Navigation light

A navigation light, also known as a running or position light, is a source of illumination on a watercraft, aircraft or spacecraft, meant to give information on the craft's position, heading, or status. Some navigation lights are colour-coded red and green to aid traffic control by identifying the craft's orientation. Their placement is mandated by international conventions or civil authorities such as the International Maritime Organization (IMO). A common misconception is that marine or aircraft navigation lights indicate which of two approaching vessels has the "right of way" as in ground traffic; this is not precisely true, as aircraft and watercraft cannot stop to allow each other to pass, as ground vehicles do. However, the red and green colours do indicate which vessel has the duty to "give way" (change course or speed) or to "stand on" (hold course and speed). In a manner consistent with the ground traffic convention, the rightmost of the two vehicles is usually given stand-on status and the leftmost must give way. Therefore a red light is used on the port (left) side to indicate "you must give way"; and a green light on the starboard (right) side indicates "I will give way; you must stand on". When two power-driven vessels approach head-on, both are required to give way.