Oldest offshore lighthouse still in operation

The first offshore lighthouse was Cordouan Lighthouse in the Gironde Estuary of western France, designed by French architect Louis de Foix and built between 1584 and 1611. Still active in 2022, it is the oldest active lighthouse in France. Situated some 7 km (4.3 mi) off the coast, it sits on a small island in a tidal zone where at low tide numerous sand banks are exposed providing limited access from the mainland. Cordouan Lighthouse underwent extensive restoration and was considerably heightened in the 1780s overseen by engineer Joseph Teulère. It now stands 68 metres (223 feet) tall.

More primitive beacons had been present intermittently on the islet of Cordouan since the late ninth century CE. A more prominent structure comprising a wooden platform with a fire was installed by the Black Prince (Prince Edward of Wales) in the 14th century when England occupied this territory. But it wasn't until the late 16th century that a permanent stone lighthouse was commissioned by the French King Henry III.

Cordouan Lighthouse was the first in the world to permanently install the much more powerful "Fresnel lens" in its lantern on 25 July 1823. It could be seen more than 20 miles (37 km) out at sea. It was developed by the French physicist and civil engineer Augustin-Jean Fresnel to use both refraction and reflection to drastically reduce light wastage (using about 80% of available light).

By contrast, open-sea (or sea-washed) lighthouses are those built in non-tidal areas that are permanently surrounded by deep waters. The oldest open-sea lighthouse still in operation is Bell Rock Lighthouse built by British civil engineer Robert Stevenson and completed in 1811 on Bell Rock, a small 130 x 70 m sandstone reef some 18 km (11 mi) off the east coast of Scotland, UK. The lighthouse is built from granite and sandstone and has been operational since 1 February 1811; it was automated in 1988.