Navigation light

A navigation light, also known as a running light, is a colored source of illumination on a waterborne vessel, aircraft and some spacecraft, used to signal a craft's position, heading, and status. Commonly, their placement is mandated by international conventions or civil authorities. Contrary to the name, these lights are not used for navigating. They indicate the craft's relative position and are thus often called position lights.

Navigation lighting systems include:

In 1838 the United States passed an act requiring steamboats running between sunset and sunrise to carry one or more signal lights; color, visibility and location were not specified. In 1848 the United Kingdom passed regulations that required steam vessels to display red and green sidelights as well as a white masthead light. In 1849 the U.S. Congress extended the light requirements to sailing vessels. In 1889 the United States convened the first International Maritime Conference to consider regulations for preventing collisions. The resulting Washington Conference Rules were adopted by the U.S in 1890 and became effective internationally in 1897. Within these rules was the requirement for steamships to carry a second mast head light. The international 1948 Safety of Life at Sea Conference recommended a mandatory second masthead light solely for power driven vessels over 150 feet in length and a fixed sternlight for almost all vessels. The regulations have changed little since then.

The International Regulations for Preventing Collisions at Sea established in 1972 stipulates the requirements for the navigation lights required on a vessel.

To avoid collisions, vessels mount navigation lights that permit other vessels to determine the type and relative angle of a vessel, and thus decide if there is a danger of collision. In general sailing vessels are required to carry a green light that shines from dead ahead to 2 points ( 22 ¹⁄₂°) abaft the beam on the starboard side (the right side from the perspective of someone on board facing forward), a red light from dead ahead to two points abaft the beam on the port side (left side) and a white light that shines from astern to two points abaft the beam on both sides. Power driven vessels, in addition to these lights, must carry either one or two (depending on length) white masthead lights that shine from ahead to two points abaft the beam on both sides. If two masthead lights are carried then the aft one must be higher than the forward one. Hovercraft at all times and some boats operating in crowded areas may also carry a yellow flashing beacon for added visibility during day or night.

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Wikipedia