Admiralty Nautical Publications

Characteristics of Lights

• Additional information about lights not found on charts can be found in the Admiralty List of Lights and Fog Signals (NP 74 to 84) or the Admiralty Sailing Directions (NP 1 to 72)
• The characteristics of a light are its sequence of light and darkness and, in some cases, its color
• Lights can be divided into three classes: fixed, rhythmic, and alternating

Fixed Lights

• Fixed lights show continuously and steadily without interruption

Rhythmic Lights

• Rhythmic lights show a sequence of intervals of light and darkness
• The whole sequence is repeated at regular intervals
• Terms used to describe rhythmic lights include:
  • Period: the time taken to complete one sequence
  • Phase: one element of a sequence (e.g. a flash, an eclipse)