Yellow for fog lights are best?

So I've been thinking of putting HIDs for my fog lights despite the lack of a lens projector. With this decision comes the responsibility of never using my fog lights in fair weather again. When it's foggy, rainy, stormy, or when visibility is no more than 15 feet, I doubt oncoming traffic can see the glare from my HID fog lights anyway. If they do see my glare, I don't think it would be blinding and they'd probably be thankful to know that my vehicle is there.



I've read (and seen) many times that yellow is the color of choice, that they penetrate fog better. Is this really true?



Before pulling the trigger on a 3000K 35w HID kit, I did a little research. As much as possible, I want my low beams and fog lights to match --6000K.



Here's what I found (link):



The common misconception-

Quote:

My understanding is that it is important for fog lights to be one color (rather than white, which is all colors) because the different wavelengths(colors) of visible light scatter off the fog droplets differently. This phenomenon is known as "dispersion," because the different colors of light in an image will separate from each other, causing the image to "disperse." If you illuminate the road with only one wavelength (color) of light, the images of the objects you see will still become somewhat blurry because of the scattering of light by the fog, but at least you won't have extra problems from dispersion. So, if we want to use just one wavelength of light, which wavelength should we use? It turns out that light with short wavelengths scatters more than light with long wavelengths (short to long: violet, indigo, blue, green, yellow, orange, red). So, a long wavelength light will be best. There's another thing to consider, too: our eyes are not equally sensitive to all colors. It turns out that we are most sensitive to yellow and green light. So, our best compromise between sensitivity for our eyes and a long wavelength for least scattering is yellow light. Now, I don't know what kind of light bulbs are used in fog lights, but another consideration used in street lighting is cost and efficiency. You may have seen some yellow street lighting in some places; this is "low-pressure sodium vapor" lighting. The special thing about this light is that it is almost entirely one (actually two very close together) wavelength of yellow light, and that it gives the most illumination for the amount of electricity. A big problem with this light, though, is that it throws off color perception. Under sodium vapor light, something blue looks gray. This makes it hard to, say, recognize your car in a parking lot. Richard Barrans Jr., Ph.D.

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First I'll give you the wrong explanation, which you can find here and there. It goes something like this. As everyone knows, scattering (by anything!) is always greater at the shortwavelength end of the visible spectrum than at the longwavelength end. Lord Rayleigh showed this, didn't he? Thus to obtain the greatest penentration of light through fog, you should use the longest wavelength possible. Red is obviously unsuitable because it is used for stop lights. So you compromise and use yellow instead. This explanation is flawed for more than one reason. Fog droplets are, on average, smaller than cloud droplets, but they still are huge compared with the wavelengths of visible light. Thus scattering of such light by fog is essentially wavelength independent. Unfortunately, many people learn (without caveats) Rayleigh's scattering law and then assume that it applies to everything. They did not learn that this law is limited to scatterers small compared with the wavelength and at wavelengths far from strong absorption. The second flaw is that in order to get yellow light in the first place you need a filter. Note that yellow fog lights were in use when the only available headlights were incandescent lamps. If you place a filter over a white headlight, you get less transmitted light, and there goes your increased penetration down the drain. There are two possible explanations for yellow fog lights. One is that the first designers of such lights were mislead because they did not understand the limitations of Rayleigh's scattering law and did not know the size distribution of fog droplets. The other explanation is that someone deemed it desirable to make fog lights yellow as a way of signalling to other drivers that visibility is poor and thus caution is in order. Designers of headlights have known for a long time that there is no magic color that gives great penetration. I have an article from the Journal of Scientific Instruments published in October 1938 (Vol. XV, pp. 317-322). The article is by J. H. Nelson and is entitled "Optics of headlights". The penultimate section in this paper is on "fog lamps". Nelson notes that "there is almost complete agreement among designers of fog lamps, and this agreement is in most cases extended to the colour of the light to be used. Although there are still many lamps on the road using yellow light, it seems to be becoming recognized that there is no filter, which, when placed in front of a lamp, will improve the penetration power of that lamp." This was written 61 years ago. Its author uses a few words ("seem", "becoming recognized") indicating that perhaps at one time lamp designers thought that yellow lights had greater penetrating power. And it may be that because of this the first fog lamps were yellow. Once the practice of making such lamps yellow began it just continued because of custom.

Reply 1 : Yellow for fog lights are best?

There is a reason 90% of foglights on factory vehicles or any of the big light manufacturers aren't yellow anymore, they aren't needed.

Reply 2 : Yellow for fog lights are best?

Gosh, I don't think I've seen yellow fog lights on a car in maybe 20 years. When driving in a snow storm at night I found the OEM fogs on the Sienna to be very effective in increasing the width of my viewing area.

Reply 3 : Yellow for fog lights are best?

It was this post that got me curious which then got me to do some research. Since I value humanoid's opinion, I considered yellow HIDs despite the ugliness (IMO). But I'm glad I found out that yellow isn't much better than any other colors. I really would like my HIDs to match.

Reply 4 : Yellow for fog lights are best?

Quote:

Originally Posted by 05Limited Gosh, I don't think I've seen yellow fog lights on a car in maybe 20 years. When driving in a snow storm at night I found the OEM fogs on the Sienna to be very effective in increasing the width of my viewing area.

All Lexus IS300's, and 98-05 Lexus GS400-430 with HID option have OEM yellow fogs.

Reply 5 : Yellow for fog lights are best?

I've finally installed my Xentec HID kit with slim digital ballasts. The install was really simple, but hiding the wires and ballasts took a little creativity. I'm pretty happy with it except for the flickering on the driver's side. The flickering eventually disappeared but I'm still worried it might come back. I also noticed that when I turned the key, the car would suddenly die. This happened about 5-6 times while I was finishing up my installation, but I couldn't recreate the problem after I finished. I don't know if maybe I left the battery terminals loose.



I used to just leave my headlights on after I had shut down the engine and the lights would stay on until a door was opened. The opposite would happen when I start the car, the engine would start first and then the lights would go on.



Out of habit, I left the HIDs on and when I shut the engine down, they turned off right after I turned the key. I realized my mistake and made a mental note to always turn off the headlights just in case this isn't good for the battery. I noticed that the headlights turn on/off at the key's turn, not the engine starting up or when opening a door when the engine is off.



Can anyone tell me if it's still a good idea to leave the headlights on when turning the engine off?



Oh, thanks to Biggoldfish for selling me his spare harness!