The journey of light :
The LED ((light-emitting diode ) is a type of diode . A diode is like a "valve" that only lets current (electricity) to flow in one direction and not the other . For the LED this flow or current also produces light .
We could say that LEDs are those little colored lights you see in electronic equipment, household appliances, toys or signs . But , as you will see later in our tour , today LEDs have far greater uses than the above.
How is light produced ?
In the simplest terms, an LED is made with two different kinds of semiconductor material: one type that has too many free electrons roaming around inside, and another that doesn't have enough. When an electron from one material (the donor) gets pushed across a thin barrier and gets into tiny spaces in the other (the holes), a photon or particle of light is produced.
The color of light depends on a number of factors, including the type of material they make the LED from and the material's quantum bandgap (how much energy each electron needs to pack in order to cross the barrier).
A smaller bandgap that fairly weak electrons can cross gives you infrared or red light, while a large bandgap that needs really strong electrons gives you light that has a blue or violet color to it.
Our tour continues with a brief explanation of the terms most used in connection with LEDs: wavelength , candela (Cd) , milicandela (mcd) , lumen , viewangle and lumen/watt:
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