Untitled Document

Mirror Magazine

Techno Page

By Harendra Alwis

What is LED?
Light emitting diodes, commonly known as LEDs, are unsung heroes in the electronics world. They do thousands of different jobs and are found in all kinds of devices. They form the numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. They can form images on a jumbo television screen or illuminate a traffic light.

Basically, LEDs are just tiny light bulbs but unlike ordinary bulbs, they don't have a filament that will burn out, and they don't get burning hot. They are illuminated solely by the movement of electrons in a semi-conductor material, and they last just as long as a standard transistor.

What is a diode?

A diode is the simplest sort of semi-conductor device. A semi-conductor is a material with a varying ability to conduct electrical current. Most semi-conductors are made of a poor conductor such as silicon, that has had impurities (atoms of another material) added to it. The process of adding impurities is called doping.

In pure silicon, all of the silicon atoms bond perfectly to their neighbours, leaving no free electrons (negatively charged particles) to conduct electric current. In doped silicon, additional atoms change the balance, either adding free electrons or creating holes where electrons can go. Either of these additions makes the material more conductive.

Diodes are made of these two types of 'doped' semiconductors arranged in a particular way. This arrangement conducts electricity in only one direction. When no voltage is applied to the diode, electrons from one material fill holes from the other material along the junction between the layers, forming a depletion zone. In a depletion zone, the semi-conductor material is returned to its original insulating state where all of the holes are filled, so there are no free electrons or empty spaces for electrons, and charge can't flow.

To get rid of the depletion zone, you have to get electrons moving from the other direction. This creates free electrons that can flow freely through the circuit. This happens when the voltage difference between the electrodes is high enough, the electrons in the depletion zone are boosted out of their holes and begin moving freely again. The depletion zone disappears and charge moves across the diode. If you try to run current the other way, the current will not flow. This is basically what a diode is.

How can a diode produce light?

Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum, but no mass. These particles, called photons, are the most basic units of light.

Photons are released as a result of moving electrons. In an atom, electrons move in orbitals around the nucleus. Electrons in different orbitals have different amounts of energy.

For an electron to jump from a lower orbital to a higher orbital, something has to boost its energy level. An electron releases energy when it drops from a higher orbital to a lower one. This energy is released in the form of a photon. A greater energy drop releases a higher-energy photon, which is characterised by a higher frequency.

Free electrons moving across a diode can fall into empty holes in the semi-conductor. This involves a drop from the conduction band to a lower orbital, so the electrons release energy in the form of photons. This happens in any diode, but you can only see the photons when the diode is composed of certain material. The atoms in a standard silicon diode are arranged in such a way that the electron drops a relatively short distance. As a result, the photon's frequency is so low that it is invisible to the human eye because it is in the infrared portion of the light spectrum. This isn't necessarily a bad thing, of course: Infrared LEDs are ideal for remote controls.

Visible light-emitting diodes (VLEDs), such as the ones that light up numbers in a digital clock, are made of materials characterised by a wider gap between the conduction band and the lower orbitals. The size of the gap determines the frequency of the photon. In other words, it determines the colour of the light.

While all diodes release light, most don't do it very effectively. In an ordinary diode, the silicon material itself ends up absorbing a lot of the light energy. LEDs are specially constructed to release a large number of photons outward. Additionally, they are housed in a plastic bulb that concentrates the light in a particular direction.

LEDs have several advantages over conventional incandescent lamps. For one thing, they don't have a filament that will burn out, so they last much longer. Additionally, their small plastic bulb makes them a lot more durable. They also fit more easily into modern electronic circuits.

But the main advantage is efficiency. In conventional incandescent bulbs, the light production process involves generating a lot of heat (the filament must be warmed). This is completely wasted energy, unless you're using the lamp as a heater, because a huge portion of the available electricity isn't going toward producing visible light. LEDs generate very little heat, relatively speaking. A much higher percentage of the electrical power is going directly to generating light, which cuts down on the electricity demands considerably.

Up until recently, LEDs were too expensive to use for most lighting applications because they're built around advanced semi-conductor material. The price of semi-conductor devices has plummeted over the past decade, making LEDs a more cost-effective lighting option for a wide range of situations. While they may be more expensive than incandescent lights up front, their lower cost in the long run can make them a better buy. In the future, they will surely play an even bigger role in the world of computers and technology.

Email: technopage_lk@yahoo.com

Back to Mirror Magazine