Nick Holonyak, Jr.'s February, 2001, Scientific American article, "In Pursuit of the Ultimate Lamp," describes light-emitting diodes (LEDs) and laser diodes. Though both diodes are made of semiconductor materials, they are designed differently to tackle different jobs. Inside the LED is a chip with layers of semiconductor material. One layer has an excess of electrons (N-type) and another layer rests on top with a dearth of electrons, or an excess of positively charged particles called "holes" (P-type). The junction of the N and P layers is the "active" layer. Applying a voltage drives the electrons and holes into the active layer where they meet. As they join, they emit photons, the basic units of light. The atomic structures of the active layer and adjoining materials on each side determine the number of photons produced and their wavelengths (the wavelengths of light determine the colors). In LEDs, the semiconductor material used is a mixture of group III and group V elements of the periodic table.

In laser diodes, the semiconductor material rests between what is essentially a pair of mirrors in the region called the "resonator cavity." When electricity goes through the semiconductor, it gives off photons, which bounce around inside the cavity, exciting nearby electron-hole pairs to release more photons at the same wavelength. The light increases continuously in intensity, with the photons moving together as they oscillate between the two mirrors. If one mirror allows just a bit of light to escape, then some of the photons exit. All at the same wavelength and in phase, these escaping and "coherent" photons produce an extremely narrow column of pure, bright light at a single wavelength. This well-defined beam is a laser, and with proper optics, it can do delicate work such as reading the fine pits on a compact disc or scanning bar codes. The word "laser" is an acronym for "light amplification by stimulated emission of radiation."

In contrast, the light emitted from LEDs is "incoherent." That is, the photons are more widely scattered and are composed of a spread of wavelengths from one area of the spectrum. While the photons an LED produces are not all the same wavelength, they are close enough to be perceived by the eye as being the same color.

Holonyak's first III-V alloy PN junction LED is the prototype for all the high-brightness LEDs made today. Through decades of improving crystal manufacturing techniques, tailoring the properties of the semiconducting layers, and even reshaping the chip itself, researchers have developed bright-light LEDs in every color of the rainbow, including white. In addition to the first red indicator lights, LEDs can be seen everywhere, lighting up traffic lights and signals, message and display boards, automotive brake and headlights, laptop displays, and interior and outdoor spaces, to name a few. During the 2008 Beijing Olympics opening ceremony, the world witnessed a thirteen-hundred-square-meter LED scroll display on the stadium floor upon which performers walked, danced, and drove. The Beijing Water Cube housed 440,000 LEDs embedded throughout its structure.

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