Characteristic light
Encyclopedia
| Symbols and abbreviations for light characteristics |
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A light characteristic is a graphic and text description of a navigational light sequence or colour displayed on a nautical chart
Nautical chart
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...
or in a Light List
Light List
The United States Coast Guard Light List is an American navigation publication in 7 volumes made available yearly by the U.S. Coast Guard which gives information on lighted navigation aids, unlighted buoys, radiobeacons, radio direction finder calibration stations, daybeacons, racons, and LORAN...
with the chart symbol for a lighthouse
Lighthouse
A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....
, lightvessel
Lightvessel
A lightvessel, or lightship, is a ship which acts as a lighthouse. They are used in waters that are too deep or otherwise unsuitable for lighthouse construction...
, buoy
Buoy
A buoy is a floating device that can have many different purposes. It can be anchored or allowed to drift. The word, of Old French or Middle Dutch origin, is now most commonly in UK English, although some orthoepists have traditionally prescribed the pronunciation...
or sea mark
Sea mark
A sea mark, also seamark and navigation mark, is a form of aid to navigation and pilotage aid which identifies the approximate position of a maritime channel, hazard and administrative area to allow boats, ships and seaplanes to navigate safely....
with a light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
on it. The graphic indicates how the real light beacon may be identified when looking at its actual light output type or sequence. Different lights use different colours, frequencies and light patterns, so mariners can find out which light they are seeing.
Abbreviations
While light characteristics can be described in prose, e.g. "Flashing white every three seconds", lists of lights use abbreviations. The abbreviation notation is slightly different from one light list to another, with dots added or removed, but it usually follow a pattern similar to the following (see the chart to the right for examples).- An abbreviation of the type of light, e.g. "Fl." for flashing, "F." for fixed.
- The color of the light, e.g. "W" for white, "G" for green.
- The cycle period, e.g. "10s" for ten seconds.
- Additional parameters are sometimes added:
- The height of the light above the chart datum for height (usually based on high waterTideTides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
). e.g. 15m for 15 metres. - The range in which the light is visible, e.g. "10M" for 10 nautical mileNautical mileThe nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
s.
An example of a complete light characteristic is "Gp Oc(3) W 10s 15m 10M". This indicates that the light is a group occulting light in which a group of three eclipses repeat every 10 seconds; the light is white; the light is 15 metres above the chart datum and is visible for 10 nautical miles (18.5 km).
Flashing light
A flashing light is a rhythmic light in which the total duration of the light in each period is clearly shorter than the total duration of the darkness and in which the flashes of light are all of equal duration. It is most commonly used for a single-flashing light which exhibits only single flashes which are repeated at regular intervals, in which case it is abbreviated simply as "Fl". It can also be used with a group of flashes which are regularly repeated, in which case the abbreviation is "Fl.(2)" or "Gr Fl.(2)", for a group of two flashes. Another possibility is a composite group, in which successive groups in the period have different numbers of flashes, e.g. "Fl. (2+1)" indicates a group of two flashes, followed by one flash.A specific case sometimes used is when the flashes are longer than two seconds. Such a light is sometimes denoted "long flashing" with the abbreviation "L.Fl".
If the frequency of flashes is large (more than 30 or 50 per minute) the light is denoted as a "quick light", see below.
Occulting light
An occulting light is a rhythmic light in which the total duration of light in each period is clearly longer than the total duration of darkness and in which the intervals of darkness (occultations) are all of equal duration. Like a flashing light, it can be used for a single occulting light that exhibits only single occultations which are repeated at regular intervals (abbreviated "Oc"), a group (Oc (3)) or a composite group (Oc (2+1)).Isophase light
An isophase light, abbreviated "Iso", is a light which has dark and light periods of equal length. The prefix derives from the Greek iso- meaning "same".Quick light
A quick light, abbreviated "Q", is a special case of a flashing light with a large frequency (more than 30 or 50 per minute). If the sequence of flashes is interrupted by regularly repeated eclipses of constant and long duration, the light is denoted "interrupted quick", abbreviated "I.Q".Group notation similar to flashing and occulting lights is also sometimes used (e.g. Q.(9)).
Another distinction sometimes made is between quick (more than 50 and less than 80 flashes per minute), very quick (more than 80 and less than 160 flashes per minutes, abbreviated "V.Q") and ultra quick (no less than 160 flashes per minute, abbreviate "U.Q"). This can be combined with notations for interruptions, e.g. I.U.Q. for interrupted ultra quick, or grouping, e.g. V.Q.(9) for a very quick group of nine flashes. Quick characteristics can also be followed by other characteristics, e.g. V.Q.(6)+L.Fl. for a very quick group of six flashes, followed by a long flash.
Morse code
A Morse code light is light in which appearances of light of two clearly different durations (dots and dashes) are grouped to represent a character or characters in the Morse CodeMorse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
. For example, "Mo. (A)" is a light in which in each period light is shown for a short period (dot) followed by a long period (dash), the Morse Code for "A".