The LED History

LED’s (light emitting diodes) are semiconductor devices that are designed to convert electrical energy to light when powered in a specific way. The construction and electrical behavior of the LED is similar to that of a rectifier diode that is used to convert alternating current to direct current.

Just like the rectifier diode, the LED is made of a junction of semi conductive P-type and N-type materials that are connected to two terminals called anode and cathode respectively. This device will, like the rectifier diode, conduct electric current when its anode is positive with respect to its cathode and block current when the applied polarity is reversed.

The development of the LED begun in the early 20th century at the Marconi Labs where researcher Henry Round reported that certain semiconductor PN junction will produce light when forward biased.

During the middle 1920s, Oleg Vladimirovich Losev reported that he had developed an LED device. Further work by RCA, Texas instrument and General Electric led to the development of practical devices for the purpose of light indicators during the sixties and seventies.

LED’s remained as light indicators until the early nineties when work by Shuji Nakamura of Nichia Corporation developed the high brightness blue LED. This development along with other developments in phosphor materials led to the development of a blue LED which when coated with a special phosphor produced a considerable amount of white light suitable for illumination.

The first commercial red LEDs were commonly used as replacements for incandescent indicators, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipments, then later in appliances such as TVs, radios, telephones, calculators, and even watches. These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Later, other colors became widely available and also appeared in appliances and equipment. As the LED materials technology became more advanced, the light output was increased, while maintaining the efficiency and the reliability to an acceptable level, causing LEDs to become bright enough to be used for illumination, in various applications such as lamps and other lighting fixtures.

Unlike incandescent light bulbs, which light up regardless of the electrical polarity, LEDs will only light with 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 to be reverse biased, very little current flows, and no light is emitted. LEDs can be operated on an alternating current voltage, but they will only light with positive voltage, causing the LED to turn on and off at the frequency of the AC supply.

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