Why Led Emit Different Colors

LED means "light emitting diode". An LED which is capable of emitting more than one color is actually composed of more than one diode. But here is the problem, why led emit different colors? And what exactly makes led emit different colors?

The material used in the semi-conducting element of an LED determines its color. The two main types of LEDs presently used for lighting systems are aluminum gallium indium phosphide alloys for red, orange and yellow LEDs; and indium gallium nitride alloys for green, blue and white LEDs. Slight changes in the composition of these alloys changes the color of the emitted light.

When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions. In the p region there are many more positive than negative charges. In the n region the electrons are more numerous than the positive electric charges. When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region. Once in the p region the electrons are immediately attracted to the positive charges due to the mutual Coulomb forces of attraction between opposite electric charges. But still we have the question, why the led emit different colours and what makes led emit different colors?

     LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. The LED is usually small in area (less than 1 mm2) with integrated optical components to shape its radiation pattern and assist in reflection. Note if you want to go any deeper understanding you need to understand physics. And it is the difference in the level of energy between the two sides of the junction that determines the frequency of the light given away. A small energy gap would release infra-red. Slightly larger gap: red. Larger still, and you have yellow or green. And eventually blue. The energy gap is a function of the composition of the semiconductors used at the junction. The above reasons explain why led emit different colors and what makes led emit different colors.