Could anyone explain to me the reason automobile headlights are not made to function on high beam with fog lights running? At least the ones I’ve owned.
Fog is basically a low hanging cloud. The small airborne water particles in fog can act almost like mirrors in terms of their ability to reflect light. This means that when your headlights shine into fog, a majority of the light output produced by your lights will strike the airborne water droplets and will be reflected right back towards your vehicle. So the more light you point towards the fog, the more glare the fog will cast back at you, and the lower your resulting visibility will be.
Fog lights are designed to emit their light towards the ground instead of straight ahead. This helps to focus the light towards the road instead of into the fog. So instead of shining light straight ahead into the fog, your fog lights will focused light on the road directly ahead of you instead. That’s why fog lights have such a narrow beam pattern, so you’re avoiding as much of the fog as possible while still illuminating the area directly ahead.
I would guess that the vehicle engineers knowing this decided to make sure that you cannot use your high beams in weather that requires the use of fog lights.