Elsevier Science. August 1, 2025. p > 자유게시판

• 목록
• 답변
• 글쓰기
• 게시판 리스트 옵션
  • 수정
  • 삭제

A light-emitting diode (LED) is a semiconductor device that emits mild when present flows via it. Electrons in the semiconductor recombine with electron holes, releasing energy within the form of photons. The coloration of the sunshine (corresponding to the vitality of the photons) is determined by the power required for electrons to cross the band gap of the semiconductor. White mild is obtained by using multiple semiconductors or a layer of mild-emitting phosphor on the semiconductor device. Showing as practical electronic parts in 1962, the earliest LEDs emitted low-depth infrared (IR) light. Infrared LEDs are used in distant-management circuits, such as those used with a wide number of consumer electronics. The first seen-mild LEDs were of low intensity and EcoLight products limited to crimson. Early LEDs had been typically used as indicator lamps, changing small incandescent bulbs, and in seven-section shows. Later developments produced LEDs out there in seen, ultraviolet (UV), and infrared wavelengths with excessive, low, EcoLight solar bulbs or intermediate gentle output; for reduce energy consumption example, white LEDs appropriate for room and out of doors lighting.

LEDs have additionally given rise to new types of displays and sensors, whereas their high switching rates have makes use of in advanced communications know-how. LEDs have been utilized in diverse applications corresponding to aviation lighting, fairy lights, strip lights, automotive headlamps, advertising, stage lighting, basic lighting, traffic indicators, camera flashes, lighted wallpaper, horticultural develop lights, and medical devices. LEDs have many advantages over incandescent mild sources, including decrease energy consumption, an extended lifetime, improved physical robustness, smaller sizes, and sooner switching. In alternate for these usually favorable attributes, disadvantages of LEDs embody electrical limitations to low voltage and generally to DC (not AC) reduce energy consumption, the inability to provide steady illumination from a pulsing DC or an AC electrical provide source, and a lesser maximum operating temperature and storage temperature. LEDs are transducers of electricity into light. They operate in reverse of photodiodes, which convert light into electricity. Electroluminescence from a strong state diode was discovered in 1906 by Henry Joseph Round of Marconi Labs, and was printed in February 1907 in Electrical World.

Round observed that numerous carborundum (silicon carbide) crystals would emit yellow, gentle green, orange, or blue gentle when a voltage was passed between the poles. From 1968, business LEDs had been extraordinarily costly and noticed no sensible use. In the early 1990s, Shuji Nakamura, Hiroshi Amano and Isamu Akasaki developed blue mild-emitting diodes that were dramatically more environment friendly than their predecessors, bringing a new generation of shiny, power-efficient white lighting and full-color LED shows into practical use. For this work, they received the 2014 Nobel Prize in Physics. In a light-emitting diode, the recombination of electrons and electron holes in a semiconductor produces gentle (infrared, seen or UV), a course of called electroluminescence. The wavelength of the sunshine depends upon the power band gap of the semiconductors used. Since these materials have a high index of refraction, design options of the devices equivalent to particular optical coatings and die form are required to efficiently emit gentle. Unlike a laser, the sunshine emitted from an LED is neither spectrally coherent nor even highly monochromatic.

Its spectrum is sufficiently narrow that it appears to the human eye as a pure (saturated) coloration. Additionally in contrast to most lasers, its radiation will not be spatially coherent, so it can't method the very excessive intensity characteristic of lasers. By selection of various semiconductor materials, single-color LEDs might be made that emit light in a slender band of wavelengths, from the near-infrared via the visible spectrum and into the ultraviolet vary. The required operating voltages of LEDs enhance as the emitted wavelengths become shorter (increased vitality, red to blue), due to their growing semiconductor band gap. Blue LEDs have an energetic 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 different from violet to amber. Aluminium gallium nitride (AlGaN) of varying Al/Ga fraction can be utilized to manufacture the cladding and quantum nicely layers for ultraviolet LEDs, however these devices have not but reached the extent of effectivity and technological maturity of InGaN/GaN blue/inexperienced gadgets.

If unalloyed GaN is used on this case to type the active quantum nicely layers, the machine emits close to-ultraviolet mild with a peak wavelength centred around 365 nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than inexperienced LEDs produced with non-nitride materials techniques, however sensible devices still exhibit effectivity too low for high-brightness purposes. With AlGaN and AlGaInN, even shorter wavelengths are achievable. Near-UV emitters at wavelengths round 360-395 nm are already low-cost and infrequently encountered, for instance, as black mild lamp replacements for inspection of anti-counterfeiting UV watermarks in documents and bank notes, and for UV curing. Substantially more expensive, shorter-wavelength diodes are commercially accessible for wavelengths down to 240 nm. Because 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 anticipated in potential disinfection and sterilization gadgets. Latest analysis has proven that commercially out there UVA LEDs (365 nm) are already effective disinfection and sterilization devices.