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50 Years of LED Technology

• http://www.wired.com, By Roberto Baldwin
 

Nick Holonyak was sure the LED would replace the incandescent light bulb when he presented it to GE executives 50 years ago. While the incandescent is still king in homes across the nation, the LED has transformed lighting in more ways than Holonyak could have imagined.

From those first dim red diodes to powerful streetlights in major cities, the LED has made its mark on the world.
 
The Ubiquitous Red LED

The first LEDs were red. This wasn’t an aesthetic choice. LEDs are made by building layers of semiconductor crystals on a wafer. As the layers are added, dopants are added to determine the color of the LED. The tiny wafer is placed into molten liquid and metal contacts and leads are then added. The mixture used in the first LEDs -- gallium arsenide phosphide -- produces a natural red color. That’s why red became the default color choice for so many indicator lights.

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