Light-emitting_diode

context: Recent developments in LEDs permit them to be used in environmental and task lighting. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes and lighted wallpaper. As of 2015[update], LEDs powerful enough for room lighting remain somewhat more expensive, and require more precise current and heat management, than compact fluorescent lamp sources of comparable output.
qas: answers: environmental
question: What type of atmosphere can LED lighting be used?

answers: longer lifetime
question: What is an advantage to using LED lighting over the normal light sources?

answers: Light-emitting diodes
question: What does LED stand for?

answers: more expensive
question: Why are some people hesitant to use LED lighting?

answers: traffic signals
question: What is a popular use for LED lighting?

context: Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector. Soviet inventor Oleg Losev reported creation of the first LED in 1927. His research was distributed in Soviet, German and British scientific journals, but no practical use was made of the discovery for several decades. Kurt Lehovec, Carl Accardo and Edward Jamgochian, explained these first light-emitting diodes in 1951 using an apparatus employing SiC crystals with a current source of battery or pulse generator and with a comparison to a variant, pure, crystal in 1953.
qas: answers: British
question: What was the nationality of the man who discovered Electroluminescence?

answers: Electroluminescence
question: LED lighting is the end result of what phenomenon?

answers: 1907
question: When was Electroluminescence discovered?

answers: Oleg Losev
question: Who is the Soviet man that created the first LED?

answers: cat's-whisker
question: What type of detector did H.J. Round use to help him in his discovery?

context: In 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance. As noted by Kroemer Braunstein".. had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier, and played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup." This setup presaged the use of LEDs for optical communication applications.
qas: answers: 1957
question: What year was it discovered that early LED instruments could be used for non-radio communication?

answers: Kroemer Braunstein
question: Who discovered non-radio uses for early LED devices?

answers: a GaAs diode
question: The current in non-radio communication had to go through what type of component?

answers: a PbS diode
question: What other component was needed to detect the first current of a non-radio signal?

answers: audio amplifier
question: What final device was needed to hear the signal from the initial GaAs diode?

context: In September 1961, while working at Texas Instruments in Dallas, Texas, James R. Biard and Gary Pittman discovered near-infrared (900 nm) light emission from a tunnel diode they had constructed on a GaAs substrate. By October 1961, they had demonstrated efficient light emission and signal coupling between a GaAs p-n junction light emitter and an electrically-isolated semiconductor photodetector. On August 8, 1962, Biard and Pittman filed a patent titled "Semiconductor Radiant Diode" based on their findings, which described a zinc diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias. After establishing the priority of their work based on engineering notebooks predating submissions from G.E. Labs, RCA Research Labs, IBM Research Labs, Bell Labs, and Lincoln Lab at MIT, the U.S. patent office issued the two inventors the patent for the GaAs infrared (IR) light-emitting diode (U.S. Patent US3293513), the first practical LED. Immediately after filing the patent, Texas Instruments (TI) began a project to manufacture infrared diodes. In October 1962, TI announced the first LED commercial product (the SNX-100), which employed a pure GaAs crystal to emit a 890 nm light output. In October 1963, TI announced the first commercial hemispherical LED, the SNX-110.
qas: answers: Texas
question: In what state what near-infrared light emission discovered? 

answers: tunnel
question: What type of diode was used to help discover near-infrared light emission?

answers: 1962
question: In what year was the patent filed for the Semiconductor Radiant Diode?

answers: GaAs infrared (IR) light-emitting diode
question: What was the first practical LED?

answers: Texas Instruments (TI)
question: The two inventors of the first practical diode were employed by what famous company?

context: The first visible-spectrum (red) LED was developed in 1962 by Nick Holonyak, Jr., while working at General Electric Company. Holonyak first reported his LED in the journal Applied Physics Letters on the December 1, 1962. M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T. P. Pearsall created the first high-brightness, high-efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.
qas: answers: General Electric Company
question: At what global company was the first visible-spectrum LED developed?

answers: Nick Holonyak, Jr.
question: What GE employee developed the visible-spectrum LED?

answers: red
question: What color is associated with the visible-spectrum LED?

answers: yellow
question: What color LED was later created in 1972?

answers: M. George Craford
question: What graduate student of Holonyak created the yellow LED?

context: The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, as well as watches (see list of signal uses). Until 1968, visible and infrared LEDs were extremely costly, in the order of US$200 per unit, and so had little practical use. The Monsanto Company was the first organization to mass-produce visible LEDs, using gallium arsenide phosphide (GaAsP) in 1968 to produce red LEDs suitable for indicators. Hewlett Packard (HP) introduced LEDs in 1968, initially using GaAsP supplied by Monsanto. These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors became widely available and appeared in appliances and equipment. In the 1970s commercially successful LED devices at less than five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with the planar process invented by Dr. Jean Hoerni at Fairchild Semiconductor. The combination of planar processing for chip fabrication and innovative packaging methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. These methods continue to be used by LED producers.
qas: answers: replacements for incandescent and neon indicator lamps
question: What was the first commercial uses of LEDs?

answers: US$200 per unit
question: How much did the early LEDs cost?

answers: calculators
question: What was one use of early LED light in products?

answers: Hewlett Packard (HP)
question: What modern company introduced LEDs in 1968?

answers: 1970s
question: In what decade were production costs greatly reduced for LEDs to enable successful commercial uses?

context: The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994 and was based on InGaN. In parallel, Isamu Akasaki and Hiroshi Amano in Nagoya were working on developing the important GaN nucleation on sapphire substrates and the demonstration of p-type doping of GaN. Nakamura, Akasaki and Amano were awarded the 2014 Nobel prize in physics for their work. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a "transparent contact" LED using indium tin oxide (ITO) on (AlGaInP/GaAs).
qas: answers: blue
question: What color LED was demonstrated in 1994?

answers: Shuji Nakamura
question: Who demonstrated the first blue LED?

answers: 2014 Nobel prize in physics
question: What did Nakamura, Akasaki, and Amano receive for their work?

answers: Alberto Barbieri
question: Who investigated the efficiency of high-brightness LED at Cardiff University in 1995?

answers: indium tin oxide
question: What substance did Barbieri use in his work with high-brightness LED?

context: The attainment of high efficiency in blue LEDs was quickly followed by the development of the first white LED. In this device a Y
3Al
5O
12:Ce (known as "YAG") phosphor coating on the emitter absorbs some of the blue emission and produces yellow light through fluorescence. The combination of that yellow with remaining blue light appears white to the eye. However using different phosphors (fluorescent materials) it also became possible to instead produce green and red light through fluorescence. The resulting mixture of red, green and blue is not only perceived by humans as white light but is superior for illumination in terms of color rendering, whereas one cannot appreciate the color of red or green objects illuminated only by the yellow (and remaining blue) wavelengths from the YAG phosphor.
qas: answers: white
question: What LED quickly followed the blue LEDs?

answers: yellow light
question: What does the YAG phosphor coating produce?

context: A P-N junction can convert absorbed light energy into a proportional electric current. The same process is reversed here (i.e. the P-N junction emits light when electrical energy is applied to it). This phenomenon is generally called electroluminescence, which can be defined as the emission of light from a semi-conductor under the influence of an electric field. The charge carriers recombine in a forward-biased P-N junction as the electrons cross from the N-region and recombine with the holes existing in the P-region. Free electrons are in the conduction band of energy levels, while holes are in the valence energy band. Thus the energy level of the holes will be lesser than the energy levels of the electrons. Some portion of the energy must be dissipated in order to recombine the electrons and the holes. This energy is emitted in the form of heat and light.
qas: answers: P-N junction
question: What converts absorbed light energy into an electric current?

answers: electroluminescence
question: What is the phenomenon where a P-N junction emits light when an electrical current is applied to it?

answers: the conduction band
question: Where are the free electrons located in the production of electroluminescence?

answers: holes existing in the P-region
question: Whose energy levels are lower than the electrons in the electroluminescence process?

answers: to recombine the electrons and the holes
question: Why is some energy in the electroluminescence process emitted as heat and light?

context: In September 2003, a new type of blue LED was demonstrated by Cree that consumes 24 mW at 20 milliamperes (mA). This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006, they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Nichia Corporation has developed a white LED with luminous efficacy of 150 lm/W at a forward current of 20 mA. Cree's XLamp XM-L LEDs, commercially available in 2011, produce 100 lm/W at their full power of 10 W, and up to 160 lm/W at around 2 W input power. In 2012, Cree announced a white LED giving 254 lm/W, and 303 lm/W in March 2014. Practical general lighting needs high-power LEDs, of one watt or more. Typical operating currents for such devices begin at 350 mA.
qas: answers: 2003
question: In what year was a new type of blue LED produced?

answers: Cree
question: Who demonstrated in 2003 the new type of blue LED?

answers: four times
question: How much more efficient as standard incandescents was the white LED commercially available in 2003?

answers: 350 mA
question: What is the typical operating current for high-power LEDs?

context: The most common symptom of LED (and diode laser) failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can also occur. Early red LEDs were notable for their short service life. With the development of high-power LEDs the devices are subjected to higher junction temperatures and higher current densities than traditional devices. This causes stress on the material and may cause early light-output degradation. To quantitatively classify useful lifetime in a standardized manner it has been suggested to use L70 or L50, which are the runtimes (typically given in thousands of hours) at which a given LED reaches 70% and 50% of initial light output, respectively.
qas: answers: loss of efficiency
question: What is a symptom of LED failure?

answers: Sudden failures
question: What is rare in LED lighting?

answers: their short service life
question: What was notable in early red LEDs?

answers: higher junction temperatures
question: What could cause early light-output degradation in LEDs?

answers: L70 or L50
question: What is a classification used in LED lighting to describe how much usefulness it will receive?

context: Since LED efficacy is inversely proportional to operating temperature, LED technology is well suited for supermarket freezer lighting. Because LEDs produce less waste heat than incandescent lamps, their use in freezers can save on refrigeration costs as well. However, they may be more susceptible to frost and snow buildup than incandescent lamps, so some LED lighting systems have been designed with an added heating circuit. Additionally, research has developed heat sink technologies that will transfer heat produced within the junction to appropriate areas of the light fixture.
qas: answers: operating temperature
question: LED efficacy is inversely proportional to what?

answers: supermarket freezer
question: Where is LED lighting very well suited?

answers: incandescent lamps
question: LEDs produce less waste heat than what other device?

answers: frost
question: What is LED lighting more susceptible to than incandescent light?

context: The first blue-violet LED using magnesium-doped gallium nitride was made at Stanford University in 1972 by Herb Maruska and Wally Rhines, doctoral students in materials science and engineering. At the time Maruska was on leave from RCA Laboratories, where he collaborated with Jacques Pankove on related work. In 1971, the year after Maruska left for Stanford, his RCA colleagues Pankove and Ed Miller demonstrated the first blue electroluminescence from zinc-doped gallium nitride, though the subsequent device Pankove and Miller built, the first actual gallium nitride light-emitting diode, emitted green light. In 1974 the U.S. Patent Office awarded Maruska, Rhines and Stanford professor David Stevenson a patent for their work in 1972 (U.S. Patent US3819974 A) and today magnesium-doping of gallium nitride continues to be the basis for all commercial blue LEDs and laser diodes. These devices built in the early 1970s had too little light output to be of practical use and research into gallium nitride devices slowed. In August 1989, Cree introduced the first commercially available blue LED based on the indirect bandgap semiconductor, silicon carbide (SiC). SiC LEDs had very low efficiency, no more than about 0.03%, but did emit in the blue portion of the visible light spectrum.[citation needed]
qas: answers: Herb Maruska and Wally Rhines
question: What students developed the first blue-violet LED?

answers: Stanford
question: The first blue-violet LED was developed at what University?

answers: 1972
question: When was the first blue-violet LED developed?

answers: zinc-doped gallium nitride
question: What substance helped demonstrate the first blue electroluminescence?

context: In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, Dr. Moustakas at Boston University patented a method for producing high-brightness blue LEDs using a new two-step process. Two years later, in 1993, high-brightness blue LEDs were demonstrated again by Shuji Nakamura of Nichia Corporation using a gallium nitride growth process similar to Dr. Moustakas's. Both Dr. Moustakas and Mr. Nakamura were issued separate patents, which confused the issue of who was the original inventor (partly because although Dr. Moustakas invented his first, Dr. Nakamura filed first).[citation needed] This new development revolutionized LED lighting, making high-power blue light sources practical, leading to the development of technologies like BlueRay, as well as allowing the bright high resolution screens of modern tablets and phones.[citation needed]
qas: answers: 1980s
question: In what decade were breakthroughs made that brought in the modern era of GaN-based optoelectronic devices?

answers: Shuji Nakamura
question: Who first patented a method to produce high-brightness blue LEDs?

answers: Dr. Moustakas
question: Who first invented a method to produce high-brightness blue LEDs?

answers: BlueRay
question: What technology was made possible by high-power blue light sources?

answers: tablets
question: What is one modern gadget that benefits from high-power blue LED lighting?

context: Nakamura was awarded the 2006 Millennium Technology Prize for his invention. Nakamura, Hiroshi Amano and Isamu Akasaki were awarded the Nobel Prize in Physics in 2014 for the invention of the blue LED. In 2015, a US court ruled that three companies (i.e. the litigants who had not previously settled out of court) that had licensed Mr. Nakamura's patents for production in the United States had infringed Dr. Moustakas's prior patent, and order them to pay licensing fees of not less than 13 million USD.
qas: answers: Physics
question: What Nobel Prize did Nakamura, Amano, and Akasaki receive in 2014?

answers: Millennium Technology Prize
question: What award did Nakamura receive in 2006 for his invention?

answers: three
question: How many companies did a judge say infringed on Dr. Moustakas's prior blue light patent in 2015?

answers: not less than 13 million USD
question: What was the fine given to the three companies?

context: By the late 1990s, blue LEDs became widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber. Aluminium gallium nitride (AlGaN) of varying Al/Ga fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of InGaN/GaN blue/green devices. If un-alloyed GaN is used in this case to form the active quantum well layers, the device will emit near-ultraviolet light with a peak wavelength centred around 365 nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems, but practical devices still exhibit efficiency too low for high-brightness applications.[citation needed]
qas: answers: active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN
question: What are cladding layers?

answers: By varying the relative In/Ga fraction in the InGaN quantum wells
question: How can light emission be varied from violet to amber?

answers: Aluminium gallium nitride
question: What does AlGaN stand for?

answers: Green
question: What LEDs are more efficient when produced from the InGaN/GaN systems than without?

context: With nitrides containing aluminium, most often AlGaN and AlGaInN, even shorter wavelengths are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti-counterfeiting UV watermarks in some documents and paper currencies. Shorter-wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 240 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with a peak at about 260 nm, UV LED emitting at 250–270 nm are to be expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices. UV-C wavelengths were obtained in laboratories using aluminium nitride (210 nm), boron nitride (215 nm) and diamond (235 nm).
qas: answers: aluminium
question: What substance does nitrides contain?

answers: Ultraviolet
question: What sort of LEDs are becoming more available on the market?

answers: 375–395 nm
question: What is the range of wavelengths for cheap UV LEDs?

answers: 240 nm
question: Shorter wavelength diodes provide wavelengths as low as what?

answers: 250–270 nm
question: What UV wavelengths are found in sterilization devices?

context: White light can be formed by mixing differently colored lights; the most common method is to use red, green, and blue (RGB). Hence the method is called multi-color white LEDs (sometimes referred to as RGB LEDs). Because these need electronic circuits to control the blending and diffusion of different colors, and because the individual color LEDs typically have slightly different emission patterns (leading to variation of the color depending on direction) even if they are made as a single unit, these are seldom used to produce white lighting. Nonetheless, this method has many applications because of the flexibility of mixing different colors, and in principle, this mechanism also has higher quantum efficiency in producing white light.[citation needed]
qas: answers: red, green, and blue
question: What colors are used to form white light?

answers: multi-color white LEDs
question: What is the method called that mixes red, green, and blue colors to form white light?

answers: electronic circuits
question: What does the multi-color white LED method need to produce the end result?

answers: RGB LEDs
question: What is another name to reference the multi-color white LED method?

context: There are several types of multi-color white LEDs: di-, tri-, and tetrachromatic white LEDs. Several key factors that play among these different methods, include color stability, color rendering capability, and luminous efficacy. Often, higher efficiency will mean lower color rendering, presenting a trade-off between the luminous efficacy and color rendering. For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. However, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficacy. Trichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability.
qas: answers: luminous efficacy
question: What is a factor that may be different in the various types of multi-color white LEDs?

answers: lower color rendering
question: Higher efficiency in multi-color white LEDs may mean what?

answers: tetrachromatic
question: What is one type of multi-color white LED?

answers: dichromatic white LEDs
question: What type has the best luminous efficacy?

answers: >70 lm/W
question: What luminous efficacy does trichromatic white LEDs have?

context: Multi-color LEDs offer not merely another means to form white light but a new means to form light of different colors. Most perceivable colors can be formed by mixing different amounts of three primary colors. This allows precise dynamic color control. As more effort is devoted to investigating this method, multi-color LEDs should have profound influence on the fundamental method that we use to produce and control light color. However, before this type of LED can play a role on the market, several technical problems must be solved. These include that this type of LED's emission power decays exponentially with rising temperature, resulting in a substantial change in color stability. Such problems inhibit and may preclude industrial use. Thus, many new package designs aimed at solving this problem have been proposed and their results are now being reproduced by researchers and scientists.
qas: answers: to form light of different colors
question: Multi-color LEDs offer what else besides the formation of white light?

answers: power decays exponentially with rising temperature
question: What problem must be solved before multi-color LEDs can play a role in the market?

answers: substantial change in color stability
question: What problem results when rising temperatures decays power?

context: This method involves coating LEDs of one color (mostly blue LEDs made of InGaN) with phosphors of different colors to form white light; the resultant LEDs are called phosphor-based or phosphor-converted white LEDs (pcLEDs). A fraction of the blue light undergoes the Stokes shift being transformed from shorter wavelengths to longer. Depending on the color of the original LED, phosphors of different colors can be employed. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively raising the color rendering index (CRI) value of a given LED.
qas: answers: phosphor-converted white LEDs (pcLEDs)
question: What method involves coating LEDs of one color with phosphors of different colors?

answers: blue
question: In pcLEDs method, a fraction of what light is used?

answers: Stokes
question: What shift does blue light undergo in the pcLEDs method?

answers: the color of the original LED
question: The different colors of phosphors that can be used is based on what?

answers: If several phosphor layers of distinct colors are applied
question: What broadens the emitted spectrum in a pcLEDs method?

context: Phosphor-based LED efficiency losses are due to the heat loss from the Stokes shift and also other phosphor-related degradation issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue (as modeled in the luminosity function). Due to the simplicity of manufacturing the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion.
qas: answers: the spectral distribution of the resultant light output
question: What do phosphor-based LEDs luminous efficacies depend on?

answers: phosphor method
question: What is the most popular method for making high-intensity white LEDs?

answers: heat loss from the Stokes shift
question: Why is efficiency sometimes lost in phosphor-based LEDs?

answers: 3 to 5 times the luminous efficacy
question: What are some of the luminous efficacies of yellow phosphor based white LED compared to blue?

answers: monochrome
question: What type of emitter is used in phosphor-based white LED methods?

context: Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stoke shift loss. Losses attributable to internal optical losses due to re-absorption in the LED chip and in the LED packaging itself account typically for another 10% to 30% of efficiency loss. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be raised by adapting better package design or by using a more suitable type of phosphor. Conformal coating process is frequently used to address the issue of varying phosphor thickness.
qas: answers: more efficient phosphors
question: What can improve the efficiency of LED-based white light?

answers: YAG phosphor
question: What is the most efficient yellow phosphor?

answers: less than 10%
question: What is the percentage of stoke shift loss in YAG phosphor?

answers: higher operation temperatures
question: What area are scientists looking into regarding phosphor LED development?

answers: adapting better package design
question: What is one method that can raise the efficiency of phosphor-based LEDs?

context: White LEDs can also be made by coating near-ultraviolet (NUV) LEDs with a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, so more energy is 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 methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.
qas: answers: near-ultraviolet (NUV) LEDs
question: White LEDs can be made by coating what?

answers: copper and aluminium-doped zinc sulfide (ZnS:Cu, Al)
question: What are near-ultraviolet LEDs coated with to create white LED?

answers: fluorescent lamps
question: What device also works in a similar way as NUV LEDs?

answers: blue
question: The method of coating NUVs less efficient than what other LEDs?

answers: UV light
question: What light can harm human eyes or skin?

context: A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire substrate in relatively small 100- or 150-mm wafer sizes. The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It is predicted that by 2020, 40% of all GaN LEDs will be made with GaN-on-Si. Manufacturing large sapphire material is difficult, while large silicon material is cheaper and more abundant. LED companies shifting from using sapphire to silicon should be a minimal investment.
qas: answers: wafers composed of gallium-nitride-on-silicon
question: What is being used to produce white LEDs?

answers: 200-mm
question: What size are the wafers used to create white LEDs?

answers: costly sapphire substrate
question: By using silicon wafers, what is being avoided?

answers: mirror-like collector
question: What needs to be used to reflect light that would otherwise be wasted?

answers: 2020
question: By what year will% of all GaN LEDs be made with gallium-nitride-on-silicon wafers?

context: Quantum dots (QD) are semiconductor nanocrystals that possess unique optical properties. Their emission color can be tuned from the visible throughout the infrared spectrum. This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering than white LEDs since the emission spectrum is much narrower, characteristic of quantum confined states. There are two types of schemes for QD excitation. One uses photo excitation with a primary light source LED (typically blue or UV LEDs are used). The other is direct electrical excitation first demonstrated by Alivisatos et al.
qas: answers: Quantum dots
question: What nanocrystals possess unique optical properties?

answers: create almost any color on the CIE diagram
question: Quantum Dot LEDs can do what special skill?

answers: better color rendering
question: The narrowing of the emission spectrum in Quantum Dot LEDs allows them to do what?

answers: two
question: How many types of schemes are there in Quantum Dot LED excitation?

context: The structure of QD-LEDs used for the electrical-excitation scheme is similar to basic design of OLEDs. A layer of quantum dots is sandwiched between layers of electron-transporting and hole-transporting materials. An applied electric field causes electrons and holes to move into the quantum dot layer and recombine forming an exciton that excites a QD. This scheme is commonly studied for quantum dot display. The tunability of emission wavelengths and narrow bandwidth is also beneficial as excitation sources for fluorescence imaging. Fluorescence near-field scanning optical microscopy (NSOM) utilizing an integrated QD-LED has been demonstrated.
qas: answers: electrical-excitation
question: What is one scheme of Quantum Dot excitation?

answers: hole-transporting materials
question: What is one material used in electrical-excitation?

answers: electrons and holes
question: During the electrical-excitation scheme, what moves into the quantum dot layer?

answers: near-field scanning optical microscopy (NSOM)
question: A Quantum Dot LED has been used in what?

context: High-power LEDs (HP-LEDs) or high-output LEDs (HO-LEDs) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Some can emit over a thousand lumens. LED power densities up to 300 W/cm2 have been achieved. Since overheating is destructive, the HP-LEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from a HP-LED is not removed, the device will fail in seconds. One HP-LED can often replace an incandescent bulb in a flashlight, or be set in an array to form a powerful LED lamp.
qas: answers: over a thousand
question: How many lumens can some high-power LEDs emit?

answers: 300 W/cm2
question: Up to how many densities have been achieved with LED power?

answers: to allow for heat dissipation
question: Why must High-power LEDs be mounted on a heat sink?

answers: the device will fail in seconds
question: What will happen if the heat from a high-power LED is not removed?

answers: incandescent bulb in a flashlight
question: What can one high-power LED replace?

context: LEDs have been developed by Seoul Semiconductor that can operate on AC power without the need for a DC converter. For each half-cycle, part of the LED emits light and part is dark, and this is reversed during the next half-cycle. The efficacy of this type of HP-LED is typically 40 lm/W. A large number of LED elements in series may be able to operate directly from line voltage. In 2009, Seoul Semiconductor released a high DC voltage LED, named as 'Acrich MJT', capable of being driven from AC power with a simple controlling circuit. The low-power dissipation of these LEDs affords them more flexibility than the original AC LED design.
qas: answers: Seoul Semiconductor
question: What company has developed LEDs that can operate on AC power?

answers: 40 lm/W
question: What is the efficacy of an AC powered HP-LED?

answers: 2009
question: When did Seoul Semiconductor release the first high DC voltage LED?

answers: more flexibility
question: What is so good about ac powered HP-LEDs?

answers: Acrich MJT
question: What did Seoul Semiconductor name their ac powered HP-LED?

context: Alphanumeric LEDs are available in seven-segment, starburst and dot-matrix format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Dot-matrix displays typically use 5x7 pixels per character. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but rising use of liquid crystal displays, with their lower power needs and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.
qas: answers: Alphanumeric
question: What type of LEDs are available in seven-segment format?

answers: dot-matrix
question: What is another format that Alphanumeric LEDs are available in?

answers: Starburst
question: Which alphanumeric LED display can display all letters?

answers: 5x7
question: What type of pixels does a dot matrix display use?

answers: liquid crystal displays
question: What has reduced the popularity of numeric LED displays?

context: Digital-RGB LEDs are RGB LEDs that contain their own "smart" control electronics. In addition to power and ground, these provide connections for data-in, data-out, and sometimes a clock or strobe signal. These are connected in a daisy chain, with the data in of the first LED sourced by a microprocessor, which can control the brightness and color of each LED independently of the others. They are used where a combination of maximum control and minimum visible electronics are needed such as strings for Christmas and LED matrices. Some even have refresh rates in the kHz range, allowing for basic video applications.
qas: answers: contain their own "smart" control electronics
question: What makes RGB LEDs different?

answers: in a daisy chain
question: How are Digital-RGB LED strobe signals connected?

answers: microprocessor
question: What object sources the data in of the first LED of a digital rgb LED?

answers: control the brightness and color of each LED independently of the others
question: The microprocessor does what in a digital RGB LED?

answers: Christmas
question: What is one example of where Digital RGB LED lights are used?

context: An LED filament consists of multiple LED dice connected in series on a common longitudinal substrate that form a thin rod reminiscent of a traditional incandescent filament. These are being used as a low cost decorative alternative for traditional light bulbs that are being phased out in many countries. The filaments require a rather high voltage to light to nominal brightness, allowing them to work efficiently and simply with mains voltages. Often a simple rectifier and capacitive current limiting are employed to create a low-cost replacement for a traditional light bulb without the complexity of creating a low voltage, high current converter which is required by single die LEDs. Usually they are packaged in a sealed enclosure with a shape similar to lamps they were designed to replace (e.g. a bulb), and filled with inert nitrogen or carbon dioxide gas to remove heat efficiently.
qas: answers: multiple LED dice
question: What does an LED filament consist of?

answers: a low cost decorative alternative for traditional light bulbs
question: How are LED filaments used?

answers: high
question: What type of voltage is needed for LED filaments?

answers: a simple rectifier
question: What helps LED filaments remain low cost?

answers: high current converter
question: Single die LEDs require what?

context: The current–voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation). This means that a small change in voltage can cause a large change in current. If the applied voltage exceeds the LED's forward voltage drop by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is to use constant-current power supplies to keep the current below the LED's maximum current rating. Since most common power sources (batteries, mains) are constant-voltage sources, most LED fixtures must include a power converter, at least a current-limiting resistor. However, the high resistance of three-volt coin cells combined with the high differential resistance of nitride-based LEDs makes it possible to power such an LED from such a coin cell without an external resistor.
qas: answers: the current is dependent exponentially on the voltage
question: How are LEDs similar to other diodes?

answers: use constant-current power supplies
question: What is a solution to preventing an LED failure?

answers: a small change in voltage
question: What can cause a large change in current in LEDs?

answers: batteries
question: What is a constant-voltage source?

answers: a power converter
question: What feature do most LED fixtures need to have?

context: The vast majority of devices containing LEDs are "safe under all conditions of normal use", and so are classified as "Class 1 LED product"/"LED Klasse 1". At present, only a few LEDs—extremely bright LEDs that also have a tightly focused viewing angle of 8° or less—could, in theory, cause temporary blindness, and so are classified as "Class 2". The opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) of 2010, on the health issues concerning LEDs, suggested banning public use of lamps which were in the moderate Risk Group 2, especially those with a high blue component in places frequented by children. In general, laser safety regulations—and the "Class 1", "Class 2", etc. system—also apply to LEDs.
qas: answers: Class 1 LED product
question: How are most LEDs classified?

answers: safe under all conditions of normal use
question: What does being a Class 1 LED product mean?

answers: extremely bright LEDs
question: What type of LED can possibly cause blindness?

answers: French
question: Which government advocated the banning of Class 2 LEDs?

answers: Class 2
question: What class are extremely bright LEDs listed as?

context: While LEDs have the advantage over fluorescent lamps that they do not contain mercury, they may contain other hazardous metals such as lead and arsenic. Regarding the toxicity of LEDs when treated as waste, a study published in 2011 stated: "According to federal standards, LEDs are not hazardous except for low-intensity red LEDs, which leached Pb [lead] at levels exceeding regulatory limits (186 mg/L; regulatory limit: 5). However, according to California regulations, excessive levels of copper (up to 3892 mg/kg; limit: 2500), lead (up to 8103 mg/kg; limit: 1000), nickel (up to 4797 mg/kg; limit: 2000), or silver (up to 721 mg/kg; limit: 500) render all except low-intensity yellow LEDs hazardous."
qas: answers: arsenic
question: What dangerous metal can LEDs contain?

answers: mercury
question: What substance does fluorescent lamps contain?

answers: low-intensity red
question: Which LEDs are considered dangerous by a 2011 study?

answers: lead
question: According to a California study, what harmful metal is in most LEDs?

answers: low-intensity yellow LEDs
question: What LEDs are considered safer than any other?

context: One-color light is well suited for traffic lights and signals, exit signs, emergency vehicle lighting, ships' navigation lights or lanterns (chromacity and luminance standards being set under the Convention on the International Regulations for Preventing Collisions at Sea 1972, Annex I and the CIE) and LED-based Christmas lights. In cold climates, LED traffic lights may remain snow-covered. Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, e.g. night time animal watching and military field use.
qas: answers: One-color light
question: What type of light is ideal for traffic signals?

answers: 1972
question: In what year were luminescence standards set?

answers: Red or yellow
question: What color LEDs are used when night vision is important?

answers: astronomy observatories
question: What is an example of a night vision needed area?

answers: exit signs
question: What is another use for one-color light?

context: Because of their long life, fast switching times, and their ability to be seen in broad daylight due to their high output and focus, LEDs have been used in brake lights for cars' high-mounted brake lights, trucks, and buses, and in turn signals for some time, but many vehicles now use LEDs for their rear light clusters. The use in brakes improves safety, due to a great reduction in the time needed to light fully, or faster rise time, up to 0.5 second faster[citation needed] than an incandescent bulb. This gives drivers behind more time to react. In a dual intensity circuit (rear markers and brakes) if the LEDs are not pulsed at a fast enough frequency, they can create a phantom array, where ghost images of the LED will appear if the eyes quickly scan across the array. White LED headlamps are starting to be used. Using LEDs has styling advantages because LEDs can form much thinner lights than incandescent lamps with parabolic reflectors.
qas: answers: brake lights for cars
question: Because of their high output, LED lights are very useful where?

answers: their long life
question: Why are LED lights sought after for various applications?

answers: 0.5 second
question: LED brake lights are how many times faster than incandescent ones?

answers: White
question: What color LEDs are now starting to be used more?

answers: thinner
question: What types of light can LEDs form better than incandescent?

context: Assistive listening devices in many theaters and similar spaces use arrays of infrared LEDs to send sound to listeners' receivers. Light-emitting diodes (as well as semiconductor lasers) are used to send data over many types of fiber optic cable, from digital audio over TOSLINK cables to the very high bandwidth fiber links that form the Internet backbone. For some time, computers were commonly equipped with IrDA interfaces, which allowed them to send and receive data to nearby machines via infrared.
qas: answers: theaters
question: Where are infrared LEDs used in everday life?

answers: to send sound to listeners' receivers
question: How are LEDs used in theaters?

answers: fiber optic
question: LEDs can send data over what type of cable?

answers: very high bandwidth
question: What type of fiber forms the backbone of the internet?

context: In the US, one kilowatt-hour (3.6 MJ) of electricity currently causes an average 1.34 pounds (610 g) of CO
2 emission. Assuming the average light bulb is on for 10 hours a day, a 40-watt bulb will cause 196 pounds (89 kg) of CO
2 emission per year. The 6-watt LED equivalent will only cause 30 pounds (14 kg) of CO
2 over the same time span. A building’s carbon footprint from lighting can therefore be reduced by 85% by exchanging all incandescent bulbs for new LEDs if a building previously used only incandescent bulbs.
qas: answers: US
question: In what country does one kilowatt-hour of electricity causes 1.34 pounds of CO 2 emission?

answers: 196 pounds
question: How much CO2 emission would a 40-watt light bulb produce after 10 hours?

answers: 30 pounds
question: A 6-watt LED left on for 10 hours a day will emit how much CO 2?

answers: 85%
question: How much can a building's carbon footprint be reduced by switching to LEDs?

context: Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used for this purpose, and this is likely to remain one of their major uses until the price drops low enough to make signaling and illumination uses more widespread. Barcode scanners are the most common example of machine vision, and many low cost products use red LEDs instead of lasers. Optical computer mice are an example of LEDs in machine vision, as it is used to provide an even light source on the surface for the miniature camera within the mouse. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:
qas: answers: Machine vision
question: LEDs are often used for what type of systems?

answers: so features of interest are easier to process
question: Why are LEDs preferred for machine vision systems?

answers: price drops
question: What can help make LEDs more widely used?

answers: Barcode scanners
question: What is the most common example of a machine vision system?

answers: Optical computer mice
question: Where are some LEDs in machine vision systems found?

context: The light from LEDs can be modulated very quickly so they are used extensively in optical fiber and free space optics communications. This includes remote controls, such as for TVs, VCRs, and LED Computers, where infrared LEDs are often used. Opto-isolators use an LED combined with a photodiode or phototransistor to provide a signal path with electrical isolation between two circuits. This is especially useful in medical equipment where the signals from a low-voltage sensor circuit (usually battery-powered) in contact with a living organism must be electrically isolated from any possible electrical failure in a recording or monitoring device operating at potentially dangerous voltages. An optoisolator also allows information to be transferred between circuits not sharing a common ground potential.
qas: answers: free space optics communications
question: Where are LEDs often used?

answers: medical equipment
question: Where are opto-isolators found?

answers: remote controls
question: What is an example of a device that uses free space optic communications?

answers: allows information to be transferred between circuits not sharing a common ground potential
question: What does an optoisolator do?

answers: LED Computers
question: In what common household item can you find infrared LEDs?

context: Many sensor systems rely on light as the signal source. LEDs are often ideal as a light source due to the requirements of the sensors. LEDs are used as motion sensors, for example in optical computer mice. The Nintendo Wii's sensor bar uses infrared LEDs. Pulse oximeters use them for measuring oxygen saturation. Some flatbed scanners use arrays of RGB LEDs rather than the typical cold-cathode fluorescent lamp as the light source. Having independent control of three illuminated colors allows the scanner to calibrate itself for more accurate color balance, and there is no need for warm-up. Further, its sensors only need be monochromatic, since at any one time the page being scanned is only lit by one color of light. Since LEDs can also be used as photodiodes, they can be used for both photo emission and detection. This could be used, for example, in a touchscreen that registers reflected light from a finger or stylus. Many materials and biological systems are sensitive to, or dependent on, light. Grow lights use LEDs to increase photosynthesis in plants, and bacteria and viruses can be removed from water and other substances using UV LEDs for sterilization.
qas: answers: Nintendo Wii
question: What video game console uses infrared LEDs?

answers: Pulse oximeters
question: What device uses infrared LEDs to measure oxygen saturation?

answers: RGB LEDs
question: Some flatbed scanners use what type of LED?

answers: warm-up
question: By using LEDs, scanners do not have to what?

answers: increase photosynthesis in plants
question: Grow lights use LEDs for what process?

context: LEDs have also been used as a medium-quality voltage reference in electronic circuits. The forward voltage drop (e.g. about 1.7 V for a normal red LED) can be used instead of a Zener diode in low-voltage regulators. Red LEDs have the flattest I/V curve above the knee. Nitride-based LEDs have a fairly steep I/V curve and are useless for this purpose. Although LED forward voltage is far more current-dependent than a Zener diode, Zener diodes with breakdown voltages below 3 V are not widely available.
qas: answers: medium-quality
question: What quality has LEDs been used as?

answers: Red
question: What LED has the flattest I/V curve above the knee?

answers: Nitride-based LEDs
question: What LEDs have a very steep I/V curve?

answers: Zener
question: LED forward voltage is more current-dependent than what diode?

answers: 3 V
question: Zener diodes below what voltage are not widely available?