Iowa Code § 321.418: Alternate road-lighting equipment.

Any motor vehicle may be operated under the conditions specified in section 321.384 when equipped with two lighted lamps upon the front thereof capable of revealing persons and objects seventy-five feet ahead in lieu of lamps required in sections 321.409 and 321.415, or section 321.417, provided, however, that at no time shall it be operated at a speed in excess of twenty miles per hour.