Recreational boats operating at night are required to display navigation lights between sunset and sunrise. Recent changes to the Inland Navigation Rules make them nearly identical to the International Rules, so we will describe the International Rules to simplify the choices.
Sidelights are red (port) and green (starboard) and shine from dead ahead to 112.5° aft on either side.
Stern lights are white and shine aft and 67.5° forward on each side. (Thus, the sidelights and stern light create a full circle of light.)
All-round lights are white and shine through 360°.
Masthead lights are white and shine from 112.5° on the port side through dead ahead to 112.5° on the starboard side. They must be above the sidelights.
Sailboats under power are considered powerboats.
Sidelights may be combined into a single "bicolor" light.
Powerboats less than 20m (65.7') in length need to show sidelights, a stern light and a masthead light. Power vessels less than 12m may show a single all-round light in lieu of the separate masthead and stern lights.
Sailing vessels less than 20m in length need to show sidelights and a stern light. These may be combined into a bicolor light and stern light, or a single tricolor light at the top of the mast. Sailing vessels under 7m must have an electric torch or lantern available for collision avoidance.
Oar-driven vessels can show either the sailboat lights, or use the electric torch/lantern option.
When anchored outside a special anchorage, power and sail vessels under 20m must display an all-round light. Vessels under 7m are exempt, unless anchored in a narrow channel or anchorage, or where other vessels usually navigate.
Sailboats with sails up during the day, but which are also under power, must fly a black "steaming cone," with its point downward, where it can be seen. When under power they must follow the rules of the road for powerboats.
Boats under power under 40' can substitute a single all-round light for separate stern and masthead lights
Boats under 65'7" can substitute a single bi-color light for sidelights
Sail boats under sail under 65'7" can substitute a tri-color light for separate sidelights and stern light.