LED information

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Please scroll to the end for a wattage comparison.

What is LED?

LED stands for Light Emitting Diode. It is a solid state semiconductor device that converts electric power into light when voltage is applied in the forward direction across its electrodes. The emitted light is incoherent monochromatic within a very narrow wavelength and is very much unidirectional, i.e. very narrow viewing angle. The wavelength of the light, or colour depends on the silicon material used in the construction of the LED. The emitted light can be near-ultraviolet, visible or infrared.

You can learn more by typing "light emitting diode" in the wikipedia. They have a huge article on LEDs.

What is the difference between incandescent lights and LEDs?

Incandescent lights convert electrical energy to light and heat. The electricity passing through the lamp filament causes the filament to heat up and become red-hot and produce light that is evenly distributed in all directions. About 60% of the energy is wasted through heat. Also a portion of the energy is wasted in the ultraviolet and infrared spectrums that are not visible to human eyes. In an LED only a very small amount of power is dissipated through heat. Most of the energy is converted to light. LEDs in general are over 10 times more efficient than a normal incandescent light source.

LEDs are the ideal choice to replace incandescent, neon, and fluorescent lamps. Some examples are: emergency signs, fringe lighting, house and shop lighting, automotive lights, advertising displays, traffic signs, garden lights, pathway and street lighting, pond and pool lighting, feature lighting. They are the number one choice in yachts as they use much less power than any other alternatives.

Unlike incandescent bulbs, which can operate with either AC or DC, LEDs require a DC supply in the correct polarity. When the voltage across the electrodes is in the correct direction the device is said to be forward biased. The voltage across the LED in this case is fixed for a given LED and is proportional to the energy of the emitted photons. If the voltage is wrong polarity, the device is said to be reverse biased, very little current flows, and no light is emitted.

The difference between LED and laser light is that in a laser all waves are of the same frequency (monochromatic) and in phase.

Advantages of LEDs:

There are numerous advantages LEDs can offer:
* Longer life - last up to 100,000 hours or about 10 years
* LED lighting will degrade over time rather than suddenly burn out and be rendered ineffective.
* Reduce maintenance and service cost
* Energy efficient
* Very low heat dissipation and UV light
* Increased efficiency due to directional light emission
* Easy to use and design with
* 100% dimmable without loss of colour and any noise
* Long lasting and durable technology
* Superior and brilliant colour range
* Easily controllable in both colour and intensity
* Fast response even in cold start condition
* Shock and vibration resistant
* Non toxic materials used in the production
* Safe low voltage operation - 2.0 to 4.0VDC

How do LEDs compare with other light sources?

Incandescent bulbs are very inefficient. They generate 16 (tungsten) to 22 (halogen) Lumen per Watt. Fluorescent tubes are more efficient - from 50 to 100 Lm/W for domestic tubes, allowing large energy savings - but are bulky, fragile and require starter circuits. LEDs are robust and moderately efficient, up to 32 lumen per watt, but are more expensive, although their cost is falling (about 25% per year). At the moment when taking into account the savings from power usage and their much longer lifespan, LEDs are actually cheaper than incandescent bulbs and are on par with fluorescent lights. The technologies for LED production are developing rapidly, brighter and more efficient LEDs are being developed every year. For example the intensity of white LEDs has increased from about 3000mcd (mili-candelas) in 2002 to over 10000mcd in 2004 accompanied also by a fall in production costs.

How do LED systems save energy and money?

In a hypothetical application where the light source is a 60W incandescent bulb being used 10 hours per day, 365 days per year and the cost of power is 25 cents per KWh (this is what it is now and rising!), the average cost per year will be:

$0.25 x (60 x 10 x 365days)/1000 = $55.00 per year ($54.75 exactly)

Using an LED light source that produces the same luminescence the cost will be:

$0.25 x (10 x 10 x 365days)/1000 = $9.13 per year

This amounts to 6 times cost reduction in the electricity bill. You will recover the initial investment cost within the first 6 months and then after you will keep saving electricity and money. With the cost of electricity increasing every year LED lighting systems make a lot of sense.

Further saving in energy is gained by using less power to cool the hot air created by incandescent lamps (remember that major portion of energy in an incandescent lamp is converted to heat).

The typical lifetime of an LED in ideal conditions is about 100,000 hours, with a half life of about 50,000 hours(70% Lumen) from initial luminous output and without any catastrophic failures (sudden burn out).

see the wikipedia "light emitting diode" for more.

Lamp Wattage Comparison:

Incandescent   CFL      Halogen      LED      High Pressure     Approximate
                                                                 Sodium              Lumen Range
 12-15W                                       1.3W                              (light output)
 25W              5-6W        25W          3W          
 40W              9-13W      50W          5W                                     450lm
 60W            13-15W      60W          7W                                     800lm

 75W            18-23W                       9W                                   1100lm
100W           25-30W                     13W                                   1600lm
150W           30-52W    150W         40W                                   2600lm

                                                    35W      150-250W              2500lm
                                                    70W      250-300W              5000lm

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