This guide is for general information only and is not legal advice. Laws change — verify current rules with your state DOT or a licensed attorney before relying on this for any legal matter. Read full disclaimer.
The rule
Iowa requires white lamp on the front, visible from a distance of at least 300 feet. For the rear, red reflector on the rear of a type approved by the iowa department of transportation, visible from a distance of 300 feet to the rear when directly in front of lawful upper-beam headlamps. a red rear lamp visible from 300 feet may be used in lieu of the reflector. The rule applies whenever it is dark. See Iowa Code § 321.397 (Bicycle equipment — lamps and reflectors).
The cheapest way to stay legal in Iowa is a USB-rechargeable front white light and a rear red light or reflector that meets the spec above. A $30 light set covers it.