[whitej47]

Please consult the chart above

[BestmpgxB]

??? It shows me the wavelength of yellow light is on the long end of the visible light spectrum.

From the Wikipedia article I cited earlier (bolding mine),

Front fog lamps
A pair of yellow fog lamps

Front fog lamps provide a wide, bar-shaped beam of light with a sharp cutoff at the top, and are generally aimed and mounted low. They may be either white or selective yellow. They are intended for use at low speed to increase the illumination directed towards the road surface and verges in conditions of poor visibility due to rain, fog, dust or snow. As such, they are often most effectively used in place of dipped-beam headlamps, reducing the glareback from fog or falling snow, although the legality varies by jurisdiction of using front fog lamps without low beam headlamps.

Use of the front fog lamps when visibility is not seriously reduced is often prohibited (for example in the United Kingdom), as they can cause increased glare to other drivers, particularly in wet pavement conditions, as well as harming the driver's own vision due to excessive foreground illumination.

The respective purposes of front fog lamps and driving lamps are often confused, due in part to the misconception that fog lamps are necessarily selective yellow, while any auxiliary lamp that makes white light is a driving lamp. Automakers and aftermarket parts and accessories suppliers frequently refer interchangeably to "fog lamps" and "driving lamps" (or "fog/driving lamps"). In most countries, weather conditions rarely necessitate the use of fog lamps, and there is no legal requirement for them, so their primary purpose is frequently cosmetic. They are often available as optional extras or only on higher trim levels of many cars. Studies have shown that in North America more people inappropriately use their fog lamps in dry weather than use them properly in poor weather.

---------- Post added 10-27-2011 at 12:17 PM ----------

From another source:

There is no good reason why fog lights are yellow. Here is an excellent explanation provided by Professor Craig Bohren of Penn State University:

"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."

[Zman]

Its added safety so other drivers can see you in poor weather.

[Waldo]

Fog lights are considered fog lights by being lower than your headlights, so when in fog, the light doesn't reflect back at you.
And if you use a filter to make your lights yellow, then you do lose some light, but hids ignight gasses, and with the proper power they output yellow (if your looking for true yellow light).
Idk if yellow is better than white, but if you like the style, who cares. As long as it does its function of lighting your way....

[whitej47]

I have Ichikoh heads when the "highs" are activated, both lights light up. I have 3000K in my highs for a fog function and it is much better for seeing in foggyness. All of the Albert Einsteins can kiss it...that is the problem with most of physics, no REAL world application.

BESTmpg, no one really regards wikipedia as a reliable source due to peer editing functions. People use it, but it isnt considered valid in most discussions. Colleges do not accept it as a source cited.

[BestmpgxB]

Whitej47,

Prof. Bohren gives a scientific explanation why yellow light isn't better, and references back to 1938 showing it's been accepted knowledge.

I've seen enough of your posts to know you're very knowledgeable, but you're going to have to give me a scientific rationale for yellow light improving seeing in fog, because testimonials are the "proof" used by scoundrels, and anti-science is the parrot-talk of scumbag politicians.

---------- Post added 10-28-2011 at 09:00 AM ----------

BTW, I was walking on a coastal trail in the Marin Headands of Golden Gate National Recreation Area some years ago, and came across an instrument alongside the trail. It had a light beam on one side and a photosensor on the other side. I can't remember other details, but after some deliberation, we agreed it was a fog sensor, to automatically trigger a light beacon and fog horn. Science is wonderful. I'd much rather fly in a plane designed by scientists than in one designed by artists.

[Zman]

I know, based on my eyesight, that yellow lights make it much easier to see in the rain, compared to white, much less glare, and more distinction.

Fog lights, even in fog, shine too low to really be helpful, in many cars/trucks.
I just think for me they help other drivers distinguish where my car is.

[Zman]

Btw don't get me started on this Jesus over science gibberish that politicians use to stir up the unintelligent masses.

[PCH]

Originally Posted by Zman

I know, based on my eyesight, that yellow lights make it much easier to see in the rain, compared to white, much less glare, and more distinction.

That's my opinion also.

[SH0RTBUS]

Slightly off topic but does anyone have pics of their xb with yellow bulbs in the factory fogs? Thinking about getting some yellow 9006 bulbs for my OEM fogs.

[whitej47]

I missed these updates somehow...

The science is not lost on me. I am 3 years post-grad with a BS in Environmental toxicology and a second in Bio-chem, so to say I have had my nose in a book is an understatement lol. I got tortured thru my physics class.

E=((h x c)/wavelength) - (read: h multiply c)



yellow light, being mid-spectrum, is on the order of 550nm. or "semi-intense" if you will. The energy of the light is inversely proportional to it's wavelength. Since "h" and "c" are both constants, the energy will depend solely on wavelength. My only guess as to why yellow is this:

-higher wavelength(lower E) than blue/purple, you can also find a similar increase with Kelvin rating on HIDs
-you can't use red (lowest E) on the front of your car for obvious reasons...did anyone actually ask "why?" lol
-if blue/purple were used they would blind oncoming drivers, much like the obnoxious raised truck bros in most of hella-so-cal
-yellow penetrates the fog and doesn't bounce back (efficiency), added clarity in fog without the self-blinding effect

That's all I got. I just know I see better with yellow. As for physical location of the fogs, there should be glaringly obvious reasons as to why the fogs aren't located in the exact headlight location(caused it's the best for vision). There are also reasons for mudding trucks to mount lights atop their vehicles for increased visibility...ultimately, I think it is a balance. But I have been in many cars with dual HIDs (heads/fogs) with the same K rating and they re useless with higher temps.

Rebuttal?

[Zman]

Originally Posted by SH0RTBUS

Slightly off topic but does anyone have pics of their xb with yellow bulbs in the factory fogs? Thinking about getting some yellow 9006 bulbs for my OEM fogs.

The Nokyas burn very hot. They look really good though, you should be fine with OEM harness, I had a different connector and it melted slightly. So now I'm running LEDs.

[supermario6582]

Originally Posted by Zman

The Nokyas burn very hot. They look really good though, you should be fine with OEM harness, I had a different connector and it melted slightly. So now I'm running LEDs.

I had those in my fogs and they got so hot they melted the wiring harness.

[Zman]

Originally Posted by supermario6582

I had those in my fogs and they got so hot they melted the wiring harness.

Maybe not!

[Zman]

I guess you'd need a special harness to run Nokyas...

[Slimatmim]

Ok I did the Walmart fogs with Krylon saint glass paint yellow and here is the out come. Thinking of putting in 3k hids in them to make them more yellow.

[Waldo]

those look nice, and hids will brighten the fogs up too

[BestmpgxB]

whitej47,

I didn't see your last reply in this thread until today. Since the thread has been revived...

Originally Posted by whitej47

I have Ichikoh heads when the "highs" are activated, both lights light up. I have 3000K in my highs for a fog function and it is much better for seeing in foggyness. All of the Albert Einsteins can kiss it...that is the problem with most of physics, no REAL world application.

??? You can't be serious. The higher up your lights are mounted and pointed (within practical headlight/fog light aiming limits), the more light scattering occurs in fog/mist/snow. If, as you claim, you're seeing better in fog with your high beams, you're not driving in fog.

As for real world application, if yellow light were more visible than white light in foggy conditions, we'd have seen yellow lighthouse lenses placed into use during the 223 year history of the U.S. Lighthouse Service and the U.S. Coast Guard. How many yellow lighthouse Fresnel lenses (as opposed to signaling panels) have you seen? How many yellow lighthouse lenses did the U.S.C.G. install over the years? The answer tells you how well yellow fog lights work in the real world.

I'll take Dr. Bohren's Ph.D. against your industrial toxicology studies. I've got a minor in physical science, myself. It's just enough education to tell me when I'm in deep water in physics discussions.

I haven't driven in rain in cars with yellow fogs. The discussion is about driving in fog, not driving in rain.