heezy545i

I've been driving through some fog lately and turning the foglights on/off don't seem to make much of a difference.

Iceman

If the visibility is less than 50 metres you can use them, without headlights, and it makes difference then.
They are for nothing else than for stand alone use on heavy fog with visibility less than 50 metres, so in any other situations they don't do anything for you, just (maybe) annoy others.

Guest

Fog lights are not designed to "cut through" fog -- instead, they are designed for wide illumination of the road immediately in front of your car so that you may see and track the lane dividers (on the left in the US) and the edge of the road (on the right in the US) in dense fog. This prevents you from going off the road or straying into other traffic in dense for.

Use of the regular headlights (or worse yet high beams) in a dense fog does not help because these are aimed too far in front of the car, which is obscured by the fog (in the case of the high beams, the particles of water in the fog actually reflect the light, which can create a blinding effect).

Rudy

Iceman, is that you?

urbo73

If the visibility is less than 50 metres you can use them, without headlights, and it makes difference then.
They are for nothing else than for stand alone use on heavy fog with visibility less than 50 metres, so in any other situations they don't do anything for you, just (maybe) annoy others.
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Incidentally, we had some NASTY fog like I've never seen in Boston here yesterday. Last night I was driving up through New Hampshire, and MAN at times the fog was crazy! It would come and go. There would be stretches of highway that you could be at 60mph on and later out of nowhere you had to slow down to 5mph since a wall of fog would just jump in front of your car. It was rather scary! Anyway, I found that the best thing was as Iceman said. I used my fog lights and just my parking lamps. The less light reflected back by the wall of fog the better. But it wasn't that great to be honest. In truth, in such fog I'd not drive if I knew.

pennetta

It is funny how misunderstood the purpose and function of fog lights. When in fog, with your headlights on, the lights beam straight out and relect back into your eyes thus making it harder to see the road ahead. Ever wonder why fog lights are almost always located on the lowest part of the car, no matter what car, model or brand.
Fog lights are lower so they throw light up at an angle (relative to your eye level, regular headlights have a smaller angle to your eye level)and the light relects back at this larger angle so less reflects back into your eyes and more above your car thus enabling you to see the road farther ahead. Thats why you don't put every light on that your car has because you will get more reflection back.
Its a similar principle with a full moon where the sun is at a smaller angle behind earth (meaning more aligned with it, like your headlights) and a 1/4 moon where the sun is at a greater angle ( father out of alignment, like your fog lights). With the full moon more light reflects back and its more difficult to see stars clearly around the moon. With the 1/4 moon less light reflects back so you can see past it better. In this example the moon represents one water droplet in the the fog.

EBMCS03

Mercedes Older ML like 2000 or 2001 has their fog lights RIGHT by the head lights basically integraetd into the headlight. and NO its not the high beams... you push the FOG button and they trun on. So I dunno how much those would help in real fog...

Iceman

Iceman, is that you?
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No, but I couldn't have it said better!
Perfect explanation!!



Yep, they are only there to help you if you get into heavy fog. When it is that foggy you shouldn't be on the road, but if you are and get into it, you have the foglights that help you find a way through it.



They don't help much.

EBMCS03

They don't help much.
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I dont think it helped at all! IT was a Horrible design... it was like high beams connected to the fog button!

New Guy

The primary fog light is, of course, the increased intensity red on the driver's side rear - it makes it easier for them to see me, from behind.

That is important... not sure though if that is in place (or legal) in the US?