Light-Emitting Diodes

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An optical disc is an electronic data storage medium that can be written to and read from using a low-powered laser beam. RAID 0 disk striping is the process of dividing a body of data into blocks and spreading the data blocks across multiple Fibre Channel is a high-speed networking technology primarily used for transmitting data among data centers, computer servers, Also see laser diode. This was last updated in September Login Forgot your password? Submit your e-mail address below. We'll send you an email containing your password. Your password has been sent to: Biard worked on varactor diodes which led to the LED as we know it.

Read the full story of their work with this PDF here. Round discovered electroluminescence when using silicon carbide and a cats whisker. Oleg Losev independently discovered the phenomena the same year. Losev studied the phenomena of light emitting diodes in radio sets. In he published a detailed report but his work was not well known until the s when his papers resurfaced.

This was the first modern LED. The discovery was made during a test of a tunnel diode using a zinc diffused area of a GaAs Gallium Arsenide semi-insulating substrate. He had started working in with semiconductor GaAs for the creation of early solar cells. He also develops a brighter red LED. It wouldn't be until the s that the blue LED would become low cost for commercial production.

Pearsall develops special high brightness LEDs for fiber optic use. This improves communications technology worldwide. Organic Light Emitting Diodes. What is an OLED? At least one of the electrodes is transparent so the photons can escape. The semiconductor in an OLED is organic which means it contains carbon.

The OLED uses one of two kinds of compounds: Read more about how it works below.

light-emitting diode (LED)

Lamps - short distance indoor lamps produces a diffused light Displays - small: Until more research is done we will not know how these lamps with new materials compare with established technology. Displays computer monitors, televisions, mobile phone screens: The OLED display is made by using multiple layer construction along with transistors which control whether each pixel is on or off.

This is very similar to EL displays. One advantage is that does not need a cold cathode fluorescent backlight like an LCD. The lack of a backlight means it can better display blacks the back light always seeps through in black areas of the screen. The OLED display may also be made into a thin flexible material which could roll up like a newspaper. That may change as engineers work to increase luminosity. The diagram above is a simple modern OLED.

There are a many new ways to construct the OLED using a variety of layer configurations. Displays will have additional layers such as an active matrix TFT thin film transistor which control pixel regions. Early OLEDs had one layer of organic material between two electrodes. Modern OLEDs are bi-layer, they have an emissive layer and conductive layer sandwiched between two electrodes see diagram above. Electric current passes from the cathode to the anode. It passes through two layers of organic molecules. The first layer the electrons pass into what is called the emissive layer.

Electrons leave the conductive layer making 'holes' positive charge. Meanwhile in the emissive layer there are excessive electrons negative. When the electrons join the holes light is emitted. Light color is dependent on the materials used in the organic or polymer layers. The transistor allows the unit to be switched on and off. They have the properties of semiconductors yet are versatile and low cost to produce. The layers that emit light are similar to an ink and will be very cheap to manufacture once stable compounds and processes are developed.

Deeper understanding of these improvements requires a basic background in chemistry and physics, you also can read more detail here. OLEDs will allow for thinner TV and computer displays, transparent "heads up" displays, flexible displays, flat roll-on surface lights on the sides of buildings or vehicles, changing camouflage displays for military vehicles, new photovoltaic applications, and much more.

We can expect a lower production cost compared to LEDs due to less part assembly. At the moment OLEDs need more lab work to reach full potential.

How Light Emitting Diodes Work | HowStuffWorks

Carbon nanotube technology is being developed for use with the OLED. The mechanical robustness and long lifetime are used in automotive lighting on cars, motorcycles, and bicycle lights. LED light emission may be efficiently controlled by using nonimaging optics principles. LED street lights are employed on poles and in parking garages. In , the Italian village of Torraca was the first place to convert its entire illumination system to LEDs.

LEDs are used in aviation lighting. LEDs are also being used now in airport and heliport lighting. LED airport fixtures currently include medium-intensity runway lights, runway centerline lights, taxiway centerline and edge lights, guidance signs, and obstruction lighting.

The lack of IR or heat radiation makes LEDs ideal for stage lights using banks of RGB LEDs that can easily change color and decrease heating from traditional stage lighting, as well as medical lighting where IR-radiation can be harmful. In energy conservation, the lower heat output of LEDs also means air conditioning cooling systems have less heat in need of disposal. LEDs are small, durable and need little power, so they are used in handheld devices such as flashlights.

This is especially useful in cameras on mobile phones , where space is at a premium and bulky voltage-raising circuitry is undesirable. LEDs are used for infrared illumination in night vision uses including security cameras. A ring of LEDs around a video camera , aimed forward into a retroreflective background , allows chroma keying in video productions. LEDs are used in mining operations , as cap lamps to provide light for miners. Research has been done to improve LEDs for mining, to reduce glare and to increase illumination, reducing risk of injury to the miners.

LEDs are now used commonly in all market areas from commercial to home use: LEDs are increasingly finding uses in medical and educational applications, for example as mood enhancement, [] and new technologies such as AmBX , exploiting LED versatility. Light can be used to transmit data and analog signals.

For example, lighting white LEDs can be used in systems assisting people to navigate in closed spaces while searching necessary rooms or objects. 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. Because LEDs can cycle on and off millions of times per second, very high data bandwidth can be achieved. Efficient lighting is needed for sustainable architecture.

A typical watt LED lamp emitted to lumens, [] which is equivalent to a standard watt incandescent bulb. The latter has an expected lifespan of 1, hours, whereas an LED can continue to operate with reduced efficiency for more than 50, hours.

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In the US, one kilowatt-hour 3. The reduction in carbon emissions depends on the source of electricity. Nuclear power in the United States produced Replacing lights that spend the most time lit results in the most savings, so LED lights in infrequently used locations bring a smaller return on investment.

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. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:. LED daytime running lights of Audi A4. LED panel light source used in an experiment on plant growth. The findings of such experiments may be used to grow food in space on long duration missions.

A green surface-mount colored LED mounted on an Arduino circuit board. The light from LEDs can be modulated very quickly so they are used extensively in optical fiber and free space optics communications. 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 lets information be transferred between circuits that don't share a common ground potential. 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. 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. 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. LEDs have also been used as a medium-quality voltage reference in electronic circuits.

The forward voltage drop e. The progressive miniaturization of low-voltage lighting technology, such as LEDs and OLEDs , suitable to incorporate into low-thickness materials has fostered experimentation in combining light sources and wall covering surfaces for interior walls. Other solutions mainly exist as prototypes or are in the process of being further refined. From Wikipedia, the free encyclopedia.

For other uses, see LED disambiguation. Not to be confused with LCD. List of LED failure modes. Electrical polarity of LEDs.

Li-Fi and fibre optics. A large LED display behind a disc jockey. Traffic light using LED. Electronics portal Energy portal. Archived from the original PDF on September 15, Retrieved September 4, Biard and Gary Pittman, Filed on Aug. Massachusetts Institute of Technology. Archived from the original on October 9, Retrieved December 21, The American heritage science dictionary. Unified modelling of electroluminescence in nanostructures.

Ieee Engineering in Medicine and Biology Society. United States Environmental Protection Agency. Retrieved 20 June The design of CMOS radio-frequency integrated circuits. Journal de Chemie Physique. A; Jamgochian, E How It Got Started". Proceedings of the IEEE.

AF33 , Rept. Archived from the original on October 14, Archived from the original on March 28, Retrieved July 29, Archived from the original PDF on August 9, Retrieved May 30, Archived from the original PDF on October 24, Retrieved on March 16, Institute of Electrical and Electronics Engineers.

Retrieved June 21, Retrieved 28 September The Royal Swedish Academy of Sciences. Retrieved 17 March Physica status solidi a. Part 2 Solid State Technology. Archived from the original on Liquid phase epitaxy of electronic, optical, and optoelectronic materials. Archived from the original PDF on March 14, Retrieved August 13, Solid-state lighting won't supplant the lightbulb until it can overcome the mysterious malady known as droop.

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Physical Review Letters, Retrieved 23 April Archived from the original on April 10, Arnold, When the Lights Go Out: Will LEDs transform traffic signals as they did exit signs? Illuminating Engineering Society of North America. Energy-efficient Alternative for Commercial Refrigeration. Investigation of thermal management technique in blue LED airport taxiway fixtures. Fred Light-emitting diodes 2nd ed.

Archived June 11, , at the Wayback Machine. Archived April 13, , at the Wayback Machine. Takeda Award Achievement Facts Sheet. Retrieved November 28, Patent 5,,A "Highly insulating monocrystalline gallium nitride thin films " Issue date: Patent 5,, "Light-emitting gallium nitride-based compound semiconductor device" Issue date: The New York Times.

Retrieved October 7, Retrieved 7 December Archived from the original PDF on May 15, A comparison of two alternative methods". Electronics and Communications in Japan. Fred; Kim, Jong Kyu Archived from the original PDF on Retrieved January 3, Retrieved January 24, Retrieved January 30, Archived August 31, , at the Wayback Machine. S; Klement, P; Jones, A. J; Yan, J; Mandrus, D. H; Xu, X Retrieved October 21, Retrieved October 25, Archived from the original on March 13, Retrieved March 16, Retrieved February 17, Archived from the original PDF on January 16, Retrieved October 26, Retrieved on January 25, Archived April 29, , at the Wayback Machine.

The standard states that throughout the standard "light emitting diodes LED are included whenever the word "laser" is used. Archived from the original on January 8, The comments note that the AMA slogan "cool it and dim it" leads to some confusion, since this refers to lighting with cooler color temperatures, which is commonly perceived as having a warmer color.

Industry Applications Conference, US Department of Energy. Advantages of LED Lighting". Retrieved October 6, Retrieved September 3, Journal of Quantitative Spectroscopy and Radiative Transfer. Can we save energy and save the night? Retrieved 5 October Lamp Spectrum and Light Pollution.

Retrieved 10 April Good for prizes, bad for insects". Retrieved 7 October Retrieved 22 January

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