Moviela

That has not been true since the sixties. Even France has given up on the yellow fog light. Osram, Kodak, and GE have all contributed to the body of research that shows humans can see better with white light in foggy or other inclement weather. If you want yellow as a fashion statement, thats fine, but fogs are white now. They should only be used when it is foggy, not so you look kewl.

traderfjp

I've been in fog and white light reflect back while yellow light makes it possible to see. I'm not sure where they are getting their research.

Moviela

Your confusion about yellow fog lights is not surprising, since a lot of the reasoning behind the selection of yellow as a fog light color had nothing to do with physics.

I've heard two reasons cited as the rationale behind the use of yellow fog lamps:

(1) yellow lamps suffer less backscatter into the eyes of the
car's driver than blue or green, allowing them to see better in the fog.

(2) yellow lamps are more readily seen by an oncoming driver, so that a car with fog lights on will be seen more readily than white lights would be.

The first point is true for light scattered off very tiny aerosol particles in fog. Blue light is scattered out of the path from the sun to the viewer of a sunset, leaving white light minus blue to reach the observer, so he/she sees yellow/red - but is pretty irrelevant for the kind of yellow lights used for fog lamps. Those lamps were generally made by putting yellow filters over a hot tungsten filament incandescent lamp, so that a lot of light is lost in trying to make the yellow light, reducing the brightness available for the driver to see, which is not such a good idea. Using a halogen gas fill increases the brightness of the bulb, but the same general principle of reduced brightness still holds. Additionally, the size of water drops in fog is generally not appropriate for producing the kind of scattering I mentioned above. If so, headlights would appear very red to oncoming traffic, which they don't.

The second point, that the yellow color is more visible to oncoming traffic is also true, but irrelevent as well. The point of fog lights is to allow the car's driver to see better, not to be seen better. If you wanted to be seen better, a flashing strobe would be more effective, but you don't see much of those in the fog light business.

Most likely, the real reason that people have used fog lamps that are yellow is that they look so cool. Realistically, most people do not drive a lot in foggy conditions. Certainly not enough in most cases to justify the cost of expensive additional lights.

Greater penetration of the fog without a "whiteout" is best realized with a low mounted lamp, with a sharp cutoff so the beam does not illuminate above the bumper. A good portion of fog encountered is about a foot to eighteen inches off the ground. White lamps with the beam focused into this space will yield the greatest visibility.