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Internal Functioning of Light Emitting Diodes (LEDs) Explained

written by: Swagatam • edited by: Lamar Stonecypher • updated: 5/6/2010

The magnificent, beautiful, dazzling colors involved with LEDs may be quite bewitching to see. But do you really know how these effects are actually created in them or rather how do LED light bulbs work? The entire inside out of LEDs is explained in this article.

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    What are LEDs?

    As the name suggests, a LED (Light Emitting Diode) is basically a small light producing device that comes under “active" semiconductor electronic components. It’s quite comparable to the normal general purpose diode, with the only big difference being its capability to emit light in different colors. The two terminals (anode and cathode) of a LED when connected to a voltage source in the correct polarity, may produce lights of different colors, as per the semiconductor substance used inside it.

    From your cell phone to the large advertising display boards, the wide range of applications of these magical light bulbs can be witnessed almost everywhere. Today their popularity and applications are increasing rapidly due to some remarkable properties they have. Specifically, LEDs are very small in size, consume very little power, and are able to produce extremely high light intensity outputs.

    Unlike age-old incandescent bulbs, LEDs does not require red hot filaments to produce light. Rather it’s more effectively done through the passage of electrons and due to the band gap effect of its semiconductor material.

    Moreover, the heat generated in the process is negligibly small, thus there is no threat to the ever rising global warming problem, and LEDs are fast emerging as a better lighting solution compared to the other forms of modern lighting devices like FTLs and CFLs.

    LEDs that can emit lights invisible to the naked eye in the infrared and ultra violet range are also produced largely and find major application in remote control devices. Here we will discuss the functioning of the more popular ones, i.e. the visible light emitting type of LEDs.

    Let’s move on and study how LED light bulbs work.

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    How do LEDs work?

    LEDs emitting colored lights, image  

    Internal composition of a LED, diagram, Image  

    The following points will explain how LEDs work and how light is actually produced through them:

    • Visible light may be defined as waves as well as particles travelling at a constant speed (in vacuum). Precisely speaking, light is made up of particles having zero mass and is an energy released as a by- product by an electron moving within the orbits of an atom.

    • Centuries ago this was discovered by Sir Isaac Newton, he named these light particles as photons, the fundamental unit of light.

    • The material used in LEDs is basically aluminum-gallium-arsenide (AlGaAs). In its original state the atoms of this material is strongly bonded. Without free electrons, conduction of electricity becomes impossible here.

    • By adding an impurity, which is known as doping, extra atoms are introduced, effectively disturbing the balance of the material.

    • These impurities in the form of additional atoms are able either to provide free electrons (N-type) into the system or suck out some of the already existing electrons from the atoms (P-Type) creating “holes" in the atomic orbits. In both ways the material is rendered more conductive. Thus in the influence of an electric current in N-type of material, the electrons are able to travel from anode (positive) to the cathode (negative) and vice versa in the P-type of material. Due to the virtue of the semiconductor property, current will never travel in opposite directions in the respective cases.

    • From the above explanation, it's clear that the intensity of light emitted from a source (LED in this case) will depend on the energy level of the emitted photons which in turn will depend on the energy released by the electrons jumping in between the atomic orbits of the semiconductor material.

    • We know that to make an electron shoot from lower orbital to higher orbita,l its energy level is required to be lifted. Conversely, if the electrons are made to fall from the higher to the lower orbitals, logically energy should be released in the process.

    • In LEDs the above phenomena is well exploited. In response to the P-type of doping, electrons in LEDs move by falling from the higher orbitals to the lower ones releasing energy in the form of photons i.e. light. The farther these orbitals are apart from each other, the greater the intensity of the emitted light.

    • Different wavelengths involved in the process determine the different colors produced from the LEDs. Modern technology has been able to dimension shorter wavelengths in them to produce a large variety of different colored LEDs.

    The topic regarding how LED light bulbs work is so vast that it may fill volumes and is difficult to contain in this article. But hopefully the above discussions should have sufficiently enlightened you regarding the subject. For further information feel free to leave a comment. (Comments require moderation and may take time to appear.)

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