In the mid to late 90s, car manufacturers started placing "fog" lights (or "driving" lights) on just about every new car. Fog lights can be very useful if designed correctly. But they can also be very dangerous to everyone else if designed poorly. <
When I was younger, I thought it looked very cool to drive around with all my lights on (I now know where the expression "running around with your headlights on" came from). I figured that if I put all the lights on, everyone would see me. When you're 19, you want everyone to see you. I also thought it made my car look "cool" - just like car commercials make driving on wet surfaces look "cool". But what I failed to recognize at the time was my fog lights didn't have the desired effect. Particularly on a clear day, they could be blinding to oncoming traffic, as well as the people driving in front of me, having the opposite effect and making it harder for me to be seen... or worse, causing other drivers to dim their mirrors of look away because of my fog lights.
When I lived in Europe, I studied many of the driving laws and discovered they took a very different approach to the use of fog lights. After I understood the motivation for their laws, I could never return to my old bad habits. Fog lights are generally for FOG and must only be used in appropriate conditions. In visibility of less than 100 yards (meters), one may use front fog lights. The rear fog light, usually a single red light as bright as a brake light, may only be used in visibility of less than 50 yards (meters). Of course, they are called fog lights because rarely does your visilbility drop to such a dangerous level in normal rain or snow like it can in fog.
When there is fog, you cannot see normal distances, particularly on the highway, and this can be very disconcerting. The better your long-distance eyesight, the more dramatic the change is from normal driving. This can cause intense anxiety. That is why you must drive so much slower in foggy conditions. Many times I would drive the Autobahn in thick fog, conscious of the news stories of horrible fog accidents (nebel unfalle), worried that I would be part of the next 100-car pile-up. In this situation, fog lights can save your life. Unlike high-beams, which simply light up the fog, fog lights light up the road below the fog. As well, the fog light reflectors are designed to spread the beam wider for a shorter distance.
Unfortunately, many fog lights on American cars are designed particularly poorly. Sadly, fog lights in many Asian and European cars are not designed well either. The US Department of Transportation has minimal regulations for these types of lamps. However, due to numerous complaints, they appear to be trying to address this situation (see this article). Fog lights that are not designed to be an integral part of the front grillwork require extreme precision to insure proper positioning. When these lights are out of adjustment, they blind oncoming traffic. Therefore, it is essential that they are adjusted properly and checked fairly frequently. Nonetheless, fog lights that are integrated into the body of the car must also be used carefully. They also may go out of adjustment, since they are often not designed as carefully as low-beam headlamps. Aftermarket fog lights are particularly sensitive to adjustment unless particular attention is paid to the design and construction of the mounting hardware.
Some people have written to me explaining that they use fog lights "to light up the edges of the road". Well, I'm sure their lights work that way, but this doesn't justify blatant disrespect for other drivers. You should think of these lights in the same manner you think of high beams and once again follow the Golden Rule: Do Unto Others... If you are alone on the road, use your fog lights all you want, since we all won't be there to be blinded by them.
So, if you want to be thought of as a courteous driver, don't light
up your car like a Christmas tree. Make sure all the normal lights
(markers, directionals, parking lights and low/hi beams) are working.
Please remember to use your headlights in the rain. Use the fog
lights only when you have very low visilibility, and don't forget
to turn them off when the fog has lifted! All those that have to share
the road with you will genuinely appreciate your kind consideration.