Light Characters

A Light character

is a graphic and/or textual description of a light used in navigation in shipping, such as lighthouses, beacons or light signs. The main characteristics of a light character are generally the sequence of the intervals of light and dark, and in some cases the sequence of the colours of the light displayed.

A light character is shown on a nautical chart or in a list of lighthouses, lightships, buoys and sea markers that are marked with a "light". The notation/picture or text on a chart, indicates how the light can be identified by looking at the type or sequence of light output. Lights (Lighthouses, Buoys etc.) use different colours, frequencies and light patterns, so that mariners can identify which light they are seeing.

Abbreviations of a Light

Although light characteristics can be described in words, such as "Flashing White every five seconds with a range of 18 nautical miles", Lists of Lights and markers on navigation charts use abbreviations to indicate a lighthouse.

This abbreviation notation varies slightly from one list of lights to another, with parameters added or removed, but in generally it follows a pattern similar to the following "Fl. W 5s 18M". (This is the light character of Buchan Ness)

The abbreviation indicates the type of light being observed. For example, "Fl." is for a flashing light; "F." is for a steady light; "Oc." is for an occulting light. The Corran Point lighthouse has an Isophase light "Iso". (see map at the right and the table below).

The color of the light that a lighthouse shows can vary. The colors for the light are; "W" for White, "G" for Green, "R" for Red, "Y" for Yellow. If no color is specified, it generally means a White light. These colors can also be combined depending on the situation.

Each light also has its own cycle period. In addition to this cycle period, each Light also has a separate "flash duration". The difference between "light" and "dark" is not always similar. A flash can last between 0.1 second and several seconds. The duration of a flash is indicated for each lighthouse separately in the list of lights but not on the sea charts. For example; the lighthouse of Buchan Ness - has a period of "5s" with a flash of 0.3 seconds and is out for 4.7 seconds.

In the example of Corran Point, this cycle period is 4 seconds "4s". In the case of Corran Point is the period between "light" and "dark" the same, due to the Iso-light (2s. - light, 2s. - dark).

The fourth parameter in the abbreviation is the height of the light in metres above sea level (based on high tide). In the case of Corran Point is that 12 meters and for Buchan Ness is this 40 metres.

The last parameter indicates the nominal range of the lighthouse. This nominal range is strongly dependent on the weather conditions. In the case of Corran Point is the nominal range for "W - White" 10 Nautical miles (~ 18.5 kilometer) and voor the "R - Red" and G - Green" is this 7 Nautical miles (~ 12.9 kilometer). Buchan Ness has a range of 18 Nautical miles (~ 33.3 kilometer).

An example of a other complete light characteristic is "Iso WRG 4s. 12m 10-7M". (Corrant Point lighthouse - above). This indicates that the light is Isophase light with a White, Red and Green sector repeat every 4 seconds; Elevation (focal height) is 12 meter above sealevel; the White light is visible for 10 nautical miles (~ 18.52 km), de Red and Green light is visible for 7 nautical miles (~ 13 km). See also the map above.

Sector limits and arcs of visibility

These are arranged clockwise and are given from the sea towards the lighthouse. For example, in the Corran Point lighthouse chart the sectors of the light are defined as: obscured from shore to 132°-, Red to 195°-, White to 215°-, Green to 020°, - White again 030° and finally Red to shore (- 069°). These are observations of the lighthouse light as seen from a ship crossing the sector lines.

Under some conditions of the atmosphere, white lights may have a reddish hue. The mariner should not judge solely by color where there are sectors but should verify this position by taking a bearing of the light. On either side of the line of demarcation between white and red there is always a small sector of uncertain color, as the edges of a sector of visibility cannot be clearly defined.

Table with Light Character examples

Type	Abbr.	General description	Example [Flash duration]	Dome	[Cycle period in seconds / Flash duration]

Fixed Light

Fixed	F.	A continuous, steady, light.	F. R

Occulting Light

Single-occulting	Oc.	The total duration of light in a period is longer than the total duration of darkness and the intervals of darkness (eclipses) are usually of equal duration. Eclipse regularly repeated.	Oc.R 6s Lit.4.5s.-ec.1.5s.

Group-occulting	Oc.(X)	An occulting light for which a group of eclipses, specified in number, is regularly repeated.	Oc.(2)G 8s Lit.6.5s.-ec.0.5s. + Lit.0.5-ec.0.5

Composite group-occulting	Oc.(X+Y)	A light similar to a group occulting light except that successive groups in a period have different numbers of eclipses.	Oc.(2+3)W 18s 2x Lit.1.0s.-ec.1.0s. + Lit.5.0s-ec.1.0s + 2x Lit. 1.0s-ec.1.0s. + Lit 4.0s.

Isophase Light

Isophase	Iso.	A light for which all durations of light and darkness are clearly equal.	Iso. G 4s Fl.2.0s.-ec.2.0s.

Flashing Light

Single-flashing	Fl.	A light for which the total duration of light in a period is shorter than the total duration of darkness and the appearances of light (flashes) are usually of equal duration (at a rate of less than 50 flashes per minute).	Fl. G 5s Fl.1.0s.-ec.4.0s.
Long-flashing	L.Fl.	A single flashing light for which an appearance of light of not less than 2 seconds duration (long flash) is regularly repeated.	L.Fl. W 10s Fl.3.0s.-ec.7.0s.
Group-flashing	Fl.(X)	A flashing light for which a group of flashes, specified in number, is regularly repeated.	Fl.(3) R 15s 2x Fl.1.0s.-ec.1.0s. + Fl.1.0s.-ec.10.0s.
Composite group-flashing	Fl.(X+Y)	A light similar to a group flashing light except that successive groups in a period have different numbers of flashes	Fl.(2+1) W 15s Fl.1.0s.-ec.1.0s. + Fl.1.0s.-ec.6.0s. + Fl.1.0s.-ec.5.0s.

Quick Flashing Light

Quick flashing	Q.	A light for which a flash is regularly repeated at a rate of not less than 50 flashes per minute but less than 80 flashes per minute	Q.W Fl.0.5s.-ec.0.5s.
Group quick flashing	Q.(X)	A light for which a specified group of flashes is regularly repeated; flashes are repeated at a rate of not less than 50 flashes per minute but less than 80 flashes per minute	Q.(3)G 9s 3x Fl.0.5s.-ec.0.5s. + ec.6.0s.
	Q(X)+L.Fl.		Q.(6)+L.Fl. R 12s 6x Fl.0.5s.-ec.0.5s. Lit.2.0s.-ec.4.0s.
Interrupted quick flasing	IQ.	The sequence of flashes is regularly interrupted by dark intervals of constant duration	IQ.(9)W 12s 9x Fl.0.5s.-ec.0.5s. + ec.3.0s.

Very Quick Flashing Light

Very Quick flashing	V.Q.	A light for which a flash is regularly repeated at a rate of not less than 80 flashes per minute but less than 160 flashes per minute.	V.Q.W Fl.0.25s.-ec.0.25s.
Group very quick flashing	V.Q.(X)	A light for which a flash is regularly repeated at a rate of not less than 80 flashes per minute but less than 160 flashes per minute.	V.Q.(3)G 4s 3x Fl.0.25s.-ec.0.25s. + ec.1.5s.
	V.Q(X)+L.Fl.		V.Q.(10)+L.Fl.R 12s 10x Fl.0.5s.-ec.0.5s. + Lit.2.0s.-ec.5.0s.
Interrupted very quick flashing	I.V.Q.	A light for which the sequence of very quick flashes is interrupted by regularly repeated eclipses of constant and long duration	IVQ(10)R 12s 10x Fl.0.25s.-ec.0.25s. + ec.7.0s.

Ultra Quick Flashing Light

Ultra Quick flashing	U.Q.	A light for which a flash is regularly repeated at a rate of not less than 160 flashes per minute.	U.Q.W Fl.0.125s.-ec.0.125s.
Itterrupted ultra quick flashing	I.U.Q.	A light for which the sequence of ultra quick flashes is interrupted by regularly repeated eclipses of constant and long duration.	I.U.Q. R 9s 24x Fl.0.125s.-ec.3.125s.

Morse Code Light

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 Fl.1.0s.-ec.0.25s. + Fl.0.5s-ec.0.25s. + Fl.1.0s.-ec.3.0s.

Fixed and Flashing Light

Fixed and Flashing	F.Fl.	A light for which a fixed light is combined with a flashing light of greater luminous intensity.>	F.Fl. Y 5s Lit.2.5s.-Fl.2.5s.

Alternating Light

Alternating	Al.	A light for which a fixed light is combined with a flashing light of greater luminous intensity.>	Al.WR 3s Lit.W 1.5s.-Lit.R 1.5s.