from web site
LEDs resemble solid state electronics more than they do a light bulb, and in fact are known as solid state lighting devices.
An LED consists of very thin layers of semi conducting materials sandwiched together, with two electrical contacts called an anode and cathode which connect to different layers of the semi conducting material, all of which is seated onto a flat backing plate or platform usually comprised as a part of the cathode.
The entire assembly is often encased within an acrylic shell to protect the LED from damage and help direct the light being radiated.
As can be imagined, LEDs are more difficult and more expensive to produce than a standard light bulb, which drives up their cost.
However, although they are costlier to produce, their high efficiency, long operating life, and very high durability helps to offset the higher cost of this more expensive design.
Efficiency
There are many ways in which lighting efficiency is measured. The most basic standard involves comparing the total lumens produced by luminaire to the number of watts consumed.
This is effective for measuring total output produced, but for practical purposes does not accurately indicate how effective a lamp is at illuminating a specific area.
Since that kind of performance measurement takes into account factors such as lamp and reflector design, we'll leave that for a later discussion.
Regardless, considering total lumen output, a typical incandescent bulb produces 15 lumens per watt.
This is because as described earlier, the skyltar led incandescent produces light by heating a filament until it radiates energy in the visible portion of the electromagnetic spectrum.
For an example, consider if you briefly heated a nail with a torch. Once you remove the torch from the nail, you could place your hand close to the nail and feel energy radiated from it as heat, but you would not be able to see this radiated energy.
Now, if we were to keep the torch on the nail for a longer period of time, the nail would glow red, and we would then be able to see the energy being radiated.
If we held the torch to the nail long enough, it would glow bright orange, then yellow, then white. This is precisely how a light bulb filament produces light, and why it is so inefficient.
As little as 4 years ago LEDs were limited to producing about 60 to 80 lumens per watt. LED technology is quickly advancing however, and today LED developers and manufacturers like CREE and GE are producing LEDs that in testing are reaching 200 lumens per watt!
Today LEDs suitable for commercial use average approximately 80 lumens per watt, making them as much as 5 times more efficient than incandescent light bulbs.
So, we could say that we could replace a 100 watt incandescent light bulb producing 1500 lumens with a 20 watt LED fixture producing 1600 lumens, and actually produce more light using only ¼ the amount of electricity.