NationMaster - Encyclopedia: Blue LED

A light-emitting diode (LED) is a semiconductor device that emits incoherent narrow-spectrum light when electrically biased in the forward direction. This effect is a form of electroluminescence. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be ultraviolet, visible or infrared.[1] Rubin Braunstein of the Radio Corporation of America first reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955.[2] Experimenters at Texas Instruments, Bob Biard and Gary Pittman, found in 1961 that gallium arsenide gave off infrared (invisible) light when electric current was applied. Biard and Pittman were able to establish the priority of their work and received the patent for the infrared light-emitting diode. Nick Holonyak Jr. of the General Electric Company developed the first practical visible-spectrum LED in 1962.[3] Image File history File linksMetadata Download high resolution version (897x665, 75 KB)R, G, and B LEDS. File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Download high resolution version (897x665, 75 KB)R, G, and B LEDS. File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ... Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. ... Coherence is the property of wave-like states that enables them to exhibit interference. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ... In electronics, voltage bias (sometimes simply called bias) is a steady-state voltage It is used to activate the active component like transistor transistor, coil or other source of load. ... 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. ... Color is an important part of the visual arts. ... Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. ... The visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ... RCA, formerly an initialism for the Radio Corporation of America, is now a trademark used by two companies for products descended from that common ancestor: Thomson Consumer Electronics, which manufactures RCA-branded televisions, DVD players, video cassette recorders, direct broadcast satellite decoders, camcorders, audio equipment, telephones, and related accessories; and... This article is about the chemical compound. ... Texas Instruments (NYSE: TXN), better known in the electronics industry (and popularly) as TI, is an American company based in Dallas, Texas, USA, renowned for developing and commercializing semiconductor and computer technology. ... Nick Holonyak Jr. ... The General Electric Company, or GE, (NYSE: GE) is a multinational technology and services company. ...

LED technology

Physical function

A LED is a unique type of semiconductor diode. Like a normal diode, it consists of a chip of semiconducting material impregnated, or doped, with impurities to create a structure called a p-n junction. As in other diodes, current flows easily from the p-side, or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers - electrons and electron holes - flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon. A semiconductor is a solid whose electrical conductivity can be controlled over a wide range, either permanently or dynamically. ... Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... A p-n junction is formed by combining N-type and P-type semiconductors together in very close contact. ... Diagram of a zinc anode in a Daniells cell. ... Diagram of a copper cathode in a Daniells cell. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. ... now. ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ...

The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect bandgap materials. The materials used for an LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light. Free standing LEDs are usually constantly illuminated when a current passes through them, but flashing LEDs are also available. Flashing LEDs resemble standard LEDs but they contain a small chip inside which causes the LED to flash with a typical period of one second. This type of LED comes most commonly as red, yellow, or green. Most flashing LEDs emit light of a single wavelength, but multicoloured flashing LEDs are available too. The wavelength is the distance between repeating units of a wave pattern. ... In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... General Name, Symbol, Number germanium, Ge, 32 Chemical series metalloids Group, Period, Block 14, 4, p Appearance grayish white Atomic mass 72. ... In semiconductor physics, an indirect bandgap is a bandgap in which the minimum energy in the conduction band is shifted by a k-vector, which is determined by the materials crystal structure. ... In semiconductor physics, a direct bandgap means that the minimum of the conduction band lies directly above the maximum of the valence band in momentum space. ...

LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors. This article is about the chemical compound. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The wavelength is the distance between repeating units of a wave pattern. ...

LEDs are usually built on an n-type substrate, with electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should match the index of the semiconductor, otherwise the produced light gets partially reflected back into the semiconductor, where it gets absorbed and turns into additional heat. Sapphire (from Hebrew: ×¡×¤Ö¼×™×¨ Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ...

Conventional LEDs are made from a variety of inorganic semiconductor materials, producing the following colors: Semiconductor materials are insulators at absolute zero temperature that conduct electricity in a limited way at room temperature (see also Semiconductor). ...

Aluminium gallium arsenide (also Aluminum gallium arsenide) (AlxGa1-xAs) is a semiconductor with very nearly the same lattice constant as GaAs, but a larger bandgap. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ... Gallium arsenide phosphide (GaAsP) is a semiconductor material, an alloy of gallium arsenide and gallium phosphide. ... The colour orange occurs between red and yellow in the visible spectrum at a wavelength of about 585â€“620 nanometres. ... Yellow is any color of light that stimulates both the red and green cone cells of the retina, but not the blue cone cells. ... Gallium phosphide (GaP), a phosphide of gallium, is a compound semiconductor material with indirect band gap of 2. ... Gallium nitride (GaN) is a wide bandgap semiconductor material used in optoelectronic, high-power and high-frequency devices. ... Blue is any of a number of similar colors. ... Indium gallium nitride (InGaN, InxGa1-xN ) is a semiconductor material made of a mix of gallium nitride and indium nitride. ... Silicon carbide (SiC) is a ceramic compound of silicon and carbon. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... Sapphire (from Hebrew: ×¡×¤Ö¼×™×¨ Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... Zinc selenide (ZnSe), is a light yellow binary solid compound. ... // For other uses, including the shape â—Š, see Diamond (disambiguation). ... Aluminium nitride (AlN) is an extremely wide bandgap semiconductor material which has potential application for deep ultraviolet optoelectronics. ... Aluminium gallium nitride (AlGaN) is a semiconductor material. ... Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. ...

Blue and white LEDs

Commercially viable blue LEDs based on the wide band gap semiconductor gallium nitride and indium gallium nitride were invented by Shuji Nakamura while working in Japan at Nichia Corporation in 1993 and became widely available in the late 1990s. They can be added to existing red and green LEDs to produce white light, though white LEDs today rarely use this principle. Image File history File links Beschreibung: UV-LED mit Lichtkegel Autor: Christian Pelant Aufnahmedatum: 10. ... Image File history File links Beschreibung: UV-LED mit Lichtkegel Autor: Christian Pelant Aufnahmedatum: 10. ... Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. ... In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ... Gallium nitride (GaN) is a wide bandgap semiconductor material used in optoelectronic, high-power and high-frequency devices. ... Indium gallium nitride (InGaN, InxGa1-xN ) is a semiconductor material made of a mix of gallium nitride and indium nitride. ... Shuji Nakamura (ä¸æ‘ ä¿®äºŒ Nakamura ShÅ«ji, born in May 22, 1954, Seto, Ehime, Japan) is a professor at the University of California, Santa Barbara (UCSB). ... 1993 (MCMXCIII) was a common year starting on Friday of the Gregorian calendar and marked the Beginning of the International Decade to Combat Racism and Racial Discrimination (1993-2003). ... See also 1990s, the band The 1990s decade refers to the years from 1990 to 1999, inclusive, sometimes informally including popular culture from the very late 1980s and from 2000 and beyond. ... White is a color, (more accurately it contains all the colors of the visible spectrum and is sometimes described as an achromatic colorâ€”black is the absence of color) that has high brightness but zero hue. ...

Most "white" LEDs in production today use a 450 nm – 470 nm blue GaN (gallium nitride) or InGaN (indium gallium nitride) LED covered by a yellowish phosphor coating usually made of cerium-doped yttrium aluminum garnet (Ce³⁺:YAG) crystals which have been powdered and bound in a type of viscous adhesive. The LED chip emits blue light, part of which is efficiently converted to a broad spectrum centered at about 580 nm (yellow) by the Ce³⁺:YAG. The single crystal form of Ce³⁺:YAG is actually considered a scintillator rather than a phosphor. Since yellow light stimulates the red and green receptors of the eye, the resulting mix of blue and yellow light gives the appearance of white, the resulting shade often called "lunar white". This approach was developed by Nichia and was used by them from 1996 for manufacturing of white LEDs. A phosphor is a substance that can exhibit the phenomenon of fluorescence (glowing during absorption of radiation of another kind) or phosphorescence (sustained glowing without further stimulus). ... General Name, Symbol, Number cerium, Ce, 58 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 140. ... In semiconductor production, doping refers to the process of intentionally introducing impurities into an intrinsic semiconductor in order to change its electrical properties. ... YAG Yttrium Aluminum Garnet Color: Wide range of colors Moh’s hardness: 8. ... A scintillator is a device or substance that absorbs high energy (ionizing) electromagnetic or charged particle radiation then, in response, fluoresces photons at a characteristic Stokes-shifted (longer) wavelength, releasing the previously absorbed energy. ... Color vision is the capacity of an organism or machine to distinguish objects based on the wavelength of the light they reflect or emit. ...

The pale yellow emission of the Ce³⁺:YAG can be tuned by substituting the cerium with other rare earth elements such as terbium and gadolinium and can even be further adjusted by substituting some or all of the aluminum in the YAG with gallium. Due to the spectral characteristics of the diode, the red and green colors of objects in its blue yellow light are not as vivid as in broad-spectrum light. Manufacturing variations and varying thicknesses in the phosphor make the LEDs produce light with different color temperatures, from warm yellowish to cold bluish; the LEDs have to be sorted during manufacture by their actual characteristics. Philips Lumileds patented conformal coating process addresses the issue of varying phosphor thickness, giving the white LEDs a more consistent spectrum of white light. General Name, Symbol, Number terbium, Tb, 65 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 158. ... General Name, Symbol, Number gadolinium, Gd, 64 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 157. ... Visible light is commonly described by its color temperature. ... Philips Lumileds is the worlds leading manufacturer of high-power light-emitting diodes (LEDs) and a pioneer in the use of solid-state lighting solutions for everyday purposes. ...

White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al). This is a method analogous to the way fluorescent lamps work. However the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in LED packaging, causing manufacturing challenges and shorter lifetimes. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness. Image File history File links Download high-resolution version (3423x2459, 179 KB) Summary Spectrum of a white LED showing blue light directly emitted by the GaN LED and the stokes shifted yellowish light emitted by the Ce:YAG phosphor. ... Image File history File links Download high-resolution version (3423x2459, 179 KB) Summary Spectrum of a white LED showing blue light directly emitted by the GaN LED and the stokes shifted yellowish light emitted by the Ce:YAG phosphor. ... Stokes shift Stokes shift is the difference (in wavelength or frequency units) between positions of the band maxima of the absorption and luminescence spectra (or fluorescence) of the same electronic transition. ... General Name, Symbol, Number europium, Eu, 63 Chemical series lanthanides Group, Period, Block ?, 6, f Appearance silvery white Atomic mass 151. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Photodegradation is degradation of a molecule caused by the absorption of photons, particularly those wavelengths found in sunlight, such as infrared radiation, visible light and ultraviolet light. ... Epoxy or polyepoxide is a thermosetting epoxide polymer that cures when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction between Epichorohydrin & Bisphenol A. The first commercial attempts to prepare resins from epichlorohydrin occurred in 1927 in the United States. ... Stokes shift Stokes shift is the difference (in wavelength or frequency units) between positions of the band maxima of the absorption and luminescence spectra (or fluorescence) of the same electronic transition. ...

The newest method used to produce white light LEDs uses no phosphors at all and is based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emits blue light from its active region and yellow light from the substrate. Zinc selenide (ZnSe), is a light yellow binary solid compound. ...

A new technique just developed by Michael Bowers, a graduate student at Vanderbilt University in Nashville, involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This technique produces a warm, yellowish-white light similar to that produced by incandescent bulbs. Vanderbilt University is a private, nonsectarian, coeducational research university in Nashville, Tennessee. ... A quantum dot is a potential well that confines electrons in three dimensions to a region of the order of the electrons de Broglie wavelength in size, a few nanometers in a semiconductor. ... The incandescent light bulb uses a glowing wire filament heated to white-hot by electrical resistance, to generate light (a process known as thermal radiation). ...

Other colors

Recent color developments include pink and purple. They consist of one or two phosphor layers over a blue LED chip. The first phosphor layer of a pink LED is a yellow glowing one, and the second phosphor layer is either red or orange glowing. Purple LEDs are blue LEDs with an orange glowing phosphor over the chip. Some pink LEDs have run into issues. For example, some are blue LEDs painted with fluorescent paint or fingernail polish that can wear off, and some are white LEDs with a pink phosphor or dye that unfortunately fades after a short time. This article or section does not cite its references or sources. ... Purple is any of a group of colors intermediate between deep blue and red. ... A phosphor is a substance that can exhibit the phenomenon of fluorescence (glowing during absorption of radiation of another kind) or phosphorescence (sustained glowing without further stimulus). ...

Ultraviolet, blue, pure green, white, pink and purple LEDs are relatively expensive compared to the more common reds, oranges, greens, yellows and infrared and are thus less commonly used in commercial applications, however, as of 2006, the "Chernobyl blue" light from blue LEDs has a certain commercial cachet [4] and is used as a styling element in many products such as mobile phones and thus the price has dropped significantly.

The semiconducting chip is encased in a solid plastic lens, which is much tougher than the glass envelope of a traditional light bulb or tube. The plastic may be colored, but this is only for cosmetic reasons or to improve the contrast ratio; the color of the packaging does not substantially affect the color of the light emitted. Plastic covers a range of synthetic or semisynthetic polymerization products. ... A lens. ... The contrast ratio is a metric of a display system, defined as the ratio of the luminosity of the brightest and the darkest color the system is capable of producing. ...

Organic light-emitting diodes (OLEDs)

If the emitting layer material of an LED is an organic compound, it is known as an Organic Light Emitting Diode (OLED). To function as a semiconductor, the organic emitting material must have conjugated pi bonds. The emitting material can be a small organic molecule in a crystalline phase, or a polymer. Polymer materials can be flexible; such LEDs are known as PLEDs or FLEDs. It has been suggested that PHOLED be merged into this article or section. ... Image File history File links Download high resolution version (1073x758, 26 KB)Combined spectra of a common blue LED, a yellow-green LED and a high brightness red LED from the bottom of a microsoft optical mouse. ... Image File history File links Download high resolution version (1073x758, 26 KB)Combined spectra of a common blue LED, a yellow-green LED and a high brightness red LED from the bottom of a microsoft optical mouse. ... A full width at half maximum (FWHM) is an expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value. ... A metre (American spelling: meter; symbol: m) is a unit of length and the current base unit of length in the International System of Units (SI). ... Benzene An organic compound is any member of a large class of chemical compounds whose molecules contain carbon, with the exception of carbides, carbonates, carbon oxides and elementary carbon. ... It has been suggested that PHOLED be merged into this article or section. ... A chemically conjugated system, is a system of atoms covalently bonded with alternating single and double bonds (e. ... In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... Quartz crystal In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... Polymer is a term used to describe molecules consisting of structural units and a large number of repeating units connected by covalent chemical bonds. ...

Compared with regular LEDs, OLEDs are lighter, and polymer LEDs can have the added benefit of being flexible. Some possible future applications of OLEDs could be:

At present (2006) OLEDs are used in small portable color video displays such as cellphone and digital camera screens, and user interfaces on MP3 players. Large-screen color displays have been demonstrated, but their life expectancy is still far too short (<1,000 Hrs) to be practical. It has been suggested that Textile be merged into this article or section. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ...

Operational parameters and efficiency

Most typical LEDs are designed to operate with no more than 30-60 milliwatts of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt. These LEDs used much larger semiconductor die sizes to handle the large power input. Also, the semiconductor dies were mounted to metal slugs to allow for heat removal from the LED die. In 2002, Lumileds made 5-watt LEDs available with efficiencies of 18-22 lumens per watt. Milliwatt (SI symbol: mW) is a unit for measuring electrical power, equal to one-thousandth (10-3) of a watt. ... 1999 (MCMXCIX) was a common year starting on Friday, and was designated the International Year of Older Persons by the United Nations. ... Philips Lumileds is the worlds leading manufacturer of high-power light-emitting diodes (LEDs) and a pioneer in the use of solid-state lighting solutions for everyday purposes. ... For album titles with the same name, see 2002 (album). ... Philips Lumileds is the worlds leading manufacturer of high-power light-emitting diodes (LEDs) and a pioneer in the use of solid-state lighting solutions for everyday purposes. ... The lumen (symbol: lm) is the SI unit of luminous flux. ...

In September 2003 a new type of blue LED was demonstrated by the company Cree, Inc. to have 35% efficiency at 20 mA. This produced a commercially packaged white light having 65 lumens per watt at 20 mA, becoming the brightest white LED commercially available at the time. In 2006 they have demonstrated a prototype with a record white LED efficiency of 131 lumens per watt at 20 mA [5]. Cree Inc. ...

Today, OLEDs operate at substantially lower efficiency than inorganic (crystalline) LEDs. The best efficiency of an OLED so far is about 10%. These promise to be much cheaper to fabricate than inorganic LEDs, and large arrays of them can be deposited on a screen using simple printing methods to create a color graphic display.

Failure modes

The most common way for LEDs (and diode lasers) to fail is the gradual lowering of light output and loss of efficiency. However, sudden failures can occur as well. A laser diode is a laser where the active medium is a semiconductor p-n junction similar to that found in a light-emitting diode. ...

The mechanism of degradation of the active region, where the radiative recombination occurs, involves nucleation and growth of dislocations; this requires a presence of an existing defect in the crystal and is accelerated by heat, high current density, and emitted light. Gallium arsenide and aluminum gallium arsenide are more susceptible to this mechanism than gallium arsenide phosphide, indium gallium arsenide phosphide, and indium phosphide. Due to different properties of the active regions, gallium nitride and indium gallium nitride are virtually insensitive to this kind of defects; however, high current density can cause electromigration of atoms out of the active regions, leading to emergence of dislocations and point defects, acting as nonradiative recombination centers and producing heat instead of light. Ionizing radiation can lead to creation of such defects as well, which leads to issues with radiation hardening of circuits containing LEDs (eg. in optoisolators). Early red LEDs were notable for their short lifetime. Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... In materials science, a dislocation is a linear crystallographic defect, or irregularity, within a crystal structure. ... This article is about the chemical compound. ... Aluminium gallium arsenide (also Aluminum gallium arsenide) (AlxGa1-xAs) is a semiconductor with very nearly the same lattice constant as GaAs, but a larger bandgap. ... Gallium arsenide phosphide (GaAsP) is a semiconductor material, an alloy of gallium arsenide and gallium phosphide. ... Indium phosphide (InP) is a semiconductor composed of indium and phosphorus. ... Gallium nitride (GaN) is a wide bandgap semiconductor material used in optoelectronic, high-power and high-frequency devices. ... Indium gallium nitride (InGaN, InxGa1-xN ) is a semiconductor material made of a mix of gallium nitride and indium nitride. ... Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. ... Ionizing radiation has many practical uses, but it is also dangerous to human health. ... Microelectronics designed for environments with high levels of ionizing radiation have special design challenges. ... In electronics, an optical isolator is a device that uses a short optical transmission path to transfer a signal between elements of a circuit while keeping them electrically isolated -- since the signal goes from an electrical signal to an optical signal back to an electrical signal, electrical contact along the...

White LEDs often use one or more phosphors. The phosphors tend to degrade with heat and age, losing efficiency and causing changes in the produced light color. A phosphor is a substance that can exhibit the phenomenon of fluorescence (glowing during absorption of radiation of another kind) or phosphorescence (sustained glowing without further stimulus). ...

High electrical currents at elevated temperatures can cause diffusion of metal atoms from the electrodes into the active region. Some materials, notably indium tin oxide and silver, are subject to electromigration. In some cases, especially with GaN/InGaN diodes, a barrier metal layer is used to hinder the electromigration effects. Mechanical stresses, high currents, and corrosive environment can lead to formation of whiskers, causing short circuits. Indium tin oxide (ITO) is a mixture of indium(III) oxide (In2O3) and tin(IV) oxide (SnO2), typically 90% In2O3, 10% SnO2 by weight. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Atomic mass 107. ... A barrier metal is a material used in integrated circuits to chemically isolate semiconductors from soft metal interconnects, while maintaining an electrical connection between them. ... Metal whiskers are a crystalline metallurgical phenomenon whereby metal grows tiny, filiform hairs. ...

High-power LEDs are susceptible to current crowding, nonhomogenous distribution of the current density over the junction. This may lead to creation of localized hot spots, which poses risk of thermal runaway. Nonhomogenities in the substrate, causing localized loss of thermal conductivity, aggravate the situation; most common ones are voids caused by incomplete soldering, or by electromigration effects and Kirkendall voiding. Thermal runaway is a common cause of LED failures. Current crowding (also current crowding effect, or CCE) is a nonhomogenous distribution of current density through a conductor or semiconductor, especially at the vicinity of the contacts and over the PN junctions. ... In geology, a hotspot is a location on the Earths surface that has experienced active vulcanism for a long period of time. ... In chemical engineering, thermal runaway is a process by which an exothermic reaction goes out of control, often resulting in explosion. ... In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat. ... (De)soldering a contact from a wire. ... The Kirkendall effect is the migration of markers that occurs when markers are placed at the interface between an alloy and a metal, and the whole is heated to a temperature where diffusion is possible; the markers will move towards the alloy region. ...

Laser diodes may be subject to catastrophic optical damage, when the light output exceeds a critical level and causes melting of the facet. Catastrophic optical damage (COD) is a failure mode of high-power semiconductor lasers. ...

Some materials of the plastic package tend to yellow when subjected to heat, causing partial absorption (and therefore loss of efficiency) of the affected wavelengths.

Sudden failures are most often caused by thermal stresses. When the epoxy resin used in packaging reaches its glass transition temperature, it starts rapidly expanding, causing mechanical stresses on the semiconductor and the bonded contact, weakening it or even tearing it off. Conversely, very low temperatures can cause cracking of the packaging. Epoxy or polyepoxide is a thermosetting epoxide polymer that cures when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction between Epichorohydrin & Bisphenol A. The first commercial attempts to prepare resins from epichlorohydrin occurred in 1927 in the United States. ... A materialâ€™s glass transition temperature, Tg, is the temperature below which molecules have little relative mobility. ... Wire bonding is a method of making interconnections between a microchip and the outside world as part of semiconductor device fabrication. ...

Electrostatic discharge (ESD) may cause immediate failure of the semiconductor junction, a permanent shift of its parameters, or latent damage causing increased rate of degradation. LEDs and lasers grown on sapphire substrate are more susceptible to ESD damage. To meet Wikipedias quality standards, this article or section may require cleanup. ... Sapphire (from Hebrew: ×¡×¤Ö¼×™×¨ Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ...

Considerations in use

Unlike incandescent light bulbs, which light up regardless of the electrical polarity, LEDs will only light with positive electrical polarity. When the voltage across the p-n junction is in the correct direction, a significant current flows and the device is said to be forward-biased. If the voltage is of the wrong polarity, the device is said to be reverse biased, very little current flows, and no light is emitted. LEDs can be operated on an Alternating current voltage, but they will only light with positive voltage, causing the LED to turn on and off at the frequency of the AC supply. Image File history File links Makroaufnahme einer Leuchtdiode, Durchmesser 5 mm. ... Image File history File links Makroaufnahme einer Leuchtdiode, Durchmesser 5 mm. ... Image File history File links Led. ... Image File history File links Led. ... Image:Light-bulb-and-filament. ... The polarity of an object is, in general, its physical alignment of atoms. ... City lights viewed in a motion blurred exposure. ...

NOTE: Neither the interior nor exterior method of determing an LED's polarity is 100% accurate. Although the length of the pins (leads) is the most accurate method for determining polarity, even this designation is sometimes reversed. Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ...

Because the voltage versus current characteristics of an LED are much like any diode (that is approximately exponential), a small voltage change results in a huge change in current. Added to deviations in the process this means that a voltage source may barely make one LED light while taking another of the same type beyond its maximum ratings and potentially destroying it. Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force. ...

Since the voltage is logarithmically related to the current it can be considered to remain largely constant over the LEDs operating range. Thus the power can be considered to be almost proportional to the current. To try and keep power close to constant across variations in supply and LED characteristics the power supply should be a current source. If high efficiency is not required (e.g. in most indicator applications), an approximation to a current source made by connecting the LED in series with a current limiting resistor to a voltage source is generally used. An ideal current source, I, driving a resistor, R, and creating a voltage V A current source is an electrical or electronic device that delivers or absorbs electric current. ...

Most LEDs have low reverse breakdown voltage ratings, so they will also be damaged by an applied reverse voltage of more than a few volts. Since some manufacturers don't follow the indicator standards above, if possible the data sheet should be consulted before hooking up an LED, or the LED may be tested in series with a resistor on a sufficiently low voltage supply to avoid the reverse breakdown. If it is desired to drive an LED direct from an AC supply of more than the reverse breakdown voltage then it may be protected by placing a diode (or another LED) in inverse parallel. Breakdown Voltage (Insulator) = The minimum voltage that makes an insulator react as a conductor. ... A data sheet is a document summarizing the characteristics of an electronic component in sufficient detail that a skilled engineer can integrate the component to a new circuit design. ... Resistor symbols (US and Japan) Resistor symbols (Europe, IEC) A pack of resistors A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohms law. ... Two antiparallel molecules run side-by-side in opposite directions. ...

LEDs can be purchased with built in series resistors. These can save PCB space and are especially useful when building prototypes or populating a PCB in a way other than its designers intended. However the resistor value is set at the time of manufacture, removing one of the key methods of setting the LEDs intensity. To increase efficiency (or to allow intensity control without the complexity of a DAC), the power may be applied periodically or intermittently; so long as the flicker rate is greater than the human flicker fusion threshold, the LED will appear to be continuously lit. Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ... Prototypes or prototypical instances combine the most representative attributes of a category. ... In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or charges). ... The flicker fusion threshold (or flicker fusion rate) is a concept in the psychophysics of vision. ...

Provided there is sufficient voltage available, multiple LEDs can be connected in series with a single current limiting resistor. Parallel operation is generally problematic. The LEDs have to be of the same type in order to have a similar forward voltage. Even then, variations in the manufacturing process can make the odds of satisfactory operation low. For more information see Nichia Application Note. Left: Series / Right: Parallel Arrows indicate direction of current. ... Left: Series / Right: Parallel Arrows indicate direction of current. ...

Bicolor LED units contain two diodes, one in each direction (that is, two diodes in inverse parallel) and each a different color (typically red and green), allowing two-color operation or a range of apparent colors to be created by altering the percentage of time the voltage is in each polarity. Other LED units contain two or more diodes (of different colors) arranged in either a common anode or common cathode configuration. These can be driven to different colors without reversing the polarity. Red is any of a number of similar colors at the lowest frequencies of light discernible by the human eye. ... Green is a color with many different shades, all within a wavelength of roughly 520â€“570 nm. ...

LED units may have an integrated multivibrator circuit that makes the LED flash. A multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops. ...

Advantages of using LEDs

Image File history File links LED_symbol. ... Image File history File links LED_symbol. ... The light bulb is one of the most significant inventions in the history of the human race, illuminating the darkness of the evening and bringing light indoors at all times in order focus on the task at hand. ... Image File history File links Download high resolution version (3392x1193, 317 KB) Photographer: Andreas Frank, --Afrank99 Date: 2005-07-31 File links The following pages link to this file: Light-emitting diode ... Image File history File links Download high resolution version (3392x1193, 317 KB) Photographer: Andreas Frank, --Afrank99 Date: 2005-07-31 File links The following pages link to this file: Light-emitting diode ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ...

Disadvantages of using LEDs

LED applications

Image File history File links Download high resolution version (1024x696, 701 KB)A panel of red LEDs used for illumination for a plant growth experiment with possible future application to food growing in space. ... Image File history File links Download high resolution version (1024x696, 701 KB)A panel of red LEDs used for illumination for a plant growth experiment with possible future application to food growing in space. ... Divisions Green algae Chlorophyta Charophyta Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) â€ Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants... Image File history File linksMetadata Download high resolution version (2268x1512, 4216 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Light-emitting diode Champlain Valley Union High School Metadata This file contains additional information, probably added... Image File history File linksMetadata Download high resolution version (2268x1512, 4216 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Light-emitting diode Champlain Valley Union High School Metadata This file contains additional information, probably added... Download high resolution version (1024x768, 212 KB)LED flashlight File links The following pages link to this file: Flashlight Categories: GFDL images ... Download high resolution version (1024x768, 212 KB)LED flashlight File links The following pages link to this file: Flashlight Categories: GFDL images ...

List of LED applications

This article needs cleanup. ... Green Flashlight Note that Flashlight is the NATO designation for the Yakovlev Yak-25 Soviet military jet. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... A television remote control A DVDplayer remote control A remote control is an electronic device used for the remote operation of a machine. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ... A bundle of optical fibers. ... Three types of lightsticks in several colours A lightstick, also called a glowstick, is a transparent plastic tube which contains chemical fluids held apart in two compartments. ... Three types of lightsticks in several colours A lightstick, also called a glowstick, is a transparent plastic tube which contains chemical fluids held apart in two compartments. ... 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. ... Reliability concerns quality or consistency. ... A parabolic reflector (also known as a parabolic dish or a parabolic mirror) is a reflective device formed in the shape of a paraboloid of revolution. ... LCD redirects here. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... In computer graphics, the gamut, or color gamut, is a certain complete subset of colors. ... Lumalive is a photonic textile, which uses cloth as a lighted graphic display medium. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... This article does not cite its references or sources. ... Total cost of ownership (TCO) is a financial estimate designed to help consumers and enterprise managers assess direct and indirect costs related to the purchase of any capital investment, such as (but not limited to) computer software or hardware. ... Light therapy or phototherapy consists of exposure to specific wavelengths of light using lasers, LEDs, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, for a prescribed amount of time. ...

Illumination applications

LEDs used as a replacement for incandescent light bulbs and fluorescent lamps are known as solid-state lighting (SSL) - packaged as a cluster of white LEDs grouped together to form a light source (pictured). LEDs are moderately efficient: the average commercial SSL currently outputs 32 lumens per watt (lm/W), and new technologies promise to deliver up to 80 lm/W. The long lifetime of LEDs make SSL very attractive. They are also more mechanically robust than incandescent light bulbs and fluorescent tubes. Currently, solid state lighting is becoming more available for household use, but is relatively expensive, although costs are decreasing. LED flashlights however already have become widely available. Recently a number of manufacturers have started marketing ultra-compact LCD video projectors that use high-powered white LEDS for the light source. Another alternative design is to use red, green, and blue LEDs in a sequential DLP design. Image File history File links Ampoules Ã LED, composÃ© de 20 LED, puissance 1 Watt. ... Image File history File links Ampoules Ã LED, composÃ© de 20 LED, puissance 1 Watt. ... Image:Light-bulb-and-filament. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Solid State Lighting (SSL) refers to a type of lighting that utilizes light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes as sources of illumination rather than electrical filaments or gas. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... The watt (symbol: W) is the SI derived unit of power. ... Green flashlight Flashlight is the NATO designation for the Yakovlev Yak-25 Soviet military jet. ... The DLP Logo Digital Light Processing (DLP) is a technology used in projectors and video projectors. ...

Incandescent bulbs are much less expensive but also less efficient, generating from about 16 lm/W for a domestic tungsten bulb to 22 lm/W for a halogen bulb. Fluorescent tubes are more efficient, providing 50 to 100 lm/W for domestic tubes (average 60 lm/W), but are bulky and fragile and require starter or ballast circuits that sometimes buzz audibly. Compact fluorescent lamps, which include a quiet integrated ballast, are relatively robust and efficient, fit in standard light bulb sockets, and are currently the best choice for efficient household lighting. General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Atomic mass 183. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... A spiral type compact fluorescent light bulb. ...

Proponents of LEDs expect that technological advances will reduce costs such that SSL can be introduced into most homes by 2020. However, they are still not commercially viable for general lighting applications, and so LEDs are found today in illumination applications where their special characteristics provide a distinct advantage. This can be seen in the widespread use of LEDs in traffic signals and indicator lamps for trucks and automobiles.

Due to their monochromatic nature, LED lights have great power advantages over white lights when a specific color is required. Unlike traditional white lights, the LED does not need a coating or diffuser that can absorb much of the emitted light. LED lights are inherently colored, and are available in a wide range of colors. One of the most recently introduced colors is the emerald green (bluish green, about 500 nm) that meets the legal requirements for traffic signals and navigation lights.

There are applications that specifically require light without any blue component. Examples are photographic darkroom safe lights, illumination in laboratories where certain photo-sensitive chemicals are used, and situations where dark adaptation (night vision) must be preserved, such as cockpit and bridge illumination, observatories, etc. Yellow LED lights are a good choice to meet these special requirements because the human eye is more sensitive to yellow light (about 500 lm/watt emitted) than that emitted by the other LEDs. Night-vision is seeing in the dark. ...

The first residence lit solely by LED's was the "Vos Pad" in London. The entire flat is lit by a combination of white and RGB (colour changing) LED's.

LED display panels

There are two types of LED panels: conventional, using discrete LEDs, and Surface Mounted Device (SMD) panels. Most outdoor screens and some indoor screens are built around discrete LEDs, also known as individually mounted LEDs. A cluster of red, green, and blue diodes is driven together to form a full-color pixel, usually square in shape. These pixels are spaced evenly apart and are measured from center to center for absolute pixel resolution. The largest LED display in the world is over 1,500 feet long and is located in Las Vegas, Nevada covering the Fremont Street Experience. Image File history File linksMetadata Download high resolution version (1541x2000, 860 KB) Summary Souce: Viva Vision Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Download high resolution version (1541x2000, 860 KB) Summary Souce: Viva Vision Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... The 1,500 foot long led display The Fremont Street Experience (FSE) is a pedestrian mall and attraction in downtown Las Vegas, Nevada. ... Surface-mount components on a keydrives circuit board Surface mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards (PCBs). ... Nickname: The Entertainment Capital of the World; Sin City Location of Las Vegas in Nevada Coordinates: County Clark Mayor Oscar B. Goodman Area - City 131. ... This article does not cite its references or sources. ... The 1,500 foot long led display The Fremont Street Experience (FSE) is a pedestrian mall and attraction in downtown Las Vegas, Nevada. ...

Most indoor screens on the market are built using SMD technology — a trend that is now extending to the outdoor market. An SMD pixel consists of red, green, and blue diodes mounted on a chipset, which is then mounted on the driver PC board. The individual diodes are smaller than a pinhead and are set very close together. The difference is that minimum viewing distance is reduced by 25% from the discrete diode screen with the same resolution.

Indoor use generally requires a screen that is based on SMD technology and has a minimum brightness of 600 candelas per square meter (unofficially called nits). This will usually be more than sufficient for corporate and retail applications, but under high ambient-brightness conditions, higher brightness may be required for visibility. Fashion and auto shows are two examples of high-brightness stage lighting that may require higher LED brightness. Conversely, when a screen may appear in a shot on a television show, the requirement will often be for lower brightness levels with lower color temperatures (common displays have a white point of 6500-9000K, which is much bluer than the common lighting on a television production set). Image File history File linksMetadata Download high resolution version (2048x1536, 661 KB) Summary Photo of Al Sheedakim and LED Panel, Winchester, MA 2004. ... Image File history File linksMetadata Download high resolution version (2048x1536, 661 KB) Summary Photo of Al Sheedakim and LED Panel, Winchester, MA 2004. ... The candela (symbol: cd) is the SI base unit of luminous intensity (that is, power emitted by a light source in a particular direction, with wavelengths weighted by the luminosity function, a standardized model of the sensitivity of the human eye). ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... This article is about the unit of measure. ...

For outdoor use, at least 2,000 nits are required for most situations, whereas higher brightness types of up to 5,000 nits cope even better with direct sunlight on the screen. Until recently, only discrete diode screens could achieve that brightness level. (The brightness of LED panels can be reduced from the designed maximum, if required.) Image File history File linksMetadata Download high-resolution version (1066x799, 331 KB) Summary The PigScreen of Donald W. Reynolds Razorback Stadium; it is the largest Smartvision LED screen. ... Image File history File linksMetadata Download high-resolution version (1066x799, 331 KB) Summary The PigScreen of Donald W. Reynolds Razorback Stadium; it is the largest Smartvision LED screen. ... Donald W. Reynolds Razorback Stadium is the home of the Arkansas Razorbacks football team of the University of Arkansas, which is located in Fayetteville, Arkansas, USA. The current head coach of the football team is coach Houston Nutt. ...

Suitable locations for large display panels are identified by factors such as line of sight, local authority planning requirements (if the installation is to become semi-permanent), vehicular access (trucks carrying the screen, truck-mounted screens, or cranes), cable runs for power and video (accounting for both distance and health and safety requirements), power, suitability of the ground for the location of the screen (check to make sure there are no pipes, shallow drains, caves, or tunnels that may not be able to support heavy loads), and overhead obstructions.

Multi-Touch Sensing

Since LEDs share some basic physical properties with photodiodes, which also use p-n junctions with band gap energies in the visible light wavelengths, they can also be used for photo detection. These properties have been known for some time, but more recently so-called bidirectional LED matrices have been proposed as a method of touch-sensing. In 2003, Dietz, Yerazunis, and Leigh published a paper[6] describing the use of LEDs as cheap sensor devices. A photodiode is an electronic component and a type of photodetector. ... Podium touchscreen Touchscreens, touch screens, touch panels or touchscreen panels are display overlays which are typically either pressure-sensitive (resistive), electrically-sensitive (capacitive), acoustically-sensitive (SAW - surface acoustic wave) or photo-sensitive (infra-red). ...

In this usage, various LEDs in the matrix are quickly switched on and off. LEDs that are on shine light onto a user's fingers or a stylus. LEDs that are off function as photodiodes to detect reflected light from the fingers or stylus. The voltage thus induced in the reverse-biased LEDs can then be read by a microprocessor, which interprets the voltage peaks and then uses them elsewhere. The website of Jeff Han features a video[7] demonstrating one such implementation of an LED matrix multi-touch sensor.

References

October 20 is the 293rd day of the year (294th in leap years) in the Gregorian Calendar, with 72 days remaining. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...

Contents

LED technology

Physical function

Blue and white LEDs

Other colors

Organic light-emitting diodes (OLEDs)

Operational parameters and efficiency

Failure modes

Considerations in use

Advantages of using LEDs

Disadvantages of using LEDs

LED applications

List of LED applications

Illumination applications

LED display panels

Multi-Touch Sensing

References

See also

External links

Contents

LED technology GA_googleFillSlot("encyclopedia_square");

Physical function

Blue and white LEDs

Other colors

Organic light-emitting diodes (OLEDs)

Operational parameters and efficiency

Failure modes

Considerations in use

Advantages of using LEDs

Disadvantages of using LEDs

LED applications

List of LED applications

Illumination applications

LED display panels

Multi-Touch Sensing

References

See also

External links

LED technology