Module 12 of 17
Visual Aids to Navigation
Lighthouses, beacons, and light characteristics used for navigation.
Why Visual Aids Matter
Visual aids to navigation — lighthouses, beacons, light vessels, and lit buoys — are essential for safe navigation, especially at night and in poor visibility. Understanding light characteristics allows you to identify exactly which light you are seeing, confirm your position, and navigate safely.
All lights are catalogued in the Admiralty List of Lights and charted on nautical charts with abbreviated descriptions of their characteristics.
Key Points
- Lighthouses and lit marks help fix position, especially at night
- Each light has a unique characteristic (colour, pattern, period)
- Light characteristics are shown on charts and in the Admiralty List of Lights
Light Characteristics
Every navigational light has a defined character — the pattern of light and dark. The most common types are: Fixed (F) — a continuous steady light. Flashing (Fl) — a single flash repeated at regular intervals, where dark is longer than light. Isophase (Iso) — equal periods of light and dark. Occulting (Oc) — steady light with regular periods of darkness (light is longer than dark).
Quick (Q) — rapid continuous flashing (50–79 per minute). Very Quick (VQ) — very rapid flashing (80–159 per minute). Group Flashing — shows groups of flashes, e.g., Fl(3) means a group of 3 flashes. Long Flash (LFl) — a flash of 2 seconds or more.
Key Points
- F = Fixed (continuous light)
- Fl = Flashing (flash shorter than dark)
- Iso = Isophase (equal light and dark)
- Oc = Occulting (light longer than dark)
- Q = Quick flashing; VQ = Very Quick flashing
- Fl(3) = Group of 3 flashes
- LFl = Long flash (≥2 seconds)
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