Editorial Feature

Light-Emitting Diodes - Their Structure and Applications

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Sep 27 2007

Image Credits: ludinko/shutterstock.com

A light-emitting diode, more commonly referred to as LED, is a semiconductor that emits visible light when an electric current passes through it, similar to an incandescent bulb. The major difference between LED and incandescent bulbs is that LED does not have a filament. For this reason, they are not prone to burning out, and they do not get significantly hot. The service life of LED is just as long as a standard transistor, and their small plastic bulb makes LED a lot more durable than conventional bulbs.

How are LEDs Made?

LEDs contain two elements of processed materials referred to as the P-type and N-type semiconductors. An LED is made with an electrode attached to the P-type semiconductor layer that is coated or deposited on an N-type semiconductor substrate, putting them in direct contact. The region where the N-type semiconductor comes in contact with the P-type semiconductor is known as the P-N junction.

LED is similar to other forms of diodes. What separates LED from other forms of diodes is that LED has a transparent package that allows infrared or visible energies to pass through, and the P-N junction area can be shaped to tailor to the particular application.

Benefits and Drawbacks of LEDs

There are a wide number of advantages LEDs have over other lighting options. When compared with incandescent bulbs, LEDs come out top in efficacy and lifetime, with one report estimating 35,000 to 50,000 hours of useful life. However, instead of burning out and failing instantly, as with incandescent bulbs, LEDs are prone to slowly dim over a length of time before fully burning out.

In terms of brightness, a disadvantage that causes particular concern is that because LEDs do not significantly heat up during use, LEDs used to light roads for traffic control can sometimes become covered with snow, potentially leading to accidents.

The brightness and color temperature have been criticized in the past, but LEDs are constantly improving in this area. The output of an LED can range from red to blue and violet. Another form of LED known as infrared-emitting diode emits infrared energy instead. An advantage of LED lights is that they are able to emit different colors without the use of colored filters, and as a whole, they are a very versatile lighting option.

Conventional LEDs are made from a variety of inorganic semiconductor materials such as those from aluminum, gallium, silicon, indium, and zinc. They are used to produce different colors, for example, aluminum gallium phosphide is used to produce green LED, aluminum gallium arsenide is used to produce red, and aluminum gallium nitride is used to produce near to far ultraviolet, etc.

Applications of LEDs

LEDs are found in a wide variety of devices. For example, they form the numbers on digital clocks and illuminate traffic lights and automotive indicator lights. When collected together, they form images on jumbo television screens. LEDs have also found use in fiber optic data transmissions, and they are used in remote controls that use infrared-emitting diodes. In home entertainment, LEDs can be used to backlight LCD panels, and are regularly used in the high-end TV market due to their ability to produce better images. Additionally, LCD TVs make use of LEDs for edge-lighting, which enables manufacturers to create thinner TV monitors.

Summary

The benefits of LED compared to other forms of illuminating devices such as incandescent or fluorescent include high efficiency and low power requirement, and when properly installed, LEDs can function for decades. While up front they can be more expensive than incandescent lights but their long-term running cost makes them a better buy. They are also believed to be more efficient for household use than incandescent bulbs and could save bill payers money in the long run.

Although LEDs are yet to completely replace other types of lighting, we are slowly seeing more and more applications across many industries. The home entertainment market is quickly adopting LEDs to improve TV screens, and as technology improves, we can expect to see more and more products and industries making use of LED lighting.