LED | Definition, Light, & Facts | Britannica
2024.10.13 21:25Subscribe Subscribe Login Home History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture Money Games & Quizzes Videos On This Day One Good Fact Dictionary New Articles History & Society Lifestyles & Social Issues Philosophy & Religion Politics, Law & Government World History Science & Tech Health & Medicine Science Technology Biographies Browse Biographies Animals & Nature Birds, Reptiles & Other Vertebrates Bugs, Mollusks & Other Invertebrates Environment Fossils & Geologic Time Mammals Plants Geography & Travel Geography & Travel Arts & Culture Entertainment & Pop Culture Literature Sports & Recreation Visual Arts Companions Demystified Image Galleries Infographics Lists Podcasts Spotlight Summaries The Forum Top Questions #WTFact 100 Women Britannica Kids Saving Earth Space Next 50 Student Center Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture Money Videos LED Table of Contents Introduction References & Edit History Quick Facts & Related Topics Images & Videos Discover How Do Hurricanes Get Their Names? What Causes the Northern and Southern Lights? How Many Electoral College Votes Does Each U.S. State Have? 6 of the World’s Deadliest Natural Disasters Inventors and Inventions of the Industrial Revolution What's the Difference Between a Solstice and an Equinox? 9 Things You Might Not Know About Adolf Hitler Contents Technology The Web & Communication Light-emitting diodes have largely replaced older lighting technologies, such as incandescent bulbs While incandescent bulbs typically abruptly burn out or stop working, LED lights dim over time. (more)
LED
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External Websites Khan Academy - LED working and advantages Engineering LibreTexts - Light Emitting Diode The University of Mississippi - Department of Physics and Astronomy - pn Junction Devices and Light Emitting Diodes Energy.gov - LED Basics National Center for Biotechnology Information - PubMed Central - Light-emitting Diodes Print Cite verified Cite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/technology/LED Feedback External Websites Feedback Thank you for your feedbackOur editors will review what you’ve submitted and determine whether to revise the article.
External Websites Khan Academy - LED working and advantages Engineering LibreTexts - Light Emitting Diode The University of Mississippi - Department of Physics and Astronomy - pn Junction Devices and Light Emitting Diodes Energy.gov - LED Basics National Center for Biotechnology Information - PubMed Central - Light-emitting Diodes Also known as: light-emissive diode, light-emitting diode Written and fact-checked by The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors. The Editors of Encyclopaedia Britannica Last Updated: Sep 13, 2024 • Article History Table of Contents In full: light-emitting diode (Show more) Key People: John J. Hopfield Shuji Nakamura Nick Holonyak, Jr. Akasaki Isamu Amano Hiroshi (Show more) Related Topics: semiconductor diode electro-optical transmitter (Show more) See all related content Ask the Chatbot a Question Ask the Chatbot a QuestionLED , in electronics , a semiconductor device that emits infrared or visible light when charged with an electric current . LED displays began to be used for consumer electronic devices starting in 1968, when Hewlett-Packard (HP) introduced the first LED display. Visible LED lights are used in many electronic devices as indicator lamps, car brake lights, and as alphanumeric displays or even full-color posters on billboards and signs. Infrared LEDs are employed in autofocus cameras and television remote controls and also as light sources in fiber-optic telecommunication systems.
The familiar but now outdated light bulb gave off light through incandescence, a phenomenon in which the heating of a wire filament by an electric current causes the wire to emit photons , the basic energy packets of light. Incandescent light bulbs were gradually phased out in the United States starting in 2007 with the Energy Independence and Security Act. They were fully banned in the European Union (EU) starting in 2012. In 2023 the Biden administration’s ban on the manufacture and sale of incandescent bulbs took effect.
LEDs, on the other hand, operate by electroluminescence , in which the emission of photons is caused by electronic excitation of a material. The material used most often in LEDs is gallium arsenide , though there are many variations on this basic compound , such as aluminum gallium arsenide or aluminum gallium indium phosphide. These compounds are members of the “III-V” group of semiconductors—that is, compounds made of elements listed in columns III and V of the periodic table . Varying the precise composition of the semiconductor can alter the wavelength (and therefore the color) of the emitted light.
LED emission is generally in the visible part of the light spectrum (i.e., with wavelengths from 0.4 to 0.7 micrometer) or in the near-infrared section (with wavelengths between 0.78 and 2.5 micrometers). The brightness of the light observed from an LED depends on the power emitted by the LED and on the relative sensitivity of the eye at the emitted wavelength. Maximum sensitivity occurs at 0.555 micrometer, which is in the yellow-orange and green region. The applied voltage in most LEDs is quite low, about 2.0 volts. The current depends on the application and ranges from a few milliamperes to several hundred milliamperes.
The term diode refers to the twin-terminal structure of the light-emitting device. In a flashlight, for example, a wire filament is connected to a battery through two terminals , one (the anode) bearing the negative electric charge and the other (the cathode) bearing the positive charge. In LEDs, as in other semiconductor devices such as transistors , the “terminals” are actually two semiconductor materials of different composition and electronic properties brought together to form a junction. In one material (the negative, or n -type, semiconductor) the charge carriers are electrons, and in the other (the positive, or p -type, semiconductor) the charge carriers are “holes” created by the absence of electrons. Under the influence of an electric field (supplied by a battery, for instance, when the LED is switched on), current can be made to flow across the p - n junction, providing the electronic excitation that causes the material to emanate light.
In a typical LED structure the clear epoxy dome serves as a structural element to hold the lead frame together, as a lens to focus the light, and as a refractive index match to permit more light to escape from the LED chip . The chip, typically 250 × 250 × 250 micrometers in dimension, is mounted in a reflecting cup formed in the lead frame. The p - n -type GaP:N layers represent nitrogen added to gallium phosphide to give green emission; the p - n -type GaAsP:N layers represent nitrogen added to gallium arsenide phosphide to give orange and yellow emission; and the p -type GaP:Zn,O layer represents zinc and oxygen added to gallium phosphide to give red emission. Two further enhancements, developed in the 1990s, are LEDs based on aluminum gallium indium phosphide, which emit light efficiently from green to red-orange, and also blue-emitting LEDs based on silicon carbide or gallium nitride. Blue LEDs can be combined on a cluster with other LEDs to give all colors, including white, for full-color moving displays.
A classic LED digital clock LED clocks were fairly common before LEDs were used as mainstream lighting. (more)Any LED can be used as a light source for a short-range fiber-optic transmission system—that is, over a distance of less than 100 meters (330 feet). For long-range fiber optics , however, the emission properties of the light source are selected to match the transmission properties of the optical fiber, and in this case the infrared LEDs are a better match than the visible-light LEDs. Glass optical fibers suffer their lowest transmission losses in the infrared region at wavelengths of 1.3 and 1.55 micrometers. To match these transmission properties, LEDs are employed that are made of gallium indium arsenide phosphide layered on a substrate of indium phosphide. The exact composition of the material may be adjusted to emit energy precisely at 1.3 or 1.55 micrometers.
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