Fog Lights, that Misused Accessory

The latest fad seems to be to run fog lights at all times. People do not seem to understand that this is actually detrimental to vision and safety on the road. It seems that untrained drivers think that because there are more lumens coming out of the front of their vehicle that this is somehow good.

It is not.

  1. Yes, there is more light. But it's in the wrong place! A fog light is supposed to light up a small area very near the front of the car, down low, and very wide to the sides; these are your 'light cane' for use when you are practically blinded by fog. Additional light in this area while driving at normal speeds is actually detrimental to your (and others') safety as it draws your eye in towards an area where you can't actually avoid anything that might be there, and away from where you should be looking. You need to be looking more forward, into the area where you can avoid something at the speed you are traveling. The faster you are traveling, the further forward you must be looking. Additional light up close is not generally helpful.

  2. Most fog lights are badly designed. A proper fog light has a sharp (and very low) cutoff in order to keep backscatter in the fog (remember fog, the nominal purpose for these things?) out of the driver's eyes. The necessity is to light the nearby ground while lighting as few of the suspended water droplets as possible. That mandates a lamp located near the ground, and shrouded to prevent light coming upwards. Without this cutoff the 'fog light' is just a bright near-field floodlight, and is in fact much like a high beam in its effect on oncoming drivers. People are usually aware of the necessity of dimming their high beams when meeting oncoming traffic, yet do nothing about their low-mount auxiliary driving lights that are sadly misnamed fog lights. European cars (Mercedes, BMW, VW) seem to get this right, mostly, whereas Dodge and Subaru (in particular) seem to be the worst offenders.

  3. Each additional lamp adds glare to oncoming drivers, especially on shiny wet/icy surfaces with the additional glare off the pavement. The pavement glare from low-mounted fog lights, even correctly designed ones, is even worse than the glare from the regular headlights, and impairs oncoming drivers' vision even more. The thing they, blinded, might run into could even be you!
In the fog, true fog that makes driving difficult and not just a thin little mist, none of these factors apply! As a decent rule of thumb, if you don't need to slow down because of the fog, you do not need the fog lights! In thick fog even the badly-designed fog lights, though perhaps blinding you from upwards backscatter, will not blind oncoming drivers; the fog itself blocks it from them.

Have you ever needed to creep along and open your door to look out next to your car in order to find the center stripe? If you have not you have not been in the conditions where good fog lights are truly necessary. I have been there, but not often. Under these conditions it is in fact sometimes helpful to be able to turn off the main headlights entirely and proceed entirely under the light from the (properly-designed) fog lights. You can creep along with the bright, low and wide fan of light illuminating your immediate frontal vicinity, avoiding deer and ditches and the odd pedestrian or stopped car. (And with good fog lights you don't need to open the door in order to find the stripe on the road, which really isn't all that safe, or comfortable anyway.) It may be practically feeling your way home by Braille, but you will get there in comfort and safety.

Once upon a time it was federally mandated (in the USA, and perhaps elsewhere) that fog lights turn off when the headlights turned off, and not come back on unless you specifically engaged them again. (I wholeheartedly support this now-defunct regulation.) The light switch in most vintage Mercedes, for example, does this well: you have to pull out on the knob to engage the fogs, and when you turn off the lights the knob pops back in automatically. I think that Subaru and Dodge both have separate fog-light mode switches where you flip the switch on once when you purchase the car, and thereafter the fogs are always on whenever the low beams are on. It seems so, anyway.

Unfortunately for these same vintage Mercedes the same set of USDOT regulations mandated that there be no more than four lamps on at a time on the front of the car, and so because they made some cars with four high beams Mercedes rewired their switch in the USA so that the fogs were tied to the low beams, so they could not be on with the high beams, which means that on such cars (unlike as originally intended) you cannot run the fogs without the low beams also on, which means that under the absolute worst foggy conditions you are at increased risk due to poor visibility. (The dazzle from the backscatter from the unwelcome low beams.) On such cars, however, it is usually fairly easy to move the wire (in the fuse box) back to the original fog-light fuse, restoring independent function of the fog lights. (This was how they were delivered in Europe, if you want just the fogs and marker lights on you can have it.) I have done this on most of our cars, and certainly on the ones that might be driven in fog. This feature is very rarely needed, but seems to me a lifesaver when it is.

People, please, think when you drive! If it's not foggy, turn off those fog lights! They're not actually helping you, and they are hurting others.

Other References

I'm not alone on my soapbox. See: Daniel Stern Lighting

in particular: his page about fog lights.

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