Light characteristic

Last updated
Symbols and abbreviations for light characteristics Light characteristics.svg
Symbols and abbreviations for light characteristics

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.

Contents

Abbreviations

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).

  • The height of the light above the chart datum for height (usually based on high water). e.g. 15m for 15 metres.
  • The range in which the light is visible, e.g. "10M" for 10 nautical miles.

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).

Light patterns

Fixed light

A fixed light, abbreviated "F", is a continuous and steady light.

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 [1] 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 [2] or 50 [1] per minute) the light is denoted as a "quick light", see below.

Occulting light

Clockwork occulting mechanism formerly in use at Coquet Island Lighthouse. Coquet Island Lighthouse, former occulting mechanism.jpg
Clockwork occulting mechanism formerly in use at Coquet Island Lighthouse.

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.

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 [2] or 50 [1] 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 [1] used, e.g. Q(9).

Another distinction sometimes [1] 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. VQ(6) LFl 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 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".

Fixed and flashing

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.

Alternating

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

Table I
Class of LightFeatureAbbr.DefinitionExampleRepresentation
1. Fixed
FA continuous, steady, light.F R Light Code F R.gif
2. Occulting
The total duration of light in each period is greater than the total duration of darkness and the dark intervals (occultations) usually have the same duration.
2.1 Single-occultingOcA dark period is repeated regularly.Oc R 6s Light Code Oc R 6s.gif
2.2 Group-occultingOc(x)A group of dark periods are repeated regularly.Oc(2) G 8s Light Code Oc (2) G 8s.gif
2.3 Composite group-occultingOc(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 Light Code Oc(2+3) W 5s.gif
3. Isophase
IsoThe duration of the light and dark periods are equal.Iso R 4s Light Code Iso R 4s.gif
4. Flashing
The total duration of light in each period is less than the total duration of the dark and light appearances (flashes) usually have the same duration.
4.1 Single-flashing
FlA flash is repeated regularly at a rate below 50 per minute.Fl G 5s Light Code Fl G 5s.gif
4.2 Long-flashingL.FlA light flash, duration of more than 2 seconds (long flash) is repeated regularly.L.Fl W 10s Light Code LFl 10s.gif
4.3 Group-flashing
Fl(x)A group of a specific number of flashes are repeated regularly.Fl(3) R 15s Light Code Fl(3) R 15s.gif
4.4 Composite group-flashingFl(x+y)Similar to group-flashing, but with several groups of flashes.Fl(2+1) W 15s Light Code Fl(2+1) W 5s.gif
5. Quick
flashes are at a frequency of between 50 and 79 flashes per minute.
5.1 Continuous quick
QQuick flashes are repeated regularly.Q W Light Code Q W.gif
5.2 Group quick
Q(x)Groups of a given number of quick flashes are repeated regularly.Q(3) G 9s Light Code Q (3) G 9s.gif
5.3 Interrupted quick
I.QThe sequence of flashes is regularly interrupted by dark intervals of constant duration.I.Q R 14s Light Code IQ R 14s.gif
6. Very quick
Flashes are repeated at a frequency between 80 and 159 flashes per minute.
6.1 Continuous very quick
VQVery quick flashes are repeated regularly.VQ W Light Code VQ.gif
6.2 Group very quick
VQ(x)Groups of a given number of very quick flashes are repeated regularly.VQ(3) G 4s Light Code VQ (3) G 4s.gif
6.3 Interrupted very quick
I.VQThe sequence of flashes is regularly interrupted by dark intervals of constant duration.I.VQ R 9s Light Code IVQ R 9s.gif
7. Ultra quick
The flashes are repeated at a frequency equal to or greater than 160 flashes per minute.
7.1 Continuous ultra quick
UQUltra quick flashes are repeated regularly.UQ W Light Code UQ.gif
7.2 Interrupted ultra quick
I.UQThe sequence of ultra quick flashes is regularly interrupted by dark intervals of constant duration.I.UQ R 6s Light Code IUQ R 6s.gif
8. Morse code
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 Light Code Mo(K) G 6s.gif
9. Fixed and flashing
F.FlA 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 Light Code FFl Y 5s.gif
10. Alternating
AlLight that alternately displays different colors
Note - The alternating light can be used in conjunction with most of the lights earlier classes.
Al WR 3s Light Code Al WR.gif

See also

Notes

  1. 1 2 3 4 5 List of Lights
  2. 1 2 Light List states at one point that only "frequency not exceeding 30 flashes per minute" is considered "Flashing", yet at another that only "a rate of 60 flashes per minute" is considered "Quick", leaving the interval in-between undefined.

Related Research Articles

Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period, T, — the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

Morse code Transmission of language with brief pulses

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.

Frame rate is the frequency (rate) at which consecutive images called frames appear on a display. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be called the frame frequency, and be expressed in hertz.

Light curve graph of light intensity of a celestial object or region, as a function of time

In astronomy, a light curve is a graph of light intensity of a celestial object or region, as a function of time. The light is usually in a particular frequency interval or band. Light curves can be periodic, as in the case of eclipsing binaries, Cepheid variables, other periodic variables, and transiting extrasolar planets, or aperiodic, like the light curve of a nova, a cataclysmic variable star, a supernova or a microlensing event or binary as observed during occultation events. The study of the light curve, together with other observations, can yield considerable information about the physical process that produces it or constrain the physical theories about it.

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.

Strobe light type of light-producing device

A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Greek strobos, meaning "act of whirling".

A distress signal, also known as a distress call, is an internationally recognized means for obtaining help. Distress signals are communicated by transmitting radio signals, displaying a visually observable item or illumination, or making a sound audible from a distance.

Safe water mark Type of sea mark

A Safe Water Mark, as defined by the International Association of Lighthouse Authorities, is a sea mark used in maritime pilotage to indicate the end of a channel. It usually implies that open, deep and safe water lies ahead, though it is sometimes also used to indicate the start and end of a buoyed section of a continuous narrow channel, or a line of these marks can be used to mark a safe route through shallow areas. It is therefore important to consult an appropriate chart to determine the exact meaning in each case. The marker is also sometimes known as a Fairway Buoy.

Fire alarm notification appliance A device to alert the user in a condition such as a fire

A fire alarm notification appliance is an active fire protection component of a fire alarm system. A notification appliance may use audible, visible, or other stimuli to alert the occupants of a fire or other emergency condition requiring action. Audible appliances have been in use longer than any other method of notification. Initially, all appliances were either electromechanical horns or electric bells, which would later be replaced by electronic sounders. Most of today's appliances produce sound pressure levels between 45 and 120 decibels at ten feet.

Photosensitive epilepsy epilepsy characterized by seizures triggered by visual stimuli that form patterns in space or time, such as flashing lights

Photosensitive epilepsy (PSE) is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights; bold, regular patterns; or regular moving patterns.

Satellite flare visual phenomenon caused by a satellite reflecting sunlight onto the Earth

Satellite flare, also known as satellite glint, is a satellite pass visible to the naked eye as a brief, bright "flare". It is caused by the reflection toward the Earth below of sunlight incident on satellite surfaces such as solar panels and antennas.

Cannabis cultivation process of planting, growing and harvesting cannabis

This article presents common techniques and facts regarding the cultivation of cannabis, primarily for the production and consumption of its infructescences. Cultivation techniques for other purposes differ.

Aerodrome beacon

An aerodrome beacon or rotating beacon or aeronautical beacon is a beacon installed at an airport or aerodrome to indicate its location to aircraft pilots at night.

Flashes Per Minute, or FPM, is simply the number of times a flashing light blinks per minute. Police and emergency vehicles use warning lights with flashing rates that typically fall in a range from 60 to 240 FPM.

Lightning detection device that detects lightning produced by thunderstorms

A lightning detector is a device that detects lightning produced by thunderstorms. There are three primary types of detectors: ground-based systems using multiple antennas, mobile systems using a direction and a sense antenna in the same location, and space-based systems.

Aircraft warning lights lights attached to tall structures to prevent collisions with aircraft

Aircraft warning lights are high-intensity lighting devices attached to tall structures as collision avoidance measures. Such devices make structures more visible to aircraft, and are usually used at night, although they may be used during the day. These lights need to be of sufficient brightness to be visible for miles around the structure.

Happisburgh Lighthouse lighthouse at Happisburgh on the North Norfolk coast, East Anglia, England

Happisburgh Lighthouse in Happisburgh on the North Norfolk coast is the only independently operated lighthouse in Great Britain. It is also the oldest working lighthouse in East Anglia.

VRB-25

The VRB-25 is a lighthouse optical system designed and built by Vega Industries Ltd. in Porirua, New Zealand. It was originally designed in 1993-95 with the assistance of the United States Coast Guard to meet USCG requirements for a robust mechanism requiring minimum maintenance. It has become the Coast Guard's standard 12 volt rotating beacon. The company's literature says there are more than 400 installations worldwide. More than a quarter of the active lighthouses in Maine have one installed.

Goods Island Light lighthouse in Queensland, Australia

Goods Island Light is an active lighthouse located on the highest point of Goods Island (Palilag), an island in the Torres Strait, belonging to Queensland, Australia. It serves as the rear light of the Goods Island Range, pointing out the entrance to Normanby Sound.

This glossary defines terms that are used in the document "Defining Video Quality Requirements: A Guide for Public Safety", developed by the Video Quality in Public Safety (VQIPS) Working Group. It contains terminology and explanations of concepts relevant to the video industry. The purpose of the glossary is to inform the reader of commonly used vocabulary terms in the video domain. This glossary was compiled from various industry sources.

References