Fog lamps were originally added to cars designs and became law/part of MOT as the original lighting system designs were easily defeated by heavy fog creating significant driving hazards. High intensity rear fog lamps were added in mitigation of this risk.
Car light design has come a long way since then. Incandescent > halogen > Xenon HID > LED. In reality fog lamps are adding very little mitigation of the original 'fog' hazard over and above stock lights these days.
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