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 luminesce. 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. 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 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. The term diode refers to the twin-terminal structure of the light-emitting device. The applied voltage in most LEDs is quite low, in the region of 2.0 volts the current depends on the application and ranges from a few milliamperes to several hundred milliamperes. Maximum sensitivity occurs at 0.555 micrometre, which is in the yellow-orange and green region. 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. LED emission is generally in the visible part of the spectrum (i.e., with wavelengths from 0.4 to 0.7 micrometre) or in the near infrared (with wavelengths between 0.7 and 2.0 micrometres). By varying the precise composition of the semiconductor, the wavelength (and therefore the colour) of the emitted light can be changed. These compounds are members of the so-called III-V group of semiconductors-that is, compounds made of elements listed in columns III and V of the periodic table. 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. LEDs operate by electroluminescence, a phenomenon in which the emission of photons is caused by electronic excitation of a material. The familiar lightbulb gives 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. Infrared LEDs are employed in autofocus cameras and television remote controls and also as light sources in fibre-optic telecommunication systems. Visible LEDs are used in many electronic devices as indicator lamps, in automobiles as rear-window and brake lights, and on billboards and signs as alphanumeric displays or even full-colour posters. LED, in full light-emitting diode, in electronics, a semiconductor device that emits infrared or visible light when charged with an electric current. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning. ![]() ![]() 100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more. ![]()
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