simon@elwood.DEC (Product Safety 237-3521) (10/21/84)
The color of the lens DOES make it fog light. This is due to the fact that the red part of the spectrum is less absorbed by water vapor and particles. Since red is allowed only in rear of a car, the closest to it, amber, is used for fog lights. Leo Simon decwrl!rhea!elwood!simon
hrs@houxb.UUCP (H.SILBIGER) (10/22/84)
Theoretically it is true that yellow is less absorbed by water vapor. However, the light loss due to the yellow filter is far greater than the small advantage the yellow provides. The net result is that you still see better with white fog lights.
wetcw@pyuxa.UUCP (T C Wheeler) (10/23/84)
Silberger has obviously never driven in a pea soup fog. White lights in a 6-foot visibility fog are useless. All you get is a big white, glaring wall in front of the car. I am talking about the type of fog that requires someone to walk in front of the car to make sure they stay on the road. Don't laugh, I have seen this stuff along the coast of Washington. The only way you could see the road without yellow fogs was to have someone walk in front of the car. Yellow fogs did, at least, allow the driver to see the side of the road and the white line, plus about ten feet ahead. Needless to say, your speed was reduced to walking speed. White lights produced a blinding glare that gave no indication of where you were on the road. T. C. Wheeler
mikey@trsvax.UUCP (10/24/84)
Ask any competition shooter what color his glasses are, if he bothers to get colored lenses at all. What color goggles do competition skiers use? Amber! Amber lets your eyes see the most definition, even at a reduced light level. Even with the absortion in the lense, a GOOD amber filter should be more beneficial than clear. But as before, the focusing of the lense will make the most difference. Some people hold out for clear, and if people buy it, it will be manufactured, but I'll hold out for amber. mikey at trsvax
kpmartin@watmath.UUCP (Kevin Martin) (10/25/84)
>Yellow fogs did, at >least, allow the driver to see the side of the road and the >white line, plus about ten feet ahead. Needless to say, your >speed was reduced to walking speed. White lights produced a >blinding glare that gave no indication of where you were on >the road. >T. C. Wheeler Are you sure it was the colour difference, and not a difference in the light pattern or the bulb position & aiming?
hrs@houxb.UUCP (H.SILBIGER) (10/25/84)
Wheeler obviously does not have good quality fog lights such as Bosch or Cibie'. The cutoff on these is so good that no light scatters upward of the lower edge of the front bumper. In Europe one does not see yellow fog lights on cars, except for France, where both headlights and foglights have to be yellow. This is done so that French driver can recognize a foreigner, and flash their brights at them. \ Herman Silbiger "I know where the yellow went"
kpmartin@watmath.UUCP (Kevin Martin) (10/28/84)
>Ask any competition shooter what color his glasses are, if he bothers >to get colored lenses at all. What color goggles do competition >skiers use? Amber! Amber lets your eyes see the most definition, >even at a reduced light level. >mikey at trsvax The yellow/amber snow goggles are to keep out the vast amounts of UV light which pour down on ski slopes. Without the goggles, you start getting mild forms of snow blindness. Such a purpose for filtering is hardly relevant on a puny 50 watt incandescent bulb. I do admit that blue light gives the least definition, but just because the info is a bit fuzzy doesn't mean you should filter it out. Besides, in fog, you don't really need fine definition (who wants to count the cracks in the pavement?), but high contrast, so you can see the large objects (like the edge of the road).
dmmartindale@watcgl.UUCP (Dave Martindale) (10/29/84)
A small nit in Kevin's explanation: Blue light actually gives the finest detail in any sort of optical system, since its wavelength is shortest and diffraction effects extend shorter distances. The reason fog lights are yellow is simply because blue light scatters the worst of all colours, again because of its short wavelength. If you filter out the blue, the ratio of light coming back from objects to light scattered by the fog goes up, giving you better vision. Filtering out the green too, leaving only red, would give even better contrast but your eye isn't too sensitive to red so it's better to leave the green in.
gmm@bunker.UUCP (Gregory M. Mandas) (10/29/84)
>Ask any competition shooter what color his glasses are, if he bothers >to get colored lenses at all. What color goggles do competition >skiers use? Amber! Amber lets your eyes see the most definition, >even at a reduced light level. >mikey at trsvax I vote for this explanation. I am a competition shooter and I would wear amber if I had the bucks for the perscription. I also have a set of white fog lamps that do little except put out more light to be reflected back into my eyes. (Yes they are aimed correctly.) One reason is that they only work with the main low beams on. The last time I was in a pea souper (could not see the front of the car) I turned off the mains and drove with the (amber) parking lights. This afforded me the most visibility of all the lighting combinations I had available. Greg (Let's shed some more fog on the subject) Mandas
prg@mgweed.UUCP (Phil Gunsul) (11/01/84)
[::::::::::::::::::::::(boy is it foggy:::::::::::::::::] Way ta' go Greg!! You started the 'driving with your parking lights on' discussion again! And since you started it [:-)], I just observed an advertisement for Buick on the television this morning. Believe it or not, they show the car approaching in the dusk with only its' parking lights on!! Obviously an illegal advertisement!! Phil Gunsul
debray@sbcs.UUCP (Saumya Debray) (11/02/84)
> Theoretically it is true that yellow is less absorbed by water vapor. > However, the light loss due to the yellow filter is far greater > than the small advantage the yellow provides. The net result > is that you still see better with white fog lights. Curious. I had the impression that the principal reason for using yellow fog lights is that the longer wavelengths (yellow, orange) are _scattered_ to a much smaller extent by water droplets suspended in air (which is what fog is), which in turn means that they tend not to be reflected back into the driver's eyes as much, and blind him with the glare. The problem with white fog lights is that precisely because shorter wavelengths are scattered to a greater extent by suspended particles, the beam won't penetrate fog as well as that from a yellow fog light. Granted, you'll see the fog better with white lights, but I'd assume that's not what you'd really want to see. -- Saumya Debray, SUNY at Stony Brook uucp: {cbosgd, decvax, ihnp4, mcvax, cmcl2}!philabs \ {amd, akgua, decwrl, utzoo}!allegra > !sbcs!debray {tektronix, metheus}!ogcvax / CSNet: debray%suny-sbcs@CSNet-Relay
hrs@houxb.UUCP (H.SILBIGER) (11/07/84)
Of course fog lights should be wired such that they can be used with parking lights and not with low beam headlights! They should not be used without parking and tail lights on, however. Item 2: Low pressure sodium vapor street lights are used because they are more efficient than any other lights source in lumens/watt. In order of efficiency, from high to low: Low pressure sodium vapor High pressure sodium vapor (bright pink) High pressure mercury vapor (blue) High pressure sodium vapor with color correction (blue-white) Fluorescent Quartz-halogen incandescent Incandescent Conversion efficiency ranges from > 50% to 17%! Herman Silbiger