How Far Could The Pigeon Point Light-house Be Seen?
The tower is 115 feet tall. The center of the lens, the “focal plane,” is 100 feet above the ground. Add to that height the fifty feet of the bluff the tower is built on, and the light from the lens is about 150 feet above the sea. Why is that important? The distance from which the light can be seen is, under clear conditions, only limited by the horizon. The distance you can see to the horizon is determined by how high you’re above the sea. For example, say you’re on the deck of a ship, maybe 10 feet above the water. At that height you could see 3.6 nautical miles. The light-house at 150 feet above sea level could be seen 14 nautical miles. Add the two together and, under clear conditions, the person standing on the deck of a ship 10 feet above the water could see the Pigeon Point Light-house 17.6 nautical miles away. What if the person at sea is up at the ship’s masthead to get a better view? Say 60 feet above the water. For an elevation of 60 the horizon would be 8.8 nautical miles.
