Editing Lighthouse (section)

===Optical systems===
[[File:Fresnel lighthouse lens diagram.png|thumb|right|Diagram depicting how a spherical [[Fresnel lens]] collimates light]]
With the development of the steady illumination of the Argand lamp, the application of optical lenses to increase and focus the light intensity became a practical possibility. [[William Hutchinson (privateer)|William Hutchinson]] developed the first practical optical system in 1777, known as a [[catoptrics|catoptric]] system.<ref>{{cite web | title=Illumination, Refraction, Fresnel Lens | website=Encyclopedia Britannica | date=9 October 1998 | url=https://www.britannica.com/technology/lighthouse/Optical-equipment#ref593050 | access-date=2 June 2024}}</ref> This rudimentary system effectively collimated the emitted light into a concentrated beam, thereby greatly increasing the light's visibility.<ref>{{cite encyclopedia|url=https://www.britannica.com/EBchecked/topic/340721/lighthouse/72152/Oil-lamps|title=Lighthouse|encyclopedia=Encyclopædia Britannica|access-date=6 January 2014}}</ref> The ability to focus the light led to the first revolving lighthouse beams, where the light would appear to the mariners as a series of intermittent flashes. It also became possible to transmit complex signals using the light flashes.

French physicist and engineer [[Augustin-Jean Fresnel]] developed the multi-part [[Fresnel lens]] for use in lighthouses. His design allowed for the construction of lenses of large [[aperture]] and short [[focal length]], without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can also capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances.

The first Fresnel lens was used in 1823 in the [[Cordouan lighthouse]] at the mouth of the [[Gironde estuary]]; its light could be seen from more than {{convert|20|mi|km}} out.<ref>Watson, Bruce. "Science Makes a Better Lighthouse Lens." ''Smithsonian''. August 1999 v30 i5 p30.
produced in ''Biography Resource Center''. Farmington Hills, Mich.: Thomson Gale. 2005.</ref> Fresnel's invention increased the [[luminosity]] of the lighthouse lamp by a factor of four and his system is still in common use.