Brief #010 · LIGHTS
How a lighthouse tells you which one it is
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Every light has a characteristic on the chart: rhythm, period, height and range. Bishop Rock is Fl(2) 15s; Round Island, six miles away, is Fl 10s.
Light rhythms are written the same way in IALA regions A and B; examples are in region A (Isles of Scilly).
Transcript
At night, every lighthouse signs its name in light. Here's how to read it.
On the chart, Bishop Rock is written like this: Fl 2, 15 s, 44 m, 20 M.
Fl 2 means flashing, in groups of two.
Flashing means the light is shorter than the dark.
Occulting is the reverse: more light than dark. Isophase: equal.
15 s is the period: one full sequence, in seconds.
Then the height, 44 metres, and the range, 20 nautical miles.
Six miles away, Round Island: Fl 10 s. One flash, every ten seconds.
Find the light on your chart, then count the period. Follow for the next brief.