A sector light is a man-made

pilotage Piloting or pilotage is the process of navigating on water or in the air using fixed points of reference on the sea or on land, usually with reference to a nautical chart or aeronautical chart to obtain a fix of the position of the vessel or ai ...

and position fixing aid that consists of strictly delineated horizontal angle light beams to guide water-borne traffic through a safe channel at night in reasonable visibility. Sector lights are most often used for safe passage through shallow or dangerous waters. This may be when leaving or entering harbour. Nautical charts (paper and electronic) give all the required information. Sectors of colored glass (or plastic) are placed in the lanterns of these lights. The light will then show these colors when observed certain bearings. Bearings referring to a sector are given in degrees

true True most commonly refers to truth, the state of being in congruence with fact or reality. True may also refer to: Places * True, West Virginia, an unincorporated community in the United States * True, Wisconsin, a town in the United States * ...

, as observed from sea. Though the colors of the light will change, the characteristics will not. The change of color is not abrupt. The transition is made through an arc of uncertainty of 2° or greater. The colors that are used, are conform to the IALA Maritime Buoyage system that is designed by the

International Association of Lighthouse Authorities The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA), previously known as International Association of Lighthouse Authorities, is an intergovernmental organization founded in 1957 to collect and provide nau ...

: * white - this sector is in the middle of the safe channel * red - indicates the

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as H ...

edge of the channel for vessels approaching the light source * green - indicates the

starboard Port and starboard are nautical terms for watercraft and aircraft, referring respectively to the left and right sides of the vessel, when aboard and facing the bow (front). Vessels with bilateral symmetry have left and right halves which ar ...

edge of the channel for vessels approaching the light source. A ship that is sailing in safe water and then sees the red (or green) color of the light has to make an alteration in course. The world has different navigation standards managed by IALA (International Association of Lighthouse Authorities). For example, the United States uses a signalling standard which is the opposite of Europe. In USA, the red light indicates the starboard side of the channel for harbour bound vessels, while the green light indicates the port side of the same channel. An expression to remind of this is "red on right returning".

Examples of sector lights

An example of a sector light is the light of the Fisgard Lighthouse in

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. The lighthouse was built to guide ships through the entrance of Esquimalt harbour. The white sector is an isophase light of 2s from 322° to 195°. If the ship sees this white light, it can pass safely. The rest shows a red light from 195 to 322°. If a vessel sees this light, it should alter its course. Another example is the

PEL sector light The PEL sector light is a projector style marine beacon which is used to guide maritime vessels. It does this by projecting a colored sector out to sea with very sharp color changes as the mariner transitions from one sector to the next. Typical ...

Diego Garcia Diego Garcia is an island of the British Indian Ocean Territory, a disputed overseas territory of the United Kingdom. It is a militarised atoll just south of the equator in the central Indian Ocean, and the largest of the 60 small islands of ...

. The PEL sector light was constructed to guide US Navy vessels into the Diego Garcia port through a narrow entrance in the lagoon. The PEL sector light produces 3.5 million candela and is visible for 10 nautical miles (18.5 km) by day. The beam with 3 colors is narrow at 1.6°. This was required because the PEL sector light was built over 7NM (13 km) from the atoll entrance and it had to illuminate a safe entrance which is only 228 meters wide. A more complex example is Kolnesholmane, on the southern approach to Risavika in SW

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...

. This has multiple white green and red sectors, indicating safe passage from several directions.

References

{{Lighthouses Lighthouses Maritime signalling Navigation