LED Lighting

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The incandescent light bulb invented by Edison has been the light technology that we have been using since light bulbs came into being. These bulbs typically delivered most of the light as byproduct of heat basically by heating a filament to glow. However this leads to gross wastage of electricity. This was followed by CFL’s or compact fluorescent lights which are quite efficient but contain mercury which is harmful to the environment. The newest technology is LED.


Red, pure green and blue LEDs of the 5mm diffused type (Courtesy Wikipedia)

LEDs — light-emitting diodes — are the promise of the future because unlike tungsten bulbs or compact fluorescent bulbs, they deliver most of their energy as light, rather than heat. An extra plus is that they don't contain dangerous mercury. LED’s have huge lifespans – typically of 50000 hours. Future LED’s which last 100 years and fill rooms with brilliant ambiance may become a reality sooner rather than later. It is estimated that in 10 years LED’s will be the only light source in the marketplace replacing incandescent and CFL bulbs.

Like a common diode, the LED (Light Emitting Diode) consists of a P-N contact. When a P-N junction is forward biased, current flows within it. This current flow will cause electrons and holes to move is a manner that an electron will move to fill a hole. When this happens, the electron will fall to a lower energy level and this will release an amount of energy in the form of photons. In a larger scale, those photons will produce light.


The inner workings of an LED(Courtesy Wikipedia)


Parts of an LED. Although not directly labeled, the flat bottom surfaces of the anvil and post embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled out from mechanical strain or vibration. (Courtesy Wikipedia)

A LED will emit a colored light not because of it's package color as many people used to believe, but because of the emitting wavelength. The wavelength that an LED will produce depends on the material used to form the p-n junction.

LED’s would need to come in red, green and blue – and with combining them generate white light. The white light from the sun is really all the colors of the rainbow. Without at least red, blue and green from the spectrum, no lighting device will be practical for home or office use. Red LED’s were invented 15 years ago. Japanese scientists invented the blue laser. But green has been elusive. In fact, the $10 LEDs that people can buy now are made to look white by aiming the blue light at a phosphor, which then emits green. It works OK, but the clunky process saps a big chunk of the efficiency from the light.

For a decade, LED researchers had tried and failed to make a reliable efficient green light by putting indium into gallium nitride. Solar-cell researchers had dealt with the same problem trying to build a solar cell with gallium indium phosphide. NREL's solar cell experts found a way around that. They put in some extra layers that gradually bridge the gap between the mismatched lattices of the cell layers. NREL scientist Angelo Mascarenhas, who holds patents in solar-cell technology, realized that an LED is just the reverse of a solar cell. One takes electricity and turns it into light; the other takes sunlight and turns it into electricity. Solar cells don't need a green, but they had begun to understand the challenges of getting to a green. Once the concept was understood, the rest was just practical science of tediously working the details.


Cluster of LEDs mounted on a screw-in baseLED spotlight using 38 individual diodes for mains voltage power (Courtesy Wikipedia)