Light-emitting diode
A light-emitting diode (LED) is a semiconductor device that produces light from electricity. LEDs last a long time and do not break easily (compared to incandescent lightbulbs). They can produce many different colors. They are efficient - most of the energy turns into light, not heat.[1]
An LED is a type of diode that makes one color of light when electricity is sent through it in the expected direction (electrically biased in the forward direction). This effect is a kind of electroluminescence.[2]
The color of the light depends on the chemical composition of the semiconducting material used, and can be near-ultraviolet, visible or infrared.[3] The color affects how much electricity is used by the LED. [4] A white LED has either two or three LEDs inside, of different colors. Modern white LEDs used for general-purpose lighting have one single-color LED inside (usually blue but sometimes violet), combined with a phosphor that converts that single color to white.
LEDs are used in many places. Early LEDs could only emit infrared, and were used in optical fiber communication. Later ones were used as red indicator lights on many electronic devices, and in the 1980s they also made other colors. In the 21st century they are used for bright advertising signs, brake lights on cars, in TVs, and more recently, light bulbs for the home. White LEDs bright enough to illuminate rooms are usually more expensive than regular lightbulbs but they last longer and burn less electricity.
LEDs, which make their own light, should not be confused with LCDs, which block light. Some displays, however, mix the two technologies, using LEDs to backlight the LCD.
Today, some LEDs are surface-mount devices (SMD), so they can be very small.
Types
Light-emitting Diode Media
IEEE 315-1975 (1993) 8.5.4
Parts of a conventional LED. The flat bottom surfaces of the anvil and post embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled out via mechanical strain or vibration.
Close-up image of a surface-mount LED
Close-up of an LED with the voltage being increased and decreased to show a detailed view of its operation
A bulb-shaped modern retrofit LED lamp with aluminum heat sink, a light diffusing dome and E27 screw base, using a built-in power supply working on mains voltage
Blue light emitting diodes (Blue LED)
Herb Maruska original blue LED College of New Jersey Sarnoff Collection
Combined spectral curves for blue, yellow-green, and high-brightness red solid-state semiconductor LEDs. FWHM spectral bandwidth is approximately 24–27 nm for all three colors.
An RGB LED projecting red, green, and blue onto a surface
Spectrum of a white LED showing blue light directly emitted by the GaN-based LED (peak at about 465 nm) and the more broadband Stokes-shifted light emitted by the Ce3+:YAG phosphor, which emits at roughly 500–700 nm
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References
- ↑ "Greenlighting: a greener world". Archived from the original on 2012-05-14. Retrieved 2012-05-31.
- ↑ "Light emitting diode structure".
- ↑ "inventors". Archived from the original on 2010-04-01. Retrieved 2006-06-17.
- ↑ "Light emitting diodes (LEDs)". Archived from the original on 2012-05-11. Retrieved 2012-05-31.
- Nikolay Zheludev 2007. The life and times of the LED – a 100-year history. Nature Photonics. 1, 189–192. [1]. [2] Archived 2017-03-31 at the Wayback Machine is a full-text version.