LED is a light-emitting diode that emits light when an electric current passes through. Therefore, atoms are excited to a high energy level that needs to be released. During this energy release light is created.
The color of the light from the LED results of the ingredients (materials) and recipes (processes) that make up the chip.
The structure of the LED is completely different than that of the light bulb and is based on chip technology. It is not anymore a matter of Tungsten filament or halogen gas, it is about light coming from a chip that replaces the traditional functionality of a bulb.
- High-levels of brightness
- High efficiency, energy efficient
- Low-voltage and low current requirements
- Low radiated heat
- High reliability (resistant to shock and vibration)
- No UV rays
- Long source life : eliminates the maintenance of replacement required by traditional lighting
- Can be easily controlled and programmed
- Lens: A precision optical piece that focuses the light from the chip into the beam shape and direction
- LED chip : the semiconductor device that produces the light. Tiny compare to the LED package – complete LED
- Lead: One of Two electrical contacts (anode and cathode) on the LED. Where current is applied.
- Wire bond: A very thin wire that connects the lead to the chip
- Heat sink slug : piece of thermally conductive material that pulls heat away from the chip
- Encapsulant : A clear material that helps couple the chip to the lens
- Case : the body of the LED, which serves as protection and adds to the robustness of the LED
- In the 60’s : the 1st LED’s were invented and were red. They were used mainly as indicators in applications.
- In the 70’s : green, yellow and orange LED were invented. The types of applications continued to grow and LED were used in calculators, digital watches and test equipment.
- Early 80’s : LED improved in light output. They were developed with new technologies. The new LED’s were more efficient, used less power and generated brightness levels ten times greater than previously. LED’s were now being used in message and outdoor signs.
- In the 90’s : the high-brightness blue LED was invented. This was later use as the basis for a white LED which combined the blue LED and phosphor to convert the blue to white light.
- Today : LED have reached performance level far exceeding early projections. White LED’s have achieved high performances, making them applicable to significant energy-saving general illumination applications.
Today many different types of LED exists: OLED (for Organic Light emitting Diode), AMOLED (for Active-Matrix Organic Light-Emitting Diode or FOLED (for flexible oled).
Source : http://www.lighting.philips.com/main/lightcommunity/trends/led/what_are_leds.wpd