The first open sea lighthouse went up on the Eddystone Rocks off England in 1696, when Henry Winstanley anchored an octagonal wooden tower with 12 iron stanchions. The Great Storm of 1703 tore it away with Winstanley inside. In 1759 John Smeaton rebuilt it in granite shaped like an oak trunk, with a broad curving base that bleeds off wave energy, blocks dovetailed together and pinned with marble dowels, and hydraulic lime that cures underwater. Site dictated form elsewhere: tall towers on flat Cape May, a light at Point Loma set so high it sat in the fog and had to be replaced, and Alexander Mitchell’s 1838 screw pile towers for sand and mud.

Light itself needed invention. Bonfires burned too fast and smoked, so Ami Argand’s 1782 lamp used a hollow wick for clean combustion, Arthur Kitson’s 1901 vaporized oil burner was six times brighter, and Gustaf Dalén made acetylene safe with a porous filler and built the sun valve, a blackened rod that switched the gas off at dawn. In 1823 Augustin Fresnel’s ringed lens at Cordouan multiplied usable light fourfold, and rotating lenses gave each tower its own flash pattern. Later, the Soviet Union powered remote Arctic lights with strontium-90 generators, many lost when the state collapsed and stripped by scavengers who were exposed to radiation.

• Visible range follows a formula: 1.22 times the square root of the light’s height gives distance in nautical miles.
• Souter Lighthouse in 1871 was the first designed specifically for electric light.
• A 1971 laser at Point Danger in Queensland was scrapped because its beam was too narrow to spot.
• Modern LEDs last up to 100,000 hours against about 1,000 for a filament bulb.
• Canada keeps human keepers at automated Machias Seal Island Lighthouse to assert its claim against the United States.