicle Equipment and Inspection, Article 66: Lighting and Electrical Systems.
Is neon underglow legal in Pennsylvania?
Pennsylvania law prohibits all additional aftermarket vehicle lighting which includes neon underglow. This means that in Pennsylvania neon underglow is illegal.
There are no provisions in PA law which would allow undercarriage lights while driving, and the law completely prohibits using any lamps not specified in the Code.
Pennsylvania vehicle lighting laws
Below are all relevant excerpts from Pennsylvania Vehicle Code that limit, restrict or allow certain aftermarket lights to be installed on vehicles.
§ 175.66. Lighting and electrical systems.
[…] (h) Ornamental lamps. A lamp not enumerated in this section and not located as described in Tables III, IV and V of this chapter, is prohibited unless it is available as original equipment. An illuminated sign is prohibited except on taxicabs, ambulances and trucks. Flashing or revolving lights are not ornamental lamps. Provisions relating to flashing or revolving lights are in Chapters 15 and 173 (relating to authorized vehicles and special operating privileges; and flashing or revolving lights on emergency and authorized vehicles).
Underglow is not specifically mentioned and not part of vehicle’s standard nor required lighting equipment. Underglow therefore falls under the “ornamental lamps” category, and as such is not legal to use in Pennsylvania.