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
Missouri requires lamp on the front emitting a white light visible from a distance of at least 500 feet to the front, required between one-half hour after sunset and one-half hour before sunrise. For the rear, red reflector on the rear of a type approved by the missouri department of public safety, visible from all distances from 100 feet to 600 feet when directly in front of lawful lower-beam headlamps. a red rear lamp visible from 500 feet may be used in addition to the reflector. The rule applies whenever it is dark. See RSMo § 307.185 (Bicycle equipment — lights).
The cheapest way to stay legal in Missouri 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.