Light Emitting Diodes
Light Emitting Diodes are very effecient sources of light - they convert electrical current directly into photons (light). As with diodes, the forward voltage across a diode must be greater than a threshold level before the current can cross the junction. Silicon emits a small quantity of light that is near infrared and the threshold is 0.6 volts, and gallium arsenide has a threshold of 1.3 volts.
More About LED's
LED's emit a very narrow wavelength band, unlike incadescent light sources. Like diodes, too much current will overheat the LED and possibly melt the semiconductor chip. When the LED begins to conduct, the voltage increases gradually while the current increases rapidly. Light emitted from a diode is directly proportional to the current through an LED. If the LED overheats, the light will decrease and possibly damage it. Different colours are achieved with different semiconductors and different voltages.