Fresnel lens

A Fresnel lens is a type of composite compact <a href="/facts/Lens_(optics)/ejlH6n5c">lens</a> 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 <a href="/facts/Dioptrics/puwjKPVj">dioptric</a> (purely <a href="/facts/Refraction/S8kvSKzM">refractive</a>) form of the lens was first proposed by <a href="/facts/Georges-Louis_Leclerc,_Comte_de_Buffon/9LqPhlul">Georges-Louis Leclerc, Comte de Buffon</a>, and independently reinvented by the French physicist <a href="/facts/Augustin-Jean_Fresnel/jb64tyGc">Augustin-Jean Fresnel</a> (1788–1827) for use in <a href="/facts/Lighthouse/HAwW4RFW">lighthouses</a>. The <a href="/facts/Catadioptric_system/vzJ2FulL">catadioptric</a> (combining refraction and reflection) form of the lens, entirely invented by Fresnel, has outer <a href="/facts/Prism_(optics)/eodBFF70">prismatic</a> elements that use <a href="/facts/Total_internal_reflection/Tm0M62NQ">total internal reflection</a> 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 <a href="/facts/Aperture/8PV11GQm">aperture</a> and short <a href="/facts/Focal_length/brGIUkEY">focal length</a> 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".

Fresnel lens open-in-new

Fresnel lens