First Fresnel lens in a lighthouse

Seeking to improve the visibility and reach of lighthouse beams, French physicist and civil engineer Augustin-Jean Fresnel developed a new type of lens in the early 19th century that used both refraction and reflection to drastically reduce light wastage (using about 80% of available light). The first of these lenses to be installed in a lighthouse was at Cordouan Lighthouse in the Gironde Estuary off western France, which was activated on 25 July 1823. It could be seen more than 20 miles (37 km) out at sea.

Fresnel developed a series of lenses that were divided into six "orders" based on size and focal length. The largest that he developed, known as 1st-class lenses, stood about 2.6 m (8 ft 6 in) tall and could project light as far as 26 mi (42 km) out to sea. In his wake, others developed even larger models, known as hyper-radials, that measured up to 7 m (23 ft) tall and weighed around 10 tonnes (11 US tons); these are the largest lighthouse optics ever to have been made.

Having proven their success, Fresnel lenses were adopted as the standard for all lighthouses in the decades that followed. The first Fresnel lens fitted in a US lighthouse was Navesink Lighthouse in New Jersey in 1841. Although originally designed to work with oil and gas lamps, the lenses worked just as well with electric-powered lights as they emerged in the latter 19th century. Some lighthouses still use their original glass Fresnel lenses to this day, though many have been replaced with more cost-effective and durable plastic versions, which nevertheless still make use of Fresnel's innovative design.

Although lighthouses are less of a necessity in modern times, thanks to developments such as GPS and radar, Fresnel lenses still have many applications in scientific research and everyday technology including cameras, solar panels, spotlights, traffic lights and ATM machines to name just a few.

Completed in 1611, the 67.5-m (221-ft) stone Cordouan Lighthouse is France's oldest active lighthouse. It sits on an islet in the Gironde Estuary, though during low tide is sometimes accessible via large sandbanks and a manmade causeway.