Neist Point

Technics of the Light's

In Salutem Omnium
For the Safety of All
Neist Point - Isle of Skye
Flag of Scotland
Composed by:
Bob Schrage
updated: 26-12-2020

Light Characteristic

A light character 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.

Abbreviations: While light characteristics can be described in words, 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).

Chart of Corran Point
Chart of the sectorlights on Corran Point
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, "R" for red, "Y" for yellow. If no color is given, a White light is generally implied. 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 water). e.g. 15m for 15 meters. The range in which the light is visible, e.g. "10 nM" for 10 nautical miles.

An example of a complete light characteristic is "Iso WRG 4s. 10-7M". This indicates that the light is Isophase light with a White, Red and Green sector repeat every 4 seconds; the White light is is visible for 18.52 km (10 nautical Mile), de Red and Green light is visible for 13 km (7 nautical Mile). See also the right-hand map

Sector limits and arcs of visibility are arranged clockwise and are given from seaward toward the light. Thus, in the (right) diagram, the sectors of the light are defined as: obscured from shore to 132°, Red to 195°, White to 215°, Green to 020°, again white 030° and as last Red to the shore (069°). These are bearings of the light as seen from a vessel 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.

When a light is obscured by adjoining land and the arc of visibility is given, the bearing on which the light disappears may vary with the distance from which it is observed. When the light is cut off by a sloping point of land or hill, the light may be seen over a wider arc by a ship farther off than by one closer.

Table with lightcharacter examples

Class Feature Abbr. Definition Example Pres. Cycle period in seconds
Cycles per seconds
1. Fixed
F A continuous, steady, light. F R
2. Occulting light:
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 (2)) or a composite group (Oc (2+1)).
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
3. 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".
Isophase Iso The duration of the light and dark periods are equal. Iso R 4s
4. 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". The duration of a flash can be different per lighthouse.
As an example: the Buchan Ness lighthouse has a white flash of 0.3s and a dark period of 4.7s. (fl. 0.3s - ec. 4.7s)

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.

4.1 Single-flashing Fl A flash is repeated regularly at a rate below 50 per minute. Fl G 5s
4.2 Long-flashing LFl A light flash, duration of less than 2 seconds (long flash) is repeated regularly. LFl 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. Quick light:
A quick light, abbreviated "Q", is a special case of a flashing light with a large frequency (more than 50 and 79 flashes 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".
5.1 Continuous quick Q Quick flashes are repeated regularly. Q W 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 IQ The sequence of flashes is regularly interrupted by dark intervals of constant duration. IQ R 14s
6. Very quick:
Flashes are repeated at a frequency between 80 and 159 lightning per minute.
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 IVQ The sequence of flashes is regularly interrupted by dark intervals of constant duration. IVQ R 9s
7. Ultra quick:
The flashes are repeated at a frequency equal to or greater than 160 flashes 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".
7.1 Continuous ultra quick UQ Ultra quick flashes are repeated regularly. UQ W
7.2 Interrupted ultra quick IUQ The sequence of ultra quick flashes is regularly interrupted by dark intervals of constant duration. IUQ R 6s
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
9. Fixed and flashing
FFl 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. FFl Y 5s
10. Alternating
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