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How does an L.E.D.(Light Emitting Diode) work? Why does light appear?
Answer 1:

An L.E.D. (Light Emitting Diode) is a semiconductor device which emits light. You may have heard of semiconductors, which are used to make computer chips because of their unusual properties. One of the unusual properties is that they can be given different level of positive and negative charges. An L.E.D. is made by placing two different types of semiconductors next to each other - one, called P type, has extra positive charges, and one, called N type, has extra negative charges. The area between them is called a junction. When the P side is connected to one terminal of a battery, and the N side to another, it forces electricity to flow through it. When electrons go from the N side (where they had lots of other electrons) to the P side (where there are lots of extra positive charges), they are attracted to the positive charges, and combine with them. When they collide, the electron loses energy as it stops moving, and this energy is given off in the form of light

Answer 2:

I found a very good article on how diodes work including light emitting diodes:
http://electronics.howstuffworks.com/led1.htm
The bottom line is that all diodes emit light when electrons move around inside the diode material but not all diodes emit visible light or are physically structured so that the light can been seen. Light emitting diodes are specially designed to emit visible light that can escape the semiconductor material so that we can see it.


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