This is what Iowa boating laws say (
http://www.iowadnr.com/law/files/boat2003.pdf)
Unpowered Vessels When Underway
Unpowered vessels are sailboats or those that are paddled,
poled and rowed.
â—† If less than 65.6 ft. (20 meters) long, these vessels must
exhibit the lights as shown in figure 2:
• Red and green sidelights visible from at least 2 miles
(or if less than 39.4 ft. long, at least 1 mile)
• A sternlight visible from at least 2 miles.
If less than 23.0 ft. (7 meters) long, these vessels:
• If practical, must exhibit the same lights as required for
unpowered vessels listed above
• If not practical, must have on hand at least one lantern
or flashlight shining a white light as shown in figure 3.
Figure 3 shows a flashlight shown on the sail.
I've almost thought of making a mount for a battery powered stern light that could go on the top of the mast when I step it....