praj-17/QA-MCQ-Open-ended huggingface dataset:
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

question: What is one scheme of Quantum Dot excitation? 

answer: electrical-excitation

question: What is one material used in electrical-excitation? 

answer: hole-transporting materials

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

answer: electrons and holes

question: A Quantum Dot LED has been used in what? 

answer: near-field scanning optical microscopy (NSOM)
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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.

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
Title: Light-emitting_diode
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."

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
Title: Light-emitting_diode
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.

question: What type of light is ideal for traffic signals? 

answer: One-color light

question: In what year were luminescence standards set? 

answer: 1972

question: What color LEDs are used when night vision is important? 

answer: Red or yellow

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

answer: astronomy observatories

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

answer: exit signs
Title: Light-emitting_diode
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.

question: Because of their high output, LED lights are very useful where? 

answer: brake lights for cars

question: Why are LED lights sought after for various applications? 

answer: their long life

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

answer: 0.5 second

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

answer: White

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

answer: thinner
Title: Light-emitting_diode
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.

question: Where are infrared LEDs used in everday life? 

answer: theaters

question: How are LEDs used in theaters? 

answer: to send sound to listeners' receivers

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

answer: fiber optic

question: What type of fiber forms the backbone of the internet? 

answer: very high bandwidth
Title: Light-emitting_diode
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.

question: In what country does one kilowatt-hour of electricity causes 1.34 pounds of CO 2 emission? 

answer: US

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

answer: 196 pounds

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

answer: 30 pounds

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

answer: 85%