1. directional function: a light illuminating a sector of very narrow angle and intended to mark a direction to follow. (IHO Dictionary, S-32, 5th Edition, 2778)
  2. leading light: a light associated with other lights so as to form a leading line to be followed. (adapted from IHO Dictionary, S-32, 5th Edition, 2794)
  3. rear/upper light
  4. front/lower light
  5. aero light: an aero light is established for aeronautical navigation and may be of higher power than marine lights and visible from well offshore. (IHO Chart Specifications, M-4, 476.1)
  6. air obstruction light: a light marking an obstacle which constitutes a danger to air navigation. (IHO Dictionary, S-32, 5th Edition, 2767)
  7. fog detector light: a light used to automatically determine conditions of visibility which warrant the turning on or off of a sound signal. (IHO Dictionary, S-32, 5th Edition, 1885)
  8. flood light: a broad beam light used to illuminate a structure or area. (adapted from The Collins Dictionary)
  9. strip light: a light whose source has a linear form generally horizontal, which can reach a length of several metres. (IHO Chart Specifications, M-4, 478.5)
  10. subsidiary light: a light placed on or near the support of a main light and having a special use in navigation. (Admiralty List of Radio Signals, UK Hydrographic Office)
  11. spotlight: a powerful light focused so as to illuminate a small area. (The Collins Dictionary)
  12. front, rear, upper, lower: terms used with leading lights to describe the position of the light on the lead as viewed from seaward.
  13. moiré effect: a short range (up to 2km) type of directional light. Sodium lighting gives a yellow background to a screen on which a vertical black line will be seen by an observer on the centre line. (IHO Chart Specifications, M-4, 475.8)
  14. emergency light: a light available as a backup to a main light which will be illuminated should the main light fail.
  15. bearing light: a light which enables its approximate bearing to be obtained without the use of a compass. (IHO Chart Specifications, M-4, 478.1)
  16. horizontally disposed: a group of lights of identical character and almost identical position, that are disposed horizontally.
  17. vertically disposed: a group of lights of identical character and almost identical position, that are disposed vertically.