Iowa Code § 321.404A: Light-restricting devices prohibited.

1. A person shall not operate a motor vehicle, motorcycle, or motorized bicycle on the highways of this state if it is equipped with a device that restricts the light output of a headlamp required under section 321.385 or 321.386, a rear lamp required under section 321.387, a signal lamp or signal device required under section 321.404, or a directional signal device as described in section 321.317.

2. A person who violates this section shall be subject to a scheduled fine under section 805.8A, subsection 3.