Lighthouse Engineering

The Lighthouse of Alexandria was built on the island of Pharos in Alexandria, Egypt, around 280 BC. Standing approximately 100-130 meters tall, it was one of the tallest structures in the ancient world and guided sailors for centuries.

The Fresnel lens, invented by French physicist Augustin-Jean Fresnel in 1822, uses concentric rings of prisms to concentrate light into a powerful beam. It could make a lighthouse visible from over 20 miles away.

The Eddystone Lighthouse was built on the treacherous Eddystone Rocks, a reef 14 miles south of Plymouth. It has been rebuilt four times since 1698, with each version overcoming the extreme challenges of building on exposed rock in the open sea.

Each lighthouse has a unique flash pattern (called its 'characteristic') so that sailors can identify exactly which lighthouse they are seeing. These patterns are published in nautical charts and 'Light Lists.'

The Stevenson family (including Robert, Alan, David, and Thomas Stevenson) designed and built over 100 lighthouses around Scotland's dangerous coastline over four generations. Robert Louis Stevenson, the famous author, was Thomas's son.

Whale oil was the primary fuel for lighthouses in the 18th and early 19th centuries, later replaced by kerosene (paraffin oil) in the mid-1800s. Kerosene was cheaper, brighter, and more readily available than whale oil.

In 1999, the entire 4,830-ton Cape Hatteras Lighthouse was moved 2,900 feet (884 meters) inland to protect it from shoreline erosion. The move took 23 days and is one of the largest structures ever relocated.

John Smeaton developed a hydraulic lime cement for the third Eddystone Lighthouse that could set underwater. This early form of concrete was revolutionary and influenced the development of Portland cement and modern concrete.

A lightship was a vessel anchored at a specific location to serve as a floating lighthouse where it was impractical or impossible to build a permanent structure, such as over deep water, shifting shoals, or busy shipping channels.

The Tower of Hercules in A Coruna, Spain, is the oldest known Roman lighthouse still in operation. Built in the 1st or 2nd century AD, it stands 55 meters tall and was designated a UNESCO World Heritage Site in 2009.

A fog signal is an audible warning device (such as a foghorn, bell, cannon, or compressed air horn) used at lighthouses and other navigation points when fog or poor visibility makes the light ineffective for guiding ships.

Robert Stevenson designed and built the Bell Rock Lighthouse on a reef that is submerged at high tide, 12 miles off the coast of Angus, Scotland. It is the world's oldest surviving sea-washed lighthouse.

GPS (Global Positioning System) and electronic chart systems largely replaced the navigational role of lighthouses by the late 20th century. Most lighthouses have been automated or decommissioned, though many are preserved as historic monuments.

West Quoddy Head Lighthouse in Lubec, Maine, marks the easternmost point of the contiguous United States. Its distinctive red and white horizontal stripes make it one of the most photographed lighthouses in America.

Range lights (or leading lights) consist of two lights placed at different heights and distances. When a vessel aligns the two lights vertically, it confirms it is on the correct course through a safe channel.