All About Fog Lamps

By Mark Gittelman in Automobile Technology

Note at the end of this all about fog lamps article will be links to some of the most popular fog light kits and replacement halogen bulbs for factory installed systems. But first didn’t you ever wonder about your cars fog lights. Why they are constructed different than headlights. Why they are mounted in positions that are far lower than regular headlamps.

When I first started to drive at 16, no cars had factory mounted driving lights. This was an aftermarket accessory that I quickly added to my vehicle so it would look cool. To my surprise not only did they look cool but they actually came in handy. I found myself driving through foggy areas often as I lived near cranberry bogs in a low lying area of New Jersey.

A side note when you are adding auxiliary lights you must make sure that your alternator and wiring are heavy duty enough to handle the increased wattage. In the case of my 1974 Dodge charger the fog lights were too much for the standard wiring and charging system. After an electrical fire that melted all the lighting circuit components I upgraded the alternator and installed new heavy gauge wiring. After the upgrades all was good.

Difference between fog lights and headlights

Ordinary headlights do not penetrate the fog very well. The focus of a powerful beam of light directly at the fog reflects most of the light back to the driver. You can verify this by switching from your high beams to your low beams on a foggy night. You can see fore yourself which one actually provides the best distance of site.

image of wide beam fog lamp — Wide beam fog lamp

I’m not a scientist but I believe it’s because the fog is made of water molecules and these tiny droplets of water are what actually reflects the beam of light back in the drivers face. Fog lights in most cases use halogen bulbs but instead of using a wide powerful beam they attempt to sneak a flat beam of light under the blanket of fog. This is one of the main reasons that fog lights are mounted as low as possible on the vehicle.

Fog is actually like a cloud that hangs near the ground. This is often generated from temperature differentials. Cold air meets the warm ground or body of warmer water for example. So much like clouds in the sky fog forms when the air becomes saturated with moisture. As a result water forms out of the air into a fine mist of water droplets. Fog can get very dense and obscure visibility quickly as it forms with little warning.

image of halogen replacement bulb — H3 Halogen Bulb

Nowadays more often than not fog lights will come standard with your vehicle and not needed to be added using aftermarket parts. In the case of my current vehicle which is a 2004 Chevrolet Blazer my fog lights are factor installed.

On my blazer you can only use the fog light if the headlights are on the low beam settings. If your fog lights are on and you switch on the high beams the fog lights are automatically turned off. In my example above when you are trying to drive in foggy conditions the brighter your headlights are the worst your vision becomes.