Light-emitting diode

An LED is a special semiconductor which emits light when current is passed through it. There are many different physical styles. The emitted color spectrum is usually very narrow. It can generally be specified as a specific wavelength in the electromagnetic spectrum. The emitted color selection is somewhat limited. The most commonly available colors are red, green, amber, yellow, blue and white. The red, green, yellow and amber have a working voltage of approximately 1.8 volts. You can refer to the data sheet for each LED to find the exact value. The actual working voltage is determined by the breakdown voltage of the particular semiconductor material.

When using an LED in a circuit, the exact working voltage is not extremely important. The most important thing is the current flow through the LED. The current through the diode must be limited by a series resistor. An LED has a specified maximum continuous current rating. Most LEDs can pass 20 milliamps continuously without damage but it is not necessary to use the maximum rated current. An LED will light with much less current. The difference between high current and low current will be the brightness of the LED. To decide what resistor value is needed, you subtract the working (forward) voltage from the power supply voltage and divide that number by the desired current flow.

Working voltage (Vf)=1.8 volts

Desired current flow=15ma (.015 amps)

Power supply voltage=12 volts

12-1.8=10.2

10.2/.015=680 ohms

A light-emitting diode (LED) is an electronic light source. The LED was first invented in Russia in the 1920s, and introduced in America as a practical electronic component in 1962. Oleg Vladimirovich Losev was a radio technician who noticed that diodes used in radio receivers emitted light when current was passed through them. In 1927, he published details in a Russian journal of the first ever LED.

All early devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness.

LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. The LED is usually small in area (less than 1 mm²) with integrated optical components to shape its radiation pattern and assist in reflection.

LEDs present many advantages over traditional light sources including lower energy consumption, longer lifetime, improved robustness, smaller size and faster switching. However, they are relatively expensive and require more precise current and heat management than traditional light sources.

Applications of LEDs are diverse. They are used as low-energy indicators but also for replacements for traditional light sources in general lighting and automotive lighting. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in communications technology.