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A light-emitting diode ( LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons.
- Light-emitting Diode Physics
Light-emitting diodes (LEDs) produce light (or infrared...
- Led Wallpaper
LED wallpaper. LED wallpaper is the integration of...
- Cat's-Whisker Detector
Crystal radios had no amplifying components to increase the...
- Seven-segment Display
A typical 7-segment LED display component, with decimal...
- Electroluminescence
Views of a liquid crystal display, both with...
- Phosphor
Example of phosphorescence Monochrome monitor Aperture...
- Lawyers' Edition
The United States Supreme Court Reports, Lawyers' Edition,...
- Wikipedia
Wikipedia is a free online encyclopedia, created and edited...
- Light-emitting Diode Physics
- Basic Circuit
- Power Source Considerations
- MOSFET Drivers
- Series Resistor
- Led Arrays
- Led Display
- Polarity
- Pulsed Operation
- Led as A Light Sensor
- See Also
The simplest circuit to drive an LED is through a series resistor. It is commonly used for indicators and digital displays in many consumer appliances. However, this circuit is not energy-efficient, because energy is dissipated in the resistor as heat. An LED has a voltage drop specified at the intended operating current. Ohm's law and Kirchhoff's ...
The voltage versus current characteristics of an LED is similar to any diode. Current is approximately an exponential function of voltage according to the Shockley diode equation, and a small voltage change may result in a large change in current. If the voltage is below or equal to the threshold no current flows and the result is an unlit LED. If ...
An active constant current source is commonly used for high power LEDs, stabilizing light output over a wide range of input voltages which might increase the useful life of batteries. Active constant current is typically regulated using a depletion-mode MOSFET (metal–oxide–semiconductor field-effect transistor), which is the simplest current limite...
Series resistorsare a simple way to stabilize the LED current, but energy is wasted in the resistor. Miniature indicator LEDs are normally driven from low voltage DC via a current-limiting resistor. Currents of 2 mA, 10 mA and 20 mA are common. Sub-mA indicators may be made by driving ultrabright LEDs at very low current. Efficiency tends to reduce...
Strings of multiple LEDs are normally connected in series. In one configuration, the source voltage must be greater than or equal to the sum of the individual LED voltages; typically the LED voltages add up to around two-thirds of the supply voltage. A single current-limiting resistor may be used for each string. Parallel operation is also possible...
LEDs are often arranged in ways such that each LED (or each string of LEDs) can be individually turned on and off. Direct drive is the simplest-to-understand approach—it uses many independent single-LED (or single-string) circuits.For example, a person could design a digital clock such that when the clock displays "12:34" on a seven-segment display...
Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will only light with the correct electrical polarity. When the voltage across the p-n junction is in the correct direction, a significant current flows and the device is said to be forward-biased. If the voltage is of the wrong polarity, the device is said...
Many systems pulse LEDs on and off, by applying power periodically or intermittently. So long as the flicker rate is greater than the human flicker fusion threshold, and the LED is stationary relative to the eye, the LED will appear to be continuously lit. Varying the on/off ratio of the pulses is known as pulse-width modulation(PWM). In some cases...
In addition to emission, an LED can be used as a photodiode in light detection. This capability may be used in a variety of applications including ambient lightdetection and bidirectional communications. As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. For example, a green LED is sens...
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 lamp or LED light [1] is an electric light that produces light using light-emitting diodes (LEDs). LED lamps are significantly more energy-efficient than equivalent incandescent lamps and fluorescent lamps.
