Is an HID Conversion Kit Legal in the US?

Not legal

HID (xenon) conversion kits fitted into halogen headlights are not legal in the US. Like LED conversion bulbs, they put a light source into a housing that was never certified for it, which FMVSS 108 does not permit.

Why?

A halogen headlight is certified as a complete assembly under FMVSS 108. Dropping an HID burner into that housing produces a beam it was not designed to control, typically scattering intense light and glare toward other drivers, so the assembly no longer meets the federal standard.

NHTSA has been explicit that these conversion kits are non-compliant equipment. The fact that they are widely sold does not make them road-legal; it just means enforcement is uneven.

Vehicles that came with factory HID/xenon systems, or a complete DOT-compliant projector assembly designed for HID, are fine. It is the conversion kit in a reflector housing that is not street-legal.

What decides if it's legal

FMVSS 108 governs headlight compliance nationwide.
HID "conversion" kits in halogen housings are not DOT-compliant.
They scatter light and dazzle, which is why they fail the standard.
Factory HID/xenon systems and compliant housings are fine.

Does it depend on your state?

The standard is federal, so an HID conversion kit is non-compliant nationwide. How strictly it is enforced varies by state and inspection regime.

Related legality guides

Find your car in the garage

Sources

This page is general guidance, not legal advice, on the rules in the US for HID conversion kit. The detail varies by exact vehicle and changes over time - confirm with your insurer and the EPA, NHTSA and your state DMV before modifying.