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)