Do Fog Lights Really Work?

I was asked the other day why fog lights were yellow. When I couldn't come up with an answer, I started asking around and discovered, to my surprise, that apparently nobody else could either.

Skiers, shooters and other outdoor types have long known that yellow goggles or glasses enhance outdoor vision. This is because the yellow lenses filter out the blue part of the spectrum and increase the contrast of a scene. But does the same thing hold the other way around? With the goggles, we are filtering reflected light entering our eyes, but is it possible to illuminate something with yellow light and achieve similar results? The answer, apparently, is no (which is likely to raise strong objections from people who have been using yellow fog lights for years).

For expert advice, I contacted the Cold Regions Research and Engineering Laboratory (CRREL) on Fort Wainwright. Captain John Craig of that group then arranged to have a computer search made on the subject of light penetration in fog and mist from CRREL's headquarters in Hanover, New Hampshire. As a result, I obtained a list of over 200 references and abstracts of articles published by researchers all over the world.

Not a single one asserted that yellow light has superior penetrating qualities, but several specifically stated that it did not. To quote from one Russian article, for example:

"Investigations and practices of automobile traffic do not confirm any substantial advantages of yellow light over white light. The advantages ascribed to it may take place only in very thin fog or may be subjectively received by some drivers owing to their individual peculiarities of vision. Therefore, it does not make any sense to switch over headlights to yellow light, although the use of yellow light in special fog lights does not raise any objections." End of quote. The phrasing is quaint, but the meaning is clear.

I had long thought that the yellow sodium-vapor street lamps that are becoming common were used specifically because they cut through fog better. I found out that there actually is a specific reason for their use, but that it is because they operate on only about half the power of conventional lamps.

So, unless you just happen to like yellow, save your money and forget about so-called "fog-lights." They don't exist.