ABCs of LEDs and LECs.

Time has come to say goodbye to good old "Edison bulbs". It was around 1900, when the Director of US Patent Office declared openly that "whatever that can be invented has already been invented". He certainly did not know what was going to come. Lets take the example of LEDs. For a given amount of light output, LEDs consume only one-fifth to one-sixth of the power consumed by incandescent bulbs. Though it sounds incredibly hi-tech, simple physics is all it takes to make an LED work. Not really true, a little bit of quantum physics is actually involved in it. Well, for starters, when an electron combines with an absence of electron (called hole), light is generated. If its so simple, why did it take so long to start using LEDs as a light source?

The answer is "it did not". The first LED was manufactured in 1962 by GE. In the late 60s and early 70s, they were being used in electronic equipments, but had very little application in everyday usage. This was due to their high manufacturing cost. However, over a period of forty years, due to advancements in material science, this cost has reduced, and now, they have plenty of applications. People would still consider LEDs as an expensive option, but I would like to throw some light on "how LEDs can be cheaper than incandescent bulbs".

Facts about incandescent bulbs : Lifetime of a 100 watt incandescent bulb is about 750 to 1000 hours. A 100 watt bulb gives a light output of 1700 lumens (a measure of how bright the light is). A typical 100 watt bulb costs around $ 1.

Facts about LEDs : Lifetime of an LED is 50000 hours. A good LED nowadays, gives a light output of 100 lumens. Hence, to get 1700 lumens, 17 LED are required. Each LED costs around 5 dollars approximately. Hence 17 LEDs would cost $ 85. However, there are some additional costs involved in using LEDs. This is because, LEDs are current driven devices, due to which, if the current passing through them varies from the specified current, its light output would vary too. Hence the requirement for LED drivers, which allow these devices to operate at a constant current. Moreover, because of the physics involved in the working of LEDs, there is a lot of heat generated along with the output light. This necessitates the use of a Heat Sink to get rid of the generated heat (the excess heat generated might fry the LEDs if not sinked).

Including all the accessory costs, using LEDs to get 1700 lumens for 50000 hours would cost around $ 100 ($ 85 for LEDs + $ 10 for an LED driver + $ 5 for a Heat Sink) without considering energy costs. Similary, using incandescent bulbs for 50000 hours would cost around $ 50, as one would need 50 bulbs to go on for 50000 hours, considering the lifetime of a bulb to be 1000 hours. Now, if you are thinking that bulbs are cheaper than LEDs, keep on reading, because, if you remember, I have already mentioned that LEDs consume only one-fifth of the power consumed by bulbs.

Elaborating more on energy costs, one would need 100 watts of power to obtain 1700 lumens from a 100 watt incandescent bulb. To go on for 50000 hours, a total of 5000 KWh of energy would be spent. Similarly one would need only 1000 KWh of energy to run LEDs at 20 watts for 50000 hours. Cost of electricity is currently around $ 0.12 per KWh, which makes the total energy cost to run bulbs to be $ 600 as compared to $ 120 only, that is required to run LEDs. You may now appreciate the fact that "LEDs are much cheaper than incandescent bulbs - a true win-win situation".

If, you have already changed your mind to switch to the "greener-cheaper" LEDs, you would need three devices to get the final light output, LEDs, LED driver and Heat Sink. Few of the best companies out there manufacturing LEDs are Cree, Nichia, Osram etc. For LED drivers, there is National Semiconductor, Analog Devices etc and for Heat Sinks, there is Aavid, Advanced Thermal and so on.

Not to mention the biggest advantage of the LEDs, they have the best color rendering index of any light source available in the industry. In common man's words, anything you see under a yellow incandescent bulb would have a yellowish shade to it. For example, a white colored paper would look yellow in a yellow colored light. This problem is totally avoided with white LEDs. If LEDs are so good, why all this fuss about LECs? Light Emitting Capacitors or LECs are simple parallel plate capacitors with a phosphor coating on the dielectric. When current is passed through the capacitor, this phosphor layer glows, causing it to behave like a light source.

As for any light source, LECs have their own pros and cons. Though they consume just one third of the power an LED would consume for a given light output, LECs have an extremely niche market at this point of time because they are far more expensive than their LED counterparts. However, I can see the LEC market to be at the exact same position as the LED market was, about 30 years ago. As history repeats itself, 30 years from now, I would expect LECs to rule the lighting industry.