Thread: Let's have a general discussion on fog lights

Originally Posted by Roverlord off road spares

remember when fog lights were yellow and areas in towns which were subjected to frequent fog had yellow overheard street lights, white lights are not very good cutting through fog.

Back in the 70's all French registered cars had yellow headlamp lenses. Then someone worked out that yellow lamps reduced glare by 15% because they reduced the light output by 15%. Now everything's white, works just as well so long as it's aimed properly.

Originally Posted by austastar

Hi,
My impression was that the beam columnation was low and flat to shine under the fog layer and along the road as much as possible so as to not illuminate airbourne fog which simply reflects as a white glare.

So I googled it

How do fog lights work? - Quora

Not exactly a peer reviewed article, but it makes sense.

Cheers

And how do you think you then See that light?

The light is flatter, and is looking to reflect back.

But on a dry clear day it reflects towards oncoming drivers... and look at the profile.
The last thing that happens is the approaching vehicle gets that beam in their face...





The beam is also only effective for around 30mtrs for the driver and at that point is losing effectiveness..

That distance is covered in 1 second at 100km/h.

Even if you did spot something hopping out from the side in that light, you can not, absolutely can not, respond to it in that 30mtr zone...

Human brains and reaction times can not calculate or react that fast.

Hence why decent driving lights are essential for regular night driving; you’re out driving the light before you can react.

Hi,
In the article I googled there was an explanation of the vertical pattern of fog lights and how they are designed to penetrate under the fog.

i.e.



The lamp is mounted as low as possible and is pointed down 4 inches in 25 ft (101mm in 7,620mm) so if the light is at (say) 200mm off the ground on a city car, the light is aimed about 14m in front of the vehicle.

• Not very far.
• Not for driving at speed.
• Only useful in fog and foul weather.

Aimed correctly (as above) they should not dazzle an oncoming driver.

My hypothesis is then, that any fog light (if indeed it is a fog light) that dazzles an oncoming driver is either:

a) not a fog light.
or
b) is incorrectly fitted.

Cheers

Im thinking of putting a pair of yellow hella fog lights on the d90. Rally style!

On my last trip out in the dust I had to do some night driving. A car, or worse a passing truck, would kick up a wall of dust for 100s of meters! Even the dipped beam glared back at me. Couldnt see a thing.

Im curious to see how much difference yellow fogs make.

Forward facing fog lights on euro cars have never bothered me. Rear foglights on the other hand can be annoying when following on a dark country road.

HID or missaligned headlights can actually dazzle. And those who forget to dip or dip late are the worst!

Originally Posted by austastar

Hi,
In the article I googled there was an explanation of the vertical pattern of fog lights and how they are designed to penetrate under the fog.

i.e.



The lamp is mounted as low as possible and is pointed down 4 inches in 25 ft (101mm in 7,620mm) so if the light is at (say) 200mm off the ground on a city car, the light is aimed about 14m in front of the vehicle.

• Not very far.
• Not for driving at speed.
• Only useful in fog and foul weather.

Aimed correctly (as above) they should not dazzle an oncoming driver.

My hypothesis is then, that any fog light (if indeed it is a fog light) that dazzles an oncoming driver is either:

a) not a fog light.
or
b) is incorrectly fitted.

Cheers

I agree in principle, however I will say that I drove for many years in Europe and I will say that fog lights even correctly aligned do dazzle, especially on wet hot mix, not so much on the roads in Australia, however the more water, the more they dazzle. Respectfully i say that although it gives an allusion of “seeing better” it actually does not make much of a difference. It just lights up the first 25 feet or so, which at 100kms is really useless and unless they are badly aligned the do not and should not shine out into the bushes on the side of the road.
Written from my point of view with no bad intentions or malicious intent. Have a good day

Fog lights are designed to not glare the driver OF THE VEHICLE USING THEM.

The low positioned beam bounces up off the road into oncoming drivers...

Light is all about reflection, refraction and absorption. Our vision depends on it.

So hypothesise as much as you like...
Factory set, correctly adjusted, fog lights will dazzle oncoming drivers.

Originally Posted by manic

Im thinking of putting a pair of yellow hella fog lights on the d90. Rally style!

On my last trip out in the dust I had to do some night driving. A car, or worse a passing truck, would kick up a wall of dust for 100s of meters! Even the dipped beam glared back at me. Couldnt see a thing.

Im curious to see how much difference yellow fogs make.

Forward facing fog lights on euro cars have never bothered me. Rear foglights on the other hand can be annoying when following on a dark country road.

HID or missaligned headlights can actually dazzle. And those who forget to dip or dip late are the worst!

In those instances you can dip to Parker’s if you’re game..

The yellow just reduces output more than anything so gives less light therefore less glare..