The lighthouse at El Morro castle is one of the unmistakable symbols of Havana. It draws a steady stream of tourists.
Workers built the lighthouse in 1844, replacing the one that had been standing since 1764, according to the Virtual Tourist.
Sperm whale oil used to light the lamps in lighthouses. Lighthouses weren't as bright back then because much of the light was scattered in all directions.
In 1822, a Frenchman named Augustine Fresnel came up with a new approach - a lens that used prisms to capture and direct more than 80 percent of the light source, according to this article on the lenses.
The lens at the lighthouse at El Morro.
Eventually, seven kinds of Fresnel lenses were created. They vary in size and strength. It looks like the lens in the El Morro lighthouse may be a Fourth-order Fresnel lens, but I'm just guessing.