(Dis)advantages of yellow fog lamps

I have an offer to buy never used yellow Hella 450 auxiliary fog lamps.

Those are quite rare, as most fog lamps are white / clear today.

After doing some search, I found out that yellow lamps (both driving and fog) used to be popular in the past, but that they have been outlawed (at least in EU) since 1990s. Yellow lamps (both fog and driving lamps) were the most popular in France by far, where some old cars still have them.


My question is:
Disregarding any legality issues, do yellow fog lamps have any practical (dis)advantages compared to typical "white" (clear) fog lamps?

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Yellow lamps are not illegal in every part of the world. Their legality is not defined in my country (meaning that they are legal).

My main curiosity is the technical aspect of being yellow. I read some old studies which claim that yellow light penetrates better through fog, but then some newer studies allegedly debunk that as false claims !?



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It really depends on what type of driving you're doing and where. There no significant evidence showing that yellow is better or not better than other lights. In addition whatever lights you get will only be effective and useful if adjusted and used correctly as designed.

Bosanek said:

I have an offer to buy never used yellow Hella 450 auxiliary fog lamps.

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They don't set the world on fire, but they're neat and would look good on the right kind of vehicle. But fog lamps generally don't offer much utility on very modern vehicles with modern headlamps.

After doing some search, I found out that yellow lamps (both driving and fog) used to be popular in the past, but that they have been outlawed (at least in EU) since 1990s.

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Nope, not outlawed in the EU. Vehicles equipped with selective yellow headlamps while they were still legal under ECE Regulation 48 (can't remember the year off hand, probably '93) could still have them, but newer cars were required to have white (although France still permits them regardless of date of manufacture). Cars then so equipped could continue to have them. They're still required in the Principality of Monaco, but probably they don't enforce it.

Yellow lamps (both fog and driving lamps) were the most popular in France by far, where some old cars still have them.

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Were they popular, or just *required until 1993*?

Disregarding any legality issues, do yellow fog lamps have any practical (dis)advantages compared to typical "white" (clear) fog lamps?

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Yellow fog lamps are legal, so no issues there. However, the phrase "legality issues aside" often leads to trouble.

Yellow fog lamps (selective yellow, not "amber"/"SAE Yellow") have an advantage in that for light of a given intensity, light that tends towards yellow is less glaring than light tending towards blue. The light is much more easily processed by the human eye. One advantage they do NOT have is that the light "penetrates fog better" because it does no such thing. It backscatters just as readily as blue light.

Aim is critical. Proper use (at night and 25mph or much slower) is critical.

You're better served with a rear fog lamp; they're useful in a broader range of conditions (for example, truly torrential rain in the daytime) to keep you from getting rear-ended by the guy who thinks his front fog lamps magically enable him to go 70 in a 65. In fact, while front fog lamps are merely regulated in the ECE, rear fog lamps are required (and have been since '79).

Can we occasionally pretend that people are at least intelligent and responsible enough to have some idea of what their local laws are concerning certain items and that they likely know better and are simply getting ideas for how they may solve a given problem. Or y'know, keep driving people away from the forums just because they have a question that they don't quite know how to phrase properly.

France actually used to require selective yellow lights for normal low beams for all registered vehicles in France. This was the result of WWII and the occupation, it allowed the army to immediately identify the invading vehicles by head lights. Of course it didn't last long for that purpose but they kept the regulation for future such events anyway. Because of the reduced glare they kept them around for some time. Eventually though there were studies done and the benefits were determined to be marginal at best. They decided it was better to simply have lights that let you see more (white light) than to require manufacturers to produce ever increasingly bright yellow lights. I believe the filter cut output by some 20-30% they found and simply switching to white improved the test subjects ability to perceive things by so much that they eliminated the requirement.

There is no real question of legality here; yellow fog lamps are legal pretty much everywhere. Yes, there are some advantages to yellow fog lamps; there's a relevant link (which also contains more relevant links) here.

Fog lamps (of either color, and of any brand/model/performance level) are substantially useless. The Hella 450 was/is not an especially super-great fog lamp in either color, though there are other fog lamps poorer than the 450. The Hella 550 was/is better, and the discontinued 550-FF (not to be confused with the current Comet FF 550) was considerably better yet.

lightfooted said:

France actually used to require selective yellow lights for normal low beams for all registered vehicles in France. This was the result of WWII and the occupation, it allowed the army to immediately identify the invading vehicles by head lights. Of course it didn't last long for that purpose but they kept the regulation for future such events anyway. Because of the reduced glare they kept them around for some time. Eventually though there were studies done and the benefits were determined to be marginal at best. They decided it was better to simply have lights that let you see more (white light) than to require manufacturers to produce ever increasingly bright yellow lights. I believe the filter cut output by some 20-30% they found and simply switching to white improved the test subjects ability to perceive things by so much that they eliminated the requirement.

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This is mostly not an accurate history, despite the existence of various car-geek (and car-geek-show) YouTube videos and writeups sprinkled around the internet. France required all road-illumination lamps on vehicles to produce selective yellow light -- not just the low beams. That "military needed to identify invading vehicles" story is one of many myths that grew like weeds over the years (and doesn't make any sense when you think about it...the Germans were probably clever enough to put yellow lenses on their invasion vehicles). There's a well-documented history of this subject here, and also at the link I provided in post #7 of this thread (link here). Peugeot is said to have claimed 20-30% intensity difference between yellow and white light, but that figure seems to have been pulled out of nowhere; if they actually made that claim they don't seem to have provided any support for it (the actual figure, again well documented, is around 15%). And whatever the figure is, a percentage difference in intensity does not necessarily translate to that, or any other, percentage improvement in ability to see. Also, elimination of the white-headlight ban/yellow-headlight requirement in France had nothing to do with test subjects' perceptions and that other stuff you mention. It was purely for uniformity of technical requirements for automobiles throughout Europe, and that is well documented.

As for test subjects and their seeing ability, well, go see those links I provided. It has been studied, but nobody found a significant difference in driver visual acuity for yellow vs. white headlamps.

lightfooted said:

Can we occasionally pretend that people are at least intelligent and responsible enough to have some idea of what their local laws are concerning certain items and that they likely know better and are simply getting ideas for how they may solve a given problem.(sic)

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We run into it time and again where someone starts off seemingly on the right track and then everything goes sideways. Or they go to great lengths to assure us their project is "off road" or "for show purposes". And when they just start off with "legality issues aside", yes, that's often a red flag. However, in this case there are a) no legality issues and b) the rest of the post has merit and is worth answering.

France actually used to require selective yellow lights for normal low beams for all registered vehicles in France. This was the result of WWII and the occupation, it allowed the army to immediately identify the invading vehicles by head lights.

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For dipped *and* main beams (low and high beams). How prescient of them to enact this nearly three and a half years before the German occupation of France in WW2! This is one of those myths that will never die; it's right up there with the "penetrating fog" myth.

Those "invading vehicles" would be using blackout lights anyway-- or if they wanted to use normal headlamps they'd just put yellow lenses on them.

Eventually though there were studies done and the benefits were determined to be marginal at best. They decided it was better to simply have lights that let you see more (white light) than to require manufacturers to produce ever increasingly bright yellow lights. I believe the filter cut output by some 20-30% they found and simply switching to white improved the test subjects ability to perceive things by so much that they eliminated the requirement.

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Selective yellow removes closer to 15% of the light, and that's the useless-to-detrimental BIV portion of the ROYGBIV produced by a properly-fed tungsten filament. This is the light transmission curve of a selective yellow filter; this is the emission spectrum of an incandescent bulb. The takeaway from this is that a) selective yellow filters are quite selective and b) there really isn't a lot of blue light output by a tungsten filament in the first place.

This has GOT to be part of where I heard the 20% from...someone else may have exaggerated it to 30% but it was due to the extra layer of filtering : Old Top Gear video https://www.youtube.com/watch?v=vArQgTQVYcw

Heard some of the war time use from family members, maybe should not have put so much credibility in it. *shrugs*

lightfooted said:

This has GOT to be part of where I heard the 20% from...someone else may have exaggerated it to 30% but it was due to the extra layer of filtering : Old Top Gear video

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Depending on the quality of the filter, it may reduce output and even change the beam pattern slightly because of refraction and certain curves in the glass. A genuine selective yellow headlamp with the color in the outer lens or on the reflector surface fares much better.

Heard some of the war time use from family members, maybe should not have put so much credibility in it. *shrugs*

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I could write a book with all the wrong stuff my family's told me!

lightfooted said:

This has GOT to be part of where I heard the 20% from...someone else may have exaggerated it to 30% but it was due to the extra layer of filtering : Old Top Gear video

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...which is exactly the video I had in mind when I made an earlier comment about "car-geek-show videos sprinkled around the internet". Ha ha, old sport! We're English; fancy a jolly good lawff at the expense of the French, old fruit?

Virgil, do you know where to source selective yellow output led's?

John_Galt said:

do you know where to source selective yellow output led's?

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This is all very familiar. You were told "no" (on two counts) before, and even if -Virgil- now has a source for the LEDs, the part where you hack into a lamp with the goal of improving it (but instead destroy it) is STILL a "No, don't do that."

...and besides, the answer's no. I haven't looked into where to source selective yellow LEDs, because I am not equipped to make productive use of them.

I did not expect that this discussion would grow to this extent. Well al least it produced some interesting info and links.

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Yellow fog lamps are, in fact, illegal in this part of the EU (Slovakia) as I found out when I took my vehicle in for the required MOT a week ago. One original (white) fog lamp was cracked and unfortunately because of that (and the pair of bosch driving lights on a small custom built bracket which apparently have to be written in to the vehicle registration papers - damned draconian!) the vehicle failed the MOT.
I wasn't worried because I was planning to replace the white fogs with a pristine set of Cibie yellow 195 fogs anyway, to which the examiner told me that yellow fog lights were illegal, and only allowed on vehicles built before 1970.
Damn and double damn.

CeeBee said:

Yellow fog lamps are, in fact, illegal in this part of the EU (Slovakia)

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Are they? Slovakia is a UNECE signatory nation and participates in the World Forum for Harmonization of Vehicle Regulations, ECE R19 permits white or selective yellow fog lamps.

Wait...Alaric, are you suggesting there's such a thing as a vehicle inspector who doesn't properly understand the applicable laws and regulations?

That said: R19 (front fog lamps) does provide for both white and selective yellow fog lamps, as does R48 (installation of lighting and light-signalling devices). Whether or not Slovakia can and does ban yellow fog lamps depends on a variety of legal and regulatory factors including whether and which UN Regulations Slovakia applies, and I don't have that info.

Thanks for the replies,
It wasn't just the inspector but also the owner of the MOT facility that mentioned this.
Slovakia also recently introduced a set of vehicle inspection regulations that seem to be the toughest in the EU, and also in some cases acting independently of it. I'm going to see what the new rules say about fog light colour but I don't hold out much hope.

-Virgil- said:

Wait...Alaric, are you suggesting there's such a thing as a vehicle inspector who doesn't properly understand the applicable laws and regulations?

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Did I mention the time I "passed" an inspection on my '65 Dart despite the handbrake not working? I said "Oh, this car was built before 1968 and it isn't legally required to have one" and the inspector was like "Oh, OK".