Lights on Boats
Hi Pat, a clarification, if I may.
For sailboats over 20 meters:
The green and red masthead lights are visible 360 degrees and are optional (not mandatory).
The white stern sternlight (with a 135-degree angle) is also mandatory for sailboats.
As Pat said, if the boat is powered by a motor, it must also display the white masthead light (225 degrees toward the bow). Two if it is over 50 meters.
The side navigation lights have already been mentioned, but I can add that the careful modeler should only make them visible 112 degrees toward the bow (this way, they will only be visible when the boat is viewed from the side or head-on).
This is what I remember after studying the COLREG.