A light characteristic is a graphic and text description of a navigational light sequence or colour displayed on a nautical chart or in a Light List with the chart symbol for a lighthouse, lightvessel, buoy or sea mark with a light on it. The graphic indicates how the real light 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 identify which light they are seeing.
While light characteristics can be described in prose, e.g. "Flashing white every three seconds", lists of lights and navigation chart annotations use abbreviations. The abbreviation notation is slightly different from one light list to another, with dots added or removed, but it usually follows a pattern similar to the following (see the chart to the right for examples).
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 (19 km).
A fixed light, abbreviated "F", is a continuous and steady 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 usedis 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 30or 50 per minute) the light is denoted as a "quick light", see below.
An occulting light is a rhythmic light in which the duration of light in each period is longer than the total duration of darkness. In other words, it is the opposite to a flashing light where the total duration of darkness is longer than the duration of light. It has the appearance of flashing off, rather than flashing on. Like a flashing light, it can be used for a single occulting light that exhibits only a single period of darkness or the periods of darkness can be grouped and repeated at regular intervals (abbreviated "Oc"), a group (Oc(3)) or a composite group (Oc(2+1)).
The term occulting is used because originally the effect was obtained by a mechanism (e.g. a vertical or rotating shutter) periodically shading the light from view.
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".
A quick light, abbreviated "Q", is a special case of a flashing light with a large frequency (more than 30or 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 sometimesused, e.g. Q(9).
Another distinction sometimesmade 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. VQ(6) LFl for a very quick group of six flashes, followed by a long flash.
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 Code. 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".
A fixed and flashing light, abbreviated "F. Fl", is a light in which a fixed low intensity light is combined with a flashing high intensity light.
An alternating light, abbreviated "Al", is a light which shows alternating colors. For example, "Al WG" shows white and green lights alternately.
|Class of Light||Feature||Abbr.||Definition||Example||Representation|
|F||A continuous, steady, light.||F R|
|2.1 Single-occulting||Oc||A dark period is repeated regularly.||Oc R 6s|
|2.2 Group-occulting||Oc(x)||A group of dark periods are repeated regularly.||Oc(2) G 8s|
|2.3 Composite group-occulting||Oc(x+y)||Light similar to group-occulting, except that successive groups in the same period contain different numbers of dark periods.||Oc(2+3) W 18s|
|Iso||The duration of the light and dark periods are equal.||Iso R 4s|
|4.1 Single-flashing||Fl||A flash is repeated regularly at a rate below 50 per minute.||Fl G 5s|
|4.2 Long-flashing||L.Fl||A light flash, duration of more than 2 seconds (long flash) is repeated regularly.||L.Fl W 10s|
|4.3 Group-flashing||Fl(x)||A group of a specific number of flashes are repeated regularly.||Fl(3) R 15s|
|4.4 Composite group-flashing||Fl(x+y)||Similar to group-flashing, but with several groups of flashes.||Fl(2+1) W 15s|
|5.1 Continuous quick||Q||Quick flashes are repeated regularly.||Q W|
|5.2 Group quick||Q(x)||Groups of a given number of quick flashes are repeated regularly.||Q(3) G 9s|
|5.3 Interrupted quick||I.Q||The sequence of flashes is regularly interrupted by dark intervals of constant duration.||I.Q R 14s|
|6.1 Continuous very quick||VQ||Very quick flashes are repeated regularly.||VQ W|
|6.2 Group very quick||VQ(x)||Groups of a given number of very quick flashes are repeated regularly.||VQ(3) G 4s|
|6.3 Interrupted very quick||I.VQ||The sequence of flashes is regularly interrupted by dark intervals of constant duration.||I.VQ R 9s|
|7.1 Continuous ultra quick||UQ||Ultra quick flashes are repeated regularly.||UQ W|
|7.2 Interrupted ultra quick||I.UQ||The sequence of ultra quick flashes is regularly interrupted by dark intervals of constant duration.||I.UQ R 6s|
|Mo(x)||The flashes have markedly different durations and are grouped together to form one or more characters in Morse code.||Mo(K) G 6s|
|F.Fl||A light that combines a fixed light with a light flashing with a stronger intensity. The flashes of light may have any of the features described in above.||F.Fl Y 5s|
|Al||Light that alternately displays different colors |
Note - The alternating light can be used in conjunction with most of the lights earlier classes.
|Al WR 3s|
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Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called dots and dashes or dits and dahs. Morse code is named for Samuel F. B. Morse, an inventor of the telegraph.
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Q-switching, sometimes known as giant pulse formation or Q-spoiling, is a technique by which a laser can be made to produce a pulsed output beam. The technique allows the production of light pulses with extremely high (gigawatt) peak power, much higher than would be produced by the same laser if it were operating in a continuous wave mode. Compared to modelocking, another technique for pulse generation with lasers, Q-switching leads to much lower pulse repetition rates, much higher pulse energies, and much longer pulse durations. The two techniques are sometimes applied together.
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