Mythbusting: Yellow Fog Lights

[4ringAR]

I was on the "Yellow Fog Light" train for a while, believing they help you see in the fog/snow/rain. But, as it turns out, there is no science to support the claims.
Here's the two most common myths:
1: Yellow is the most visible color to the human eye.
2: Yellow has a relatively long wavelength and therefore is less refracted by the moisture in the air.

Lets start mythbusting:

1: Yellow is the most visible color to the human eye.
Nope. While it(the 575nm range) is one of the more visible colors, it is actually green, at 555nm.
Here's the response spectra of the cone's in your eyes, normalized.

And here's the normalized relative brightness over all visible light. As you can see its greenish yellow, right around 555nm.

From the Plankian Locus(below) we can see that 555nm correlates to about 5500Kelvin of color temperature.

As it turns out, thats damn close to the temperature of the sun(5800K). It is no coincidence that the human eye is most sensitive to light from the sun.
So, for best visibility, choose an HID bulb in the 5500K range.



2: Yellow has a relatively long wavelength and therefore is less refracted by the moisture in the air.
This is based in truth, 575 is one of the longer wavelengths in the visible range(but not as long as red) and Lord Rayleigh discovered "Rayleigh Scattering" which essentially says that light is reflected/diffused by the molecules in the air, which is why the sky is blue(a mixture of diffused light, more blue and violet, the shorter wavelengths). Similarly, this is also why when you turn your brights on in the fog or snow it practically blinds you, the light is hitting "molecules" and reflecting the light around. So, longer wavelengths become less scattered, this is true, but it is essentially negligible when dealing with "molecules" the size of rain, snow, and fog.


As much as I wanted it to be true that yellow fog lights improve vision....science says it is not.

But atleast they look cool


Feel free to chime in if you have more knowledge in the subject. Ive been exposed to radiation/light in my heat transfer course, but Im mostly self taught in the subject, so maybe my facts arent totally straight.

[awdjunkies]

Nooo!! Say it isn't so. I love my Yellow fogs!!!

[Dcass08]

I got mine because they just look good on the car. I actually almost never use them.

[davvinchi]

While scientifically speaking your theory is partially true, it is not the whole truth, blue is actually harder to focus on than yellow because of where our eyes focus it when focusing all light, because we have more receptors in the green/yellow spectrum as you noted, our eyes can make a sharper image with light in that range. Think about it in terms of dpi for a camera, you have twice the dpi in the yellow/green spectrum as you do in the blue. This is why blue light causes glare, or an inability of our eyes to focus. See the following website for reference. Keep your fogs yellow if you want. Honestly one more reason I think the yellow fogs work is because aside from the fact that the fogs are lower on the car and focused down toward the road, the yellow light is different than the diffused blue ambient light already in the fog (at least during partial sunlight) and gives you some definition between where your fogs are pointing helping you focus better and judge distances.
http://www.danielsternlighting.com/t...ght_color.html

[audinepa]

Thanks for the research, power of suggestion is sometimes stronger than what science can prove or disprove to the human mind.

[TLO03]

Yellow is euro

[aysix]

yellow = ew

[tchuck]

Great thread, thanks.

SfmDRuT2

[eejimm]

I always believe in facts and first principle analysis, being an engineer and coming from a research background. Having said that, I can tell you from years of 4-wheeling in the mountains in the winter that yellow fog/driving lights don't reflect back as much as white ones in heavy snow/blizzard conditions. This is from years of actual driving in these conditions, including in snow-cats on mountains and ski areas. The proper amber lights can make an otherwise impossible situation driveable. It probably depends a great deal on the beam pattern as much as the color, but it is an observable effect. Doesn't mean there's anything wrong with your analysis; it's quite good IMHO. But there may be other effects going on here that are not being accounted for.

I do not have as much experience with this in rain, since out here in the southwestern US nightime driving in rain doesn't happen all that often. Maybe some folks with experience from Michigan or the Northwest or back east or Europe can chime in here.
Jim

[jmgraham78]

so green fog lights?

[4ringAR]

Yellow is euro

French, to be precise ;)

I always believe in facts and first principle analysis, being an engineer and coming from a research background. Having said that, I can tell you from years of 4-wheeling in the mountains in the winter that yellow fog/driving lights don't reflect back as much as white ones in heavy snow/blizzard conditions. This is from years of actual driving in these conditions, including in snow-cats on mountains and ski areas. The proper amber lights can make an otherwise impossible situation driveable. It probably depends a great deal on the beam pattern as much as the color, but it is an observable effect. Doesn't mean there's anything wrong with your analysis; it's quite good IMHO. But there may be other effects going on here that are not being accounted for.

I do not have as much experience with this in rain, since out here in the southwestern US nightime driving in rain doesn't happen all that often. Maybe some folks with experience from Michigan or the Northwest or back east or Europe can chime in here.
Jim

Also being an engineer, I like to base things on quantitative data from controlled experiments, not just personal experiences without controlled variables.
As you noted, a LOT of it has to do with the beam pattern if the light is reflecting back at your eyes, but did you consider that most yellow/amber lights are made with selective-yellow filters, which somewhat reduces the light intensity, meaning there is less light to be reflected back? It would be interesting to measure the intensity reduction of bulbs with yellow coatings, amber lenses, lower temperature bulbs, against a control.

While scientifically speaking your theory is partially true, it is not the whole truth, blue is actually harder to focus on than yellow because of where our eyes focus it when focusing all light, because we have more receptors in the green/yellow spectrum as you noted, our eyes can make a sharper image with light in that range. Think about it in terms of dpi for a camera, you have twice the dpi in the yellow/green spectrum as you do in the blue. This is why blue light causes glare, or an inability of our eyes to focus. See the following website for reference. Keep your fogs yellow if you want. Honestly one more reason I think the yellow fogs work is because aside from the fact that the fogs are lower on the car and focused down toward the road, the yellow light is different than the diffused blue ambient light already in the fog (at least during partial sunlight) and gives you some definition between where your fogs are pointing helping you focus better and judge distances.
http://www.danielsternlighting.com/t...ght_color.html

But noted the most receptors are at about 550nm, so if the temperature of the light peaks at around 550nm, THAT is the most sensitive to our eyes.