Will pencil beams penetrate fog?

[CeeBee]

Hello
I'm new to the forum and have a question to which the answer has been eluding me for 40 years.

Back in 1976 I bought a small book called 'performance rallying'. In it were chapters written on various topics, including a chapter on lighting written by a man called Kern Fisher, who sold, among other things, Marchal lights.

In describing the various lighting options on rally cars, he said of spot lamps - I take it he meant pencil beams - "Spot lamps have occasionally been used to penetrate heavy fog although the scatter will normally create glare. If you can tolerate the glare, the intensity will illuminate an object before any other light".

Now I've never rallied but do own an old pair of Bosch Rallye 8" pencil beams that I had on my 4x4 pickup back when I lived in Canada. I took them off after the first outing as they were simply useless for everyday use - two little dots dancing far into the distance, illuminating everything but the road in front of you - and never had a chance to use them in heavy fog to test their usefulness. Heck, where I lived we didn't have any fog.

Now, while I still have the lights, I live in Europe and those big lights hanging off the front of my Renault are not an option on these roads. I use the stock (useless) fog lights and low beams and slow down like everyone else in heavy fog.

I would really like to know if anyone has had experience using pencil beams to cut through fog. Does it actually work? And if it does, how far can you see with them in fog?

 

[FRITZHID]

Well, as far as fog goes, you'd want your lights as close to the ground as possible, but after that, yes pencil beams punch thru fog quite nicely but like your post says, the backscatter can be blinding, hence the lower the light, the better.

 

[greenlight]

They will certainly will help people to see you.

 

[Alaric Darconville]

The extreme backscatter will mean that your pencil beams will leave you worse off than before.

Real fog lamps produce a wide beam of light designed to light up the road edges and lane markings for super-low crawling ahead.

 

[CeeBee]

Thanks for the replies.

I take it that mounted anything above license plate height the glare would defeat the purpose, mounted around the same height as fog lights they will cut through fog to some extent without the glare being so intolerable?

 

[-Virgil-]

No. Spot beams are not the right tool for the job of driving in fog. And fog lamps (of any kind...real ones or spot lights make-believed into fog lamps) are not for helping other drivers see you.

Ken Fisher had a lot of ideas about lighting. Some of them were valid, others were, well, not.

Also, this is not correct:

I take it that mounted anything above license plate height the glare would defeat the purpose

 

[Thom2022]

I'm gunna chime in with some more fuel for the fire. Low level super bright yellow light <3000k is better in fog that super bright pencil beams so I am lead to believe. Never used pencil beams but yellow lights made a massive difference over stock white. Fog is less dense closer to the ground, so having lights lower means the light is effectively shining under the fog and yellow light is better because it's easier to see yellow light though fog than it is white light. This was info given to me by my driving instructor 10 years ago who was an auto grass racer and is (apparently) also why JDM cars all tend to have yellow front fogs.

 

[-Virgil-]

The real info on yellow light is here. Yellow (properly, "selective yellow") light is not "3000K", that is marketing baloney. Japan does not require yellow fog lamps, but they're popular there. The main reason why you want the fog lamps mounted as low as practicable is to make the height distance as great as possible between the lamp location and the driver's eyes. Fog is tiny water droplets suspended in air. What causes the veiling glare effect of driving with car lights in fog is retroreflection of light off water droplets back to the driver's eye. Retroreflection off water droplets is significant until the angle between the light rays' line of travel and the observer's line of sight is greater than ~60 degrees; at greater angles, retroreflection drops off sharply. The greater the distance between the light source (fog lamp) and the driver's eyes, the greater is that angle and the less is the retroreflection.

There's a kernel of truth to this idea of using spot or "pencil" lights: a narrow, high-intensity beam, mounted as far as possible below the driver's eye height, will give better seeing in fog than a wide, low-intensity beam. This is because a smaller part of the driver's visual field will be "noised" with backglare. You can read about this here. But spot/pencil beam lights would not do; they have no light/dark cutoff and no control over stray light because they are intended for use only in clear weather, and there is no special aim setting that will make a spot/pencil light serve the purpose effectively and safely. The idea only works with a narrow beam that has low levels of stray light and sharp control of where the light does/doesn't go (a cutoff).

No lights like this are commercially available -- Marchal used to make some that approximated, years ago, but they are no longer available. And the evolution of fog lamp technical standards has been more in line with what people want (a wider beam) rather than what they need (a narrower beam).

 

[CeeBee]

Thanks for the very useful reply Virgil.

It was interesting to read - in the link provided - about the experiments to find effective lighting combos for adverse conditions, particularly the notion of turning off the drivers side headlight and relying on just the passenger side light and auxiliary to avoid glare.

If I haven't overstayed my welcome already, how well do ships searchlights cut through fog. Is it the same glare problem?

 

[FRITZHID]

..................

If I haven't overstayed my welcome already, how well do ships searchlights cut through fog. Is it the same glare problem?

well those lights are much different then any automotive lighting. they typically employ a high wattage arc lamp in as tight a beam as possible (1-3 Deg) thus the beam uses sheer power to punch thru fog but even they are limited if it's dense enough, also, they are often mounted far enough away from the user that glare isn't as much of an issue like it is when looking directly down the beam path.

 

[CeeBee]

Thanks
I was of the opinion that ships searchlights were of similar build to vehicle pencil beams, only much bigger.

Thanks for clearing that up.

 

[Hamilton Felix]

Long ago, I corresponded a bit with Gene Schiermeister, who ran a business called Apogee Enterprises and published The Whole Light Catalog (which was mostly a three-ring collection of Cibie, Marchal, etc. catalogs all in one place). I think he'd raced back in the 30's and he'd been selliing lights for years. I know this is ancient history; you can't even find him or his catalog on Google today. He'd be long gone now. We conversed in the early 1980's. He was a guy who would try all sorts of things, just to see. I brought up the idea of mounting a really strong pencil beam, perhaps aircraft landing light, very low and blocking ALL upwards glare, even if you had to go to the extreme of mounting it back under the middle of the car or something.

Turned out Gene had tried some experiments along this line. He'd had some success with "punching" a beam out beheath the fog, but you still could not escape back glare. Sometimes fog hangs a foot or two above the ground, so a really low mounted light has some appeal. But completely aside from the impracticality due to physical damage to the light, low mounted lights cause a "skimming" effect, leaving roadway depressions black and strongly lighting rises in the road.

In light to moderate fog, I've found my Cibie Booster Beam auxiliary low beams can be helpful. Aux. lows are rare now, but the Booster Beam is sort of a fog pattern with a central hot spot, like fog and spot combined but with upward glare limited as it is in fog lights. These lights must be very carefully aimed, and they are not a magic answer in heavy fog, but I often see moderate fog, frequently combined with heavy rain.

Last night, I was out at our other property, maneuvering an old Ford Supercab around sharp turns and avoiding trees and rocks. It was rainy, a bit foggy, cab maybe still a bit foggy when I left. I found myself wishing for the big old 175 fog "see around corners" lights I used on my old International 4x4. I think I may mount my old "vintage collectible" Per-lux 200T lights on that truck, just to help me see to the sides and maybe assist in moderate fog.

You can find spots with total filament shielding, so no direct glare escapes, only controlled light from the reflector. Heck, I used to have a pair of nice little Carello spot driving lights like that, used one in one of my Unity spotlights for a while. So feel free to experiment for yourself. But there is no magic answer for fog. You just have to go slow and not lose the road.

I can't recall the legal requirements right now, but it sticks in my head that fog lights are supposed to be 12 to 16 inches from the ground, but no lower.

 

[CeeBee]

Hi Hamilton and thanks for your reply.
I'm not planning on installing my pencil beams to use in fog, this was just a question that had nagged at me for many years, particularly here in Central Europe where the fog season starts in November and people don't tend to slow down that much. A little extra reach ahead would be nice.

Talking about those Cibié 175's, They, along with used 35's, 75's and 95's are still readily available for very decent prices on French auction sites (as long as you like yellow!) 40 euros for a good condition set of Cibié 35's being a common price. I'm toying with the idea of picking up a set of 175's and modifying my bumper to take them.

 

[Hamilton Felix]

With their size, deep reflectors, great lenses and 8 degree vertical by 120 degree horizontal beam pattern, I think the Cibie 175 is still one of the best fog lights made. After using clear ones for years, I decided I prefer selective yellow for use in fog or snow. A good place to use a tired and somewhat sandblasted set of clear 175s is on your offroad 4x4 truck.