Are Spotlights Legal in the US?

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Auxiliary spotlights and driving lamps are legal in the US within the federal lighting standard and your state's rules. They must be white or amber, aimed correctly, and limited in number and mounting height, and they must not dazzle other drivers.

Why?

Extra forward lighting is allowed as auxiliary equipment, but it has to fit inside FMVSS 108 and each state's lighting code. That means the right color (white, or amber for fog use), proper aim, and a mounting height within the permitted range rather than mounted wherever is convenient.

States commonly cap how many auxiliary lamps can be lit at once and govern when driving lights may be used, typically tied to your high beams and switched off for oncoming traffic. Off-road-style flood lamps are treated like a light bar: fine off the road, restricted on it.

So a sensible pair of aimed driving or fog lamps is road-legal when set up to the color, aim, height and number rules; a wall of unaimed lights that blinds other drivers is not.

What decides if it's legal

Auxiliary driving lamps are regulated by FMVSS 108 and state lighting law.
Forward lamps must be white or amber and correctly aimed.
States limit the number, mounting height and use of auxiliary lights.
They must not dazzle oncoming traffic or be used improperly with high beams.

Does it depend on your state?

Partly. The color and no-dazzle basics are federal, but the number of auxiliary lamps allowed, their mounting height and when they may be used are set by state law, so the details vary.

Related legality guides

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Sources

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