Light characteristics in their real rhythm
At night a light gives itself away only by its rhythm: flashing, quick, isophase or occulting, single or in groups. To learn light characteristics you need the rhythm in your head, not just the abbreviation on the chart. Pick one and watch the lights in their real rhythm.
Quiz: which light is that?
Watch a few cycles, count the flashes and tap the characteristic.
Characteristics at a glance
The abbreviations as printed on the chart, with the period after which the rhythm repeats.
- F
- Fixed light, steady. Often on pier heads and harbour entrances, usually red or green.
- Iso 4s
- Isophase, light and dark equal. White often marks safe water or a landfall buoy.
- Oc 4s
- Occulting, light longer than dark. White often marks safe water; coloured also on lateral marks.
- Oc(2) 8s
- Group occulting, two eclipses. On leading lights and lateral marks, colour by side.
- Fl 5s
- Flashing, short light, long dark. Red or green on lateral buoys, red to port when entering.
- Fl(2) 5s
- Group flashing, two. White: isolated danger mark, black with a red band and two balls.
- Fl(3) 10s
- Group flashing, three. Red or green on lateral marks, often to tell neighbouring buoys apart.
- Fl(2+1) 10s
- Composite group flashing 2+1. Red or green on preferred channel marks where a channel divides.
- LFl 10s
- Long flash, at least two seconds. White every ten seconds: safe water mark.
- Q
- Quick, 50 to 79 per minute. White continuous: north cardinal mark.
- VQ
- Very quick, 80 to 159 per minute. White continuous: also a north cardinal mark.
- Q(3) 10s
- Quick group of three. White: east cardinal, three like three o’clock.
- Q(6)+LFl 15s
- Six quick plus a long flash. White: south cardinal, six like six o’clock.
- Q(9) 15s
- Quick group of nine. White: west cardinal, nine like nine o’clock.
- Mo(A) 8s
- Morse code A, short long. White: safe water or landfall buoy.
Simplified for learning. The chart and the list of lights are what count.
