This article is about wave reflectors (mainly, specular reflection of visible light). For other uses, see Mirror (disambiguation).
"Looking glass" redirects here. For other uses, see Looking Glass (disambiguation).
"Mirrors" redirects here. For other uses, see Mirrors (disambiguation).
A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light, such as flat-white paint.
The most familiar type of mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image.
Mirrors are commonly used for personal grooming or admiring oneself (where they are also called looking-glasses), for viewing the area behind and on the sides on motor vehicles while driving, for decoration, and architecture. Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for visible light; however, mirrors designed for other wavelengths of electromagnetic radiation are also used.
Types of glass mirrors
There are many types of glass mirrors, each representing a different manufacturing process and reflection type.
An aluminium glass mirror is made of a float glass manufactured using vacuum coating, i.e. aluminium powder is evaporated (or "sputtered") onto the exposed surface of the glass in a vacuum chamber and then coated with two or more layers of waterproof protective paint.
A low aluminium glass mirror is manufactured by coating silver and two layers of protective paint on the back surface of glass. A low aluminium glass mirror is very clear, light transmissive, smooth, and reflects accurate natural colors. This type of glass is widely used for framing presentations and exhibitions in which a precise color representation of the artwork is truly essential or when the background color of the frame is predominantly white.
A safety glass mirror is made by adhering a special protective film to the back surface of a silver glass mirror, which prevents injuries in case the mirror is broken. This kind of mirror is used for furniture, doors, glass walls, commercial shelves, or public areas.
A silkscreen printed glass mirror is produced using inorganic color ink that prints patterns through a special screen onto glass. Various colors, patterns, and glass shapes are available. Such a glass mirror is durable and more moisture resistant than ordinary printed glass and can serve for over 20 years. This type of glass is widely used for decorative purposes (e.g., on mirrors, table tops, doors, windows, kitchen chop boards, etc.).
A silver glass mirror is an ordinary mirror, coated on its back surface with silver, which produces images by reflection. This kind of glass mirror is produced by coating a silver, copper film and two or more layers of waterproof paint on the back surface of float glass, which perfectly resists acid and moisture. A silver glass mirror provides clear and actual images, is quite durable, and is widely used for furniture, bathroom and other decorative purposes.
Decorative glass mirrors are usually handcrafted. A variety of shades, shapes and glass thickness are often available.
See also: Mirror image and Specular reflection
Shape of a mirror's surface
A beam of light reflects off a mirror at an angle of reflection equal to its angle of incidence (if the size of a mirror is much larger than the wavelength of light). That is, if the beam of light is shining on a mirror's surface, at a ° angle vertically, then it reflects from the point of incidence at a ° angle from vertically in the opposite direction. This law mathematically follows from the interference of a plane wave on a flat boundary (of much larger size than the wavelength).
- In a plane mirror, a parallel beam of light changes its direction as a whole, while still remaining parallel; the images formed by a plane mirror are virtual images, of the same size as the original object (see mirror image).
- In a concave mirror, parallel beams of light become a convergent beam, whose rays intersect in the focus of the mirror. Also known as converging mirror
- In a convex mirror, parallel beams become divergent, with the rays appearing to diverge from a common point of intersection "behind" the mirror.
- Spherical concave and convex mirrors do not focus parallel rays to a single point due to spherical aberration. However, the ideal of focusing to a point is a commonly used approximation. Parabolic reflectors resolve this, allowing incoming parallel rays (for example, light from a distant star) to be focused to a small spot; almost an ideal point. Parabolic reflectors are not suitable for imaging nearby objects because the light rays are not parallel.
Main article: Mirror image
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 his body). However, a mirror does not usually "swap" left and right any more than it swaps top and bottom. A mirror typically reverses the forward/backward axis. To be precise, it reverses the object in the direction perpendicular to the mirror surface (the normal). Because left and right are defined relative to front-back and top-bottom, the "flipping" of front and back results in the perception of a left-right reversal in the image. (If you stand side-on to a mirror, the mirror really does reverse your left and right, because that's the direction perpendicular to the mirror.)
Looking at an image of oneself with the front-back axis flipped results in the perception of an image with its left-right axis flipped. When reflected in the mirror, your right hand remains directly opposite your real right hand, but it is perceived as the left hand of your image. When a person looks into a mirror, the image is actually front-back reversed, which is an effect similar to the hollow-mask illusion. Notice that a mirror image is fundamentally different from the object and cannot be reproduced by simply rotating the object.
For things that may be considered as two-dimensional objects (like text), front-back reversal cannot usually explain the observed reversal. In the same way that text on a piece of paper appears reversed if held up to a light and viewed from behind, text held facing a mirror will appear reversed, because the observer is behind the text. Another way to understand the reversals observed in images of objects that are effectively two-dimensional is that the inversion of left and right in a mirror is due to the way human beings turn their bodies. To turn from viewing the side of the object facing the mirror to view the reflection in the mirror requires the observer to look in the opposite direction. To look in another direction, human beings turn their heads about a vertical axis. This causes a left-right reversal in the image but not an up-down reversal. If a person instead turns by bending over and looking at the mirror image between his/her legs, up-down will appear reversed but not left-right. This sort of reversal is simply a change relative to the observer and not a change intrinsic to the image itself, as with a three-dimensional object.
The first mirrors used by humans were most likely pools of dark, still water, or water collected in a primitive vessel of some sort. 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 wave-length 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 in Anatolia (modern-day Turkey) have been dated to around 6000 B.C. Mirrors of polished copper were crafted in Mesopotamia from 4000 B.C., and in ancient Egypt from around 3000 B.C. Polished stone mirrors from Central and South America date from around 2000 B.C. onwards. In China, bronze mirrors were manufactured from around 2000 B.C., some of the earliest bronze and copper examples being produced by the Qijia culture. Mirrors made of other metal mixtures (alloys) such as copper and tin speculum metal may have also been produced in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were only owned by the wealthy. These stone and metal mirrors could be made in very large sizes, but were difficult to polish and get perfectly flat; a process that became more difficult with increased size; so they often produced warped or blurred images. Stone mirrors often had poor reflectivity compared to metals, yet metals scratch or tarnish easily, so they frequently needed polishing. Depending upon the color, both often yielded reflections with poor color rendering. The poor image quality of ancient mirrors explains 1 Corinthians 13's reference to seeing "as in a mirror, darkly."
In her history of the mirror, Sabine Melchior-Bonnet draws significant attention to the relation of the mirror to Greek philosophy, specifically Socrates:
If well used, however, the mirror can aid moral meditation between man and himself. Socrates, we are told by Diogenes, 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. The mirror, a tool by which to "know thyself," invited man to not mistake himself for God, to avoid pride by knowing his limits, and to improve himself. His was thus not a passive mirror of imitation but an active mirror of transformation. (p.106)
Glass was a desirable material for mirrors. Because the surface of glass is naturally smooth, it produces reflections with very little blur. In addition, glass is very hard and scratch-resistant. However, glass by itself has little reflectivity, so people began coating it with metals to increase the reflectivity. Metal-coated glass mirrors are said by the Roman scholar Pliny the Elder to have been invented in Sidon (modern-day Lebanon) in the first century A.D., although no archeological evidence of them date from before the third century. According to Pliny, the people of Sidon developed a technique for creating crude mirrors by coating blown glass with molten lead. Glass mirrors backed with gold leaf are mentioned by Pliny in his Natural History, written in about 77 A.D. Because there were few ways to make a smooth piece of glass with a uniform thickness, these ancient glass-mirrors were made by blowing a glass bubble, and then cutting off a small, circular section, producing mirrors that were either concave or convex. These circular mirrors were typically small, from only a fraction of an inch to as much as eight inches in diameter. These small mirrors produced distorted images, yet were prized objects of high value. These ancient glass mirrors were very thin, thus very fragile, because the glass needed to be extremely thin to prevent cracking when coated with a hot, molten metal. Due to the poor quality, high cost, and small size of these ancient glass mirrors, solid metal-mirrors primarily of steel were usually preferred until the late nineteenth century.
Parabolic mirrors were described and studied in classical antiquity 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 the physicist Ibn Sahl in the tenth century, and Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries, carried out a number of experiments with mirrors, and solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point. By the 11th century, glass mirrors were being produced in Moorish Spain.
In China, people began making mirrors by coating metallic objects with silver-mercury amalgams as early as 500 A.D. This was accomplished by coating the mirror with the amalgam, and then heating it until the mercury boiled away, leaving only the silver behind.
The problems of making metal-coated, glass mirrors was due to the difficulties in making glass that was very clear, as most ancient glass was tinted green with iron. This was overcome when people began mixing soda, limestone, potash, manganese, and fern ashes with the glass. There was also no way for the ancients to make flat panes of glass with uniform thicknesses. The earliest methods for producing glass panes began in France, when people began blowing glass bubbles, and then spinning them rapidly to flatten them out into plates from which pieces could be cut. However, these pieces were still not uniform in thickness, so produced distorted images as well. A better method was to blow a cylinder of glass, cut off the ends, slice it down the center, and unroll it onto a flat hearth. This method produced the first mirror-quality glass panes, but it was very difficult and resulted in a lot of breakage. Even windows were primarily made of oiled paper or stained glass, until the mid-nineteenth century, due to the high cost of making clear, flat panes of glass.
The method of making flat panes of clear glass from blown cylinders began in Germany and evolved through the Middle Ages, until being perfected by the Venetians in the sixteenth century. The Venetians began using lead glass for its crystal-clarity and its easier workability. Some time during the early Renaissance, European manufacturers perfected a superior method of coating glass with a tin-mercury amalgam, producing an amorphous coating with better reflectivity than crystalline metals and causing little thermal shock to the glass. The exact date and location of the discovery is unknown, but in the sixteenth century, Venice, a city famed for its glass-making expertise, became a center of mirror production using this new technique. Glass mirrors from this period were extremely expensive luxuries. 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. These Venetian mirrors were limited in size to a maximum area of around 40 inches (100 cm) square, until modern glass panes began to be produced during the Industrial Revolution. The Saint-Gobain factory, founded by royal initiative in France, 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 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 the greater availability of affordable mirrors. In the modern age, 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.
Vacuum deposition began with the study of the sputtering phenomenon during the 1920s and 1930s, which was a common problem in lighting in which metal ejected from the electrodes coated the glass, blocking output. However, turning sputtering into a reliable method of coating a mirror did not occur until the invention of semiconductors in the 1970s. Evaporation coating was pioneered by John Strong in 1912. Aluminum was a desirable material for mirrors, but was too dangerous to apply with electroplating. Strong used evaporation coating to make the first aluminum telescope mirrors in the 1930s. The first dielectric mirror was created in 1937 by Auwarter using evaporated rhodium, while the first metallic mirror to be enhanced with a dielectric coating of silicon dioxide was created by Hass the same year. In 1939 at the Schott Glass company, Walter Geffcken invented the first dielectric mirrors to use multilayer coatings (stacks).
Mirrors are manufactured by applying a reflective coating to a suitable substrate. The most common substrate is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish. The reflective coating is typically applied to the back surface of the glass, so that the reflecting side of the coating is protected from corrosion and accidental damage by the glass on one side and the coating itself and optional paint for further protection on the other.
In classical antiquity, mirrors were made of solid metal (bronze, later silver) and were too expensive for widespread use by common people; they were also prone to corrosion. Due to the low reflectivity of polished metal, these mirrors also gave a darker image than modern ones, making them unsuitable for indoor use with the artificial lighting of the time (candles or lanterns).
The method of making mirrors out of plate glass was invented by 13th-century Venetian glassmakers on the island of Murano, who covered the back of the glass with an amorphous coat of tin using a fire-gilding technique, obtaining near-perfect and undistorted reflection. For over one hundred years, Venetian mirrors installed in richly decorated frames served as luxury decorations for palaces throughout Europe, but the secret of the mercury process eventually arrived in London and Paris during the 17th century, due to industrial espionage. French workshops succeeded in large-scale industrialization of the process, eventually making mirrors affordable to the masses, although mercury's toxicity (a primary ingredient in gilding, which was boiled away forming noxious vapors) remained a problem.
In modern times, the mirror substrate is shaped, polished and cleaned, and is then coated. Glass mirrors are most often coated with silver or aluminium, implemented by a series of coatings:
- Tin(II) chloride
- Chemical activator
The tin(II) chloride is applied because silver will not bond with the glass. The activator causes the tin/silver to harden. Copper is added for long-term durability. The paint protects the coating on the back of the mirror from scratches and other accidental damage.
In some applications, generally those that are cost-sensitive or that require great durability, such as for mounting in a prison cell, mirrors may be made from a single, bulk material such as polished metal. However, metals consist of small crystals (grains) separated by grain boundaries. Thus, crystalline metals do not reflect with perfect uniformity. Other methods like wet-deposition or electroplating produce a non-crystalline coating of amorphous metal (metallic glass). Lacking any grain boundaries, the amorphous coatings have higher reflectivity than crystalline metals of the same type. Electroplating must be performed by first coating the glass with carbon, to make the surface electrically conductive, thus the adhesion is often not as good as with wet-deposition. Both lack the ability to produce perfectly uniform thicknesses with high precision. When high precision or reflectivity is not a requirement, the coating may be placed on the back of the mirror so that the light passes through the glass, and the coating is the second surface it encounters. Therefore, these are called second-surface mirrors, which have the added benefit of high durability, because the glass substrate can protect the coating from damage.
For technical applications such as laser mirrors, the reflective coating is typically applied by vacuum deposition. Vacuum deposition provides an effective means of producing a very uniform coating, and controlling the thickness with high precision. In applications where great precision and low losses are required, the coated side of the mirror may be the first material encountered by the light, referred to as a first-surface mirror. This eliminates refraction and double reflections, also called "ghost reflections" (a weak reflection from the surface of the glass, and a stronger one from the reflecting metal), and reduces absorption of light by the mirror. Technical mirrors may use a silver, aluminium, or gold coating (the latter typically for infrared mirrors), and achieve reflectivities of 90–95% when new. A hard, protective, transparent overcoat may be applied to prevent oxidation of the reflective layer and scratching of the soft metal. Applications requiring higher reflectivity or greater durability, where wide bandwidth is not essential, use dielectric coatings, which can achieve reflectivities as high as 99.997% over a limited range of wavelengths. Because the coatings are usually transparent, absorption losses are negligible. Unlike with metals, the reflectivity of the individual dielectric-coatings is a function of Snell's law known as the Fresnel equations, determined by the difference in refractive index between layers. Therefore, the thickness and material of the coatings can be adjusted to be centered on any wavelength. Vacuum deposition can be achieved in a number of ways, including sputtering, evaporation deposition, arc deposition, reactive-gas deposition, and ion plating, among many others.
Mirrors can be manufactured to a wide range of engineering tolerances, including reflectivity, surface quality, surface roughness, or transmissivity, depending on the desired application. These tolerances can range from low, such as found in a normal household-mirror, to extremely high, like those used in lasers or telescopes. Increasing the tolerances allows better and more precise imaging or beam transmission over longer distances. In imaging systems this can help reduce anomalies (artifacts), distortion or blur, but at a much higher cost. Where viewing distances are relatively close or high precision is not a concern, lower tolerances can be used to make effective mirrors at affordable costs.
The reflectivity of a mirror is determined by the percentage of reflected light per the total of the incident light. The reflectivity may vary with wavelength. All or a portion of the light not reflected is absorbed by the mirror, while in some cases a portion may also transmit through. Although some small portion of the light will be absorbed by the coating, the reflectivity is usually higher for first-surface mirrors, eliminating both reflection and absorption losses from the substrate. The reflectivity is often determined by the type and thickness of the coating. When the thickness of the coating is sufficient to prevent transmission, all of the losses occur due to absorption. Aluminum is harder, less expensive, and more resistant to tarnishing than silver, and will reflect 85 to 90% of the light in the visible to near-ultraviolet range, but is a poor reflector of infrared wavelengths longer than 800 nm. Gold is very soft and easily scratched, costly, yet does not tarnish. Gold is greater than 96% reflective to near and far-infrared light between 800 and 12000 nm, but poorly reflects visible light with wavelengths shorter than 600 nm (yellow). Silver is expensive, soft, and quickly tarnishes, but has the highest reflectivity in the visual to near-infrared of any metal. Silver can reflect up to 98 or 99% of light to wavelengths as long as 2000 nm, but loses nearly all reflectivity at wavelengths shorter than 350 nm. Dielectric mirrors can reflect greater than 99.99% of light, but only for a narrow range of wavelengths, ranging from a bandwidth of only 10 nm to as wide as 100 nm for tunable lasers. However, dielectric coatings can also enhance the reflectivity of metallic coatings and protect them from scratching or tarnishing. Dielectric materials are typically very hard and relatively cheap, however the number of coats needed generally makes it an expensive process. In mirrors with low tolerances, the coating thickness may be reduced to save cost, and simply covered with paint to absorb transmission.
Surface quality, or surface accuracy, measures the deviations from a perfect, ideal surface shape. Increasing the surface quality reduces distortion, artifacts, and aberration in images, and helps increase coherence, collimation, and reduce unwanted divergence in beams. For plane mirrors, this is often described in terms of flatness, while other surface shapes are compared to an ideal shape. The surface quality is typically measured with items like interferometers or optical flats, and are usually measured in wavelengths of light (λ). These deviations can be much larger or much smaller than the surface roughness. A normal household-mirror made with float glass may have flatness tolerances as low as 9--14λ per inch, equating to a deviation of 5600 through 8800 nanometers from perfect flatness. Precision ground and polished mirrors intended for lasers or telescopes may have tolerances as high as λ/50 (1/50 of the wavelength of the light, or around 12 nm). The surface quality can be affected by factors such as temperature changes, internal stress in the substrate, or even bending effects that occur when combining materials with different coefficients of thermal expansion, similar to a bimetallic strip.
Surface roughness describes the texture of the surface, often in terms of the depth of the microscopic scratches left by the polishing operations. Surface roughness determines how much of the reflection is specular and how much diffuses, controlling how sharp or blurry the image will be. For perfectly specular reflection, the surface roughness must be kept smaller than the wavelength of the light. Microwaves, which sometimes have a wavelength greater than an inch (2.5 cm) can reflect specularly off a metal screen-door, continental ice-sheets, or desert sand, while visible light, having wavelengths of only a few hundred nanometers (a few hundred-thousandths of an inch), must meet a very smooth surface to produce specular reflection. For wavelengths that are approaching or are even shorter than the diameter of the atoms, such as X-rays, specular reflection can only be produced by surfaces that are at a grazing incidence from the rays. Surface roughness is typically measured in microns, wavelength, or grit size (with ~ 80,000 to 100,000 grit (λ/2--λ/4) being "optical quality").
Transmissivity is determined by the percentage of light transmitted per the incident light. Transmissivity is usually the same from both first and second surfaces. The combined transmitted and reflected light, subtracted from the incident light, measures the amount absorbed by both the coating and substrate. For transmissive mirrors, such as one-way mirrors, beam splitters, or laser output couplers, the transmissivity of the mirror is an important consideration. The transmissivity of metallic coatings are often determined by their thickness. For precision beam-splitters or output couplers, the thickness of the coating must be kept at very high tolerances to transmit the proper amount of light. For dielectric mirrors, the thickness of the coat must always be kept to high tolerances, but it is often more the number of individual coats that determine the transmissivity. For the substrate, the material used must also have good transmissivity to the chosen wavelengths. Glass is a suitable substrate for most visible-light applications, but other substrates such as zinc selenide or synthetic sapphire may be used for infrared or ultraviolet wavelengths.
Mirrors are commonly used as aids to personal grooming. They may range from small sizes, good to carry with oneself, to full body sized; they may be handheld, mobile, fixed or adjustable. A classic example of the latter is the cheval glass, which may be tilted.
Safety and easier viewing
- Convex mirrors
- Convex mirrors provide a wider field of view than flat mirrors, and are often used on vehicles, especially large trucks, to minimize blind spots. They are sometimes placed at road junctions, and corners of sites such as parking lots to allow people to see around corners to avoid crashing into other vehicles or shopping carts. They are also sometimes used as part of security systems, so that a single video camera can show more than one angle at a time. . Convex mirrors as decoration are used in interior design to provide a predominantly experiential effect. 
- Mouth mirrors or "dental mirrors"
- Mouth mirrors or "dental mirrors" are used by dentists to allow indirect vision and lighting within the mouth. Their reflective surfaces may be either flat or curved. Mouth mirrors are also commonly used by mechanics to allow vision in tight spaces and around corners in equipment.
- Rear-view mirrors
- Rear-view mirrors are widely used in and on vehicles (such as automobiles, or bicycles), to allow drivers to see other vehicles coming up behind them. On rear-view sunglasses, the left end of the left glass and the right end of the right glass work as mirrors.
One-way mirrors and windows
Main article: One-way mirror
- One-way mirrors
- One-way mirrors (also called two-way mirrors) work by overwhelming dim transmitted light with bright reflected light. A true one-way mirror that actually allows light to be transmitted in one direction only without requiring external energy is not possible as it violates the second law of thermodynamics: if one placed a cold object on the transmitting side and a hot one on the blocked side, radiant energy would be transferred from the cold to the hot object. Thus, though a one-way mirror can be made to appear to work in only one direction at a time, it is actually reflective from either side.
- One-way windows
- One-way windows can be made to work with polarized light in the laboratory without violating the second law. This is an apparent paradox that stumped some great physicists, although it does not allow a practical one-way mirror for use in the real world.Optical isolators are one-way devices that are commonly used with lasers.
Main article: Heliograph
With the sun as light source, a mirror can be used to signal by variations in the orientation of the mirror. The signal can be used over long distances, possibly up to 60 km on a clear day. This technique was used by Native American tribes and numerous militaries to transmit information between distant outposts.
Mirrors can also be used for search to attract the attention of search and rescue helicopters. Specialized type of mirrors are available and are often included in military survival kits.
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 mentioned above) is "folded" by one or more mirrors so that the television set is compact.
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.
See also: Mirror support cell
Telescopes and other precision instruments use front silvered or first surface mirrors, where the reflecting surface is placed on the front (or first) surface of the glass (this eliminates reflection from glass surface ordinary back mirrors have). Some of them use silver, but most are aluminium, which is more reflective at short wavelengths than silver. All of these coatings are easily damaged and require special handling. They reflect 90% to 95% of the incident light when new. The coatings are typically applied by vacuum deposition. A protective overcoat is usually applied before the mirror is removed from the vacuum, because the coating otherwise begins to corrode as soon as it is exposed to oxygen and humidity in the air. Front silvered mirrors have to be resurfaced occasionally to keep their quality. There are optical mirrors such as mangin mirrors that are second surface mirrors (reflective coating on the rear surface) as part of their optical designs, usually to correct optical aberrations.
The reflectivity of the mirror coating can be measured using a reflectometer and for a particular metal it will be different for different wavelengths of light. This is exploited in some optical work to make cold mirrors and hot mirrors. A cold mirror is made by using a transparent substrate and choosing a coating material that is more reflective to visible light and more transmissive to infrared light.
A hot mirror is the opposite, the coating preferentially reflects infrared. Mirror surfaces are sometimes given thin film overcoatings both to retard degradation of the surface and to increase their reflectivity in parts of the spectrum where they will be used. For instance, aluminum mirrors are commonly coated with silicon dioxide or magnesium fluoride. The reflectivity as a function of wavelength depends on both the thickness of the coating and on how it is applied.
For scientific optical work, dielectric mirrors are often used. These are glass (or sometimes other material) substrates on which one or more layers of dielectric material are deposited, to form an optical coating. By careful choice of the type and thickness of the dielectric layers, the range of wavelengths and amount of light reflected from the mirror can be specified. The best mirrors of this type can reflect >99.999% of the light (in a narrow range of wavelengths) which is incident on the mirror. Such mirrors are often used in lasers.
In astronomy, adaptive optics
Since the dawn of man, the art of storytelling was utilized to pass on critically deemed information about society, life, and everything. During the early days, much of our history was transposed orally through song and spoken word.
Eventually, people started writing things down on scrolls and books. It made accurately passing down the information much more reliable. Finally, literature was born as more people piled onto the written works of humanity. It began taking shape in various form, Poetry, Epics, Novels and much more.
In many instances, literature is merely the reflection of society. It is the individualistic perspective of a series of events depicted by the author. Whether a philosophical point of view or a mere fabrication of the imagination, literature allows us to see humanity through the eyes of another person. It will enable us to objectively look at the ‘bigger picture’ and gain understanding about different perspectives.
Does Art Reflect Society or Does Society Reflect Art
Literature, like many art forms, is expressionism. It’s taking a thought and converting it into a tangible object that can be interpreted by others.
While many argue that literature is merely the mirror to society, there have been instances where it was the other way around. For example, the George Orwell novel 1984 spoke of a dystopian future governed by an authoritarian regime that created a singular narrative for society to follow.
33 years later, we find ourselves living in a community that is eerily similar to the premise of 1984. While some may argue that Mr. Orwell just created a fictional scenario based on past governments, one cannot eliminate the possibility that the novel itself also helped shape the society we live in today.
The interweaving nature of real life and art establishes what the premise of this essay suggests – a Mirror.
Literature is a reflection of society, and similarly, organization mirrors writing.
We are the stories we believe
To fully understand the premise of the essay, we need first to understand ‘our unique interpretation of reality.’ If you come to think about it, we are merely the construct of the stories we believe. Whether you are a religious person or a firm believer in science, the mechanism for our reasoning revolves around the ideas that govern our minds.
Your political preferences, your moral compass all based on stories that have been taught to you throughout your life either by your parents, teachers and the collective narrative of society itself.
Most of these narratives come from literature passed down through the generations of human existence. Research, being the mere reflection of our societal constructs, in turn, reshapes our perceptive filters and influences our reality.
When a narrative becomes a dominant belief, society establishes norms surrounding the story and influences individual behavior which in turn affects the literature produced.
This never-ending cycle will continue to feed into itself, shaping and reshaping society based on the self-reflecting nature of literature.
In other words, society will influence the literature we produce which in turn will consume by itself that will ultimately change the way society behaves. And the cycle continues.
Literature Provides the Big Picture
Whereas the individual lives on a linear timeline and is locked in the present, research provides us with a timeless perspective. It shows us the evolution of society through the works produced. We can see this with the different tasks created in different eras.
The work produced right after the enlightenment period steered away from the oligarchic paradigm and focused more on the individual. Over time, the complexities of our literature became more apparent.
The story started to reflect real life with much more precision. Things like conflict, dialogue, plot structure and so forth evolved alongside technologies, political ideologies, religious views and so forth. As time progresses, our means of reflecting society becomes more apparent.
Literature is a way for us to create fictional scenarios that allow our minds to contemplate the “Bigger Picture” of the human condition. It establishes a methodology to explore our perceptive filters and expands our awareness of our surroundings.
The Future of Literature
Over the past few years, we have seen significant innovation in the field of technology. One of the humanity’s most notable accomplishments was to create the internet. No longer is society restricted to a geographical location, but the world is becoming a singular society.
What happens in China can affect an individual living in Colombia; no longer is literature limited to a single region.
With millions of independent authors, thinkers, philosophers and so forth having the ability to produce literature at will and publish it for the entire world to see…society will undergo rapid transformation through the ‘sharing of ideas.’
About author: Joan Young is an aspiring journalist and copywriter with deep interest in sociology, inventions and technological progress. In a spare from traveling minute, she provides online tutoring sessions to international students and finds immense pleasure in witnessing their writing progress. Some of her insights can be found in her author’s column on AdvancedWriters.com blog. You can easily contact the author here.
About the author
Joan Young is an aspiring journalist and copywriter with deep interest in sociology, inventions and technological progress. In a spare from traveling minute, she provides online tutoring sessions to international students and finds immense pleasure in witnessing their writing progress. Contact the author.