nc33/MultiSpan_SQUAD huggingface dataset:
Light-emitting_diode

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]

Question: What are cladding layers?
Answer: active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN

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

Question: What does AlGaN stand for?
Answer: Aluminium gallium nitride

Question: What LEDs are more efficient when produced from the InGaN/GaN systems than without?
Answer: Green
Light-emitting_diode

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).

Question: What substance does nitrides contain?
Answer: aluminium

Question: What sort of LEDs are becoming more available on the market?
Answer: Ultraviolet

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

Question: Shorter wavelength diodes provide wavelengths as low as what?
Answer: 240 nm

Question: What UV wavelengths are found in sterilization devices?
Answer: 250–270 nm
Light-emitting_diode

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]

Question: What colors are used to form white light?
Answer: red, green, and blue

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

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

Question: What is another name to reference the multi-color white LED method?
Answer: RGB LEDs
Light-emitting_diode

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.

Question: What is a factor that may be different in the various types of multi-color white LEDs?
Answer: luminous efficacy

Question: Higher efficiency in multi-color white LEDs may mean what?
Answer: lower color rendering

Question: What is one type of multi-color white LED?
Answer: tetrachromatic

Question: What type has the best luminous efficacy?
Answer: dichromatic white LEDs

Question: What luminous efficacy does trichromatic white LEDs have?
Answer: >70 lm/W
Light-emitting_diode

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.

Question: Multi-color LEDs offer what else besides the formation of white light?
Answer: to form light of different colors

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

Question: What problem results when rising temperatures decays power?
Answer: substantial change in color stability
Light-emitting_diode

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.

Question: What method involves coating LEDs of one color with phosphors of different colors?
Answer: phosphor-converted white LEDs (pcLEDs)

Question: In pcLEDs method, a fraction of what light is used?
Answer: blue

Question: What shift does blue light undergo in the pcLEDs method?
Answer: Stokes

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

Question: What broadens the emitted spectrum in a pcLEDs method?
Answer: If several phosphor layers of distinct colors are applied
Light-emitting_diode

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.

Question: What do phosphor-based LEDs luminous efficacies depend on?
Answer: the spectral distribution of the resultant light output

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

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

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

Question: What type of emitter is used in phosphor-based white LED methods?
Answer: monochrome
Light-emitting_diode

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.

Question: What can improve the efficiency of LED-based white light?
Answer: more efficient phosphors

Question: What is the most efficient yellow phosphor?
Answer: YAG phosphor

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

Question: What area are scientists looking into regarding phosphor LED development?
Answer: higher operation temperatures

Question: What is one method that can raise the efficiency of phosphor-based LEDs?
Answer: adapting better package design
Light-emitting_diode

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.

Question: White LEDs can be made by coating what?
Answer: near-ultraviolet (NUV) LEDs

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

Question: What device also works in a similar way as NUV LEDs?
Answer: fluorescent lamps

Question: The method of coating NUVs less efficient than what other LEDs?
Answer: blue

Question: What light can harm human eyes or skin?
Answer: UV light
Light-emitting_diode

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.

Question: What is being used to produce white LEDs?
Answer: wafers composed of gallium-nitride-on-silicon

Question: What size are the wafers used to create white LEDs?
Answer: 200-mm

Question: By using silicon wafers, what is being avoided?
Answer: costly sapphire substrate

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

Question: By what year will% of all GaN LEDs be made with gallium-nitride-on-silicon wafers?
Answer: 2020
Light-emitting_diode

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.

Question: What nanocrystals possess unique optical properties?
Answer: Quantum dots

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

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

Question: How many types of schemes are there in Quantum Dot LED excitation?
Answer: two
Light-emitting_diode

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.

Question: How many lumens can some high-power LEDs emit?
Answer: over a thousand

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

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

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

Question: What can one high-power LED replace?
Answer: incandescent bulb in a flashlight
Light-emitting_diode

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.

Question: What company has developed LEDs that can operate on AC power?
Answer: Seoul Semiconductor

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

Question: When did Seoul Semiconductor release the first high DC voltage LED?
Answer: 2009

Question: What is so good about ac powered HP-LEDs?
Answer: more flexibility

Question: What did Seoul Semiconductor name their ac powered HP-LED?
Answer: Acrich MJT
Light-emitting_diode

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.

Question: What type of LEDs are available in seven-segment format?
Answer: Alphanumeric

Question: What is another format that Alphanumeric LEDs are available in?
Answer: dot-matrix

Question: Which alphanumeric LED display can display all letters?
Answer: Starburst

Question: What type of pixels does a dot matrix display use?
Answer: 5x7

Question: What has reduced the popularity of numeric LED displays?
Answer: liquid crystal displays
Light-emitting_diode

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.

Question: What makes RGB LEDs different?
Answer: contain their own "smart" control electronics

Question: How are Digital-RGB LED strobe signals connected?
Answer: in a daisy chain

Question: What object sources the data in of the first LED of a digital rgb LED?
Answer: microprocessor

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

Question: What is one example of where Digital RGB LED lights are used?
Answer: Christmas
Light-emitting_diode

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.

Question: What does an LED filament consist of?
Answer: multiple LED dice

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

Question: What type of voltage is needed for LED filaments?
Answer: high

Question: What helps LED filaments remain low cost?
Answer: a simple rectifier

Question: Single die LEDs require what?
Answer: high current converter
Light-emitting_diode

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.

Question: How are LEDs similar to other diodes?
Answer: the current is dependent exponentially on the voltage

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

Question: What can cause a large change in current in LEDs?
Answer: a small change in voltage

Question: What is a constant-voltage source?
Answer: batteries

Question: What feature do most LED fixtures need to have?
Answer: a power converter
Light-emitting_diode

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.

Question: How are most LEDs classified?
Answer: Class 1 LED product

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

Question: What type of LED can possibly cause blindness?
Answer: extremely bright LEDs

Question: Which government advocated the banning of Class 2 LEDs?
Answer: French

Question: What class are extremely bright LEDs listed as?
Answer: Class 2
Light-emitting_diode

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."

Question: What dangerous metal can LEDs contain?
Answer: arsenic

Question: What substance does fluorescent lamps contain?
Answer: mercury

Question: Which LEDs are considered dangerous by a 2011 study?
Answer: low-intensity red

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

Question: What LEDs are considered safer than any other?
Answer: low-intensity yellow LEDs