Fog doesn’t play favorites with lights

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 did nothing to help you see in fog.

As you probably know, fog reflects the light produced by your headlights, making it hard to see.

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.

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.

Decipher your oil light

Dear Car Talk: When the oil light is on, is the oil pressure low or is the oil level low?

— Bob

Yes.

Unless otherwise noted, a red light that says “OIL” on the dashboard means your oil pressure is dangerously low. Of course, the pressure could be low because you don’t have enough oil in there.

But oil pressure can also be low because your oil pump is failing, because your engine bearings are all worn out and they’re too loose to maintain pressure or for a number of other reasons — none of which are good news.

So when you see a red light that just says “OIL,” that means your pressure is low, and you’ll want to pull over and shut off the engine as quickly as it’s safe to do so.

There are a few cases where the oil light comes on simply because the oil pressure sensor is bad. That’s a lucky break. But, generally speaking, seeing the oil light come on while you’re driving is bad news.

On the other hand, lots of newer cars also come with an oil level light, which is different.The oil level light is designed to eliminate your need to check your oil with a dipstick.

If your car has an oil level light, and it comes on, that’s just a sign that you need more oil.

To sum up Bob, we’re going to send you to your owner’s manual. Look up “oil light” in the index at the back of the book.If you have two different oil lights, you’ll need to know that.

Got a question? Email via the website at cartalk.com.