LEDs, or light emitting diodes, are an electronic light source. LEDs were first discovered in Russia in the mid 1920’s however no commercial use could be found for them until 1962 when they were introduced as a commercially viable electronic component. Early LED’s were manufactured from gallium arsenide and produced a low intensity red and infrared light. Now other materials are added to the gallium allowing the creation of shorter light wavelengths and varying colours.
LEDs, like all diodes, are made of very thin layers of semiconductor material, one layer will have an excess of electrons, while the next will have a deficit of electrons. The LED consists of a chip of semiconducting material impregnated with other materials to produce the required colour. current flows easily from the positive of the chip into the negative, but will not flow easily in the opposite direction – cathode or P-type, to the negative side – cathode or N-Type. This is commonly known as a P-N Junction. Electrons and holes – known as charge carriers flow into the electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon
The wavelength, or colour of the light emitted depends on the energy gap or bandgap of the materials used in the manufacture of the P-N Junction. LEDs are all manufactured from direct bandgap materials to produce light in the visible spectrum.
Typical indicator LEDs required very little power to operate, generally between 2V – 4V at no more than 20mW – 7W – 8W LED chips are now being made available to the general illumination market by manufacturers, and it is estimated they will directly replace incandescent light bulbs within the next 5 years. Higher power and light output poses specific challenges for LED chip manufacturers to create a reliable product for the commercial market. Today’s high power LED’s require much larger semiconductor dies for mounting, and also needed specially designed heat sinks to remove the excess heat from the semiconductor. Heat drastically reduces the life expectancy of the diode.
LEDs are the most efficient form of lighting available today. LED manufacturer Lumileds in 2002 released a 5W LED chip. 2003 saw a breakthrough in commercially available LEDs with Cree releasing an LED chip with a luminous efficiency of 65lm/w. In 2008 Nexxus Lighting released the Array range of LED lamps, with a luminous efficiency of 105lm/W, the brightest, most efficient LED available commercially today. By comparison, halogen and incandescent lamps have a luminous efficiency of around 15lm/W, while fluorescent tubes produce 100lm/W. With LED manufacturing technology improving daily, it is easy to see why LEDs will be the lighting source of the future.
Source by Mike Brunt