I’ve been listening to a podcast where they cover the mystery of the Flannan Island lighthouse and it struck me that i’ve never actually understood how a lighthouse works other than shining a beam of light at the ocean? How do the ships know what do and how to steer through the water?
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During the daytime, navigation around coastlines is relatively simple – you just compare the land you see with your charts and you can pinpoint your location.
Around coastlines this can be very important, as the boundary between the land and sea can be very dangerous, with hidden rocks and reefs that can damage the hull of a ship, and unpredictable currents that will change based on tides and other factors. So by being able to locate yourself on your charts, you can make sure to avoid the dangerous bits.
At night however, or when caught in a bad storm, you lose this point of reference – you may not be able to see exactly where the land is, or in enough detail to locate yourself accurately, which puts you in a dangerous position.
The lighthouse is a solution to this – a tall tower with a flashing light at the top means it will be visible from long distances, even in pretty poor weather, so being able to spot a lighthouse means you have something to align yourself with on your charts.
In addition to this, you can also use the flashing light to send a message – by flashing using different speeds or patterns, you can make it so that every lighthouse is different, which means a sailor can compare the pattern they see against the list of different lighthouses and pinpoint where they are.
A lot of this is pretty superfluous nowadays – modern technology like GPS means you always know where you are and what is around you, but jump back a few hundred years to a boat coming into sight of land after crossing the Atlantic, and spotting a lighthouse would let you pinpoint your location on a currently unknown coastline, and allow you to find port.
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