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Encyclopedia > Light
A beam of white light (entering upwards from the right) is dispersed into its constituent colors by its passage through a prism. The fainter beam of white light exiting to the upper right has been reflected (without dispersion) off the first surface of the prism.

Light is electromagnetic radiation of a wavelength (~400–700nm) that is visible to the human eye (visible light). In a scientific context, the word light is sometimes used to refer to the entire electromagnetic spectrum.[1] Light is composed of an elementary particle called a photon. Look up light in Wiktionary, the free dictionary. ... prism splitting light Source: NASA File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... prism splitting light Source: NASA File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Diagram of a triangular prism, dispersing light Lamps as seen through a prism. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... For other uses, see Wavelength (disambiguation). ... A nanometre (American spelling: nanometer, symbol nm) (Greek: Î½Î¬Î½Î¿Ï‚, nanos, dwarf; Î¼ÎµÏ„ÏÏŽ, metrÏŒ, count) is a unit of length in the metric system, equal to one billionth of a metre (or one millionth of a millimetre), which is the current SI base unit of length. ... For other uses, see Eye (disambiguation). ... For the scientific journal named Science, see Science (journal). ... Legend Î³ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... For the novel, see The Elementary Particles. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...

Three primary properties of light are:

Light can exhibit properties of both waves and particles. This property is referred to as wave–particle duality. The study of light, known as optics, is an important research area in modern physics. In physics, intensity is a measure of the time-averaged energy flux. ... Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. ... For other uses, see Frequency (disambiguation). ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... Surface waves in water This article is about waves in the most general scientific sense. ... Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... In physics and chemistry, wave-particle duality is a conceptualization that all objects in our universe exhibit properties of both waves and of particles. ... For the book by Sir Isaac Newton, see Opticks. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ...

## Speed of light GA_googleFillSlot("encyclopedia_square");

Main article: Speed of light
A line showing the speed of light on a scale model of Earth and the moon, about 1.2 seconds.

Different physicists have attempted to measure the speed of light throughout history. Galileo attempted to measure the speed of light in the seventeenth century. A good early experiment to measure the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Using a telescope, Ole observed the motions of Jupiter and one of its moons, Io. Noting discrepancies in the apparent period of Io's orbit, Rømer calculated that light takes about 18 minutes to traverse the diameter of Earth's orbit. Unfortunately, this was not a value that was known at that time. If Ole had known the diameter of the earth's orbit, he would have calculated a speed of 227,000,000 m/s. Galileo can refer to: Galileo Galilei, astronomer, philosopher, and physicist (1564 - 1642) the Galileo spacecraft, a NASA space probe that visited Jupiter and its moons the Galileo positioning system Life of Galileo, a play by Bertolt Brecht Galileo (1975) - screen adaptation of the play Life of Galileo by Bertolt Brecht... Ole RÃ¸mer. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek á¿™ÏŽ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ...

Another, more accurate, measurement of the speed of light was performed in Europe by Hippolyte Fizeau in 1849. Fizeau directed a beam of light at a mirror several kilometers away. A rotating cog wheel was placed in the path of the light beam as it traveled from the source, to the mirror and then returned to its origin. Fizeau found that at a certain rate of rotation, the beam would pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau was able to calculate the speed of light as 313,000,000 m/s. Armand Hippolyte Louis Fizeau Armand Hippolyte Louis Fizeau (September 23, 1819-1896), French physicist, was born in Paris. ... Year 1849 (MDCCCXLIX) was a common year starting on Monday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Saturday of the 12-day slower Julian calendar). ...

## Refraction

Main article: Refraction

Light in a vacuum propagates at a maximum finite speed, defined above, and denoted by the symbol c. While passing through any other transparent medium, the speed of light slows to some fraction of c. The reduction of the speed of light traveling in a transparent medium is indicated by the refractive index, n, which is defined as: For the property of metals, see refraction (metallurgy). ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ...

$n = frac{c}{v} ;!$

Where v denotes the speed that light travels in the transparent medium.

Note, n = 1 in a vacuum and n > 1 in a transparent medium.

When a beam of light crosses the boundary between a vacuum and another medium, or between two different mediums, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal to the boundary, the change in wavelength results in a change in the direction of the beam. This change of direction is known as refraction. In mathematics, orthogonal is synonymous with perpendicular when used as a simple adjective that is not part of any longer phrase with a standard definition. ...

The refraction quality of lenses is frequently used to manipulate light in order to change the apparent size of images. Magnifying glasses, spectacles, contact lenses, microscopes and refracting telescopes are all examples of this manipulation. This article is about the optical device. ... A magnifying glass (called a hand lens in laboratory contexts) is a convex lens which is used to produce a magnified image of an object. ... Glasses, spectacles, or eyeglasses are frames bearing lenses worn in front of the eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection. ... A pair of contact lenses, positioned with the concave side facing upward. ... Robert Hookes microscope (1665) - an engineered device used to study living systems. ... Image of a refracting telescope from the Cincinnati Observatory in 1848 A refracting or refractor telescope is a dioptric telescope that uses a lens as its objective to form an image. ...

## Optics

Main article: Optics

The study of light and the interaction of light and matter is termed optics. The observation and study of optical phenomena such as rainbows and the Aurora Borealis offer many clues as to the nature of light as well as much enjoyment. For the book by Sir Isaac Newton, see Opticks. ... This article is about matter in physics and chemistry. ... For the book by Sir Isaac Newton, see Opticks. ... An optical phenomenon is any observable event which results from the interaction of light and matter. ... For other uses, see Rainbow (disambiguation). ... Aurora borealis Polar aurorae are optical phenomena characterized by colorful displays of light in the night sky. ...

## Light sources

Mist illuminated by sunlight
A cloud illuminated by sunlight

Atoms emit and absorb light at characteristic energies. This produces "emission lines" in the spectrum of each atom. Emission can be spontaneous, as in light-emitting diodes, gas discharge lamps (such as neon lamps and neon signs, mercury-vapor lamps, etc.), and flames (light from the hot gas itself—so, for example, sodium in a gas flame emits characteristic yellow light). Emission can also be stimulated, as in a laser or a microwave maser. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... In physics, emission is the process by which the energy of a photon is released by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... Spontaneous emission is the process by which a molecule in an excited state drops to the ground state, resulting in the creation of a photon. ... â€œLEDâ€ redirects here. ... -1... Lighting neon lamp, two 220/230 volt and 110 V neon lamps and a screwdriver with neon lamp inside A neon lamp is a gas discharge lamp containing primarily neon gas at low pressure. ... Neon signs are often used to advertise for hotels, bars and entertainment venues. ... A Mercury-vapor lamp is a gas discharge lamp which uses mercury in an excited state to produce light. ... For sodium in the diet, see Edible salt. ... In optics, stimulated emission is the process by which, when perturbed by a photon, matter may lose energy resulting in the creation of another photon. ... For other uses, see Laser (disambiguation). ... A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser is a device that produces coherent electromagnetic waves through amplification due to stimulated emission. ...

Certain chemicals produce visible radiation by chemoluminescence. In living things, this process is called bioluminescence. For example, fireflies produce light by this means, and boats moving through water can disturb plankton which produce a glowing wake. Lightsticks Chemoluminescence (sometimes chemiluminescence) is the emission of light (luminescence) as the result of a chemical reaction. ... Bioluminescence is the production and emission of light by a living organism as the result of a chemical reaction during which chemical energy is converted to light energy. ... For the science fiction television series, see Firefly (TV series). ...

Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence. This is used in fluorescent lights. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence. Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... Fluorescent lamps in Shinbashi, Tokyo, Japan Assorted types of fluorescent lamps. ... In common use, phosphorescence also refers to the emission of light by bioluminescent plankton, and some other forms of chemoluminescence. ...

Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example of this. This mechanism is used in cathode ray tube televisions. Cathodoluminescence is an optical and electrical phenomenon whereby a beam of electrons is generated by an electron gun (e. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT: 1. ...

Certain other mechanisms can produce light:

When the concept of light is intended to include very-high-energy photons (gamma rays), additional generation mechanisms include: Scintillation is a flash of light produced in a transparent material by an ionizing event. ... Animation of LCD, both unlit and with electroluminiscent backlight switched on Electroluminescence (EL) is an optical phenomenon and electrical phenomenon where a material emits light in response to an electric current passed through it, or to a strong electric field. ... Long exposure image of multi-bubble sonoluminescence created by a high intensity ultrasonic horn immersed in a beaker of liquid. ... Triboluminescence is an optical phenomenon in which light is generated via the breaking of asymmetrical bonds in a crystal when that material is scratched, crushed, or rubbed. ... Cherenkov radiation glowing in the core of a TRIGA reactor Cherenkov radiation (also spelled Cerenkov or sometimes ÄŒerenkov) is electromagnetic radiation emitted when a charged particle passes through an insulator at a speed greater than the speed of light in that medium. ...

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... Corresponding to most kinds of particle, there is an associated antiparticle with the same mass and opposite charges. ...

## Theories about light

### Indian theories

In ancient India, the philosophical schools of Samkhya and Vaisheshika, from around the 6th5th century BC, developed theories on light. According to the Samkhya school, light is one of the five fundamental "subtle" elements (tanmatra) out of which emerge the gross elements. The atomicity of these elements is not specifically mentioned and it appears that they were actually taken to be continuous. This article does not cite any references or sources. ... Samkhya, also Sankhya, (Sanskrit: à¤¸à¤¾à¤‚à¤–à¥à¤¯, IAST: SÄá¹ƒkhya - Enumeration) is one of the six schools of classical Indian philosophy. ... Vaisheshika, also Vaisesika, (Sanskrit: à¤µà¥ˆà¤¶à¥†à¤·à¤¿à¤•)is one of the six Hindu schools of philosophy (orthodox Vedic systems) of India. ... (2nd millennium BC - 1st millennium BC - 1st millennium) The 6th century BC started on January 1, 600 BC and ended on December 31, 501 BC. // Monument 1, an Olmec colossal head at La Venta The 5th and 6th centuries BC were a time of empires, but more importantly, a time... The 5th century BC started the first day of 500 BC and ended the last day of 401 BC. // The Parthenon of Athens seen from the hill of the Pnyx to the west. ... Concern has been expressed that this article or section is missing information about: discussions of existence of atoms among prominent physicists up to the end of 19th century. ...

On the other hand, the Vaisheshika school gives an atomic theory of the physical world on the non-atomic ground of ether, space and time. (See Indian atomism.) The basic atoms are those of earth (prthivı), water (apas), fire (tejas), and air (vayu), that should not be confused with the ordinary meaning of these terms. These atoms are taken to form binary molecules that combine further to form larger molecules. Motion is defined in terms of the movement of the physical atoms and it appears that it is taken to be non-instantaneous. Light rays are taken to be a stream of high velocity of tejas (fire) atoms. The particles of light can exhibit different characteristics depending on the speed and the arrangements of the tejas atoms. Around the first century BC, the Vishnu Purana correctly refers to sunlight as the "the seven rays of the sun". This article focuses on the historical models of the atom. ... Hinduism (Tattva) and Buddhism (MahÄbhÅ«ta) Vayu / Pavan â€” Air / Wind Agni/Tejas â€” Fire Akasha â€” Aether Prithvi / Bhumi â€” Earth Ap / Jala â€” Water Chinese (Wu Xing) Japanese (Godai) Earth (åœ°) | Water (æ°´) | Fire (ç«) | Air / Wind (é¢¨) | Void / Sky / Heaven (ç©º) BÃ¶n MÄori According to ancient and medieval science, Aether (Greek Î±á¼°Î¸Î®Ï, aithÄ“r[1... Concern has been expressed that this article or section is missing information about: discussions of existence of atoms among prominent physicists up to the end of 19th century. ... Properties For other meanings of Atom, see Atom (disambiguation). ... The Vishnu Purana is one of the oldest of the Puranas (dating to maybe the 5th century), containing some 23,000 shlokas, presented as a dialogue between Parasara with his disciple Maitreya. ... Prism splitting light High Resolution Solar Spectrum Sunlight in the broad sense is the total spectrum of the electromagnetic radiation given off by the Sun. ...

The Indian Buddhists, such as Dignāga in the 5th century and Dharmakirti in the 7th century, developed a type of atomism that is a philosophy about reality being composed of atomic entities that are momentary flashes of light or energy. They viewed light as being an atomic entity equivalent to energy, similar to the modern concept of photons, though they also viewed all matter as being composed of these light/energy particles. A replica of an ancient statue found among the ruins of a temple at Sarnath Buddhism is a philosophy based on the teachings of the Buddha, SiddhÄrtha Gautama, a prince of the Shakyas, whose lifetime is traditionally given as 566 to 486 BCE. It had subsequently been accepted by... DignÄga (5th century AD), was an Indian scholar and one of the Buddhist founders of Indian philosophical logic. ... Europe in 450 The 5th century is the period from 401 to 500 in accordance with the Julian calendar in the Christian Era. ... Dharmakirti (circa 7th century), was an Indian scholar and one of the Buddhist founders of Indian philosophical logic. ... The 7th century is the period from 601 - 700 in accordance with the Julian calendar in the Christian Era. ... Concern has been expressed that this article or section is missing information about: discussions of existence of atoms among prominent physicists up to the end of 19th century. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...

### Greek and Hellenistic theories

In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. He believed that Aphrodite made the human eye out of the four elements and that she lit the fire in the eye which shone out from the eye making sight possible. If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun. Emission theory has at least two meanings: First, it refers to Newtons proposal that light is emitted from luminous objects in the form of particles or corpuscles. ... Empedocles (Greek: , ca. ... Several ancient Classical Element ideas exist. ... The Birth of Venus, (detail) by Sandro Botticelli, 1485 For other uses, see Aphrodite (disambiguation). ...

In about 300 BC, Euclid wrote Optica, in which he studied the properties of light. Euclid postulated that light travelled in straight lines and he described the laws of reflection and studied them mathematically. He questioned that sight is the result of a beam from the eye, for he asks how one sees the stars immediately, if one closes one's eyes, then opens them at night. Of course if the beam from the eye travels infinitely fast this is not a problem. For other uses, see Euclid (disambiguation). ...

In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote: Centuries: 2nd century BC - 1st century BC - 1st century Decades: 100s BC 90s BC 80s BC 70s BC 60s BC - 50s BC - 40s BC 30s BC 20s BC 10s BC 0s BC Years: 60 BC 59 BC 58 BC 57 BC 56 BC 55 BC 54 BC 53 BC 52... Lucretius Titus Lucretius Carus (c. ... Concern has been expressed that this article or section is missing information about: discussions of existence of atoms among prominent physicists up to the end of 19th century. ...

"The light and heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove." - On the nature of the Universe

Despite being similar to later particle theories, Lucretius's views were not generally accepted and light was still theorized as emanating from the eye.

Ptolemy (c. 2nd century) wrote about the refraction of light, and developed a theory of vision that objects are seen by rays of light emanating from the eyes. This article is about the geographer, mathematician and astronomer Ptolemy. ... The 2nd century is the period from 101 - 200 in accordance with the Julian calendar in the Christian Era. ... For the property of metals, see refraction (metallurgy). ...

### Optical theory

Main article: Book of Optics

He also carried out the first experiments on the dispersion of light into its constituent colors. His major work Kitab al-Manazir was translated into Latin in the Middle Ages, as well his book dealing with the colors of sunset. He dealt at length with the theory of various physical phenomena like shadows, eclipses, the rainbow. He also attempted to explain binocular vision, and gave a correct explanation of the apparent increase in size of the sun and the moon when near the horizon. Because of his extensive research on optics, Al-Haytham is considered the father of modern optics. For other uses, see Latin (disambiguation). ... The Middle Ages formed the middle period in a traditional schematic division of European history into three ages: the classical civilization of Antiquity, the Middle Ages, and modern times, beginning with the Renaissance. ... For the book by Sir Isaac Newton, see Opticks. ...

Al-Haytham also correctly argued that we see objects because the sun's rays of light, which he believed to be streams of tiny particles travelling in straight lines, are reflected from objects into our eyes. He understood that light must travel at a large but finite velocity, and that refraction is caused by the velocity being different in different substances. He also studied spherical and parabolic mirrors, and understood how refraction by a lens will allow images to be focused and magnification to take place. He understood mathematically why a spherical mirror produces aberration.

### The 'plenum'

René Descartes (1596-1650) held that light was a disturbance of the plenum, the continuous substance of which the universe was composed. In 1637 he published a theory of the refraction of light that assumed, incorrectly, that light travelled faster in a denser medium than in a less dense medium. Descartes arrived at this conclusion by analogy with the behaviour of sound waves. Although Descartes was incorrect about the relative speeds, he was correct in assuming that light behaved like a wave and in concluding that refraction could be explained by the speed of light in different media. As a result, Descartes' theory is often regarded as the forerunner of the wave theory of light. Descartes redirects here. ... For the property of metals, see refraction (metallurgy). ... This article is about audible acoustic waves. ...

### Particle theory

Pierre Gassendi (1592-1655), an atomist, proposed a particle theory of light which was published posthumously in the 1660s. Isaac Newton studied Gassendi's work at an early age, and preferred his view to Descartes' theory of the plenum. He stated in his Hypothesis of Light of 1675 that light was composed of corpuscles (particles of matter) which were emitted in all directions from a source. One of Newton's arguments against the wave nature of light was that waves were known to bend around obstacles, while light travelled only in straight lines. He did, however, explain the phenomenon of the diffraction of light (which had been observed by Francesco Grimaldi) by allowing that a light particle could create a localised wave in the aether. Pierre Gassendi (January 22, 1592 â€“ October 24, 1655) was a French philosopher, scientist and mathematician, best known for attempting to reconcile Epicurean atomism with Christianity and for publishing the first official observations of the Transit of Mercury in 1631. ... Events and Trends Samuel Pepys begins his famous diary in 1660 and ends it, due to failing eyesight in 1669. ... Sir Isaac Newton FRS (4 January 1643 â€“ 31 March 1727) [ OS: 25 December 1642 â€“ 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ... Francesco Maria Grimaldi (April 2, 1618 - December 28, 1663) was an Italian mathematician and physicist who taught at the Jesuit college in Bologna. ... Hinduism (Tattva) and Buddhism (MahÄbhÅ«ta) Vayu / Pavan â€” Air / Wind Agni/Tejas â€” Fire Akasha â€” Aether Prithvi / Bhumi â€” Earth Ap / Jala â€” Water Chinese (Wu Xing) Japanese (Godai) Earth (åœ°) | Water (æ°´) | Fire (ç«) | Air / Wind (é¢¨) | Void / Sky / Heaven (ç©º) BÃ¶n MÄori According to ancient and medieval science, Aether (Greek Î±á¼°Î¸Î®Ï, aithÄ“r[1...

Newton's theory could be used to predict the reflection of light, but could only explain refraction by incorrectly assuming that light accelerated upon entering a denser medium because the gravitational pull was greater. Newton published the final version of his theory in his Opticks of 1704. His reputation helped the particle theory of light to hold sway during the 18th century. The reflection of a bridge in Indianapolis, Indianas Central Canal. ... For the property of metals, see refraction (metallurgy). ... Free space is the most simple and elementary electromagnetic medium. ... Gravity is a force of attraction that acts between bodies that have mass. ... Opticks or a treatise of the reflections, refractions, inflections and colours of light Opticks is a book written by English physicist Isaac Newton that was released to the public in 1704. ... Events Building of the Students Monument in Aiud, Romania. ... In physics, wave-particle duality holds that light and matter simultaneously exhibit properties of waves and of particles (or photons). ... (17th century - 18th century - 19th century - more centuries) As a means of recording the passage of time, the 18th century refers to the century that lasted from 1701 through 1800. ...

### Wave theory

In the 1660s, Robert Hooke published a wave theory of light. Christiaan Huygens worked out his own wave theory of light in 1678, and published it in his Treatise on light in 1690. He proposed that light was emitted in all directions as a series of waves in a medium called the Luminiferous ether. As waves are not affected by gravity, it was assumed that they slowed down upon entering a denser medium. Events and Trends Samuel Pepys begins his famous diary in 1660 and ends it, due to failing eyesight in 1669. ... Robert Hooke, FRS (July 18, 1635 â€“ March 3, 1703) was an English polymath who played an important role in the scientific revolution, through both experimental and theoretical work. ... Surface waves in water This article is about waves in the most general scientific sense. ... Christiaan Huygens (pronounced in English (IPA): ; in Dutch: ) (April 14, 1629 â€“ July 8, 1698), was a Dutch mathematician, astronomer and physicist; born in The Hague as the son of Constantijn Huygens. ... Events Giovanni Domenico Cassini observes differential rotation within Jupiters atmosphere. ... The luminiferous aether: it was hypothesised that the Earth moves through a medium of aether that carries light In the late 19th century the luminiferous aether (light-bearing aether), or ether, was a substance postulated to be the medium for the propagation of light. ...

Thomas Young's sketch of the two-slit experiment showing the diffraction of light. Young's experiments supported the theory that light consists of waves.

Another supporter of the wave theory was Leonhard Euler. He argued in Nova theoria lucis et colorum (1746) that diffraction could more easily be explained by a wave theory. Leonhard Paul Euler (pronounced Oiler; IPA ) (April 15, 1707 â€“ September 18 [O.S. September 7] 1783) was a pioneering Swiss mathematician and physicist, who spent most of his life in Russia and Germany. ... // Events Catharine de Ricci (born 1522) canonized. ... The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ...

Later, Augustin-Jean Fresnel independently worked out his own wave theory of light, and presented it to the Académie des Sciences in 1817. Simeon Denis Poisson added to Fresnel's mathematical work to produce a convincing argument in favour of the wave theory, helping to overturn Newton's corpuscular theory. Augustin Fresnel Augustin-Jean Fresnel (pronounced [] in AmE (or fray-NELL), [] in French) (May 10, 1788 â€“ July 14, 1827), was a French physicist who contributed significantly to the establishment of the theory of wave optics. ... The French Academy of Sciences (AcadÃ©mie des sciences) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. ... 1817 was a common year starting on Wednesday (see link for calendar). ... Simeon Poisson. ...

The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. A hypothetical substance called the luminiferous aether was proposed, but its existence was cast into strong doubt in the late nineteenth century by the Michelson-Morley experiment. The luminiferous aether: it was hypothesised that the Earth moves through a medium of aether that carries light In the late 19th century luminiferous aether (light-bearing aether) was the term used to describe a medium for the propagation of light. ... The Michelson-Morley experiment, one of the most important and famous experiments in the history of physics, was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University, and is considered by some to be the first strong evidence against the theory of...

Newton's corpuscular theory implied that light would travel faster in a denser medium, while the wave theory of Huygens and others implied the opposite. At that time, the speed of light could not be measured accurately enough to decide which theory was correct. The first to make a sufficiently accurate measurement was Léon Foucault, in 1850. His result supported the wave theory, and the classical particle theory was finally abandoned. The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... ... For the game, see: 1850 (board game) 1850 (MDCCCL) was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Sunday [1] of the 12-day-slower Julian calendar). ...

### Electromagnetic theory

A linearly-polarized light wave frozen in time and showing the two oscillating components of light; an electric field and a magnetic field perpendicular to each other and to the direction of motion (a transverse wave).

In 1845, Michael Faraday discovered that the angle of polarization of a beam of light as it passed through a polarizing material could be altered by a magnetic field, an effect now known as Faraday rotation. This was the first evidence that light was related to electromagnetism. Faraday proposed in 1847 that light was a high-frequency electromagnetic vibration, which could propagate even in the absence of a medium such as the ether. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ... Magnetic field lines shown by iron filings Magnetostatics Electrodynamics Electrical Network Tensors in Relativity This box:      In physics, the magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles. ... A light wave is an example of a transverse wave. ... 1845 was a common year starting on Wednesday (see link for calendar). ... Michael Faraday, FRS (September 22, 1791 â€“ August 25, 1867) was an English chemist and physicist (or natural philosopher, in the terminology of that time) who contributed to the fields of electromagnetism and electrochemistry. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ... In physics, the Faraday effect or Faraday rotation is an interaction between light and a magnetic field. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ...

Faraday's work inspired James Clerk Maxwell to study electromagnetic radiation and light. Maxwell discovered that self-propagating electromagnetic waves would travel through space at a constant speed, which happened to be equal to the previously measured speed of light. From this, Maxwell concluded that light was a form of electromagnetic radiation: he first stated this result in 1862 in On Physical Lines of Force. In 1873, he published A Treatise on Electricity and Magnetism, which contained a full mathematical description of the behaviour of electric and magnetic fields, still known as Maxwell's equations. Soon after, Heinrich Hertz confirmed Maxwell's theory experimentally by generating and detecting radio waves in the laboratory, and demonstrating that these waves behaved exactly like visible light, exhibiting properties such as reflection, refraction, diffraction, and interference. Maxwell's theory and Hertz's experiments led directly to the development of modern radio, radar, television, electromagnetic imaging, and wireless communications. James Clerk Maxwell (13 June 1831 â€“ 5 November 1879) was a Scottish mathematician and theoretical physicist from Edinburgh, Scotland, UK. His most significant achievement was aggregating a set of equations in electricity, magnetism and inductance â€” eponymously named Maxwells equations â€” including an important modification (extension) of the AmpÃ¨res... 1873 (MDCCCLXXIII) was a common year starting on Wednesday (see link for calendar). ... A young Maxwell at university. ... For thermodynamic relations, see Maxwell relations. ... Heinrich Rudolf Hertz (February 22, 1857 - January 1, 1894) was the German physicist and mechanician for whom the hertz, an SI unit, is named. ...

### The special theory of relativity

The wave theory was wildly successful in explaining nearly all optical and electromagnetic phenomena, and was a great triumph of nineteenth century physics. By the late nineteenth century, however, a handful of experimental anomalies remained that could not be explained by or were in direct conflict with the wave theory. One of these anomalies involved a controversy over the speed of light. The constant speed of light predicted by Maxwell's equations and confirmed by the Michelson-Morley experiment contradicted the mechanical laws of motion that had been unchallenged since the time of Galileo, which stated that all speeds were relative to the speed of the observer. In 1905, Albert Einstein resolved this paradox by revising the Galilean model of space and time to account for the constancy of the speed of light. Einstein formulated his ideas in his special theory of relativity, which radically altered humankind's understanding of space and time. Einstein also demonstrated a previously unknown fundamental equivalence between energy and mass with his famous equation Galileo redirects here. ... â€œEinsteinâ€ redirects here. ... Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. ... This article is about the idea of space. ... Look up time in Wiktionary, the free dictionary. ... 15ft sculpture of Einsteins 1905 E = mcÂ² formula at the 2006 Walk of Ideas, Germany In physics, mass-energy equivalence is the concept that all mass has an energy equivalence, and all energy has a mass equivalence. ... For other uses, see Mass (disambiguation). ...

$E = mc^2 ,$

where E is energy, m is mass, and c is the speed of light. The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ...

### Particle theory revisited

Another experimental anomaly was the photoelectric effect, by which light striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage. Experimental measurements demonstrated that the energy of individual ejected electrons was proportional to the frequency, rather than the intensity, of the light. Furthermore, below a certain minimum frequency, which depended on the particular metal, no current would flow regardless of the intensity. These observations clearly contradicted the wave theory, and for years physicists tried in vain to find an explanation. In 1905, Einstein solved this puzzle as well, this time by resurrecting the particle theory of light to explain the observed effect. Because of the preponderance of evidence in favor of the wave theory, however, Einstein's ideas were met initially by great skepticism among established physicists. But eventually Einstein's explanation of the photoelectric effect would triumph, and it ultimately formed the basis for wave–particle duality and much of quantum mechanics. A diagram illustrating the emission of electrons from a metal plate, requiring energy gained from an incoming photon to be more than the work function of the material. ... Electric current is the flow (movement) of electric charge. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... For other uses, see Frequency (disambiguation). ... In physics, intensity is a measure of the time-averaged energy flux. ... In physics and chemistry, wave-particle duality is a conceptualization that all objects in our universe exhibit properties of both waves and of particles. ... For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ...

### Quantum theory

A third anomaly that arose in the late 19th century involved a contradiction between the wave theory of light and measurements of the electromagnetic spectrum emitted by thermal radiators, or so-called black bodies. Physicists struggled with this problem, which later became known as the ultraviolet catastrophe, unsuccessfully for many years. In 1900, Max Planck developed a new theory of black-body radiation that explained the observed spectrum correctly. Planck's theory was based on the idea that black bodies emit light (and other electromagnetic radiation) only as discrete bundles or packets of energy. These packets were called quanta, and the particle of light was given the name photon, to correspond with other particles being described around this time, such as the electron and proton. A photon has an energy, E, proportional to its frequency, f, by As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... The ultraviolet catastrophe, also called the Rayleigh-Jeans catastrophe, was a prediction of early 20th century classical physics that an ideal black body at thermal equilibrium will emit radiation with infinite power. ... â€œPlanckâ€ redirects here. ... In physics, the spectral intensity of electromagnetic radiation from a black body at temperature T is given by the Plancks law of black body radiation: where: I(&#957;) is the amount of energy per unit time per unit surface area per unit solid angle per unit frequency. ... In physics, a quantum (plural: quanta) is an indivisible entity of energy. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... For other uses, see Electron (disambiguation). ... For other uses, see Proton (disambiguation). ...

$E = hf = frac{hc}{lambda} ,!$

where h is Planck's constant, λ is the wavelength and c is the speed of light. Likewise, the momentum p of a photon is also proportional to its frequency and inversely proportional to its wavelength: A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ...

$p = { E over c } = { hf over c } = { h over lambda }.$

As it originally stood, this theory did not explain the simultaneous wave- and particle-like natures of light, though Planck would later work on theories that did. In 1918, Planck received the Nobel Prize in Physics for his part in the founding of quantum theory. Hannes AlfvÃ©n (1908â€“1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ...

### Wave–particle duality

The modern theory that explains the nature of light includes the notion of wave–particle duality, described by Albert Einstein in the early 1900s, based on his study of the photoelectric effect and Planck's results. Einstein asserted that the energy of a photon is proportional to its frequency. More generally, the theory states that everything has both a particle nature and a wave nature, and various experiments can be done to bring out one or the other. The particle nature is more easily discerned if an object has a large mass, so it took until a bold proposition by Louis de Broglie in 1924 to realise that electrons also exhibited wave–particle duality. The wave nature of electrons was experimentally demonstrated by Davission and Germer in 1927. Einstein received the Nobel Prize in 1921 for his work with the wave–particle duality on photons (especially explaining the photoelectric effect thereby), and de Broglie followed in 1929 for his extension to other particles. In physics and chemistry, wave-particle duality is a conceptualization that all objects in our universe exhibit properties of both waves and of particles. ... â€œEinsteinâ€ redirects here. ... A diagram illustrating the emission of electrons from a metal plate, requiring energy gained from an incoming photon to be more than the work function of the material. ... For other uses, see Frequency (disambiguation). ... Louis-Victor-Pierre-Raymond, 7th duc de Broglie, generally known as Louis de Broglie (August 15, 1892â€“March 19, 1987), was a French physicist and Nobel Prize laureate. ... Properties The electron (also called negatron, commonly represented as e&#8722;) is a subatomic particle. ...

### Quantum electrodynamics

The quantum mechanical theory of light and electromagnetic radiation continued to evolve through the 1920's and 1930's, and culminated with the development during the 1940's of the theory of quantum electrodynamics, or QED. This so-called quantum field theory is among the most comprehensive and experimentally successful theories ever formulated to explain a set of natural phenomena. QED was developed primarily by physicists Richard Feynman, Freeman Dyson, Julian Schwinger, and Shin-Ichiro Tomonaga. Feynman, Schwinger, and Tomonaga shared the 1965 Nobel Prize in Physics for their contributions. Quantum electrodynamics (QED) is a relativistic quantum field theory of electrodynamics. ... Quantum field theory (QFT) is the quantum theory of fields. ... This article is about the physicist. ... Freeman John Dyson FRS (born December 15, 1923) is an English-born American theoretical physicist and mathematician, famous for his work in quantum mechanics, solid-state physics, nuclear weapons design and policy, and for his serious theorizing in futurism and science fiction concepts, including the search for extraterrestrial intelligence. ... Julian Seymour Schwinger (February 12, 1918 -- July 16, 1994) was an American theoretical physicist. ... Sin-Itiro Tomonaga or Shinichir&#333; Tomonaga (&#26397;&#27704; &#25391;&#19968;&#37070; Tomonaga Shinichir&#333;, March 31, 1906&#8211;July 8, 1979) was a Japanese physicist, influential in the development of quantum electrodynamics, work for which he was jointly awarded the Nobel Prize in Physics in 1965 along with...

## Light pressure

Main article: Radiation pressure

Light pushes on objects in its way, just as the wind would do. This pressure is most easily explainable in particle theory: photons hit and transfer their momentum. Light pressure can cause asteroids to spin faster,[2] acting on their irregular shapes as on the vanes of a windmill. The possibility to make solar sails that would accelerate spaceships in space is also under investigation.[citation needed] Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ... For other uses, see Asteroid (disambiguation). ... A Dutch tower windmill, sporting sails, surrounded by tulips A windmill is an engine powered by the wind to produce energy, often contained in a large building as in traditional post mills, smock mills and tower mills. ... Solar sails (also called light sails or photon sails, especially when they use light sources other than the Sun) are a proposed form of spacecraft propulsion using large membrane mirrors. ...

Although the motion of the Crookes radiometer was originally attributed to light pressure, this interpretation is incorrect; the characteristic Crookes rotation is the result of a partial vacuum.[3] This should not be confused with the Nichols radiometer, in which the motion is directly caused by light pressure.[4] The Crookes radiometer, also known as the light mill or solar engine, consists of an airtight glass bulb, containing a partial vacuum. ... A Nichols radiometer is the apparatus used by Nichols and Hull in 1901 for the measurement of radiation pressure. ...

## Spirituality

The sensory perception of light plays a central role in spirituality (vision, enlightenment, darshan, Tabor Light), and the presence of light as opposed to its absence (darkness) is a universal metaphor of good and evil, knowledge and ignorance, and similar concepts. In religion, visions comprise inspirational renderings, generally of a future state and/or of a mythical being, and are believed (by followers of the religion) to come from a deity, directly or indirectly via prophets, and serve to inspire or prod believers as part of a revelation or an epiphany. ... Enlightenment broadly means the acquisition of new wisdom or understanding enabling clarity of perception. ... Darshan is a Sanskrit and Hindu (also used to some extent in Urdu) term meaning sight (in the sense of an instance of seeing something or somebody), vision, apparition, or a glimpse. ... In Eastern Orthodox theology, Tabor Light (also Tabors Light, Taboric Light; Greek , also Uncreated Light, Divine Light; Russian ) is the light revealed on Mount Tabor at the Transfiguration of Jesus, identified with the light seen by Paul at his conversion. ... Darkness is the absence of light. ... This article or section does not cite any references or sources. ... This article needs additional references or sources for verification. ... Look up ignorance in Wiktionary, the free dictionary. ...

## References

1. ^ What Is a Light Source?.
2. ^ Kathy A. (02.05.2004). Asteroids Get Spun By the Sun. Discover Magazine.
3. ^ P. Lebedev, Untersuchungen über die Druckkräfte des Lichtes, Ann. Phys. 6, 433 (1901).
4. ^ Nichols, E.F & Hull, G.F. (1903) The Pressure due to Radiation, The Astrophysical Journal,Vol.17 No.5, p.315-351

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Image File history File links Commons-logo. ... Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 150 languages. ... Image File history File links This is a lossless scalable vector image. ... Wikiquote is one of a family of wiki-based projects run by the Wikimedia Foundation, running on MediaWiki software. ... The lighting system of a motor vehicle consists of lighting and signalling devices mounted or integrated to the front, sides and rear of the vehicle. ... Ballistic Photons are the light photons that travel through the scattering (turbid) media in straight line. ... The CIE 1931 x,y chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature Color temperature is a characteristic of visible light that has important applications in photography, videography, publishing and other fields. ... According to the Corpuscular theory of light, set forward by Sir Isaac Newton, light is made up of small discrete particles called corpuscles (little particles). ... Legend Î³ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... Wave Refraction in the manner of Huygens. ... Fermats principle assures that the angles given by Snells law always reflect lights quickest path between P and Q. Fermats principle in optics states: This principle was first stated by Pierre de Fermat. ... The CIE 1931 color space chromaticity diagram with wavelengths in nanometers. ... The items in the Metroid series are the driving force behind its gameplay. ... This time exposure photo of New York City shows sky glow, one form of light pollution. ... Not to be confused with lightning. ... ACHOO syndrome is inherited in an autosomal dominant fashion. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... In United Kingdom Law, A right to light will come into existence if it has been enjoyed uninterrupted for 20 years or more, granted by deed, or registered under the Rights of Light Act 1959. ... Spectroscopy is the study of spectra, ie. ...

Results from FactBites:

 The Light Group, Las Vegas Nightclubs, Restaurants, Bars, Lounges, and Real Estate, the Best Las Vegas Night Clubs and ... (1969 words) Light Las Vegas night club was thoughtfully, artistically designed by Lian Waisbrod with Studio Gaia of New York City. Whether you prefer a high-energy Las Vegas nightclub or more intimate Las Vegas night club experience, Light Las Vegas Nightclub is sure to satisfy with various distinct VIP service areas with Las Vegas table reservations and European bottle service dedicated to suit your comfort. The Light Group, renowned for providing VIP service at its sophisticated and stylish Las Vegas nightlife and Las Vegas restaurant properties, brings its exceptional operational prowess to Bare Pool Lounge at The Mirage, providing an exclusive adult alternative to the typical Las Vegas pool experience.
 light. The Columbia Encyclopedia, Sixth Edition. 2001-05 (1379 words) The term “light” is often extended to adjacent wavelength ranges that the eye cannot detect—to infrared radiation, which has a frequency less than that of visible light, and to ultraviolet radiation and fl light, which have a frequency greater than that of visible light. Light that is all of the same wavelength and phase (all the waves are in step with one another) is called “coherent”; one of the most important modern applications of light has been the development of a source of coherent light—the laser. The scientific study of the behavior of light is called optics and covers reflection of light by a mirror or other object, refraction by a lens or prism, diffraction of light as it passes by the edge of an opaque object, and interference patterns resulting from diffraction.
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