Any motor vehicle may be equipped with not to exceed two auxiliary driving lamps mounted on the front at a height not less than twelve inches nor more than forty-two inches above the level surface upon which the vehicle stands, and every such auxiliary driving lamp or lamps shall be so aimed and used that no part of the high-intensity portion of the beam will be directed to the left of the prolongation of the extreme left side of the vehicle nor more than one hundred feet ahead of the vehicle.