Navigation lights are colored illumination devices used on aircraft, watercraft, and spacecraft. They are used to alert other crafts or vessels of the signaling craft's position, status, and/or heading. Most aircraft and marine vessels are required by governing bodies to carry right-of-way lights, which are nav light system consisting of a red light on the left (port) side of the vessel and a green light on the right (starboard). By interpreting this system a nearby vessel can determine the craft's direction and right-of-way. Other specialized nav lights include strobes; typically fitted to aircraft, they emit a burst of high intensity light to enable signaling in low-visibility conditions.
Typical nav light designs (left) and some common marine nav light configurations.
Image credit: West Marine | Phuket Sail