View source for Fresnel lens

{{Short description|Compact composite lens}}
[[File:MuseeMarine-phareFresnel-p1000466.jpg|thumb|First-order rotating catadioptric Fresnel lens, dated 1870, displayed at the ''[[Musée national de la Marine]]'', Paris. In this case the dioptric prisms (inside the bronze rings) and catadioptric prisms (outside) are arranged to concentrate the light from the central lamp into four revolving beams, seen by sailors as four flashes per revolution. The assembly stands {{convert|2.54|m|feet}} tall and weighs about {{convert|1.5|tonne|lb}}.]]

A '''Fresnel lens''' ({{IPAc-en|'|f|r|ei|n|ɛ|l|,_|-|n|əl}} {{respell|FRAY|nel|,_|-|nəl}}; {{IPAc-en|'|f|r|ɛ|n|ɛ|l|,_|-|əl}} {{respell|FREN|el|,_|-|əl}}; or {{IPAc-en|f|r|eɪ|ˈ|n|ɛ|l}} {{respell|fray|NEL}}<ref>{{cite book|mode=cs2|author=J.&nbsp;Wells|author-link=John C. Wells|title=Longman Pronunciation Dictionary|publisher=Pearson Longman|edition=3rd|date=3 April 2008|isbn=978-1-4058-8118-0}}.</ref>) is a type of composite compact [[lens (optics)|lens]] which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections.

The simpler [[Dioptrics|dioptric]] (purely [[refraction|refractive]]) form of the lens was first proposed by [[Georges-Louis Leclerc, Comte de Buffon]]{{r|chisholm-1911-lighthouse}}, and independently reinvented by the French physicist [[Augustin-Jean Fresnel]] (1788–1827) for use in [[lighthouse]]s.<ref>{{cite encyclopedia |mode=cs2 |url=http://www.merriam-webster.com/dictionary/fresnel%20lens |title=Fresnel lens |dictionary=[[Merriam-Webster]] |access-date=19 March 2013 |url-status=live |archive-url=https://web.archive.org/web/20131217120005/http://www.merriam-webster.com/dictionary/fresnel%20lens |archive-date=17 December 2013}}.</ref><ref>{{cite book|mode=cs2 |last=Wells|first=John|author-link=John C. Wells|title=Longman Pronunciation Dictionary|publisher=Pearson Longman|edition=3rd|date=3 April 2008|isbn=978-1-4058-8118-0}}.</ref> The [[Catadioptric system|catadioptric]] (combining refraction and reflection) form of the lens, entirely invented by Fresnel, has outer [[Prism (optics)|prismatic]] elements that use [[total internal reflection]] as well as refraction to capture more oblique light from the light source and add it to the beam, making it visible at greater distances.

The design allows 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.

Because of its use in lighthouses, it has been called "the invention that saved a million ships".<ref>{{cite news|mode=cs2 |url=http://www.bbc.com/travel/story/20190620-the-invention-that-saved-a-million-ships |title=The invention that saved a million ships |last=Bernhard |first=Adrienne |publisher=BBC |date=21 June 2019 |access-date=2019-08-04}}.</ref>

== History ==

=== Forerunners ===

The first person to focus a lighthouse beam using a lens was the London glass-cutter Thomas Rogers, who proposed the idea to [[Trinity House]] in 1788.{{r|tag-prior}} The first Rogers lenses, {{Convert|53|cm|in|abbr=in}} in diameter and {{Convert|14|cm|in|abbr=in}} thick at the center, were installed at the [[Old Lower Lighthouse]] at [[Portland Bill]] in 1789. Behind each lamp was a back-coated spherical glass mirror, which reflected rear radiation back through the lamp and into the lens. Further samples were installed at [[Baily Lighthouse|Howth Baily]], [[North Foreland]], and at least four other locations by 1804. But much of the light was wasted by absorption in the glass.{{r|tag-prior}}<ref>Levitt, 2013, p.{{nbsp}}57.</ref>

In 1748, [[Georges-Louis Leclerc, Comte de Buffon]] was the first to replace a convex lens with a series of concentric [[Annulus (mathematics)|annular]] prisms, ground as steps in a single piece of glass,{{r|chisholm-1911-lighthouse}} to reduce weight and absorption. In 1790{{r|condorcet-1790}} (although secondary sources give the date as 1773{{r|appleton-1861|p=609}} or 1788{{r|tag-2017}}), the [[Marquis de Condorcet]] suggested that it would be easier to make the annular sections separately and assemble them on a frame; but even that was impractical at the time.{{r|tag-fres}}<ref name=levitt-p71>Levitt, 2013, p.{{nbsp}}71.</ref> These designs were intended not for lighthouses,{{r|chisholm-1911-lighthouse}} but for [[burning glass]]es.{{r|appleton-1861|p=609}} [[David Brewster]], however, proposed a system similar to Condorcet's in 1811,{{r|chisholm-1911-lighthouse|tag-2017|ripley-dana-1879}} and by 1820 was advocating its use in British lighthouses.{{r|chisholm-1911-brewster}}

=== Publication and refinement ===
[[File:Fresnel lighthouse lens diagram.png|thumb|Cross-section of a first-generation Fresnel lighthouse lens, with sloping mirrors&nbsp;''m,{{hsp}}n'' above and below the refractive panel&nbsp;''RC'' (with central segment&nbsp;''A''). The design was later improved by replacing the mirrors with reflective prisms to reduce losses. If the cross-section in every vertical plane through the lamp&nbsp;''L'' is the same (cylindrical symmetry), the light is spread evenly around the horizon.]]

The French {{ill|Commission des Phares|fr|Commission des phares (France)}} (Commission of Lighthouses) was established by Napoleon in 1811, and placed under the authority of French physicist [[Augustin-Jean Fresnel]]'s employer, the Corps of Bridges and Roads. As the members of the commission were otherwise occupied, it achieved little in its early years.<ref>Levitt, 2013, pp.&nbsp;49–50.</ref> However, on 21&nbsp;June 1819—three months after winning the physics {{lang|fr|Grand Prix}} of the Academy of Sciences for his celebrated memoir on [[diffraction]]—Fresnel was "temporarily" seconded to the commission on the recommendation of [[François Arago]] (a member since 1813), to review possible improvements in lighthouse illumination.{{r|tag-fres}}<ref>Levitt, 2013, pp.&nbsp;51, 53; Elton, 2009, p.{{nbsp}}190; Fresnel, 1866–70, vol.&nbsp;1, p.{{nbsp}}xcvii, and vol.&nbsp;3, p.{{nbsp}}xxiv. ("July 21" in Levitt, 2013, p.{{nbsp}}240, is a transcription error, inconsistent with the primary source cited.)</ref>

By the end of August 1819, unaware of the Buffon-Condorcet-Brewster proposal,{{r|tag-fres|ripley-dana-1879}} Fresnel made his first presentation to the commission,<ref>Fresnel, 1866–70, vol.&nbsp;3, pp.&nbsp;5–14; on the date, see p.{{nbsp}}6n. Levitt (2013, p.{{nbsp}}58) gives the date only as August 1819.</ref> recommending what he called {{lang|fr|lentilles à échelons}} ('lenses by steps') to replace the reflectors then in use, which reflected only about half of the incident light.<ref>Levitt, 2013, pp.&nbsp;56, 58.</ref> Another report by Fresnel, dated 29 August 1819 (Fresnel, 1866–70, vol.&nbsp;3, pp.&nbsp;15–21), concerns tests on reflectors, and does not mention stepped lenses except in an unrelated sketch on the last page of the manuscript. The minutes of the meetings of the Commission go back only to 1824, when Fresnel himself took over as Secretary.<ref>Fresnel, 1866–70, vol.&nbsp;3, p.{{nbsp}}6n.</ref> Thus the exact date on which Fresnel formally recommended {{lang|fr|lentilles à échelons}} is unknown.{{citation needed|date=April 2023}} Much to Fresnel's embarrassment, one of the assembled commissioners, [[Jacques Charles]], recalled Buffon's suggestion.<ref name=levitt-p59 /> However, whereas Buffon's version was [[Lens (optics)#Types of simple lenses|biconvex]] and in one piece,<ref>Levitt, 2013, p.{{nbsp}}59. The biconvex shape may be inferred from Buffon's description, quoted in Fresnel, 1822, tr.&nbsp;Tag, at p.{{nbsp}}4.</ref> Fresnel's was [[Lens (optics)#Types of simple lenses|plano-convex]] and made of multiple prisms for easier construction.

With an official budget of 500 francs, Fresnel approached three manufacturers. The third, François Soleil, found a way to remove defects by reheating and remolding the glass. Arago assisted Fresnel with the design of a modified [[Argand lamp]] with concentric wicks (a concept that Fresnel attributed to [[Benjamin Thompson|Count Rumford]]<ref>Fresnel, 1822, tr.&nbsp;Tag, p.{{nbsp}}11.</ref>), and accidentally discovered that [[fish glue]] was heat-resistant, making it suitable for use in the lens. The prototype, finished in March 1820, had a square lens panel {{Convert|55|cm|in|abbr=in}} on a side, containing 97 polygonal (not annular) prisms—and so impressed the Commission that Fresnel was asked for a full eight-panel version. This model, completed a year later in spite of insufficient funding, had panels {{Convert|76|cm|in|abbr=in}} square. In a public spectacle on the evening of 13&nbsp;April 1821, it was demonstrated by comparison with the most recent reflectors, which it suddenly rendered obsolete.<ref>Levitt, 2013, pp.&nbsp;59–66. Levitt gives the size of the eight-panel version as {{convert|28+1/3|inch|mm|order=flip|abbr=on}}. Elton (2009, p.{{nbsp}}193) gives it as 76{{nbsp}}cm (30 inches) and indicates that the first panel was tested on 31 October 1820; cf. Fresnel, 1866–70, vol.&nbsp;3, pp.&nbsp;xxxii & xxxiv, and Fresnel, 1822, tr.&nbsp;Tag, p.{{nbsp}}7.</ref>

Soon after this demonstration, Fresnel published the idea that light, including apparently [[polarization (waves)|unpolarized]] light, consists exclusively of [[transverse wave]]s, and went on to consider the implications for [[birefringence|double refraction]] and partial reflection.<ref>A. Fresnel, "Note sur le calcul des teintes que la polarisation développe dans les lames cristallisées" et&nbsp;seq., ''Annales de Chimie et de Physique'', Ser.{{nbsp}}2, vol.&nbsp;17, pp.&nbsp;102–111 (May 1821), 167–196 (June 1821), 312–315 ("Postscript", July 1821); reprinted in Fresnel, 1866–1870, vol.&nbsp;1, pp.&nbsp;609–648; translated as "On the calculation of the tints that polarization develops in crystalline plates, &amp;&nbsp;postscript", {{Zenodo|4058004}} / {{doi|10.5281/zenodo.4058004}}, 2021.</ref>

Fresnel acknowledged the British lenses and Buffon's invention in a memoir read on 29&nbsp;July 1822 and printed in the same year.<ref>Fresnel, 1822, tr.&nbsp;Tag, pp.&nbsp;2–4.</ref> The date of that memoir may be the source of the claim that Fresnel's lighthouse advocacy began two years later than Brewster's;{{r|chisholm-1911-brewster}} but the text makes it clear that Fresnel's involvement began no later than 1819.<ref>Fresnel, 1822, tr.&nbsp;Tag, p.{{nbsp}}1.</ref>

Fresnel's next lens was a rotating apparatus with eight "bull's-eye" panels, made in annular arcs by [[Saint-Gobain]],<ref name=levitt-p71 /> giving eight rotating beams—to be seen by mariners as a periodic flash. Above and behind each main panel was a smaller, sloping bull's-eye panel of trapezoidal outline with trapezoidal elements.{{r|gombert-2017}} This refracted the light to a sloping plane mirror, which then reflected it horizontally, 7&nbsp;degrees ahead of the main beam, increasing the duration of the flash.<ref>Fresnel, 1822, tr.&nbsp;Tag, pp.&nbsp;13, 25.</ref> Below the main panels were 128 small mirrors arranged in four rings, stacked like the slats of a [[louver]] or [[Venetian blind]]. Each ring, shaped like a [[frustum]] of a [[cone]], reflected the light to the horizon, giving a fainter steady light between the flashes. The official test, conducted on the unfinished {{lang|fr|[[Arc de Triomphe]]|italic=no}} on 20 August 1822, was witnessed by the Commission—and by [[Louis XVIII]] and his entourage—from {{convert|20|mi|km|order=flip}} away. The apparatus was stored at [[Bordeaux]] for the winter, and then reassembled at [[Cordouan Lighthouse]] under Fresnel's supervision—in part by Fresnel's own hands. On 25&nbsp;July 1823, the world's first lighthouse Fresnel lens was lit.<ref>Elton, 2009, p.{{nbsp}}195; Levitt, 2013, pp.&nbsp;72–76.</ref> As expected, the light was visible to the horizon, more than {{convert|20|mi|km|order=flip}} out.{{r|watson-1999}}

The day before the test of the Cordouan lens in Paris, a committee of the Academy of Sciences reported on Fresnel's memoir and supplements on double refraction—which, although less well known to modern readers than his earlier work on diffraction, struck a more decisive blow for the wave theory of light.<ref>Buchwald, 1989, pp.&nbsp;260, 288–290, 297; cf.&nbsp;Born & Wolf, 1999, p.{{nbsp}}xxviii.</ref> Between the test and the reassembly at Cordouan, Fresnel submitted his papers on [[photoelasticity]] (16&nbsp;September 1822), [[elliptical polarization|elliptical]] and [[circular polarization]] and [[optical rotation]] (9&nbsp;December), and partial reflection and [[total internal reflection]] (7&nbsp;January 1823),<ref>Fresnel, 1866–1870, vol.&nbsp;1, pp.&nbsp;713–718, 731–751, 767–799.</ref> essentially completing his reconstruction of [[physical optics]] on the [[transverse wave]] hypothesis. Shortly after the Cordouan lens was lit, Fresnel started coughing up blood.<ref name=levitt-p97>Levitt, 2013, p.{{nbsp}}97.</ref>

In May 1824,{{r|ripley-dana-1879}} Fresnel was promoted to Secretary of the {{lang|fr|Commission des Phares}}, becoming the first member of that body to draw a salary,<ref>Levitt, 2013, p.{{nbsp}}82.</ref> albeit in the concurrent role of Engineer-in-Chief.<ref>Elton, 2009, p.{{nbsp}}190.</ref> Late that year, being increasingly ill, he curtailed his fundamental research and resigned his seasonal job as an examiner at the {{lang|fr|[[École Polytechnique]]|italic=no}}, in order to save his remaining time and energy for his lighthouse work.{{r|brock-1909}}<ref>Young, 1855, p.{{nbsp}}399; Boutry, 1948, pp.&nbsp;601–602.</ref>

In the same year he designed the first ''fixed'' lens—for spreading light evenly around the horizon while minimizing waste above or below.{{r|tag-fres}} Ideally the curved refracting surfaces would be segments of [[toroid]]s about a common vertical axis, so that the dioptric panel would look like a cylindrical drum. If this was supplemented by reflecting ([[catoptrics|catoptric]]) rings above and below the refracting (dioptric) parts, the entire apparatus would look like a beehive.<ref>Cf. Elton, 2009, p.{{nbsp}}198, Figure&nbsp;12.</ref> The second Fresnel lens to enter service was indeed a fixed lens, of third order, installed at Dunkirk by 1 February 1825.<ref>Levitt, 2013, p.{{nbsp}}84.</ref> However, due to the difficulty of fabricating large toroidal prisms, this apparatus had a 16-sided polygonal plan.<ref>Elton, 2009, pp.&nbsp;197–198.</ref>

In 1825 Fresnel extended his fixed-lens design by adding a rotating array outside the fixed array. Each panel of the rotating array was to refract part of the fixed light from a horizontal fan into a narrow beam.{{r|tag-fres}}<ref>Elton, 2009, pp.&nbsp;198–199.</ref>

Also in 1825, Fresnel unveiled the {{lang|fr|Carte des Phares}} ('lighthouse map'), calling for a system of 51 lighthouses plus smaller harbor lights, in a hierarchy of lens sizes called "orders" (the first being the largest), with different characteristics to facilitate recognition: a constant light (from a fixed lens), one flash per minute (from a rotating lens with eight panels), and two per minute (16 panels).<ref>Levitt, 2013, pp.&nbsp;82–84.</ref>

In late 1825,<ref>Elton, 2009, p.{{nbsp}}200.</ref> to reduce the loss of light in the reflecting elements, Fresnel proposed to replace each mirror with a catadioptric prism, through which the light would travel by refraction through the first surface, then [[total internal reflection]] off the second surface, then refraction through the third surface.<ref>Levitt, 2013, pp.&nbsp;79–80.</ref> The result was the lighthouse lens as we now know it. In&nbsp;1826 he assembled a small model for use on the {{lang|fr|[[Canal Saint-Martin]]|italic=no}},{{r|musee}} but he did not live to see a full-sized version: he died on 14&nbsp;July 1827, at the age of 39.

=== After Fresnel ===

The first stage of the development of lighthouse lenses after the death of Augustin Fresnel consisted in the implementation of his designs. This was driven in part by his younger brother Léonor—who, like Augustin, was trained as a civil engineer but, unlike Augustin, had a strong aptitude for management. Léonor entered the service of the Lighthouse Commission in 1825, and went on to succeed Augustin as Secretary.<ref>Levitt, 2013, pp.&nbsp;28, 72, 99.<!-- Elton, (2009, p.190) says Leonor became Secretary in "1837", which is either a mistyping of "1827" or a misreading of the primary source cited. --></ref>

The first fixed lens to be constructed with toroidal prisms was a first-order apparatus designed by the Scottish engineer [[Alan Stevenson]] under the guidance of Léonor Fresnel, and fabricated by Isaac Cookson & Co. using French glass; it entered service at the [[Isle of May]], Scotland, on 22 September 1836.<ref>Elton, 2009, pp.&nbsp;199, 200, 202; Levitt, 2013, pp.&nbsp;104–105.</ref> The first large catadioptric lenses were made in 1842 for the lighthouses at Gravelines and [[Île Vierge]], France; these were fixed third-order lenses whose catadioptric rings (made in segments) were one metre in diameter. Stevenson's first-order [[Skerryvore]] lens, lit in 1844, was only partly catadioptric; it was similar to the Cordouan lens except that the lower slats were replaced by French-made catadioptric prisms, while mirrors were retained at the top. The first ''fully'' catadioptric first-order lens, installed at Pointe d'Ailly in 1852, also gave eight rotating beams plus a fixed light at the bottom; but its top section had eight catadioptric panels focusing the light about 4&nbsp;degrees ahead of the main beams, in order to lengthen the flashes. The first fully catadioptric lens with ''purely revolving'' beams—also of first order—was installed at [[Saint-Clément-des-Baleines]] in 1854, and marked the completion of Augustin Fresnel's original ''Carte des Phares''.<ref>Levitt, 2013, pp.&nbsp;108–110, 113–116, 122–123. Elton (2009, p.{{nbsp}}208) notes that although the Skerryvore lens was lit on 1&nbsp;February 1844, the catadioptric portion was yet to be added.</ref>

[[Thomas Stevenson]] (younger brother of Alan) went a step beyond Fresnel with his "holophotal" lens, which focused the light radiated by the lamp in nearly all directions, forward or backward, into a single beam.<ref>Elton, 2009, pp.&nbsp;209–210, 238.</ref> The first version, described in 1849, consisted of a standard Fresnel bull's-eye lens, a paraboloidal reflector, and a rear hemispherical reflector (functionally equivalent to the Rogers mirror of 60&nbsp;years earlier, except that it subtended a whole hemisphere). Light radiated into the forward hemisphere but missing the bull's-eye lens was deflected by the paraboloid into a parallel beam surrounding the bull's-eye lens, while light radiated into the backward hemisphere was reflected back through the lamp by the spherical reflector (as in Rogers' arrangement), to be collected by the forward components. The first unit was installed at North Harbour, [[Peterhead]], in August 1849. Stevenson called this version a "catadioptric holophote", although each of its elements was either purely reflective or purely refractive. In the second version of the holophote concept, the bull's-eye lens and paraboloidal reflector were replaced by a catadioptric Fresnel lens—as conceived by Fresnel, but expanded to cover the whole forward hemisphere. The third version, which Stevenson confusingly called a "dioptric holophote", was more innovative: it retained the catadioptric Fresnel lens for the front hemisphere, but replaced the rear hemispherical reflector with a hemispherical array of annular prisms, each of which used ''two'' total internal reflections to turn light diverging from the center of the hemisphere back toward the center. The result was an all-glass holophote, with no losses from metallic reflections.<ref>Elton, 2009, pp.&nbsp;210–213.</ref>

[[James Timmins Chance]] modified Thomas Stevenson's all-glass holophotal design by arranging the double-reflecting prisms about a vertical axis. The prototype was shown at the [[1862 International Exhibition]] in London. Later, to ease manufacturing, Chance divided the prisms into segments, and arranged them in a cylindrical form while retaining the property of reflecting light from a single point back to that point. Reflectors of this form, paradoxically called "dioptric mirrors", proved particularly useful for returning light from the landward side of the lamp to the seaward side.<ref>Elton, 2009, pp.&nbsp;221–223.</ref>

[[File:Fresnel Lens at Point Arena Lighthouse Museum.jpg|thumb|First-order group-flashing Fresnel lens, on display at the Point Arena Lighthouse Museum, [[Point Arena Light]]house, [[Mendocino County, California]]. The three dioptric panels (inside the brass rings) and three catadioptric panels (outside) are partly split in two, giving three double-flashes per rotation.]]

As lighthouses proliferated, they became harder to distinguish from each other, leading to the use of colored filters, which wasted light. In 1884, [[John Hopkinson]] eliminated the need for filters by inventing the "group-flashing" lens, in which the dioptric and/or the catadioptric panels were split so as to give multiple flashes—allowing lighthouses to be identified not only by frequency of flashes, but also by multiplicity of flashes. Double-flashing lenses were installed at Tampico (Mexico) and [[Little Basses Reef Lighthouse|Little Basses]] (Sri&nbsp;Lanka) in 1875, and a triple-flashing lens at [[Casquets lighthouses|Casquets Lighthouse]] ([[Channel Islands]]) in 1876.<ref>Elton, 2009, pp.&nbsp;227–230; Levitt, 2013, p.{{nbsp}}219.</ref> The example shown (right) is the double-flashing lens of the [[Point Arena Light]], which was in service from 1908 to 1977.<ref>Point Arena Lighthouse Keepers, Inc., [https://www.pointarenalighthouse.com/about/lighthouse-history/ "Lighthouse History"] {{Webarchive|url=https://web.archive.org/web/20210119171021/https://www.pointarenalighthouse.com/about/lighthouse-history/ |date=19 January 2021 }}, accessed 1&nbsp;March 2021.</ref>

The development of hyper-radial lenses was driven in part by the need for larger light sources, such as gas lights with multiple jets, which required a longer focal length for a given beam-width, hence a larger lens to collect a given fraction of the generated light. The first hyper-radial lens was built for the Stevensons in 1885 by [[Barbier, Benard, et Turenne|F.&nbsp;Barbier & Cie]] of France, and tested at [[South Foreland Lighthouse]] with various light sources. [[Chance Brothers]] (Hopkinson's employers) then began constructing hyper-radials, installing their first at [[Bishop Rock, Isles of Scilly|Bishop Rock]] Lighthouse in 1887.<ref>Elton, 2009, p.{{nbsp}}233; Levitt, 2013, pp.&nbsp;222–224.</ref> In the same year, Barbier installed a hyper-radial at [[Tory&nbsp;Island]]. But only about 30 hyper-radials went into service{{r|tag-hyper}} before the development of more compact bright lamps rendered such large optics unnecessary (see ''[[Hyperradiant Fresnel lens]]'').

Production of one-piece stepped dioptric lenses—roughly as envisaged by Buffon—became feasible in 1852, when John L. Gilliland of the [[Corning Inc.|Brooklyn Flint-Glass Company]] patented a method of making lenses from pressed and molded glass. The company made small bull's-eye lenses for use on railroads, steamboats, and docks;{{r|tag-us}} such lenses were common in the United States by the 1870s.{{r|ripley-dana-1879|p=488}} In 1858 the company produced "a&nbsp;very small number of pressed flint-glass sixth-order lenses" for use in lighthouses—the first Fresnel lighthouse lenses made in America.{{r|tag-us}} By the 1950s, the substitution of plastic for glass made it economic to use Fresnel lenses as condensers in overhead projectors.<ref>A. Finstad, "New developments in audio-visual materials", ''Higher Education'', vol.&nbsp;8, no.{{nbsp}}15 (1&nbsp;April 1952), pp.&nbsp;176–178, at p.{{nbsp}}176.</ref>

== Design ==
[[File:Fresnel lens.svg|thumb|left|upright|1: Cross-section of Buffon/Fresnel lens. <br />2:&nbsp;Cross-section of conventional [[lens (optics)#Types of simple lenses|plano-convex lens]] of equivalent power. (Buffon's version was [[lens (optics)#Types of simple lenses|biconvex]].<ref name=levitt-p59>Levitt, 2013, p.{{nbsp}}59.</ref>)]]
[[File:Flat flexible plastic sheet lens.JPG|thumb|Close-up view of a flat Fresnel lens shows concentric circles on the surface]]

The Fresnel lens reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections. An ideal Fresnel lens would have an infinite number of sections. In each section, the overall thickness is decreased compared to an equivalent simple lens. This effectively divides the continuous surface of a standard lens into a set of surfaces of the same curvature, with stepwise discontinuities between them.

In some lenses, the curved surfaces are replaced with flat surfaces, with a different angle in each section. Such a lens can be regarded as an array of prisms arranged in a circular fashion with steeper prisms on the edges and a flat or slightly convex center. In the first (and largest) Fresnel lenses, each section was actually a separate prism. 'Single-piece' Fresnel lenses were later produced, being used for automobile headlamps, brake, parking, and turn signal lenses, and so on. In modern times, [[CNC|computer-controlled milling equipment (CNC)]] or [[3-D printing|3-D printers]] might be used to manufacture more complex lenses.{{Citation needed|date=March 2023}}

Fresnel lens design allows a substantial reduction in thickness (and thus mass and volume of material) at the expense of reducing the imaging quality of the lens, which is why precise imaging applications such as photography usually still use larger conventional lenses.

Fresnel lenses are usually made of glass or plastic; their size varies from large (old historical lighthouses, meter size) to medium (book-reading aids, OHP viewgraph projectors) to small ([[Twin-lens reflex camera|TLR]]/[[Single-lens reflex camera|SLR]] camera screens, micro-optics). In many cases they are very thin and flat, almost flexible, with thicknesses in the {{convert|1|to|5|mm|in|frac=32|abbr=on}} range.{{Citation needed|date=March 2023}}

Most modern Fresnel lenses consist only of refractive elements. Lighthouse lenses, however, tend to include both refracting and reflecting elements, the latter being ''outside'' the metal rings seen in the photographs. While the inner elements are sections of refractive lenses, the outer elements are reflecting prisms, each of which performs two refractions and one [[total internal reflection]], avoiding the light loss that occurs in reflection from a silvered mirror.

== Lighthouse lens sizes ==
{{anchor|Sizes of lighthouse lenses}}<!-- This is linked to by several redirects [[First order Fresnel lens]], [[Second order Fresnel lens]], [[Third order Fresnel lens]], [[Fourth order Fresnel lens]], [[Fifth order Fresnel lens]], [[Sixth order Fresnel lens]], [[Seventh order Fresnel lens]], [[Eighth order Fresnel lens]]
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[[File:Block Island Southeast Light, Spring Street and Mohegan Trail at Mohegan Bluffs, New Shoreham, Washington County, RI HAER RI,5-NESH,1- (sheet 8 of 12).png|thumb|upright|Description of lens orders, from [[Block Island Southeast Light]], Rhode Island.]]
[[File:Fresnel lens - Chiba - 2021 5 23.webm|thumb|Walking around a fresnel lens on display in [[Chiba Prefecture|Chiba]], [[Japan]].]]

Fresnel designed six sizes of lighthouse lenses, divided into four ''orders'' based on their size and focal length.<ref name="Baiges">{{ cite web| mode = cs2 | url = http://memory.loc.gov/cgi-bin/displayPhoto.pl?path=/pnp/habshaer/ri/ri0300/ri0392/sheet&topImages=00008a.gif&topLinks=00008r.tif,00008a.tif | title = Fresnel Orders | access-date = 9 September 2012 | first = Mabel A. | last = Baiges | date = 1988 | format = TIFF | url-status = live | archive-url = https://web.archive.org/web/20150921173248/http://memory.loc.gov/cgi-bin/displayPhoto.pl?path=%2Fpnp%2Fhabshaer%2Fri%2Fri0300%2Fri0392%2Fsheet&topImages=00008a.gif&topLinks=00008r.tif%2C00008a.tif | archive-date = 21 September 2015}}.</ref>  The 3rd and 4th orders were sub-divided into "large" and "small". In modern use, the orders are classified as first through sixth order. An intermediate size between third and fourth order was added later, as well as sizes above first order and below sixth.

A first-order lens has a focal length of {{convert|920|mm|in|abbr=on|frac=8}} and stands about {{convert|2.59|m|ftin|frac=2|abbr=on}} high, and {{convert|1.8|m|ft|0|abbr=on}} wide. The smallest (sixth) order has a focal length of {{convert|150|mm|in|frac=4|abbr=on}} and a height of {{convert|433|mm|in|frac=16|abbr=on}}.<ref name="Baiges" /><ref>{{cite web|mode=cs2 |url=http://www.marinecitymich.org/Blank%20Page.htm |title=Fresnel lenses |url-status=dead |archive-url=https://web.archive.org/web/20070927021951/http://www.marinecitymich.org/Blank%20Page.htm |archive-date=27 September 2007}}.</ref><ref>{{cite web|mode=cs2 |url=http://www.michiganlights.com/fresnel.htm |title=Fresnel lenses |date=31 January 2008 |publisher=Michigan Lighthouse Conservancy |access-date=27 February 2021 |url-status=live |archive-url=https://web.archive.org/web/20120921153832/http://www.michiganlights.com/fresnel.htm |archive-date=21 September 2012}}.</ref>

The largest Fresnel lenses are called [[hyperradiant Fresnel lens|hyperradiant]] (or hyper-radial). One such lens was on hand when it was decided to build and outfit the [[Makapuu Point Light]] in Hawaii. Rather than order a new lens, the huge optic construction, {{convert|12|ft|m|1|order=flip}} tall and with over a thousand prisms, was used there.<ref name="LHF">{{cite web|mode=cs2 |url=http://www.lighthousefriends.com/light.asp?ID=141|title=Makapu'u, HI|author=Anderson, Kraig|work= Lighthouse Friends|access-date=26 February 2009|url-status=live|archive-url=https://web.archive.org/web/20081005185157/http://www.lighthousefriends.com/light.asp?ID=141|archive-date=5 October 2008}}.</ref>
{{table alignment}}
{| class="wikitable plainrowheaders col3right col6center"
|+ Lighthouse lens orders<ref>United States Lighthouse Society, [https://uslhs.org/fresnel-lens-orders-sizes-weights-quantities-and-costs "Fresnel Lens Orders, Sizes, Weights, Quantities and Costs"] {{Webarchive|url=https://web.archive.org/web/20230627061512/https://uslhs.org/fresnel-lens-orders-sizes-weights-quantities-and-costs |date=27 June 2023 }}.</ref>
|-
! scope="col" | Modern order
! scope="col" | Fresnel order
! scope="col" | Focal length (mm)
! scope="col" colspan=2 | Height (m)
! scope="col" | First installed
! scope="col" | Application
|-
! scope="row" | Hyper-radial
|
| 1330
| {{decimal cell|3.76}}
| 1887
| Major "landfall" lighthouses
|-
! scope="row" | Mesoradial
|
| 1125
| {{decimal cell|3.20}}
| 1909
| Two Brazilian lighthouses
|-
! scope="row" | 1st
| 1st
| 920
| {{decimal cell|2.59}}
| 1823
| Large seacoast lights
|-
! scope="row" | 2nd
| 2nd
| 700–750
| {{decimal cell|2.07}}
|
| [[Great Lakes]] lighthouses, seacoasts, islands, sounds
|-
! scope="row" | 3rd
| 3rd (large)
| 500
| {{decimal cell|1.58}}
| 1825
|Seacoast sounds, river entry, bays, channels, range lights
|-
! scope="row" | {{frac|3|1|2}}
| 
| 375
| {{decimal cell|1.09}}
|
|-
! scope="row" | 4th
| 3rd (small)
| 250
| {{decimal cell|0.722}}
|
| Shoals, reefs, harbor lights, islands in rivers and harbors
|-
! scope="row" | 5th
| 4th (large)
| 187.5
| {{decimal cell|0.541}}
|
| Breakwaters, river and channel lights, Small islands in sounds
|-
! scope="row" | 6th
| 4th (small)
| 150
| {{decimal cell|0.433}}
|
| Pier and breakwater lights in harbors
|-
! scope="row" | 7th
| 
| 100–140
| {{decimal cell|0.165}}
|
| Used in Scotland and Canada
|-
! scope="row" | 8th
| 
| 70–75
| {{decimal cell|0.0826}}
|
| Used in Scotland and Canada
|}
{{clear}}
<gallery mode=packed heights=160>
Image:1st order Fresnel lighthouse lens.jpg|First-order lens.
File:Cape Meares Lighthouse lens - Oregon.jpg|First-order lens ([[Cape Meares Lighthouse]])
File:First-order lens from Destruction Island WA.jpg|First-order lens from Destruction Island WA, built in France 1888. Currently at Westport Maritime Museum.
Image:Lighthouse Lens.jpg|Close-up of a second-order lens.
File:St. Simons Lighthouse, close-up of top, Georgia, USA.JPG|Third-order lens ([[St. Simons Island Light]]).
Image:Oita_sekizaki_lighthouse_old_lense.jpg|Fourth-order lens (Sekizaki Lighthouse, [[Ōita, Ōita|Oita]], Japan).
File:Fourth order Fresnel Lens originally from Cape Arago Lighthouse OR.jpg|Fourth order lens from Cape Arago Lighthouse. Currently at Coos History Museum.
File:Fifth-order Fresnel lens, lighthouse at Key West, FL, US.jpg|Fifth-order lens, at [[Key West Lighthouse]]
File:Ponce de Leon Inlet Lighthouse Lens Museum - Replica 6th Order Lens - March 2016 (25919436890).jpg|Sixth-order lens ([[Ponce de Leon Inlet Light]])
File:First- and fourth-order Fresnel lenses, Key West, FL, US.jpg|Comparison of first- and fourth-order lenses (Key West Lighthouse)
</gallery>

== Types ==

There are two main types of Fresnel lens: ''imaging'' and ''non-imaging''. Imaging Fresnel lenses use segments with curved cross-sections and produce sharp images, while non-imaging lenses have segments with flat cross-sections, and do not produce sharp images.<ref>R. Winston, J. C. Miñano, and P. G. Benítez, ''Nonimaging Optics'', Academic Press, 2005.</ref> As the number of segments increases, the two types of lens become more similar to each other. In the abstract case of an infinite number of segments, the difference between curved and flat segments disappears.

Imaging lenses can be classified as:

; Spherical: A spherical Fresnel lens is equivalent to a [[simple lens|simple]] [[spherical lens]], using ring-shaped segments that are each a portion of a sphere, that all focus light on a single point. This type of lens produces a sharp image, although not quite as clear as the equivalent simple spherical lens due to diffraction at the edges of the ridges. This type is sometimes called a [[kinoform]] when the ridges are microscopic, at the wavelength scale.
; Cylindrical: A cylindrical Fresnel lens is equivalent to a simple [[cylindrical lens]], using straight segments with circular cross-section, focusing light on a single line. This type produces a sharp image, although not quite as clear as the equivalent simple cylindrical lens due to diffraction at the edges of the ridges.

Non-imaging lenses can be classified as:

; Spot: A non-imaging spot Fresnel lens uses ring-shaped segments with cross sections that are straight lines rather than circular arcs. Such a lens can focus light on a small spot, but does not produce a sharp image. These lenses have application in solar power, such as focusing sunlight on a solar panel. Fresnel lenses may be used as components of [[Köhler illumination]] optics resulting in very effective [[nonimaging optics]] Fresnel-Köhler (FK) solar concentrators.<ref name="IntroNio2e">{{cite book|mode=cs2 | first = Julio | last = Chaves | title = Introduction to Nonimaging Optics, Second Edition | url = https://books.google.com/books?id=e11ECgAAQBAJ | publisher = [[CRC Press]] | year = 2015 | isbn = 978-1-4822-0673-9}}.</ref>
; Linear: A non-imaging linear Fresnel lens uses straight segments whose cross sections are straight lines rather than arcs. These lenses focus light into a narrow band. They do not produce a sharp image, but can be used in solar power, such as for focusing sunlight on a pipe, to heat the water within.<ref>{{Cite web|title=Linear Concentrator System Concentrating Solar-Thermal Power Basics|url=https://www.energy.gov/eere/solar/linear-concentrator-system-concentrating-solar-thermal-power-basics|access-date=2021-05-31|website=Energy.gov|language=en}}</ref>

== Uses ==

=== Illumination ===
[[File:Inchkeith lighthouse Fresnel lens.JPG|thumb|right|upright=0.3|[[Inchkeith]] lighthouse lens and drive mechanism]]
High-quality glass Fresnel lenses were used in lighthouses, where they were considered state of the art in the late 19th and through the middle of the 20th centuries. These lighthouse Fresnel lens systems typically include extra annular [[Prism (optics)|prismatic]] elements, arrayed in faceted domes above and below the central planar Fresnel, in order to catch all light emitted from the light source. The light path through these elements can include an [[internal reflection]], rather than the simple [[refraction]] in the planar Fresnel element.<ref name=Pepper-Fresnel>{{cite web |url=http://www.terrypepper.com/lights/closeups/illumination/fresnel/fresnel.htm |title=The incredible Fresnel lens |first=Terry |last=Pepper |date=December 2, 2007 |website=Seeing The Light |access-date=31 December 2024}}</ref> These lenses conferred many practical benefits upon the designers, builders, and users of lighthouses and their illumination. Among other things, smaller lenses could fit into more compact spaces. Greater light transmission over longer distances, and varied patterns, made it possible to triangulate a position.<ref name=Pepper-Fresnel/><ref>{{cite web |url=https://www.parks.ca.gov/?page_id=22008 |title=The Lens |publisher=California State Parks |website=Pigeon Point Light Station State Historic Park |access-date=31 December 2024}}</ref> Starting in the mid-20th century, most lighthouses have retired glass Fresnel lenses from service and replaced them with much less expensive and more durable [[aerobeacon]]s<ref>{{cite web |url=http://www.terrypepper.com/lights/closeups/illumination/aerobeacon/dcb224.htm |title=The DCB Series Aerobeacon |first=Terry |last=Pepper |date=December 2, 2007 |website=Seeing The Light |access-date=31 December 2024}}</ref><ref>{{cite news |url=https://www.mvtimes.com/2024/03/08/gay-head-light-requires-upgrade/ |title=Auinnah lighthouse undergoing beacon change |first=Daniel |last=Greenman |date=March 8, 2024 |newspaper=Martha's Vineyard Times |access-date=31 December 2024 |quote=The Carlisle & Finch company's 'DCB-224 aerobeacon' lights were produced so that airports could signal to planes. But they also became common in lighthouses nationwide by the middle of the 20th century.}}</ref> or similar systems, including the Vega Industries [[VRB-25]], which contains plastic Fresnel lens panels.<ref>{{cite news |url=https://uslhs.org/sites/default/files/articles_pdf/VRB25_Summer_2009.pdf |title=Vega VRB-25: Last of the Lighthouse Rotating Beacons as We Know Them |first=Bob |last=Trapani Jr. |date=Summer 2009 |work=The Keeper's Log |publisher=U.S. Lighthouse Society |access-date=31 December 2024}}</ref>

[[File:Chevrolet Bel Air 1956 4door Sedan lamp.jpg|thumb|left|upright=0.5|1956 [[Chevrolet Bel Air|Bel Air]], with Fresnel lenses in round headlamp and rectangular marker lamp]]
Perhaps the most widespread use of Fresnel lenses, for a time, occurred in [[automobile]] [[headlamp]]s, where they can shape the roughly parallel beam from the parabolic reflector to meet requirements for dipped and main-beam patterns, often both in the same headlamp unit (such as the European [[H4 lamp|H4]] design). For reasons of economy, weight, and impact resistance, newer cars have dispensed with glass Fresnel lenses for [[Parabolic aluminized reflector|sealed beam]] headlamp units, instead using [[multifaceted reflector]]s with plain [[polycarbonate]] lenses. However, Fresnel lenses continue in wide use in automobile tail, marker, and reversing lights.

[[Image:Colortran Fresnel.JPG|thumb|right|A Fresnel lantern with the lens open to show the ridges]]
Glass Fresnel lenses also are used in lighting instruments for [[theatre]] and [[motion pictures]] (see [[Fresnel lantern]]); such instruments are often called simply ''Fresnels''. The entire instrument consists of a metal housing, a reflector, a lamp assembly, and a Fresnel lens. Many Fresnel instruments allow the lamp to be moved relative to the lens' [[Focus (optics)|focal point]], to increase or decrease the size of the light beam. As a result, they are very flexible, and can often produce a beam as narrow as 7° or as wide as 70°.<ref>Mumm, Robert C., ''Photometrics Handbook'', 2nd&nbsp;Ed., Broadway Press, 1997, p.{{nbsp}}36.</ref> The Fresnel lens produces a very soft-edged beam, so is often used as a wash light. A holder in front of the lens can hold a colored plastic film (''gel'') to tint the light or wire screens or frosted plastic to diffuse it. The Fresnel lens is useful in the making of motion pictures not only because of its ability to focus the beam brighter than a typical lens, but also because the light is a relatively consistent intensity across the entire width of the beam of light.

[[File:Optical Landing System, night, aboard USS Dwight D. Eisenhower (CVN-69).jpg|thumb|[[Optical landing system]] on US Navy aircraft carrier [[USS Dwight D. Eisenhower|USS ''Dwight D. Eisenhower'']]]]

[[Aircraft carrier]]s and naval air stations typically use Fresnel lenses in their [[optical landing system]]s. The "meatball" light aids the pilot in maintaining proper glide slope for the landing. In the center are amber and red lights composed of Fresnel lenses. Although the lights are always on, the angle of the lens from the pilot's point of view determines the color and position of the visible light. If the lights appear above the green horizontal bar, the pilot is too high. If it is below, the pilot is too low, and if the lights are red, the pilot is very low.<ref>{{Cite web |title=Fresnel Lens Optical Landing System |url=https://www.history.navy.mil/content/history/museums/nnam/explore/exhibits/permanent-exhibits/mezzanine/fresnel-lens-optical-landing-system.html |access-date=2022-04-16 |website=NHHC |language=en-US }}</ref>

Fresnel lenses are also commonly used in [[searchlight]]s, [[Spotlight (theatre lighting)|spotlights]], and [[flashlight]]s. Another use of such Lenses are in 300 mm (12 inch) code beacons placed on [[Radio masts and towers|radio and television towers]]. The number of such beacons being a function of height as specified by the [[Federal Aviation Administration|FAA]]. These beacons contain two 300 watt [[Incandescent light bulb|incandescent lamps]]. Perhaps unlike the lenses in lighthouses these two piece beacons were made of circular cast glass. The latest technology is to utilize [[Light-emitting diode|LED]] optics in a non Fresnel configuration to supply the needed obstruction characteristics.

=== Imaging ===
[[File:Magnifying-fresnel-lens.jpg|thumb|right|A plastic Fresnel lens sold as a TV-screen enlarging device]]
[[File:SinclairFTV1fresnellens1.JPG|thumb|The Fresnel lens used in the [[TV80|Sinclair FTV1]] portable CRT TV, which enlarges the vertical aspect of the display only]]

Fresnel lenses are used as simple hand-held [[Magnifying glass|magnifiers]]. They are also used to correct several visual disorders, including ocular-motility disorders such as [[strabismus]].<ref>{{cite journal|mode=cs2 |last1=Shishavanf |first1=Amir Asgharzadeh |last2=Nordin |first2=Leland |last3=Tjossem |first3=Paul |last4=Abramoff |first4=Michael D. |last5=Toor |first5=Fatima |editor3-first=Nikolay I |editor3-last=Zheludev |editor2-first=Mikhail A. |editor2-last=Noginov |editor1-first=Nader |editor1-last=Engheta |title=PMMA-based ophthalmic contact lens for vision correction of strabismus |journal=Metamaterials |series=Metamaterials, Metadevices, and Metasystems 2016 |year=2016 |volume=9918 |pages=99180C |url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9918/1/PMMA-based-ophthalmic-contact-lens-for-vision-correction-of-strabismus/10.1117/12.2237994.short?SSO=1 |publisher=Society of Photo-Optical Instrumentation Engineers |doi=10.1117/12.2237994 |bibcode=2016SPIE.9918E..0CA |s2cid=125689110 |access-date=21 June 2020|url-access=subscription }}.</ref> Fresnel lenses have been used to increase the visual size of [[CRT display]]s in pocket [[television]]s, notably the [[Sinclair Research Ltd.|Sinclair]] [[TV80]]. They are also used in [[traffic light]]s.

Fresnel lenses are used in left-hand-drive European [[Lorry|lorries]] entering the UK and Republic of Ireland (and vice versa, right-hand-drive Irish and British trucks entering mainland Europe) to overcome the blind spots caused by the driver operating the lorry while sitting on the wrong side of the cab relative to the side of the road the car is on. They attach to the passenger-side window.<ref>{{cite book|mode=cs2 |url=https://books.google.com/books?id=XG4du9fwEUYC&q=vosa%20fresnel%20lenses&pg=PA321|title=Lowe's Transport Manager's and Operator's Handbook 2012|last=Lowe|first=David|date=2011-12-03|publisher=[[Kogan Page Publishers]]|isbn=978-0-7494-6410-3}}.</ref>

Another automobile application of a Fresnel lens is a rear view enhancer, as the [[Wide-angle lens|wide view angle]] of a lens attached to the rear window permits examining the scene behind a vehicle, particularly a tall or bluff-tailed one, more effectively than a [[rear-view mirror]] alone. Fresnel lenses have been used on rangefinding equipment and [[Moving map display|projected map display]] screens.<ref>{{cite web |url=https://rochesteravionicarchives.co.uk/collection/navigation-inertial/projected-map-display |title=Projected Map Display [PMD] |website=Rochester Avionic Archives |access-date=2024-08-17}}</ref>

Fresnel lenses have also been used in the field of popular entertainment. The British rock artist [[Peter Gabriel]] made use of them in his early solo live performances to magnify the size of his head in contrast to the rest of his body, for dramatic and comic effect. In the [[Terry Gilliam]] film ''[[Brazil (1985 film)|Brazil]]'', Fresnel lenses are used as magnifiers for small CRT monitors in the Ministry of Information. The lenses occasionally appear between the actors and the camera, distorting the scale and composition of the scene to humorous effect. In the [[Pixar]] movie [[Wall-E]], the protagonist watches the musical [[Hello, Dolly! (film)|''Hello, Dolly!'']] on an [[iPod]], magnified by a Fresnel lens.

[[Virtual reality]] headsets, such as the [[Meta Quest 2]] and the [[HTC Vive|HTC Vive Pro]] use Fresnel lenses,<ref>{{Cite web |last=Poore |first=Shaun |date=2022-04-21 |title=What Tech is Inside of a VR Headset? (Quest 2 Teardown) |url=https://www.shaunpoore.com/inside-a-vr-headset/ |access-date=2022-10-27 |website=ShaunPoore.com |language=en}}</ref> as they allow a thinner and lighter form factor than regular lenses.<ref>{{Cite web |date=2016-03-08 |title=How Lenses for Virtual Reality Headsets Work |url=https://vr-lens-lab.com/lenses-for-virtual-reality-headsets/ |access-date=2022-10-27 |website=VR Lens Lab |language=en-US |archive-date=27 October 2022 |archive-url=https://web.archive.org/web/20221027133146/https://vr-lens-lab.com/lenses-for-virtual-reality-headsets/ |url-status=dead }}</ref> Newer devices, such as the [[Meta Quest Pro]], have switched to a [[pancake lens]] design<ref>{{Cite web |title=Introducing Meta Quest Pro, an Advanced VR Device for Collaboration and Creation |url=https://www.oculus.com/blog/meta-quest-pro-price-release-date/ |access-date=2022-10-27 |website=www.oculus.com |language=en}}</ref> due to its smaller form factor and less [[chromatic aberration]] than Fresnel lenses.<ref>{{Cite web |last=C |first=Mark |date=2022-04-26 |title=The difference between pancakes lenses and current fresnel lenses found on VR headsets |url=https://vr-expert.com/the-difference-between-pancakes-lenses-and-current-fresnel-lenses-found-on-vr-headsets/ |access-date=2022-10-27 |website=VR Expert {{!}} Enterprise VR/AR Hardware Supplier |language=en-GB}}</ref>

Multi-focal Fresnel lenses are also used as a part of [[retinal scan|retina identification]] cameras, where they provide multiple in- and out-of-focus images of a fixation target inside the camera. For virtually all users, at least one of the images will be in focus, thus allowing correct eye alignment.

Many cameras are equipped with viewfinders which project the scene through a lens onto a [[ground glass]] screen for focusing and composition, including [[view camera|view]], [[twin-lens reflex camera|twin-lens reflex]], and [[single-lens reflex camera]]s; often a Fresnel condenser lens is applied to the ground glass to increase the perceived brightness of the projected image and make the illumination more even from center to corner.<ref>{{cite book |url=https://archive.org/details/usingviewcamera00simm/page/28/mode/2up |title=Using the view camera |first=Steve |last=Simmons |date=1987 |publisher=Amphoto |isbn=0-8174-6347-X |page=29 |url-access=registration}}</ref><ref>{{cite book |url=https://archive.org/details/minoltaguide0000wolf/page/22/mode/2up |title=The Minolta Guide |first=John |last=Wolf |date=1979 |publisher=Amphoto |isbn=0-8174-2453-9 |lccn=78-21451 |page=23 |url-access=registration |quote=The matte screens all have fine-ground translucent surfaces, on which the image from the mirror is projected. These have a Fresnel or field lens, and condenser, which direct light from all parts of the screen's surface to the eyepiece uniformly, creating an image with corner-to-corner brightness.}}</ref> For example, the [[Polaroid SX-70]] camera uses a Fresnel reflector as part of its viewing system.<ref>{{cite journal |doi=10.1364/AO.21.000196 |title=Unusual optics of the Polaroid SX-70 Land camera |first=William T. |last=Plummer |journal=Applied Optics |volume=21 |date=1982 |issue=2 |pages=196–202|pmid=20372431 |bibcode=1982ApOpt..21..196P }}</ref>

==== Projection ====
[[Image:OHP-sch.JPG|thumb|right|An overhead projector in use]]
The use of Fresnel lenses for image projection reduces image quality,<ref>{{Cite web |last=Salazar |first=Andrea |date=2024-05-31 |title=Exploring the Diverse Applications of Fresnel Lenses |url=https://www.azooptics.com/Article.aspx?ArticleID=2624 |access-date=2025-09-02 |website=AZoOptics |language=en}}</ref> so they tend to occur only where quality is not critical or where the bulk of a solid lens would be prohibitive. Cheap Fresnel lenses can be stamped or molded of transparent plastic and are used in [[overhead projector]]s and [[projection television]]s.

Fresnel lenses of different focal lengths (one [[collimator]], and one collector) are used in commercial and [[DIY]] projection. The collimator lens has the lower focal length and is placed closer to the light source, and the collector lens, which focuses the light into the triplet lens, is placed after the projection image (an [[active matrix LCD]] panel in [[LCD projector]]s). Fresnel lenses are also used as collimators in [[overhead projector]]s.

=== Solar power ===
[[File:Luftaufnahme PE 1.JPG|thumb|Solar power plant based on linear Fresnel lenses]]
Since plastic Fresnel lenses can be made larger than glass lenses, as well as being much cheaper and lighter, they are used to concentrate sunlight for heating in [[solar cooker]]s, in solar forges, and in [[Solar thermal collector|solar collectors]] used to heat water for domestic use.<ref>{{cite book |url=https://archive.org/details/directuseofsunse0000dani_b8v1/page/66/mode/2up |title=Direct use of the sun's energy |first=Farrington |last=Daniels |date=1977 |orig-year=1964 |page=66 |publisher=Yale University Press |location=New Haven |isbn=0-300-00399-4 |lccn=64-20913 |url-access=registration |quote=Another device for focusing solar energy is the Fresnel lens. A nest of circular grooves is cut in a sheet of transparent plastic with the sides of each successive ring set in such a way that the light passing through each groove is refracted at a slightly different angle and converges on a point. Such lenses have been pressed out in plastic sheets and they are effective in giving a sharp focus.}}</ref> They can also be used to generate steam or to power a [[Stirling engine]] to generate electricity.<ref>{{cite journal |url=https://archive.org/details/Prt3A978-1-4419-0851-32F2/1-s2.0-S0196890413004494-main/ |title=Performance testing of a Fresnel/Stirling micro solar energy conversion system |first1=Fatih |last1=Aksoy |first2=Halit |last2=Karabulut |date=November 2013 |journal=Energy Conversion and Management |volume=75 |pages=629–634 |doi=10.1016/j.enconman.2013.08.001|bibcode=2013ECM....75..629A }}</ref>

Fresnel lenses can concentrate sunlight onto [[solar cell]]s with a ratio of almost 500:1.<ref>{{cite web|mode=cs2 |url=http://www.soitec.com/en/technologies/concentrix/ |title=Soitec's Concentrix technology |access-date=3 September 2013 | url-status = dead |archive-url=https://web.archive.org/web/20110417051836/http://www.soitec.com/en/technologies/concentrix/ |archive-date=17 April 2011}}.</ref> This allows the active solar-cell surface to be reduced, lowering cost and allowing the use of more efficient cells that would otherwise be too expensive.<ref>{{ cite web| mode = cs2 | title = Soitec's high-performance Concentrix technology | url = http://www.soitec.com/en/technologies/concentrix/components/ | access-date = 27 February 2021 | url-status = dead | archive-url = https://web.archive.org/web/20130923032544/http://www.soitec.com/en/technologies/concentrix/components/ | archive-date = 23 September 2013}}.</ref> In the early 21st century, Fresnel reflectors began to be used in [[concentrating solar power]] (CSP) plants to concentrate solar energy. One application was to preheat water at the coal-fired [[Liddell Power Station]], in Hunter Valley Australia.

Fresnel lenses can be used to [[Sintering|sinter]] sand, allowing [[3D printing]] in glass.<ref>{{cite web|mode=cs2 |author=M. Margolin |url=https://www.vice.com/en/article/this-3d-printer-runs-on-sand-and-sun/ |title=This 3D printer runs on sand and sun |work=Vice |date=24 August 2016 |access-date=2021-02-27 |url-status=live |archive-url=https://web.archive.org/web/20171201182205/https://motherboard.vice.com/en_us/article/wnxpe9/this-3d-printer-runs-on-sand-and-sun|archive-date=1 December 2017}}.</ref>

=== Anidolic focusing for detection purposes ===

Where [[Nonimaging optics|imaging is not required]], a [[passive infrared sensor]] equipped with multiple low-quality Fresnel lenses can be used to collect infrared energy from a wide area and focus it for motion detection in both area-protection and energy-saving applications. The plastic used is selected for its transparency to infrared energy as well as being UV-stabilised for outdoor durability.

<gallery mode=packed heights=160px>
File:PIR Motion Sensor-Sensinova (SN-PR11).png|PIR motion sensor design
File:Motion Detector with Beam Pattern.jpg|alt=Passive Infrared motion detector with sensitivity beam pattern.|Motion detector with superimposed beam pattern. The length of the beams is a measure of the detector's sensitivity in that direction.
</gallery>

== See also ==

* [[Fresnel imager]]
* [[Fresnel zone plate]]
* [[Lenticular lens]]
* [[Linear Fresnel reflector]]
* [[Prism lighting]]

== References ==
<references>
<ref name=appleton-1861>D. Appleton &amp; Co., [https://archive.org/stream/appletonsdiction02appl#page/606/mode/2up "Sea-lights"], ''Dictionary of Machines, Mechanics, Engine-work, and Engineering'', 1861, vol.&nbsp;2, pp.&nbsp;606–618.</ref>
<ref name=brock-1909>H.M. Brock, [[s:Catholic Encyclopedia (1913)/Augustin-Jean Fresnel|"Fresnel, Augustin-Jean"]], ''Catholic Encyclopedia'', 1907–12, vol.&nbsp;6&nbsp;(1909).</ref>
<ref name=chisholm-1911-brewster>{{cite EB1911|mode=cs2|wstitle=Brewster, Sir David|volume=4|pages=513–514}}.</ref>
<ref name=chisholm-1911-lighthouse>{{cite EB1911|mode=cs2|wstitle=Lighthouse|volume=16|pages=627–651}}.</ref>
<ref name=condorcet-1790>N. de Condorcet, [https://books.google.com/books?id=o99ZAAAAcAAJ ''Éloge de M.&nbsp;le Comte de Buffon''], Paris: Chez&nbsp;Buisson, 1790, pp.&nbsp;11–12. (This obituary also appeared in ''Histoire de l'Académie Royale des Sciences'' for 1788, printed in 1791.)</ref>
<ref name=gombert-2017>D. Gombert, photograph of the [https://www.flickr.com/photos/gebete29/32970312394/in/photostream/ ''Optique de Cordouan''] in the collection of the ''Musée des Phares et Balises'', [[Ushant|Ouessant]], France, 23&nbsp;March 2017.</ref>
<ref name=musee>Musée national de la Marine, [http://mnm.webmuseo.com/ws/musee-national-marine/app/collection/record/9067 "Appareil catadioptrique, Appareil du canal Saint-Martin"], accessed 26 August 2017; [https://web.archive.org/web/20170826030358/http://mnm.webmuseo.com/ws/musee-national-marine/app/collection/record/9067 archived] 26 August 2017.</ref>
<ref name=ripley-dana-1879>G. Ripley and C.A.&nbsp;Dana (eds.), [https://archive.org/stream/americancyclopae07ripluoft#page/486/mode/2up "Fresnel, Augustin Jean"], ''American Cyclopædia'', 1879, vol.&nbsp;7, pp.&nbsp;486–489.<!-- Contrary to this entry&nbsp;(p.&nbsp;486), calcite and quartz were ''not'' the only doubly refractive crystals known before Fresnel; see (e.g.) Young, 1855, p.{{nbsp}}250 (written 1810) and pp.&nbsp;262, 266, 277 (written 1814), and Lloyd, 1834, pp.&nbsp;376–377. --></ref>
<ref name=tag-2017>T. Tag, [http://uslhs.org/chronology-lighthouse-events "Chronology of Lighthouse Events"], U.S. Lighthouse Society, accessed 22 August 2017; [https://web.archive.org/web/20170408105558/http://uslhs.org/chronology-lighthouse-events archived] 8 April 2017.</ref>
<ref name=tag-fres>T. Tag, [http://uslhs.org/fresnel-lens "The Fresnel lens"], U.S. Lighthouse Society, accessed 12 August 2017; [https://web.archive.org/web/20160722002916/http://uslhs.org/fresnel-lens archived] 22 July 2017.</ref>
<ref name=tag-hyper>T. Tag, [http://uslhs.org/hyper-radial-lenses "Hyper-Radial Lenses"], U.S. Lighthouse Society, accessed 28 February 2021; [https://web.archive.org/web/20210211202401/https://uslhs.org/hyper-radial-lenses archived] 11 February 2021.</ref>
<ref name=tag-prior>T. Tag, [https://uslhs.org/node/1481 "Lens use prior to Fresnel"], U.S. Lighthouse Society, accessed 12 August 2017; [https://web.archive.org/web/20170520114102/http://uslhs.org/lens-use-prior-fresnel archived] 20 May 2017.</ref>
<ref name=tag-us>T. Tag, [http://uslhs.org/american-made-fresnel-lenses-0 "American-Made Fresnel Lenses"], U.S. Lighthouse Society, accessed 1&nbsp;March 2021; [https://web.archive.org/web/20210221163206/https://uslhs.org/american-made-fresnel-lenses-0 archived] 21 February 2021.</ref>
<ref name=watson-1999>B.&nbsp;Watson, [https://www.smithsonianmag.com/science-nature/science-makes-a-better-lighthouse-lens-170677431/ "Science Makes a Better Lighthouse Lens"], ''Smithsonian'', vol.&nbsp;30 no.{{nbsp}}5 (August 1999), pp&nbsp;30&ndash;31.</ref>
</references>

== Bibliography ==

* M. Born and E. Wolf, ''Principles of Optics'', 7th&nbsp;Ed., Cambridge, 1999.
* G.-A. Boutry, 1948, "Augustin Fresnel: His time, life and work, 1788–1827", ''Science Progress'', vol.&nbsp;36, no.&nbsp;144 (October 1948), pp.&nbsp;587–604; [https://www.jstor.org/stable/43413515 jstor.org/stable/43413515].
* J. Z. Buchwald, 1989, ''[https://archive.org/details/riseofwavetheory0000buch The Rise of the Wave Theory of Light: Optical Theory and Experiment in the Early Nineteenth Century]'', University of Chicago Press, {{ISBN|978-0-226-07886-1}}.
* J. Elton, 2009, "A Light to Lighten our Darkness: Lighthouse Optics and the Later Development of Fresnel's Revolutionary Refracting Lens 1780–1900", ''International Journal for the History of Engineering & Technology'', vol.&nbsp;79, no.&nbsp;2 (July 2009), pp.&nbsp;183–244; {{doi|10.1179/175812109X449612}}.
* A. Fresnel, 1822, "Mémoire sur un nouveau système d'éclairage des phares", read 29 July 1822; reprinted in Fresnel, 1866–1870, vol.&nbsp;3, [https://archive.org/details/oeuvrescompltes01fresgoog/page/n182 pp.&nbsp;97–126]; translated by T.&nbsp;Tag as [http://uslhs.org/sites/default/files/attached-files/Fresnel%27s%20Memoire%20-%20Translation.pdf "Memoir upon a new system of lighthouse illumination"], U.S. Lighthouse Society, accessed 26 August 2017; [https://web.archive.org/web/20160819111647/http://uslhs.org/sites/default/files/attached-files/Fresnel's%20Memoire%20-%20Translation.pdf archived] 19 August 2016. (Cited page numbers refer to the translation.)
* A. Fresnel (ed. H. de Sénarmont, E.&nbsp;Verdet, and L.&nbsp;Fresnel), 1866–1870, ''Oeuvres complètes d'Augustin Fresnel'' (3&nbsp;vols.), Paris: Imprimerie Impériale; [https://books.google.com/books?id=1l0_AAAAcAAJ vol.&nbsp;1&nbsp;(1866)], [https://books.google.com/books?id=g6tzUG7JmoQC vol.&nbsp;2&nbsp;(1868)], [https://archive.org/details/oeuvrescompltes01fresgoog vol.&nbsp;3&nbsp;(1870)].
* {{cite book |first=T. H. |last=Levitt |date=2013 |title=A Short Bright Flash: Augustin Fresnel and the Birth of the Modern Lighthouse |location=New York |publisher=W.W.&nbsp;Norton |isbn=978-0-393-35089-0 |url=https://archive.org/details/shortbrightflash0000levi_s2d8 |url-access=subscription}}
* T. Young (ed. G.&nbsp;Peacock), 1855, ''Miscellaneous Works of the late Thomas Young'', London: J.&nbsp;Murray, [https://books.google.com/books?id=GyzPAAAAMAAJ vol.&nbsp;1].

== Further reading ==

* {{cite magazine |url=https://uslhs.org/sites/default/files/articles_pdf/TheFresnelLens.pdf |title=The Fresnel Lens |first=Wayne |last=Wheeler |magazine=The Keeper's Log |date=Winter 1985 |pages=12–14 |publisher=U.S. Lighthouse Society}}
* [[United States Coast Guard|U.S. Coast Guard]], ''Aids to Navigation'', Washington, DC: [[U.S. Government Printing Office]], 1945.
* U.S. Coast Guard, [https://web.archive.org/web/20220201232556/https://media.defense.gov/2017/Jul/03/2001772523/-1/-1/0/ATON_LIGHTHOUSEBIB2007.PDF ''Lighthouses, Lenses, Illuminants, Engineering, & Augustin Fresnel: A Historical Bibliography on Works Published Through 2007''].

== External links ==
{{commons category|Fresnel lenses}}

* [https://uslhs.org/ United States Lighthouse Society], especially "[https://uslhs.org/history/fresnel-lenses Fresnel Lenses] {{Webarchive|url=https://web.archive.org/web/20210302174800/https://uslhs.org/history/fresnel-lenses |date=2 March 2021 }}".
* W. A. Britten, [http://lighthousegetaway.com/lights/fresnel.html "The Fresnel lens"] (with photographs).
* J. Francis, [https://web.archive.org/web/20090520054046/http://www.digitalartform.com/archives/2009/04/fresnel_lens_-.html "Fresnel Lens - Maxwell Simulation"], 13&nbsp;April 2009.
* J. Hare, [http://vega.org.uk/video/programme/226 "How the Fresnel lens works"] (5-minute video), Vega Science Trust, 2008.
* {{cite web|mode=cs2 |url=http://www.terrypepper.com/lights/index.htm |author=T. Pepper |title=Seeing the Light: Lighthouses on the western Great Lakes |archive-url=https://web.archive.org/web/20080130074143/http://www.terrypepper.com/lights/index.htm |archive-date=30 January 2008}}.
* [https://www.youtube.com/watch?v=fQufI-QJLZg The Fresnel Lens: the Invention That Saved 1000 Ships]

{{Lighthouses}}

{{Use dmy dates|date=March 2020}}

[[Category:Lenses]]
[[Category:Lighthouse fixtures]]
[[Category:Solar thermal energy]]
[[Category:French inventions]]