California does allow them A vehicle may be equipped with not more than two red fog tail lamps mounted on the rear which may be lighted, in addition to the required tail lamps, only when atmospheric conditions, such as fog, rain, snow, smoke, or dust, reduce the daytime or nighttime visibility of other vehicles to less than 500 feet. When two lamps are installed, one shall be mounted at the left side and one at the right side at the same level and as close as practical to the sides. When one lamp is installed, it shall be mounted as close as practical to the left side or on the center of the vehicle The lamps shall be mounted not lower than 12 inches nor higher than 60 inches The edge of the lens of the lamp shall be no closer than four inches from the edge of the lens of any stop lamp. A non-flashing amber pilot light that is lighted when the lamps are turned on shall be mounted in a location readily visible to the driver.