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LED Demystified

Posted on September 23, 2013 by Hugh Kollosche
Abbreviations used in LED technology: LED – Light Emitting Diode COB – Chip On Board SMD – Surface Mounted Device Chip – Electrical term to describe a semiconductor Driver – Electrical device used to reduce operating voltage and convert voltage from Alternating Current (AC) to Direct Current (DC)

The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak, Jr. and he is seen as the "father of the light-emitting diode".

Over the years the efficiency of the LED has been improved many times and you can see it in use today in just about every electrical appliance as warning light to let you know a device is on or in standby mode. These small LED warning lights use very little power to run (fractions of a watt) and because they have no filament or moving parts and thus very little heat, their life expectancy can be measured in hundreds of thousands of hours. In the search to find more energy efficient forms of artificial light, technology turned to the humble LED for an answer. Early attempts to produce ample light from LED’s was very limited and relied on concentrating the beam and using magnifying lenses to get sufficient light to be of any use. However this resulted in a spot light effect and as a result many fittings were required to get adequate light coverage to be of any practical use. The cost of the fittings and installation outweighed the power savings, so the search went on. The evolution of LED to what we see today are masses of LED’s used in each fitting in the form of SMD’s or COB’s powered by a Driver which can be internal or external to the fitting, to produce enough light for it to take the place of a more conventional filament light source. These fittings will often have an opal diffuser to hide the appearance of the yellow LED chips and electrical circuitry. The opal diffuser also has the added effect of spreading the light more evenly. LED’s produce very little heat, this is why they are so efficient, only a small amount of the electrical energy used is wasted as heat in the conversion of electrical energy to light. However, the flip side to this is that LED’s are very susceptible to heat, so as we drive LED’s harder and harder to produce more light we have had to find ways of keeping them cool. On most LED fittings you will find many metal fins these are called a heat sink and will probably be found on the hidden part of the fitting or possible they will be incorporated into the design. These fins are designed to increase the surface area of the fitting to allow for quick and easy dissipation of heat. The type of material used for the heat sink will determine how well the heat sink works, for example pure aluminium will be better then cast alloy because the particles in pure aluminium are closer together and the heat can move from one particle to the next more quickly, with the result that the critical area around the LED’s is kept cooler. Many claims are being made about the life expectancy of LED’s, however it must be remembered that they will never last as long as their earlier incantation, the humble warning light. This is because we are driving or working them so much harder to produce the light we want from them. Many of the life expectancy claims currently being made, 50,000, 30,000 or even 20,000 hours have simply not been tested by the time the product has gone to the market and are based on estimates from shorter tests done under laboratory conditions. In addition to the life of the LED, the Drivers life expectancy must also be considered. The Driver is a delicate electrical device with many components, it can be affected by voltage fluctuations, brown outs, power surges, electrical storms, heat, and the list goes on, including simple old age. Bear in mind hundreds of thousands of these complicated devices are manufactured at very affordable prices to supply the hungry markets around the world. There has recently been some new Driverless LED technology developed. Some new products designed under the patent of this new technology are being distributed in Australia by Econolight. It will be interesting to see how these fare, perhaps this is the next stage of LED development. When considering if LED is the right choice for your home there are two main things you should consider. What is the light output (lumens) of the product and the power consumption (wattage)? These two questions must be asked together, unlike conventional incandescent (filament) type lamps the higher the wattage does not necessarily mean the higher the light output. If the power consumption of the LED product you are looking at is high and the light output is low you may be buying an expensive light that is perhaps not as efficient as a CFL (compact fluorescent lamp) or perhaps it is a little more efficient but against the initial cost the savings are lost, again this will depend on how long the LED fitting is going to last. Why do LED vary in power consumption and light output? The two main reasons are; the quality of the LED Chip and quality of the components in the Driver. First the LED Chip, there are a number of well known LED Chip manufacturers, such as; Cree, Epistar, Bridgelux, Sharp and Samsung to name the major five. There are even more unknown Chinese brands whose materials used to manufacture the LED are inferior, resulting in poorer light output. In the case of the Driver, depending on the quality of the semiconductor components used there may be power losses before it even gets to the LED. Again it comes back to heat, power losses in the driver must convert to some other form of energy and this will be heat. Ultimately heat will destroy both the LED and the Driver so it is of the utmost importance that any LED fittings you have installed are allowed plenty of ventilation.