Mirror - WikiHQ

thumb|A mirror reflecting the image of a [[vase]]

thumb|A [[first-surface mirror coated with aluminium and enhanced with dielectric coatings. The angle of the incident light (represented by both the light in the mirror and the shadow behind it) exactly matches the angle of reflection (the reflected light shining on the table).]]

thumb|-tall acoustic mirror near [[Kilnsea Grange, East Yorkshire, UK, from World War I. The mirror magnified the sound of approaching enemy Zeppelins for a microphone placed at the focal point. Sound waves are much longer than light waves, thus the object produces diffuse reflections in the visual spectrum.]]

A mirror, also known as a looking glass, is an object that reflects an image. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera. Mirrors reverse the direction of light at an angle equal to its incidence. This allows the viewer to see themselves or objects behind them, or even objects that are at an angle from them but out of their field of view, such as around a corner. Natural mirrors have existed since prehistoric times, such as the surface of water, but people have been manufacturing mirrors out of a variety of materials for thousands of years, like stone, metals, and glass. In modern mirrors, metals like silver or aluminium are often used due to their high reflectivity, applied as a thin coating on glass because of its naturally smooth and very hard surface.

A mirror is a wave reflector. Light consists of waves, and when light waves reflect from the flat surface of a mirror, those waves retain the same degree of curvature and vergence, in an equal yet opposite direction, as the original waves. This allows the waves to form an image when they are focused through a lens, just as if the waves had originated from the direction of the mirror. The light can also be pictured as rays (imaginary lines radiating from the light source, that are always perpendicular to the waves). These rays are reflected at an equal yet opposite angle from which they strike the mirror (incident light). This property, called specular reflection, distinguishes a mirror from objects that diffuse light, breaking up the wave and scattering it in many directions (such as flat-white paint). Thus, a mirror can be any surface in which the texture or roughness of the surface is smaller (smoother) than the wavelength of the waves.

When looking at a mirror, one will see a mirror image or reflected image of objects in the environment, formed by light emitted or scattered by them and reflected by the mirror towards one's eyes. This effect gives the illusion that those objects are behind the mirror, or (sometimes) in front of it. When the surface is not flat, a mirror may behave like a reflecting lens. A plane mirror yields a real-looking undistorted image, while a curved mirror may distort, magnify, or reduce the image in various ways, while keeping the lines, contrast, sharpness, colors, and other image properties intact.

A mirror is commonly used for inspecting oneself, such as during personal grooming; hence the old-fashioned name "looking glass".

The terms "mirror" and "reflector" can be used for objects that reflect any other types of waves. An acoustic mirror reflects sound waves. Objects such as walls, ceilings, or natural rock-formations may produce echos, and this tendency often becomes a problem in acoustical engineering when designing houses, auditoriums, or recording studios. Acoustic mirrors may be used for applications such as parabolic microphones, atmospheric studies, sonar, and seafloor mapping. The requirements for making a good mirror are a surface with a very high degree of flatness (preferably but not necessarily with high reflectivity), and a surface roughness smaller than the wavelength of the light.

The earliest manufactured mirrors were pieces of polished stone such as obsidian, a naturally occurring volcanic glass. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze and copper examples being produced by the Qijia culture. Such metal mirrors remained the norm through to Greco-Roman Antiquity and throughout the Middle Ages in Europe.

By structural material

The most common structural material for mirrors is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish.

Back-silvered mirrors

The most common mirrors consist of a plate of transparent glass, with a thin reflective layer on the back (the side opposite to the incident and reflected light) backed by a coating that protects that layer against abrasion, tarnishing, and corrosion. The glass is usually soda-lime glass, but lead glass may be used for decorative effects, and other transparent materials may be used for specific applications.

A plate of transparent plastic may be used instead of glass, for lighter weight or impact resistance. Alternatively, a flexible transparent plastic film may be bonded to the front and/or back surface of the mirror, to prevent injuries in case the mirror is broken. Lettering or decorative designs may be printed on the front face of the glass, or formed on the reflective layer. The front surface may have an anti-reflection coating.

Front-silvered mirrors

Mirrors which are reflective on the front surface (the same side of the incident and reflected light) may be made of any rigid material.

Flexible mirrors

Thin flexible plastic mirrors are sometimes used for safety, since they cannot shatter or produce sharp flakes. Their flatness is achieved by stretching them on a rigid frame. These usually consist of a layer of evaporated aluminium between two thin layers of transparent plastic.

By reflective material

thumb|A dielectric mirror-stack works on the principle of [[thin-film interference. Each layer has a different refractive index, allowing each interface to produce a small amount of reflection. When the thickness of the layers is proportional to the chosen wavelength, the multiple reflections constructively interfere. Stacks may consist of a few to hundreds of individual coats.]]

thumb|A hot mirror used in a camera to reduce red eye

In common mirrors, the reflective layer is usually some metal like silver, tin, nickel, or chromium, deposited by a wet process; or aluminium,

Objects viewed in a (plane) mirror will appear laterally inverted (e.g., if one raises one's right hand, the image's left hand will appear to go up in the mirror), but not vertically inverted (in the image a person's head still appears above their body). Convex mirrors as decoration are used in interior design to provide a predominantly experiential effect.

Technology

Televisions and projectors

Microscopic mirrors are a core element of many of the largest high-definition televisions and video projectors. A common technology of this type is Texas Instruments' DLP. A DLP chip is a postage stamp-sized microchip whose surface is an array of millions of microscopic mirrors. The picture is created as the individual mirrors move to either reflect light toward the projection surface (pixel on), or toward a light-absorbing surface (pixel off).

Other projection technologies involving mirrors include LCoS. Like a DLP chip, LCoS is a microchip of similar size, but rather than millions of individual mirrors, there is a single mirror that is actively shielded by a liquid crystal matrix with up to millions of pixels. The picture, formed as light, is either reflected toward the projection surface (pixel on), or absorbed by the activated LCD pixels (pixel off). LCoS-based televisions and projectors often use 3 chips, one for each primary color.

Large mirrors are used in rear-projection televisions. Light (for example from a DLP as discussed above) is "folded" by one or more mirrors so that the television set is compact.

Optical discs

Optical discs are modified mirrors which encode binary data as a series of physical pits and lands on an inner layer between the metal backing and outer plastic surface. The data is read and decoded by observing distortions in a reflected laser beam caused by the physical variations in the inner layer. Optical discs typically use aluminum backing like conventional mirrors, though ones with silver and gold backings also exist.

Solar power

thumb|Parabolic troughs near [[Harper Lake in California]]

Mirrors are integral parts of a solar power plant. The one shown in the adjacent picture uses concentrated solar power from an array of parabolic troughs.

Hamlet has a throne room with mirrored walls. Hamlet, played by Kenneth Branagh, gives his famous speech with the words "to be or not to be," looking into these mirrors.
Harry Potter and the Philosopher's Stone includes the magical Mirror of Erised.
Inception contains mirrors created in a dream sequence. Ariadne creates two mirrors facing each other that form an infinite number of reflected mirrors.
Lady in the Lake, a 1947 film noir, was shot from the point of view of the protagonist, who is seen only when a mirror is included in the shot.
Last Night in Soho is a psychological horror movie with several mirror scenes. The character Ellie occasionally sees her mother's ghost in mirrors.
The Matrix uses various reflections and mirrors throughout the film. Neo watches a broken mirror mend itself, and different objects create reflections.
Mirror is a drama film by Andrei Tarkovsky that includes several scenes with mirrors and several scenes shot in reflection.
Mirror Mirror is a fantasy comedy film based on Snow White that features a Mirror House and Mirror Queen.
Mirrors is a horror film about haunted mirrors that reflect different scenes than those in front of them.
Persona relies on mirror sequences to show how the two women, Bibi and Liv, reflect each other and become more alike.
Poltergeist III features mirrors that do not reflect reality and which can be used as portals to an afterlife.
Psycho by Alfred Hitchock has several shots with mirrors that reflect characters.
Oculus is a horror film about a haunted mirror that causes people to hallucinate and commit acts of violence.
Orpheus includes an important theme of mirrors in connection to aging and death.
Sailor Moon in the fourth story arc has a major theme pertaining to mirrors, which entrap several of the Sailor Senshi, the fiancée of the protagonist, and the villain in the arc.
Taxi Driver has a notable scene with a mirror in which the character Travis, played by Robert De Niro, asks himself the famous line, "You talkin' to me?"
The Lady from Shanghai has a climatic hall of mirrors scene that has become a trope in cinema narratives.
Raging Bull ends with the character Jake talking to himself in a mirror, a scene that was reused in Boogie Nights.
The Shining is a horror movie that includes several scenes with mirrors. Every time the character Jack encounters a ghost, a mirror is present.
The 10th Kingdom miniseries requires the characters to use a magic mirror to travel between New York City (the 10th Kingdom) and the Nine Kingdoms of fairy tale.
The Twilight Zone episode "The Mirror" features a mirror that the character Clemente believes can provide visions and information about enemies.
Us is a horror film that includes a girl seeing a doppelgänger of herself in a house of mirrors in a funhouse. The mirror images reflect the similarities in the clones throughout the film.
Vertigo includes several appearances of mirrors with both Scottie and Madeleine in the frame.

Literature

thumb|upright|An illustration from page 30 of [[:is:Mjallhvít|Mjallhvít (Snow White) an 1852 Icelandic translation of the Grimm-version fairytale]]

thumb|upright|[[Yin and yang|Taijitu within a frame of trigrams and a demon-warding mirror. These charms are believed to frighten away evil spirits and to protect a dwelling from bad luck]]

Mirrors featured in literature:

Christian Bible passages, 1 Corinthians 13:12 ("Through a Glass Darkly") and 2 Corinthians 3:18, reference a dim mirror-image or poor mirror-reflection.
Narcissus of Greek mythology wastes away while gazing, self-admiringly, at his reflection in water.
Elsewhere in Greek Mythology, Perseus is said to have defeated the Gorgon Medusa with the aid of a mirrored shield which allowed him to avoid the petrifying effect of her visage by only viewing her reflection.
The Song dynasty history Zizhi Tongjian Comprehensive Mirror in Aid of Governance by Sima Guang is so titled because "mirror" (鑑, jiàn) is used metaphorically in Chinese to refer to gaining insight by reflecting on past experience or history.
In the late 6th century Chinese folktale The Broken Mirror Restored two lovers who are separated by war break a mirror in two so that they might find each other again by identifying the other half of the mirror. The phrase "broken mirror restored", or "broken mirror joined together" has been used as an idiom to suggests the happy reunion of a separated couple.
In the European fairy tale, Snow White (collected by the Brothers Grimm in 1812), the evil queen asks, "Mirror, mirror, on the wall... who's the fairest of them all?"
In the Aarne-Thompson-Uther Index tale type ATU 329, "Hiding from the Devil (Princess)", the protagonist must find a way to hide from a princess, who, in many variants, owns a magical mirror that can see the whole world.
In Tennyson's famous poem The Lady of Shalott (1833, revised in 1842), the titular character possesses a mirror that enables her to look out on the people of Camelot, as she is under a curse that prevents her from seeing Camelot directly.
Hans Christian Andersen's fairy tale The Snow Queen, features the devil, in a form of an evil troll,

<span id="Mirrors and animals"></span> Mirror test

Only a few animal species have been shown to have the ability to recognize themselves in a mirror, most of them mammals. Experiments have found that the following animals can pass the mirror test:

Humans. Humans tend to fail the mirror test until they are about 18 months old, or what psychoanalysts call the "mirror stage".

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External links

How Mirrors Are Made (video), Glass Association of North America (GANA)
July 2019 "The Ugly History of Beautiful Things: Mirrors" by Katy Kelleher for Longreads