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Construction

Let me say something about how we built light-houses in my day. The Pigeon Point Light-house is an 1870's style American light-house. The tallest light-house in America, the Cape Hatteras light-house in North Carolina, was the first one built in this style. Pigeon Point was built of bricks with no additional reinforcement. The walls are very thick here at the base. As you go up higher in the structure, the walls are thinner.

The 1870 style light-houses use double wall construction. They did this for three reasons: First, the air space between the two walls improved the insulation. The inside was warmer in the winter and cooler in the summer. Second, they could build a light-house with fewer bricks. Fewer bricks mean they were able to save money. About 500,000 bricks were used to build the Pigeon Point Light-house. Third, since the tower was lighter than a solid brick wall tower, it could be built on ground that wouldn't support a more massive structure. We knew how to build them well in the old days. In the famous 1906 earthquake, this light-house came through with flying colors.

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. 8.8 nautical miles plus the light-house's 14 nautical miles means the person at sea up at the masthead could see Pigeon Point's light from 22.8 nautical miles away.