Lighthouses are essential landmarks for navigation at sea, providing sailors with indications of their position and the dangers to be avoided. But how do you determine how far away you can see a lighthouse? Several notions come into play: luminous range, geographical range and nominal range.
The different ranges of a lighthouse
- Geographical scope
This is the maximum distance at which a lighthouse can be seen, depending on the Earth's curvature and the observer's altitude. It is calculated using the formula :
Geographic range = 2.10 × (?Height of lighthouse + ?Height of observer)
With heights expressed in metres, the range obtained is in nautical miles. The higher the lighthouse and the observer, the greater the geographical range. - Light range
It depends on the power of the light source and weather conditions. A clear atmosphere allows you to observe a lighthouse from a greater distance, while fog greatly reduces this distance. - L he nominal range
The nominal range of a lighthouse is the distance at which its light is visible in clear weather, with standard meteorology (visibility of 10 nautical miles). It is indicated on nautical charts and allows navigators to anticipate the perception of the lighthouse according to navigation conditions.
Classifying lighthouses by range and function
Headlights are classified according to their position and role:
- Coastal lighthouses they are located on land and serve as a reference for navigators along the coast. Their range can reach 25 to 30 nautical miles.
- Landing lights erected on islands or promontories, they guide ships to ports or access channels.
- Lighthouses on the high seas they are placed on rocks or submerged sandbanks, to indicate isolated hazards. They are often the most exposed to storms.
