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Navigational Light Characteristics.

Navigational chart light characteristics.
Light pattern. Chart
abbrev. 		Description.
  F. Continuous fixed light.
______     ______     ______     ______ Fl. Flashing. Light shorter than dark.
___           ___           ___           ___ Occ. Occulting. Dark shorter than light.
___      ___      ___      ___      ___      _ Iso. Isophase. Equal amounts of light and dark.
___  _  _  ___  _  _  ___  _  _  ___  _  _  Gp.Fl.(3) Group flashing. In this case, groups of three.
_  _            _  _            _  _            _  _ Gp.Occ.(2) Group occulting. In this case, groups of two.
___  _  __  _____  _  __  _____  _  __  Gp.Fl.(2+1) Composite group flashing.
_  _  _  _  _  _  _  _  _  _  _  _  _  _  _  _  Qk.Fl. Quick flashing 50 or 60 per minute.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ V.Qk.Fl. Very quick flashing 100 0r 120 per minute.
_  _  _  _  _  _  _  _  _  ____  _  _  _  _  Int.Qk.Fl. Interrupted quick flashing.
_ _ _ _ _ _ _ _ _ _ _ ______ _ _ _ _ _ _ Int.V.Qk.Fl. Interrupted very quick flashing 100 0r 120 per minute.
___      ___      ___      ___      ___      _ Alt. Alternating. Changing colour. In this case white and red.
Notes.
  • The period of a light is the length of time taken (in seconds) to complete one full cycle. E.g. 10s is a period of ten seconds.
  • The height (in metres) of a light above 'mean high water springs' (MHWS) is denoted by a small m. E.g. 15m indicates a height of fifteen metres.
  • The range (in nautical miles) at which a light can be seen in good visibility is denoted by a capital M. E.g. 25M indicates a range of twenty five nautical miles.
  • The colour of a light is usually denoted by the first letter. e.g. R is red, G is green.
Example.
A light marked on a chart as 'Gp.Fl.(3)20s 15m 25M' would indicate, a light flashing in groups of three every twenty seconds at a height of fifteen metres above MHWS that could be seen at a distance of twenty five nautical miles in good visibility.

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