Why are fog lights located so much lower than hi/lo beam lights?

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I’m no expert but, in heavy fog/snow. It reflects light back at you. So you want the light to be throwing lower down to the ground because high beams can reflect off heavy snow/fog and actually limit visibility

this is super super basic explanation and could also be incorrect

 

The answer is one that's complicated to explain without drawing a diagram. I'll attempt it anyway.

The simple summary is all about airborne particulate. Little tiny particles in the air that have a high reflectance, like water vapor (fog) or worse, snow. Shine a flashlight at that particulate, and it's going to reflect light 180 degrees right back at the source. But because the individual particles are not a perfect mirror, that 180 degrees of reflection has a cone shaped scattering that's going to shine the eyes of whomever is holding the light source.

Think about the path of light from your headlights to your eyes. They shine the road 150 feet ahead, reflect, and return to your eyes at an angle. Even though the headlights are a few feet lower than your head, the angles are narrow enough that you can still see the light reflecting off of airborne particles. So your eyes are detecting both light from these particles plus light reflecting from your desired object (that you want to see). Your brain interprets this as "hazy."

Fog lights are not only mounted lower than headlights (thus increasing the offset angle of reflection), but they also have a sharp beam cutoff so the light does not project upward. Both geometrical aspects translate into the fact that when light emitted from the fogs strikes an airborne particle, the reflection does not reach (and confuse) the viewers eye and does not obscure the light reflecting off the desired object (road). Therefore the fog light has the illusion of penetrating fog.

But then you'll ask, why are headlights not just mounted down low like fogs? Because you still need to light up close-distance objects like street signs and other things that you'd like to avoid a collision with. Headlights just happen to be mounted at a more ideal angle to throw light both near and far. The trade-off is that the closer to ideal positioning the headlight gets, the more it's going to get interfered with by that pesky particulate.


If you want diagrams, look up a quick diagram on offsetting a camera flash for underwater photography. Same principle, that's why scuba nerds put their camera lights on goofy long booms away from the camera.

 

Isn't it as simple as, fog does reach the ground. So the lights shine under it.