thumb|400px|Symbols and abbreviations for light characteristics

<!--thumb|400px|Symbols and abbreviations for light characteristics-->

<!-- thumb|400px|Flørauden seamark in Norway with its light characteristics and [[sector light ]]-->

A light characteristic is all of the properties that make a particular navigational light identifiable. Graphical and textual descriptions of navigational light sequences and colours are displayed on nautical charts and in Light Lists with the chart symbol for a lighthouse, lightvessel, buoy or sea mark with a light on it. Different lights use different colours, frequencies and light patterns, so mariners can identify which light they are seeing.

Standardisation

The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) publishes a recommendation R1001, "The IALA Maritime Buoyage System (MBS)", which is stated within to be adopted by almost all marine aids to navigation authorities. This recommendation sets out recommended light characteristics for different types of marine aids to navigation within the categories of lateral marks, cardinal marks, isolated danger marks, safe water marks, special marks, emergency wreck marks and other marks such as lighthouses. Depending on the marine aid to navigation, this recommendation includes specification of light colours (such as "red") and light patterns (such as "Fl" for flashing).

Light colours are defined in recommendation R0201, "Marine Signal Lights-Colours (E200-1)". This recommendation specifies for each named colour a polygon within the CIE 1931 color space for acceptable shades of the named colour a marine aid to navigation may exhibit.

Light patterns, including abbreviations, are defined in recommendation R0110, "Rhythmic Characters of Lights on Aids to Navigation".

Abbreviations

right|thumb|400px|Lightcharacter of the "Egmond aan Zee" (NL) lighthouse

While light characteristics can be described in prose, e.g. "Flashing white every two 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 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, "Bu" for blue. 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 metres.

:* The range in which the light is visible, e.g. "10M" for 10 nautical miles. (ca. 18.5 kilometers)

:* A light that only shines in one direction, "Dir.". This is also indicated by a sector in which the light can be seen. In the figure of the lighthouse at "Egmond aan Zee" (Netherlands) two sectors are indicated; a white sector from 10° to 175° and a red sector from 175° to 188°.

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 the nominal range is 10 nautical miles.

Light patterns

Fixed light

Fixed lights, abbreviated "F", 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