Dear Car Talk:
Why aren’t the fog lights on newer cars yellow in color? They are often plain glass, with white lights. They don’t even use yellow bulbs. Why is that? -- Ross
Because yellow lights don’t help with fog.
I guess someone once thought that yellow light somehow cut through fog better. He probably mansplained about the Rayleigh law and wavelengths of various colored light. And he was completely wrong.
But he was apparently very convincing. And hugely influential in the fog light industry. Because back in the 1960s and ’70s pretty much all fog lights had yellow lenses.
They certainly looked cool. I’ll give them that. But they did nothing to help you see in fog.
As you probably know, fog -- which is droplets of water -- reflects the light produced by your headlights, making it hard to see.
You probably also know that turning on your bright lights in fog only makes visibility worse because more light gets scattered and reflected back to you.
The only thing that helps at all in fog are lights that are positioned and aimed very low, toward the street. And that’s what proper fog lights try to do: light up the actual road right in front of you, shining as little light as possible directly into the fog at eye level.
Under certain conditions, that can help. But honestly, fog is tough. Sometimes, you just have to slow way down or pull over and wait it out.
The good news is that while yellow light doesn’t do any better in fog than white light, it doesn’t do any worse, either.
I mean, a yellow lens (or anything other than a clear lens) will reduce the sheer amount of light that gets through. But the color itself won’t aggravate the situation. So if you like yellow, Ross, go get a highlighter and have at it.