Reading Light Descriptions on Charts
On a chart, a light is described in a standard format, e.g., 'Fl(2) WR 10s 15m 12M'. This reads: Group flashing (2 flashes), White and Red sectors, period 10 seconds, height 15 metres above MHWS, nominal range 12 nautical miles.
The period is the time for one complete cycle of the light pattern. The range is the 'nominal range' — the distance the light can be seen in clear visibility (meteorological visibility of 10 nautical miles). The height is measured above Mean High Water Springs (MHWS).
Key Points
- Chart format: Character Colour Period Height Range
- Example: Fl(2) WR 10s 15m 12M
- Period = time for one complete cycle
- Height = above Mean High Water Springs (MHWS)
- Range = nominal range in nautical miles (in clear visibility)
Tip: Use the period to confirm identification: count the time for one complete cycle with a watch and match it to the chart.