Uses
Images
Fresnel lenses are used as simple hand-held magnifiers. They are also used to correct various visual disorders, including ocular motility disorders such as strabismus. Fresnel lenses have been used to increase the visual size of CRT screens in pocket televisions, notably the Sinclair TV80. They are also used in traffic lights.
Fresnel lenses are used on European left-hand drive trucks entering the United Kingdom and the Republic of Ireland (and vice versa, Irish and British right-hand drive trucks entering continental Europe) to overcome blind spots caused by the driver operating the truck while sitting on the wrong side of the cab relative to the side of the road the car is on. They stick to the passenger side window.[4].
Another automotive application of a Fresnel lens is as a rear view enhancer, as the wide angle of view of a lens placed in the rear window allows the scene behind a vehicle, particularly a tall or taillight vehicle, to be examined more effectively than a rear view using a mirror alone.
Multifocal Fresnel lenses are also used as part of retinal identification cameras, where they provide multiple in-focus and out-of-focus images of a fixation target within the camera. For virtually all users, at least one of the images will be in focus, allowing for proper eye alignment.
Fresnel lenses have also been used in the field of popular entertainment. British rock artist Peter Gabriel used 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 comedic effect. In Terry Gilliam's film Brazil, plastic Fresnel screens appear ostensibly as magnifying glasses for the small CRT monitors used in the offices of the Ministry of Information. However, they occasionally appear between the actors and the camera, distorting the scale and composition of the scene to humorous effect. The Pixar film Wall-E features a Fresnel lens in scenes where the protagonist watches the musical Hello, Dolly! enlarged on an iPod.
Photograph
Canon and Nikon have used Fresnel lenses to reduce the size of telephoto lenses. Photographic lenses that include Fresnel elements can be much shorter than the corresponding conventional lens design. Nikon calls the technology Phase Fresnel.[5][6].
The Polaroid SX-70 camera used a Fresnel reflector as part of its viewing system.
View and large format cameras can use a Fresnel lens in conjunction with ground glass, to increase the perceived brightness of the image projected by a lens onto the ground glass, thus helping to adjust focus and composition.
Lightning
High-quality glass Fresnel lenses were used in lighthouses, where they were considered cutting-edge in the late 19th century and into the mid-20th century; Most lighthouses have removed glass Fresnel lenses from service and replaced them with much less expensive and more durable aerodynamic beacons, often containing plastic Fresnel lenses. Lighthouse Fresnel lens systems typically include additional annular prismatic elements, arranged in faceted domes above and below the central planar Fresnel, to capture all of the light emitted by the light source. The path of light through these elements may include internal reflection, rather than simple refraction, in the planar Fresnel element. These lenses conferred many practical benefits to designers, builders and users of lighthouses and their lighting. 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.
Perhaps the most widespread use of Fresnel lenses, for a time, occurred in automobile headlights, where they can shape the roughly parallel beam of the parabolic reflector to meet the requirements of high and low beam patterns, often both in the same headlight unit (such as the European H4 design). For reasons of economy, weight and impact resistance, newer cars have dispensed with Fresnel glass lenses, using multifaceted reflectors with smooth polycarbonate lenses. However, Fresnel lenses remain in widespread use in automotive tail, marker, and reverse lights.
Fresnel glass lenses are also used in theater and film lighting instruments (see Fresnel flashlight); such instruments are often simply called Fresnels. The entire instrument consists of a metal casing, a reflector, a lamp assembly and a Fresnel lens. Many Fresnel instruments allow the lamp to move relative to the focal point of the lens, 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°.[7] The Fresnel lens produces a very soft-edged beam, which is why it is often used as a wash light. A support in front of the lens may contain a colored plastic film (gel) to tint the light or wire or frosted plastic screens to diffuse it. The Fresnel lens is useful in motion picture film making not only because of its ability to focus the light beam brighter than a typical lens, but also because the light has a relatively constant intensity across the width of the light beam.
Aircraft carriers and naval air stations often use Fresnel lenses in their landing optical systems. The "meatball" light helps the pilot maintain the proper glide slope for landing. In the center are amber and red lights made up 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 too low.
Projection
Using Fresnel lenses for imaging reduces image quality, so they tend to be used 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 from clear plastic and are used in overhead projectors and projection televisions.
Fresnel lenses of different focal lengths (a collimator and a collector) are used in commercial and DIY projections. The collimator lens has the lowest focal length and is placed closest to the light source, and the collecting lens, which focuses the light onto the triple lens, is placed after the projection image (an active matrix LCD panel in LCD projectors). Fresnel lenses are also used as collimators in overhead projectors.
Solar energy
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 cookers, in solar forges, and in solar collectors used to heat water for domestic use. They can also be used to generate steam or to power a Stirling engine.
Fresnel lenses can concentrate sunlight on solar cells at a ratio of almost 500:1.[8] This allows the surface area of active solar cells to be reduced, which reduces costs and allows the use of more efficient cells that would otherwise be too expensive.[9] At the beginning of the 21st century, Fresnel reflectors began to be used to concentrate the sun's radiation in solar power plants (CSP). One application was to preheat water at the Liddell coal-fired power station in the Hunter Valley, Australia.
Fresnel lenses can be used to sinter sand, enabling 3D printing in glass.[10].