Any motor vehicle may be equipped with not to exceed two fog lamps mounted on the front at a height of not less than twelve inches nor more than thirty inches above the level surface upon which the vehicle stands and so aimed that, when the vehicle is not loaded, none of the high-intensity portion of the light to the left of the center of the vehicle shall at a distance of twenty-five feet ahead project higher than a level of four inches below the level of the center of the lamp from which it comes.