78-491: A mirror , also known as a looking glass , is an object that reflects an image . Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the image in an equal yet opposite angle from which the light shines upon it. 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
156-480: A circular cylinder or of a parabolic cylinder . 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. 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
234-437: A mirror ) the angle at which the wave is incident on the surface equals the angle at which it is reflected. In acoustics , reflection causes echoes and is used in sonar . In geology, it is important in the study of seismic waves . Reflection is observed with surface waves in bodies of water. Reflection is observed with many types of electromagnetic wave , besides visible light . Reflection of VHF and higher frequencies
312-471: A torus . Note that these are theoretical ideals, requiring perfect alignment of perfectly smooth, perfectly flat perfect reflectors that absorb none of the light. In practice, these situations can only be approached but not achieved because the effects of any surface imperfections in the reflectors propagate and magnify, absorption gradually extinguishes the image, and any observing equipment (biological or technological) will interfere. In this process (which
390-432: A virtual image of whatever is in the opposite angle from the viewer, meaning that objects in the image appear to exist in a direct line of sight —behind the surface of the mirror—at an equal distance from their position in front of the mirror. Objects behind the observer, or between the observer and the mirror, are reflected back to the observer without any actual change in orientation; the light waves are simply reversed in
468-455: A century, Venice retained the monopoly of the tin amalgam technique. Venetian mirrors in richly decorated frames served as luxury decorations for palaces throughout Europe, and were very expensive. For example, in the late seventeenth century, the Countess de Fiesque was reported to have traded an entire wheat farm for a mirror, considering it a bargain. However, by the end of that century the secret
546-405: A complex conjugating mirror, it would be black because only the photons which left the pupil would reach the pupil. Materials that reflect neutrons , for example beryllium , are used in nuclear reactors and nuclear weapons . In the physical and biological sciences, the reflection of neutrons off of atoms within a material is commonly used to determine the material's internal structure. When
624-418: A concave parabolic mirror (whose surface is a part of a paraboloid of revolution) will reflect rays that are parallel to its axis into rays that pass through its focus . Conversely, a parabolic concave mirror will reflect any ray that comes from its focus towards a direction parallel to its axis. If a concave mirror surface is a part of a prolate ellipsoid , it will reflect any ray coming from one focus toward
702-432: 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
780-426: A different image in the same mirror. Thus, the images observed in a mirror depend upon the angle of the mirror with respect to the eye. The angle between the object and the observer is always twice the angle between the eye and the normal, or the direction perpendicular to the surface. This allows animals with binocular vision to see the reflected image with depth perception and in three dimensions. The mirror forms
858-400: A direction perpendicular to the mirror. However, when viewer is facing the object and the mirror is at an angle between them, the image appears inverted 180° along the direction of the angle. 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
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#1732838617686936-402: A flat surface forms a mirror image , which appears to be reversed from left to right because we compare the image we see to what we would see if we were rotated into the position of the image. Specular reflection at a curved surface forms an image which may be magnified or demagnified; curved mirrors have optical power . Such mirrors may have surfaces that are spherical or parabolic . If
1014-771: 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 . Examples of obsidian mirrors found at Çatalhöyük in Anatolia (modern-day Turkey) have been dated to around 6000 BCE. Mirrors of polished copper were crafted in Mesopotamia from 4000 BCE, and in ancient Egypt from around 3000 BCE. Polished stone mirrors from Central and South America date from around 2000 BCE onwards. By
1092-415: A layer of paint applied over it. Mirrors for optical instruments often have the metal layer on the front face, so that the light does not have to cross the glass twice. In these mirrors, the metal may be protected by a thin transparent coating of a non-metallic ( dielectric ) material. The first metallic mirror to be enhanced with a dielectric coating of silicon dioxide was created by Hass in 1937. In 1939 at
1170-409: A left-hand glove into a right-hand glove or vice versa). When a person raises their left hand, the actual left hand raises in the mirror, but gives the illusion of a right hand raising because the imaginary person in the mirror is literally inside-out, hand and all. If the person stands side-on to a mirror, the mirror really does reverse left and right hands, that is, objects that are physically closer to
1248-400: A longitudinal sound wave strikes a flat surface, sound is reflected in a coherent manner provided that the dimension of the reflective surface is large compared to the wavelength of the sound. Note that audible sound has a very wide frequency range (from 20 to about 17000 Hz), and thus a very wide range of wavelengths (from about 20 mm to 17 m). As a result, the overall nature of
1326-770: A mirror is said to bring seven years of bad luck . 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 . An atomic mirror reflects matter waves and can be used for atomic interferometry and atomic holography . The first mirrors used by humans were most likely pools of still water, or shiny stones. The requirements for making
1404-401: A person's head still appears above their body). However, a mirror does not actually "swap" left and right any more than it swaps top and bottom. A mirror swaps front and back. To be precise, it reverses the object in the direction perpendicular to the mirror surface (the normal), turning the three dimensional image inside out (the way a glove stripped off the hand can be turned inside out, turning
1482-413: A point are usually made in the shape of a paraboloid of revolution instead; they are used in telescopes (from radio waves to X-rays), in antennas to communicate with broadcast satellites , and in solar furnaces . A segmented mirror , consisting of multiple flat or curved mirrors, properly placed and oriented, may be used instead. Mirrors that are intended to concentrate sunlight onto a long pipe may be
1560-470: A protective transparent coating is added on top of the reflecting layer, to protect it against abrasion, tarnishing, and corrosion, or to absorb certain wavelengths. 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. In common mirrors,
1638-581: A small fraction of the rays are reflected. In flying relativistic mirrors conceived for X-ray lasers , the reflecting surface is a spherical shockwave (wake wave) created in a low-density plasma by a very intense laser-pulse, and moving at an extremely high velocity. A phase-conjugating mirror uses nonlinear optics to reverse the phase difference between incident beams. Such mirrors may be used, for example, for coherent beam combination. The useful applications are self-guiding of laser beams and correction of atmospheric distortions in imaging systems. When
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#17328386176861716-408: A sufficiently narrow beam of light is reflected at a point of a surface, the surface's normal direction n → {\displaystyle {\vec {n}}} will be the bisector of the angle formed by the two beams at that point. That is, the direction vector u → {\displaystyle {\vec {u}}} towards the incident beams's source,
1794-404: A way similar to the way a conventional mirror reflects visible light . Atomic mirrors can be made of electric fields or magnetic fields , electromagnetic waves or just silicon wafer ; in the last case, atoms are reflected by the attracting tails of the van der Waals attraction (see quantum reflection ). Such reflection is efficient when the normal component of the wavenumber of the atoms
1872-456: 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
1950-507: Is a dichroic mirror that efficiently reflects the entire visible light spectrum while transmitting infrared wavelengths. A hot mirror is the opposite: it reflects infrared light while transmitting visible light. Dichroic mirrors are often used as filters to remove undesired components of the light in cameras and measuring instruments. In X-ray telescopes , the X-rays reflect off a highly precise metal surface at almost grazing angles, and only
2028-423: Is also known as phase conjugation), light bounces exactly back in the direction from which it came due to a nonlinear optical process. Not only the direction of the light is reversed, but the actual wavefronts are reversed as well. A conjugate reflector can be used to remove aberrations from a beam by reflecting it and then passing the reflection through the aberrating optics a second time. If one were to look into
2106-441: 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 . Mirrors which are reflective on the front surface (the same side of the incident and reflected light) may be made of any rigid material. The supporting material does not necessarily need to be transparent, but telescope mirrors often use glass anyway. Often
2184-403: Is important for radio transmission and for radar . Even hard X-rays and gamma rays can be reflected at shallow angles with special "grazing" mirrors. Reflection of light is either specular (mirror-like) or diffuse (retaining the energy , but losing the image) depending on the nature of the interface. In specular reflection the phase of the reflected waves depends on the choice of
2262-404: Is located at the imaginary intersection of the mirrors. A square of four mirrors placed face to face give the appearance of an infinite number of images arranged in a plane. The multiple images seen between four mirrors assembling a pyramid, in which each pair of mirrors sits an angle to each other, lie over a sphere. If the base of the pyramid is rectangle shaped, the images spread over a section of
2340-400: Is no archeological evidence of glass mirrors before the third century. These early glass mirrors were made by blowing a glass bubble, and then cutting off a small circular section from 10 to 20 cm in diameter. Their surface was either concave or convex, and imperfections tended to distort the image. Lead-coated mirrors were very thin to prevent cracking by the heat of the molten metal. Due to
2418-430: Is not desired, since the light would then be directed back into the headlights of an oncoming car rather than to the driver's eyes. When light reflects off a mirror , one image appears. Two mirrors placed exactly face to face give the appearance of an infinite number of images along a straight line. The multiple images seen between two mirrors that sit at an angle to each other lie over a circle. The center of that circle
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2496-498: Is returned in the direction from which it came. When flying over clouds illuminated by sunlight the region seen around the aircraft's shadow will appear brighter, and a similar effect may be seen from dew on grass. This partial retro-reflection is created by the refractive properties of the curved droplet's surface and reflective properties at the backside of the droplet. Some animals' retinas act as retroreflectors (see tapetum lucidum for more detail), as this effectively improves
2574-441: Is small or comparable to the effective depth of the attraction potential (roughly, the distance at which the potential becomes comparable to the kinetic energy of the atom). To reduce the normal component, most atomic mirrors are blazed at the grazing incidence . At grazing incidence, the efficiency of the quantum reflection can be enhanced by a surface covered with ridges ( ridged mirror ). The set of narrow ridges reduces
2652-468: Is the inverse of one produced by a single mirror. A surface can be made partially retroreflective by depositing a layer of tiny refractive spheres on it or by creating small pyramid like structures. In both cases internal reflection causes the light to be reflected back to where it originated. This is used to make traffic signs and automobile license plates reflect light mostly back in the direction from which it came. In this application perfect retroreflection
2730-441: Is used as a means of focusing waves that cannot effectively be reflected by common means. X-ray telescopes are constructed by creating a converging "tunnel" for the waves. As the waves interact at low angle with the surface of this tunnel they are reflected toward the focus point (or toward another interaction with the tunnel surface, eventually being directed to the detector at the focus). A conventional reflector would be useless as
2808-407: 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
2886-515: The Bronze Age most cultures were using mirrors made from polished discs of bronze , copper , silver , or other metals. The people of Kerma in Nubia were skilled in the manufacturing of mirrors. Remains of their bronze kilns have been found within the temple of Kerma. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze and copper examples being produced by
2964-451: The Caliphate mathematician Ibn Sahl in the tenth century. Mirrors can be classified in many ways; including by shape, support, reflective materials, manufacturing methods, and intended application. Typical mirror shapes are planar and curved mirrors. The surface of curved mirrors is often a part of a sphere . Mirrors that are meant to precisely concentrate parallel rays of light into
3042-733: The Qijia culture . Such metal mirrors remained the norm through to Greco-Roman Antiquity and throughout the Middle Ages in Europe . During the Roman Empire silver mirrors were in wide use by servants. Speculum metal is a highly reflective alloy of copper and tin that was used for mirrors until a couple of centuries ago. Such mirrors may have originated in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were only owned by
3120-643: The Schott Glass company, Walter Geffcken invented the first dielectric mirrors to use multilayer coatings. The Greek in Classical Antiquity were familiar with the use of mirrors to concentrate light. Parabolic mirrors were described and studied by the mathematician Diocles in his work On Burning Mirrors . Ptolemy conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical, and concave spherical mirrors in his Optics . Parabolic mirrors were also described by
3198-505: The angle of incidence between n → {\displaystyle {\vec {n}}} and u → {\displaystyle {\vec {u}}} , but of opposite sign. This property can be explained by the physics of an electromagnetic plane wave that is incident to a flat surface that is electrically conductive or where the speed of light changes abruptly, as between two materials with different indices of refraction. More specifically,
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3276-602: The van der Waals attraction of atoms to the surfaces and enhances the reflection. Each ridge blocks part of the wavefront, causing Fresnel diffraction . Such a mirror can be interpreted in terms of the Zeno effect . We may assume that the atom is "absorbed" or "measured" at the ridges. Frequent measuring (narrowly spaced ridges) suppresses the transition of the particle to the half-space with absorbers, causing specular reflection . At large separation L {\displaystyle ~L~} between thin ridges,
3354-417: The 16th century, was to blow a cylinder of glass, cut off the ends, slice it along its length, and unroll it onto a flat hot plate. Venetian glassmakers also adopted lead glass for mirrors, because of its crystal-clarity and its easier workability. During the early European Renaissance , a fire-gilding technique developed to produce an even and highly reflective tin coating for glass mirrors. The back of
3432-494: The 1st century CE , with the development of soda-lime glass and glass blowing . The Roman scholar Pliny the Elder claims that artisans in Sidon (modern-day Lebanon ) were producing glass mirrors coated with lead or gold leaf in the back. The metal provided good reflectivity, and the glass provided a smooth surface and protected the metal from scratches and tarnishing. However, there
3510-513: The X-rays would simply pass through the intended reflector. When light reflects off of a material with higher refractive index than the medium in which is traveling, it undergoes a 180° phase shift . In contrast, when light reflects off of a material with lower refractive index the reflected light is in phase with the incident light. This is an important principle in the field of thin-film optics . Specular reflection forms images . Reflection from
3588-411: The angle of incidence equals the angle of reflection. In fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive index. In the most general case, a certain fraction of the light is reflected from the interface, and the remainder is refracted . Solving Maxwell's equations for a light ray striking a boundary allows
3666-404: The animals' night vision. Since the lenses of their eyes modify reciprocally the paths of the incoming and outgoing light the effect is that the eyes act as a strong retroreflector, sometimes seen at night when walking in wildlands with a flashlight. A simple retroreflector can be made by placing three ordinary mirrors mutually perpendicular to one another (a corner reflector ). The image produced
3744-453: The auditory feel of a space. In the theory of exterior noise mitigation , reflective surface size mildly detracts from the concept of a noise barrier by reflecting some of the sound into the opposite direction. Sound reflection can affect the acoustic space . Seismic waves produced by earthquakes or other sources (such as explosions ) may be reflected by layers within the Earth . Study of
3822-410: The bulb's walls. This phenomenon was developed into the method of evaporation coating by Pohl and Pringsheim in 1912. John D. Strong used evaporation coating to make the first aluminium -coated telescope mirrors in the 1930s. The first dielectric mirror was created in 1937 by Auwarter using evaporated rhodium . The metal coating of glass mirrors is usually protected from abrasion and corrosion by
3900-460: The deep reflections of waves generated by earthquakes has allowed seismologists to determine the layered structure of the Earth . Shallower reflections are used in reflection seismology to study the Earth's crust generally, and in particular to prospect for petroleum and natural gas deposits. Atomic mirror In physics , an atomic mirror is a device which reflects neutral atoms in
3978-465: The derivation of the Fresnel equations , which can be used to predict how much of the light is reflected, and how much is refracted in a given situation. This is analogous to the way impedance mismatch in an electric circuit causes reflection of signals. Total internal reflection of light from a denser medium occurs if the angle of incidence is greater than the critical angle . Total internal reflection
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#17328386176864056-432: The forward radiation cancels the incident light, and backward radiation is just the reflected light. Light–matter interaction in terms of photons is a topic of quantum electrodynamics , and is described in detail by Richard Feynman in his popular book QED: The Strange Theory of Light and Matter . When light strikes the surface of a (non-metallic) material it bounces off in all directions due to multiple reflections by
4134-403: The glass is the combination of the forward radiation of the electrons and the incident light. The reflected light is the combination of the backward radiation of all of the electrons. In metals, electrons with no binding energy are called free electrons. When these electrons oscillate with the incident light, the phase difference between their radiation field and the incident field is π (180°), so
4212-405: The glass was coated with a tin-mercury amalgam, and the mercury was then evaporated by heating the piece. This process caused less thermal shock to the glass than the older molten-lead method. The date and location of the discovery is unknown, but by the 16th century Venice was a center of mirror production using this technique. These Venetian mirrors were up to 40 inches (100 cm) square. For
4290-422: The greater availability of affordable mirrors. Mirrors are often produced by the wet deposition of silver, or sometimes nickel or chromium (the latter used most often in automotive mirrors) via electroplating directly onto the glass substrate. Glass mirrors for optical instruments are usually produced by vacuum deposition methods. These techniques can be traced to observations in the 1920s and 1930s that metal
4368-439: The incident rays are parallel among themselves but not parallel to the mirror's axis, or are divergent from a point that is not the focus – as when trying to form an image of an object that is near the mirror or spans a wide angle as seen from it. However, this aberration can be sufficiently small if the object image is sufficiently far from the mirror and spans a sufficiently small angle around its axis. Mirrors reflect an image to
4446-537: The individual atoms (or oscillation of electrons, in metals), causing each particle to radiate a small secondary wave in all directions, like a dipole antenna . All these waves add up to give specular reflection and refraction, according to the Huygens–Fresnel principle . In the case of dielectrics such as glass, the electric field of the light acts on the electrons in the material, and the moving electrons generate fields and become new radiators. The refracted light in
4524-414: The light is reflected with equal luminance (in photometry) or radiance (in radiometry) in all directions, as defined by Lambert's cosine law . The light sent to our eyes by most of the objects we see is due to diffuse reflection from their surface, so that this is our primary mechanism of physical observation. Some surfaces exhibit retroreflection . The structure of these surfaces is such that light
4602-402: 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
4680-434: The microscopic irregularities inside the material (e.g. the grain boundaries of a polycrystalline material, or the cell or fiber boundaries of an organic material) and by its surface, if it is rough. Thus, an 'image' is not formed. This is called diffuse reflection . The exact form of the reflection depends on the structure of the material. One common model for diffuse reflection is Lambertian reflectance , in which
4758-516: The mirror always appear closer in the virtual image, and objects farther from the surface always appear symmetrically farther away regardless of angle. Reflection (physics) Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light , sound and water waves . The law of reflection says that for specular reflection (for example at
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#17328386176864836-444: The normal vector n → {\displaystyle {\vec {n}}} , and direction vector v → {\displaystyle {\vec {v}}} of the reflected beam will be coplanar , and the angle between n → {\displaystyle {\vec {n}}} and v → {\displaystyle {\vec {v}}} will be equal to
4914-447: The observer. However, unlike a projected image on a screen, an image does not actually exist on the surface of the mirror. For example, when two people look at each other in a mirror, both see different images on the same surface. When the light waves converge through the lens of the eye they interfere with each other to form the image on the surface of the retina , and since both viewers see waves coming from different directions, each sees
4992-468: The origin of coordinates, but the relative phase between s and p (TE and TM) polarizations is fixed by the properties of the media and of the interface between them. A mirror provides the most common model for specular light reflection, and typically consists of a glass sheet with a metallic coating where the significant reflection occurs. Reflection is enhanced in metals by suppression of wave propagation beyond their skin depths . Reflection also occurs at
5070-456: The other focus. A convex parabolic mirror, on the other hand, will reflect rays that are parallel to its axis into rays that seem to emanate from the focus of the surface, behind the mirror. Conversely, it will reflect incoming rays that converge toward that point into rays that are parallel to the axis. A convex mirror that is part of a prolate ellipsoid will reflect rays that converge towards one focus into divergent rays that seem to emanate from
5148-529: The other focus. Spherical mirrors do not reflect parallel rays to rays that converge to or diverge from a single point, or vice versa, due to spherical aberration . However, a spherical mirror whose diameter is sufficiently small compared to the sphere's radius will behave very similarly to a parabolic mirror whose axis goes through the mirror's center and the center of that sphere; so that spherical mirrors can substitute for parabolic ones in many applications. A similar aberration occurs with parabolic mirrors when
5226-791: The poor quality, high cost, and small size of glass mirrors, solid-metal mirrors (primarily of steel) remained in common use until the late nineteenth century. Silver-coated metal mirrors were developed in China as early as 500 CE. The bare metal was coated with an amalgam , then heated until the mercury boiled away. The evolution of glass mirrors in the Middle Ages followed improvements in glassmaking technology. Glassmakers in France made flat glass plates by blowing glass bubbles, spinning them rapidly to flatten them, and cutting rectangles out of them. A better method, developed in Germany and perfected in Venice by
5304-432: The reflecting surface is very smooth, the reflection of light that occurs is called specular or regular reflection. The laws of reflection are as follows: These three laws can all be derived from the Fresnel equations . In classical electrodynamics , light is considered as an electromagnetic wave, which is described by Maxwell's equations . Light waves incident on a material induce small oscillations of polarisation in
5382-402: The reflection varies according to the texture and structure of the surface. For example, porous materials will absorb some energy, and rough materials (where rough is relative to the wavelength) tend to reflect in many directions—to scatter the energy, rather than to reflect it coherently. This leads into the field of architectural acoustics , because the nature of these reflections is critical to
5460-405: The reflective layer is usually some metal like silver, tin, nickel , or chromium , deposited by a wet process; or aluminium, deposited by sputtering or evaporation in vacuum. The reflective layer may also be made of one or more layers of transparent materials with suitable indices of refraction . The structural material may be a metal, in which case the reflecting layer may be just the surface of
5538-588: The same. Metal concave dishes are often used to reflect infrared light (such as in space heaters ) or microwaves (as in satellite TV antennas). Liquid metal telescopes use a surface of liquid metal such as mercury. Mirrors that reflect only part of the light, while transmitting some of the rest, can be made with very thin metal layers or suitable combinations of dielectric layers. They are typically used as beamsplitters . A dichroic mirror , in particular, has surface that reflects certain wavelengths of light, while letting other wavelengths pass through. A cold mirror
5616-928: 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". This use, which dates from prehistory, overlaps with uses in decoration and architecture . Mirrors are also used to view other items that are not directly visible because of obstructions; examples include rear-view mirrors in vehicles, security mirrors in or around buildings, and dentist's mirrors . Mirrors are also used in optical and scientific apparatus such as telescopes , lasers , cameras , periscopes , and industrial machinery. According to superstitions breaking
5694-439: The surface of transparent media, such as water or glass . In the diagram, a light ray PO strikes a vertical mirror at point O , and the reflected ray is OQ . By projecting an imaginary line through point O perpendicular to the mirror, known as the normal , we can measure the angle of incidence , θ i and the angle of reflection , θ r . The law of reflection states that θ i = θ r , or in other words,
5772-409: 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
5850-649: The wealthy. Common metal mirrors tarnished and required frequent polishing. Bronze mirrors had low reflectivity and poor color rendering , and stone mirrors were much worse in this regard. These defects explain the New Testament reference in 1 Corinthians 13 to seeing "as in a mirror, darkly." The Greek philosopher Socrates urged young people to look at themselves in mirrors so that, if they were beautiful, they would become worthy of their beauty, and if they were ugly, they would know how to hide their disgrace through learning. Glass began to be used for mirrors in
5928-431: Was an important manufacturer, and Bohemian and German glass, often rather cheaper, was also important. The invention of the silvered-glass mirror is credited to German chemist Justus von Liebig in 1835. His wet deposition process involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate . This silvering process was adapted for mass manufacturing and led to
6006-425: Was being ejected from electrodes in gas discharge lamps and condensed on the glass walls forming a mirror-like coating. The phenomenon, called sputtering , was developed into an industrial metal-coating method with the development of semiconductor technology in the 1970s. A similar phenomenon had been observed with incandescent light bulbs : the metal in the hot filament would slowly sublimate and condense on
6084-458: Was leaked through industrial espionage. French workshops succeeded in large-scale industrialization of the process, eventually making mirrors affordable to the masses, in spite of the toxicity of mercury's vapor. The invention of the ribbon machine in the late Industrial Revolution allowed modern glass panes to be produced in bulk. The Saint-Gobain factory, founded by royal initiative in France,
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