Largest lighthouse lenses

The largest type of lens ever to be fitted in lighthouses were known as "hyper-radials" or "hyper-radiants" with a focal length of 1,330 mm (52.4 in); these giant glass lenses measured up to 7 m (23 ft) tall and could weigh in excess of 10 tonnes (11 US tons). A supersized version of the existing Fresnel lens, they were first conceived of in the mid-19th century with the earliest prototype developed in 1885. The first hyper-radial in operation was in the Tory Island Lighthouse in Ireland in 1887. In all, only 33 hyper-radial lenses were ever installed (in 31 lighthouses).

Hyper-radial lenses were first proposed by the Scottish engineer Thomas Stevenson of the Northern Lighthouse Board in 1869. The need for larger lenses was deemed necessary to maintain brightness as the fuel source/burning apparatus for lighthouse lanterns changed from oil and wicks to more modern fuels such as kerosene, coal gas and electricity. A series of tests was conducted at South Foreland Lighthouse in Kent, UK, in 1884-85 to determine the most proficient lens design and fuel.

The first prototype hyper-radial lens was produced by the F Barbier Company of Paris, France, in 1885 for use in the trials at South Foreland (now on display at the National Museum of Scotland). The first hyper-radial to be lit in a lighthouse was created by West Midlands glassmakers, Chance Brothers Co (UK) in 1887.

Of the 33 lenses installed, only a handful are thought to remain intact and still in situ in their lighthouses to this day including Makapu'u Point in Hawaii, USA (installed in 1887), Cabo de Santa Marta in Brazil (installed in 1891), Hyskeir in Scotland's Inner Hebrides, UK (installed in 1904) and Cape Race in Newfoundland, Canada (installed in 1907).

Seeking to improve the visibility and range 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 was at Cordouan Lighthouse (built in 1611) 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.

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 lighthouses are less of a necessity in modern times, thanks to developments in GPS, radar and communication technology, 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.