LED Basics and Understanding

There can be no question about it the light bulb is up there as one of the greatest inventions that mankind has made. Since it’s first appearance it has been improved in many ways, yet has not changed in concept since it was invented. A filament in a vacuum with current passing through it. The introduction of fluorescent light bulbs was a one of the first real advances in lighting. Then the appearance of halogen bulbs and next by the arrival of energy saving bulbs. Yet still the light source was basically a filament with current passing through it. Raise electrons to a high energy state and as they drop they emit a photon.

The first real lighting advance into a new technology was the LED light bulb. These bulbs are approximately 35 times more efficient than an incandescent bulb and about 10 times more energy efficient than a fluorescent lamp. They come in many different colours as standard and can easily create a completely different lighting mood, depending on the color chosen. The purity of the produced light is not achievable in normal filament light bulbs.

An LED (Light Emitting Diode) is a form of semiconductor device that emits light when an electrical charge is passed through the semiconductor junction. The type of light that emanates from the semiconductor depends upon the composition of the encapsulating material and can vary from ultra violet to infrared.

There are many advantages of using LED bulbs over the standard incandescent bulbs. The main advantage is the energy efficiency aspect. An LED bulb is brighter than a standard bulb and generates much less heat for the amount of light output. They use only about 10% of the energy used by a standard bulb and come in many colours as standard.

Unlike filament lamps, LED elements are usually encapsulated in plastic that acts as a lens thus allowing a very precise focus on the light with the LED element its self. The very high power LED elements 3W and up usually do not have lensing associated with the basic element.

One of the most widely used application of LED bulbs is in the automotive industry. A cluster of LEDs in place of a bulb are brighter and more reliable than a single bulb whilst using much less electricity. The other advantage is that if one led fails in the cluster the rest continue to work, thus giving and obvious health and safety benefit. This is clearly evident in the traffic signals all going to LED and stop tail lights now going LED, we are also starting to see headlights being LED clusters also.

Another application for led bulbs is within the decoration industry. Because LED bulbs use so much less power than traditional decorative lights they can be powered from a simple battery pack rather than have the need for a transformer and electricity supply.

One disadvantage of LEDs is their operational characteristics they are sensitive to changes in the current passing through them and the higher the current the shorter the life and reliability. LED's must have precise current control to ensure long life and reliability. Generally a simple resistor current limit is not a good idea if the LED performs an important function. The main issue associated with high power output LEDs is heat. In order for the high power devices to function reliably with long life the LED element needs to be mounted on a large heatsink drawing the heat away from the element to protect it and ensure long life. As an example a typical 100W LED element needs 600,000mm2 of heat sink area to run reliably.

Colour purity in LED's is another issue, while high light output can be obtained from driving the LED at its limit or beyond, its life will be shortened and also the spectral purity of the output might change. This can be seen in white LED's that will drift to the blue end of the spectrum. This can be caused by poor quality LED's or being driven too hard.

All in all LED bulbs are a fantastic replacement for more traditional forms of light bulb and they will continue to gain popularity over the coming years. Who knows, one day Edison’s original incandescent invention may be a dim memory.