All Round Plug-in Light is a white light shining constantly over the horizon at an arc of 360 degrees. The arc of the lights and colour allows you to determine the direction a vessel is moving. Four Types of Navigation Lights: Sidelights, Sternlight, Masthead, and All-Around White Light. Power-driven vessels less than 12m / 39.4 feet in length, may combine a masthead light and sternlight into a single white light that can be seen by other vessels from any direction. When sidelights are off, this light serves as an anchor light.