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About this Article
Written by: Tian Li Woon
Written on: October 10th, 2005
Tags: electrical engineering
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About the Author
Tian Li Woon was a junior majoring in Electrical Engineering with emphasis on integrated circuits at University of Southern California, Los Angeles, CA in the fall of 2005.
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Volume VII Issue III > The Little Plastic Bulb
Since being introduced in the 1960's the light emitting diode (LED) has found applications in many areas due to its power efficiency, low power consumption, long life and toughness. Applications include indicator lights on electronic devices, backlights for liquid crystal display screens on cell phones and laptops, traffic lights and even wireless communications and counterfeit detection methods. It has also started to replace conventional lighting sources such as incandescent and fluorescent lighting in some areas. Despite its widespread use, the LED is often overlooked and taken for granted. This article will introduce you to the physics behind the "little plastic bulb," its many advantages and some insight into its wide spectrum of applications.

Introduction

The 20th century saw the prominent rise of semiconductors. The ability to fabricate transistors from semiconductors has brought about the "Electronic Revolution" and the world has changed drastically since then. Astonishingly, it has only been about 60 years since the invention of the first solid state transistor. Almost anything around you from computers to cell phones to a simple digital alarm clock has a semiconductor chip in it. All the hype surrounding the complex semiconductor chips found in computers' central processing units (CPUs) or graphics cards (GPUs) have long obscured another simple semiconductor device that is just as widespread as, if not more, than its more complex counterparts. This simple semiconductor device is the light emitting diode, or better known as the LED. You have probably seen LEDs in many devices but have not given it a second thought. You see it on computers, optical mice, remote controls, microwave ovens, traffic lights, billboard signs and even your cell phone display and keypad are lit up by little LEDs. The list goes on and is set to continue growing indefinitely simply because the LED has yet to realize its full potential and much research is still going on to improve its already amazing energy efficiency and to emit photons across a wider spectrum of frequencies.
[image=649 file="800pxRBGLED.jp​g" placement="right"]Fi​gure 1: Red, green, and blue LED lights.[/image]The first LED made in the early 1960's emitted radiation in the infrared range, invisible to human eyes. Further research and discovery of new materials enabled the production of light at higher frequencies. The first LED that emitted light in the visible range was invented by Nick Holonyak Jr. at General Electric Corp. in Syracuse, N.Y. in the l962. It emitted very low intensity (in the millicandela range) light and could only be used as indicator lights and not for general illumination. Over time, LEDs moved up the color spectrum moving into red-orange, then green. It was only in the 1990's that the blue LED was created by Shuji Nakamura at Nichia Chemical Industries Ltd. and the primary colour triumvirate was finally completed. Developmentof LEDs did not stop there, but went on to the violet and even the ultraviolet frequencies. This in turn led to the production of white LEDs, which is often made using a blue LED coated with yellow phosphors. While the LEDs climbed the frequency ladder, the brightness of the emitted light also improved dramatically (see Fig. 1). This improvement in light intensity, combined with the creation of white LEDs, introduced LEDs into the competition for "the rights to general illumination" with rivals being the incandescent and fluorescent lighting.
In this article we will look at the physics behind the LED, some of its advantages and disadvantages over conventional lighting and some of its many applications in our daily life.