Iowa Code § 321.398: Lamps on other vehicles and equipment.

All vehicles, including animal-drawn vehicles and including those referred to in section 321.383 not specifically required to be equipped with lamps, shall at the times specified in section 321.384 be equipped with at least one lighted lamp or lantern exhibiting a white light visible from a distance of five hundred feet to the front of such vehicle and, except for animal-drawn vehicles, with a lamp or lantern exhibiting a red light visible from a distance of five hundred feet to the rear. Animal-drawn vehicles shall be equipped with a flashing amber light visible from a distance of five hundred feet to the rear of the vehicle during the time specified in section 321.384.