Fog lightsUnited States
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183. Fog lights
Fog lights are vehicle lights designed for use in conditions where visibility is seriously reduced by fog, snow or other severe weather. Front fog lights illuminate the road ahead at a low level, while rear fog lights make the vehicle more visible to road users approaching from behind.
Fog lights should only be used in the conditions permitted by local traffic rules. Rear fog lights are particularly bright and can dazzle or distract following drivers when visibility is good.
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What are front fog lights used for?
Front fog lights provide additional low-level illumination in poor visibility such as fog, snowfall or heavy rain. Their design helps illuminate the road close to the vehicle.
What are rear fog lights used for?
Rear fog lights produce an intense red light that makes a vehicle easier to see from behind when visibility is seriously reduced.
Should fog lights be used in normal weather?
No. Fog lights should only be used when the applicable traffic rules and weather conditions justify them. Rear fog lights in particular can cause unnecessary glare when visibility is good.

Traffic rules
United States