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.

Marine navigation In 1838 the United States passed an act requiring steamboats running between sunset and sunrise to carry one or more signal lights; colour, visibility and location were not specified. In 1846 the United Kingdom passed the Steam Navigation Act 1846 (9 & 10 Vict. c. 100) enabling the Lord High Admiral to publish regulations requiring all sea-going steam vessels to carry lights. The Admiralty exercised these powers in 1848 and required steam vessels to display red and green sidelights as well as a white masthead light whilst under way and a single white light when at anchor. 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 (46 m) 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 (COLREGs) established in 1972 stipulates the requirements for navigation lights required on a vessel.

Basic lighting Watercraft navigation lights must 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. Small power-driven vessels (under 12 metres (39 ft)) may carry a single all-round white light in place of the two or three white lights carried by larger vessels, they must also carry red and green navigation lights. Vessels under 7 metres (23 ft) with a maximum speed of less than 7 knots (13 km/h; 8.1 mph) are not required to carry navigation lights, but must be capable of showing a white light. 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.

Lights of special significance In addition to red, white and green running lights, a combination of red, white and green mast lights placed on a mast higher than all the running lights, and viewable from all directions, may be used to indicate the type of craft or the service it is performing. See "User Guide" in external links.

Ships at anchor display one or two white anchor lights (depending on the vessel's length) that can be seen from all directions. If two lights are shown then the forward light is higher than the aft one. Boats classed as "small" are not compelled to carry navigation lights and may make use of a hand-held flashlight.

Aviation navigation

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