Editing Sector light (section)

{{Short description|Man-made pilotage and position fixing aid}}
[[File:Botveskär.jpg|thumb|Sector light at Botveskär on the approach to [[Kapellskär]], Sweden<ref>{{cite book |title=Baltic Pilot |date=1920 |publisher=[[United States Hydrographic Office]] |location=Washington DC |pages=292–293 |edition=2|volume=1|oclc=37374157}}</ref>]]
[[Image:Leitfeuer_001.svg|thumb|Example of a sector light. The ship is navigating in the safe sector (white light is commonly marked as yellow in nautical charts).<ref name=UKHO>{{cite book |editor1-last=Myers |editor1-first=J. A. L. |title=Symbols and Abbreviations Used on Admiralty Charts |date=1991 |publisher=[[United Kingdom Hydrographic Office|Admiralty Hydrographic Office]] |location=Taunton |pages=45, 47 |edition=1995|oclc= 980318575}}</ref>]]

A '''sector light''' is a man-made [[pilotage]] 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.<ref name=UKHO/>

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 north|true]], as observed from sea.<ref name=Hobbs>{{cite book |last1=Hobbs |first1=Richard R |title=Marine Navigation 1 |publisher=[[US Naval Institute]] |location=Annapolis, MD|date=1974|edition=1981 |pages=84–5|volume= Piloting|isbn=978-94-011-7372-8}}</ref> 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]]:
* white - this sector is in the middle of the safe channel
* red - indicates the [[port (nautical)|port]] edge of the channel for vessels approaching the light source
* green - indicates the [[starboard]] 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".