LED lighting

LEDs (light emitting diodes) are now recognized as the energy saving light source of the future. Initially developed in the 1920s tey were first made commercially viable as indicator lights in the mid 1960s. With the technology developing rapidly LED's have progressed from being simple indicator lights to now being used to replace halogen and flourescent light bulbs.

LED's, 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 side - cathode or P-type, to the negative side - cathode or N-Type. This is commonly known as a P-N Juntcion. Charge-carriers, electrons and holes flow into the junction from electrictrodes with differing 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. LED's are all manufactured from direct bandgap materials to produce light in the visible spectrum.

Typcial indicator LEDs required very little power to operate, generally between 2V - 4V at no more than 20mW - 60mW (milliwatts), however in order to generate higher light outputs power consumption in general illumination LEDs, chips are now being developed up to 8W with the aim of replacing incandescent light bulbs. The increased power and light output does have its limitations and design considerations. The high power LED's required much larger semiconductor dies for mounting, and also needed specially designed heat sinks to remove the excess heat from the semiconductor. Excess heat will dramatically reduce the life expectancy of the LED.

With labs and manufacturers claiming luminous efficieny of up to 145lm/W and commercially available units producing 105lm/W, LED's 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 flourescent tubes produce 100lm/W. LED efficiency as improving at a similar rate to modern computer chips, with light output and luminous flux (lm/W) doubling every two years, it wont be long before 3W - 5W LED chips will replace tradiional 50W halogen light bulbs.

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