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How Do Rear Fog Lights Work?

Cars.com photo by Angela Conners

CARS.COM — Driving home one night, I pulled onto the highway on a dark but clear evening behind an older Jaguar XJ sedan and was blinded by the driver’s fog lights, even though there wasn’t a bit of fog that evening. How could I tell that his fog lights were on from behind the car? Because, like so many Americans, this driver didn’t seem to understand what the fog light switch does in his fancy European luxury vehicle: Sometimes, the switch for the fog lights turns on a light in the rear.

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In a number of high-end European cars, the fog light button not only illuminates additional driving lights in the front bumper, it also brightens part of the taillights so that your car is more visible to vehicles behind you in the fog. These fog lights are especially useful on Europe’s high-speed highways, but also in any situation of decreased visibility, like snowstorms, thick fog, heavy rain, etc. What this looks like varies from one model to another. In some vehicles, it looks like the driver has their foot on the brake. In others, it might just be a small but brilliantly lit bulb in a larger taillight assembly. Rear fog lights are not common in the U.S., but since they are present on some high-end vehicles, it’s important to understand them. 

Cars.com photo by Angela Conners

Rear Fog Lights

While not common in the U.S., rear fog lights are mandatory in Europe. Typically, the rear fog light is a bright red light that is the same brightness as your brake lights. The job of the rear fog lamp is to reveal the position of your vehicle when driving in the fog, snow or other conditions that limit visibility. Your normal taillights are fairly dim, so they are not as likely be seen in foggy weather. Rear fog lights are often placed on the left side of the vehicle. This lets other drivers know approximately where the vehicle is located in a travel lane. Some newer models, however, have rear fog lights on both sides to further improve visibility. Like the fog lights on the front of your car help make you more visible to oncoming traffic, rear fog lights make you more visible to people behind you. There are several types of rear fog lights. Some take xenon or halogen headlight bulbs, but other rear fog lamps are made up of LED lights. LED lights are bright, long lasting and common on newer vehicles with rear lamps.

In the case of the 2016 Volvo S60 (pictured), a couple rear lights illuminate when you push the button, making the Volvo much easier to spot on the highway in the fog and other poor conditions. Volvo lights are one of the most common examples of rear fog lights. The rear fog lamp is a useful safety feature, but issues arise when drivers are unaware of the feature and switch on the fog lights in normal driving conditions. Sure, you might get a little extra forward road illumination, but you’re also unknowingly blinding drivers behind you and sometimes even making them think you’re braking. Therefore, these optional fog lights should not be used as normal driving lights. If your vehicle has rear fog lights, only switch them on when you are driving in fog, snow or other conditions that may prevent another driver from seeing your vehicle. 

Does Your Car Have Fog Lights in the Rear? 

Take a minute to see if your car has rear fog lights. Put the car in Park, turn on the engine and then turn on the headlights. Walk around to see how your car looks with just the headlights switched on from the rear. See the pattern of the taillights? If you have someone who can help you, have them press the brake pedal so you can see what your brake lights look like. Now push the fog light button and return to the rear of the car. Notice any brighter lights that are similar in brightness to your brake lights? Then you’ve got rear fog lights as well. Now that you’re aware of this, using them should be restricted to poor visibility conditions — and not to annoy the poor guy behind you. Feel free to illuminate your headlights, driving lights and even front fog lamps (if they can be turned on independently from the rear fog lamps), but save your rear fog lamps for foggy weather. 

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