What's the deal with fog lights?

February 1, 2007 3:28 AM

How best to use the fog lights on my car?

So I grew up in a place with infrequent fog, and only recently have owned a car with fog lights (small, white forward facing lights at the bottom of the front of the car).
Presumably, I should just turn them on whenever it is foggy, but since I've never had a discussion with anybody about them...
Are they mainly for use in fog during daylight? Turn them on with my main headlights or without?
To tell the truth they don't seem to do much. Are they meant for visibility to other drivers? And if so, why mount them low?

posted by bystander to Travel & Transportation (23 answers total)

Generally I find that using the fog lights in heavy fog (visibility under 40 feet or so) makes it harder to see anything except the fog. How to use them will vary with your car and the sort of fog you have. Use them if they help, and always use your main low beams in the fog so other drivers can see you.
posted by yohko at 3:57 AM on February 1, 2007

The rationale for positioning fog lamps as low (or high, if you've got an SUV with rollbar lights) as possible is that the increased angle of illumination (relative to your eyes) reduces the glare of the lights off millions of water droplets.

If your car's headlights are already pretty low to the ground, or the fog lamps are significantly brighter than the head lights, or the fog lamps aren't aimed properly, there's no point to them, and a pair of properly aimed low beam headlights are just as good and meet vehicle code as well.
posted by ardgedee at 4:19 AM on February 1, 2007

I have the idea that what some car builders are calling "fog lights" are nothing of the kind. Fog lights should be used in heavy fog instead of the main headlights, not in addition. The theory is that the fog lights are aimed lower, and not as much of their light is reflected back at the driver by the fog. On some cars, you can't turn the "fog" lights on without having the main lights on. Those are useful for lighting the areas off to the sides of the main lights, like when making a turn, but using them in fog isn't much help. Also, using them on the highway in clear weather is useless and borderline rude.
posted by Kirth Gerson at 4:21 AM on February 1, 2007 [1 favorite]

I agree with Kirth Gerson.
When in fog use only the fog lights.
Turning on your main lights negates the effect.
posted by lorbus at 5:32 AM on February 1, 2007

I have a toyota matrix ... the fog lights only go on in addition to the always-on headlights. I've tried to use them in fog and they really do nothing to help my visibility. Sometimes on really dark roads with no street lights, they help my visibility by giving me a wider field of light.

I see a lot of people driving with their fog lights on all the time, probably either unaware that they are on, ignorant about how to turn them off, or arrogant about having four lights on instead of two. Sometimes the additional lights are positioned to be more blinding at night to other drivers.
posted by indigo4963 at 6:10 AM on February 1, 2007

Hmm. I am one of those borderline rude folks who drives with his fog lights on during the day. I can use them independent of my main lights. I thought (and am not yet convinced otherwise) that I was providing a benefit to other drivers and thus myself. It gives others the ability to see me or be aware that I am there (more visibility). I also assumed that they were better than my low beams because they sit so much lower and had a much lower probability of causing glare in the rear view mirror of the person in front of me. I drive a small pickup, but my low beam lights are higher off the ground than most cars although on par with most SUV's. I don't understand the rudeness part of using your fog lights in clear weather. They add visibility.

Rude is when I flash my high beams or honk at you to get the fuck out of the passing lane when you are not passing anyone. Rude is when I give you the finger for going slower than me. Rude is when I am on my cell phone not paying attention to the road. Rude is riding on the shoulder of a heavily trafficed highway just to get to the exit faster. Rude is when, in stop and go traffic, I pass 4 cars by going into the onramp. Rude is when I am burining oil and leave that wonderful bluish cloud behind me for all to suck on. Rude is not letting you move into the right lane to get off at the next exit because I have been sitting in this stopped traffic for the last two hours and I'll be damned if I let one person get ahead of me.

Rude is not using your fog lights on a clear day.
posted by JohnnyGunn at 6:45 AM on February 1, 2007

My Subaru is one of those where you have to have the headlights on to use the fog lights, like indigo4963's Matrix. It also has daytime running lights, which further compromises the fog light's utility. Ideally, turning on the fog lights should turn off the headlights and daytime running lights, but keep the taillights on. Maybe I can find someone to make that modification.
posted by Kirth Gerson at 6:47 AM on February 1, 2007

Johnny, I wasn't talking about using fog lights alone, in the daytime; I meant using them at night, along with main lights, and - as I said - on the highway.
posted by Kirth Gerson at 6:52 AM on February 1, 2007

I agree with Kirth on this one.

The reality is that the "fog lights" on most new cars are pretty useless. Use them as daytime driving lights if you want to get your money out of that option!
posted by HuronBob at 7:03 AM on February 1, 2007

JohnnyGunn, dear god no you're not doing anyone a favor, unless you think blinding them is a favor! Roads do reflect light, you know! It's not as bad during the day as it is at night, I'll grant. If you're doing it in the rain, you're just being an asshole.

Also, I've always been told fog lights aren't to help you see better, they are to help other drivers see you.

On the car I drive with them, I use them in combination with the high beams at night, as they are really just better for illuminating the road directly in front of the vehicle, which the high beams don't do. When passing a car, I turn off both the high beams and the "fog" lights.

BTW, your owner's manual should indicate the conditions under which the fog lights are appropriate to use. ;)
posted by wierdo at 7:12 AM on February 1, 2007

Fog lights are used to light the lower ground area immediately in front of the car. The lower height and direct angle helps to mitigate the Tindall Effect of suspended water in fog causing blinding reflection. Fog lights should only be used in a situation when fog is very thick, to the extent you can see the edge of the road and not go off the path. Fog thick enough to require fog lights means you can't drive more than 20mph.

What happens when you use fog lights all the time, in non-foggy applications? The fog lights cause a bright reflection on the road more immediately in front of you, compared to the lighting pattern of your headlights. This causes a bright region closer to your car and effectively limits your night-time vision. You will actually see less driving at speed with fog lights, than with just headlights, or with high beams.
posted by morallybass at 7:35 AM on February 1, 2007 [1 favorite]

There are also pretty usefull on mountain roads by night, to see what's on the side of the road before a very steep turn.
posted by rom1 at 7:41 AM on February 1, 2007

I do not use my fog lights at night. Ever. They are a waste as far as seeing in fog or adding illumination to my low or high beams. I use them to make myself more visible in the daytime rather than have my low beams on during the day.

My question is do the fog lights cause the same reflection during the day off the road as mentioned by morallybass and weirdo? If it was a binary decision between fog lights positioned in my front bumper or my low beams for use as added visibility of my truck to other cars on the road during the day which would be safer or less intrusive to other drivers?

My goal is and has been to help the situation not cause problems. Why do many new imported cars have their headlights automatically on during the day?
posted by JohnnyGunn at 7:43 AM on February 1, 2007

In many jurisdictions, running fog lights independent of headlights is illegal.

Why do many new imported cars have their headlights automatically on during the day?

Daytime running lights make your car more visible to others.

In most cases this is why I use my fog lamps in poor weather. My car is fog colored so anything to help people see me is good.

My car also has a read fog lamp. It is bright red and at first blush looks like I have an extra bright brake light, just on one side. Again, this used so people can see me. It also comes in handy for when assholes are tailgating me to get them to back off.
posted by birdherder at 8:36 AM on February 1, 2007

Good question! Thanks bystander. My 92 Saab convertible has (had) factory fog lights. Like many others, mine got smashed off with repeated scraping against steep driveways. So, I have been considering installing new ones, but frankly, mostly for looks. But I have read other Saab owners opinions that they really do help most in situations where you might use your high beams. Supplementing the high beams with the fog lights is supposed to give better overall visibility. Living in Montana, with plenty of areas where high beams are in use, the fog lights might be a good idea.

Sorry this answer is based on my own experience. But this usage of "fog" lights is what I am basing my upcoming purchase on.
posted by The Deej at 8:37 AM on February 1, 2007

I asked this question on Askville a few months ago: "What's the etiquette for using fog lights on a car? " There were some pretty good answers, including references to semi-expert opinion:

- Daniel Stern Lighting, What are Fog Lamps Really For?
- Fog Lights are for FOG!!

After reading those articles, and thinking about the subject a while, my opinion is: Fog lights are useless on any lit road. They're useless if you're going high speed. If you're going low speed on an unlit road, fog lights can "fill" the gap between the normal headlight and the bumper of the car. Depending on the model of car and how the headlights are aimed, that gap can be tiny, and on those cars, fog lights are pretty much useless, too.

I still think they look kind of cool, though.
posted by IvyMike at 8:58 AM on February 1, 2007

There are two types of "auxiliary" lights on cars: Driving lights and fog lights.

Driving lights are usually white colored and are aimed far into the distance to light the road when driving in good conditions. They are sometimes used in place of or in conjunction with high beams. These are generally not be be used if there is oncoming traffic (for the same reason high beams are not to be used- they blind oncoming traffic).

Fog lights are ideally yellow lights and are aimed low, below your normal low beams. They make it easier to see the road immediately in front of your car in fog, heavy rain or snow, and the yellow light helps make things more distinguishable. Good fog lights work well when used with your normal low beam headlights.

Nowadays, a lot of fog lights (especially the white ones) aren't really fog lights at all; they are just bling to make the car look pretty.

If your car has fog lights that are properly aimed as fog lights (when you turn them on when the car is pointing at a wall, you see a distinct cutoff below your low beams), but they are white, you can make them more effective as foglights by switching to a yellow-colored fog light bulb.
posted by Doohickie at 9:01 AM on February 1, 2007

JohnnyGunn, if it's daytime, and it's not raining, just turn the damn lights off, unless it's an issue of the sun being behind you.

Daytime running lights are for Canadians and for ignorant people who will drive around in the rain and heavy snow without any lights on.

And as others said, if your fog lights aren't yellow, they're not fog lights at all. When I was growing up we had a Mercedes that had awesome yellow fog lights that would cut right through the fog (and made the car much more visible to others). The car I use the fog lights in conjunction with the high beams on has yellow fog lights.

My Honda just runs both low and high beam bulbs when the high beams are on, negating the need for extra lighting, although there are times I would appreciate some yellow lighting.

I really need to learn to read, as I didn't notice that bystander had pointed out in the question that the "fog" lights in question are white.
posted by wierdo at 9:44 AM on February 1, 2007

Consider my fog lights turned off.
I'll be the guy doing 70 answering emails on his Blackberry while driving the Major Deegan or Cross Bronx Expwy without his fog lights on.
posted by JohnnyGunn at 10:40 AM on February 1, 2007

One other thing... Many states allow no more than 2 pairs of projecting lights on the front of the car be on at a time.

So, you can have low beams and fogs,

Or low beams and driving lights,

Or low beams and high beams (on many cars, low beams stay on when high beams are on),

but NOT low beams, high beams and fog lights or low beams, high beams and driving lights. You can get a ticket for that.

(That's one of the reasons many cars are wired to turn off fog lights when you put on your high beams.)
posted by Doohickie at 11:29 AM on February 1, 2007

More light is better than less, I always have mine on when I have my lights on.

However the rear fog I only use in poor visibility (as it is a distraction to drivers.)
posted by mphuie at 2:29 PM on February 1, 2007

More light is better than less

Not if you're aiming into the eyes of oncoming drivers...
posted by Doohickie at 6:56 AM on February 2, 2007

This is good info, thanks. I just bought a new GTI and was wondering a. when to use them and b. why they were yellow. The car has lovely xenon headlights, such that I never feel the need for more light or visibility. At least, not yet anyways.
posted by jimmythefish at 10:32 PM on February 4, 2007