The problem a lighthouse solves
A ship approaching land at night or in poor weather faces a simple danger: it cannot see rocks, shoals or the shape of the coast until it is too late. A lighthouse is a fixed, recognizable mark, visible from far enough away to give a navigator a position and a warning. Almost everything about the history of the coastal lighthouse comes down to two questions: how to make the light brighter, and how to make the tower last.
Fires and the Pharos
The earliest navigational lights were probably open fires on hills or headlands, and the practice is hard to date. The most famous ancient lighthouse was the Pharos of Alexandria, built on an island at the harbor entrance during the reign of the early Ptolemies, in the third century BCE. It was counted among the Seven Wonders of the Ancient World and was said to be extremely tall, though accounts of its height vary. It was damaged by earthquakes over the centuries and eventually collapsed, and the word for lighthouse in several languages, such as the French phare, comes from its name.
The Romans built towers with fires at various ports, and the Tower of Hercules at A Coruña in Spain, a Roman-era structure that was later restored, is often mentioned as one still standing in some form. Through the medieval period, coastal lights were lit by wood or coal fires in iron baskets, or by candles. They were smoky, sometimes unreliable, and in some places maintained by local authorities, religious houses or trade guilds rather than any national system.
From coal fires to oil lamps
By the seventeenth and eighteenth centuries, coal fires still burned on many British and European towers. A major step came in the 1780s with the Argand lamp, an oil lamp with a hollow circular wick that let air reach the flame from inside as well as outside. This produced a steadier and brighter light with less smoke. Lighthouse engineers combined such lamps with polished metal reflectors, often parabolic or similar in shape, to project the beam out to sea. Different fuels followed, including whale oil and colza oil, and later mineral oil as petroleum refining developed in the second half of the nineteenth century.
Building on rocks: the Eddystone
Some of the most dangerous reefs lay far out at sea, and building on them was a challenge. The Eddystone rocks off Plymouth in England had a series of lighthouses beginning in the late seventeenth century. Earlier towers of wood were destroyed by storms or fire. John Smeaton’s tower, completed in 1759, used interlocking blocks of granite and a hydraulic lime mortar that set even in damp conditions. His experiments with mortar are often mentioned alongside the ancient Roman concrete tradition, though his work was original in its own right. Smeaton’s design, narrow at the top and flared at the base like an oak trunk, influenced later towers.
The Fresnel lens
The greatest advance in optics came from the French physicist Augustin-Jean Fresnel. In the early 1820s, he developed a lens made of many glass rings and prisms arranged around a central bull’s-eye. Instead of a thick lump of glass, this design used concentric sections that bent light from the lamp into a narrow beam, while collecting much more of the lamp’s output than a mirror reflector. The first installation is usually given as the Cordouan lighthouse at the mouth of the Gironde in France, around 1823.
Fresnel lenses were made in standardized sizes, or “orders”, from large first-order lenses for major coastal lights down to smaller ones for harbors. Rotating the lens, often on a clockwork mechanism, created a flashing signal, so that each lighthouse could be identified by its pattern of flashes and pauses, called its characteristic. Mariners could look up that pattern on a chart and know which light they were seeing.
Keepers, fog signals and new light sources
Many lighthouses were staffed by keepers who trimmed wicks, cleaned lenses, wound clockwork and maintained the tower, often with their families living nearby. Weather could hide any light, so fog signals such as bells, horns and sirens were added at many stations.
Light sources kept changing. Some lighthouses tried electric arc lamps in the later nineteenth century. In the twentieth century, electric lighting gradually replaced oil, and the incandescent bulb became standard inside Fresnel lenses. Many lighthouses were automated, and keepers were withdrawn from most stations over the second half of the century. Modern lights are often LED-based, and some are small solar-powered beacons.
Do lighthouses still matter
Satellite navigation and radar detection have made it far easier for ships to find their position, and the number of staffed lighthouses has fallen sharply. Even so, many lights remain in service, partly because electronic systems can fail and partly because a visible mark is a useful independent check. Many historic towers are preserved as museums or landmarks, and surviving Fresnel lenses are valued for their craftsmanship.