Iowa Code Title VIII. Transportation [Chs. 306-330B] § 321.384. When lighted lamps required

1. Every motor vehicle upon a highway within the state, at any time from sunset to sunrise, and at such other times when conditions such as fog, snow, sleet, or rain provide insufficient lighting to render clearly discernible persons and vehicles on the highway at a distance of five hundred feet ahead, shall display lighted headlamps as provided in section 321.415, subject to exceptions with respect to parked vehicles as provided in this chapter. However, an all-terrain vehicle shall display lighted headlamps as provided in section 321.415 at all times while the vehicle is operated on a highway.

2. Whenever a requirement is established in this chapter as to the distance from which certain lamps and devices shall render objects visible or within which such lamps or devices shall be visible, that requirement shall apply during the times stated in subsection 1 of this section upon a straight level unlighted highway under normal atmospheric conditions unless a different time or condition is expressly stated.