From Light Bulbs to LEDs

In conventional incandescent bulbs, the direct descendants of Edison’s invention, resistance causes a wound tungsten filament inside a globe to heat up and glow when an electric current passes through it. The vast majority of the energy is released as heat, a bit as light. Fluorescent lights work by introducing an electric arc to excite mercury atoms. The excited mercury atoms emit ultraviolet radiation, which is converted to visible light after it strikes a phosphor coating on the inside of the long glass tube (or wound glass tube in the case of compact fluorescent bulbs).

An LED works on an entirely different principle, that of the diode. A silicon-based semiconductor material is used to create a “p-n” (positive-negative) junction. Electrons flow from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. As the electrons transit the p-n junction they fall into a lower energy level, which causes them to give off a photon of light. The color of the light — red, green, blue, or amber — depends on the semiconductor materials used to make the diode. White light is created by combining light from different colored LEDs, or by coating a blue LED lens with phosphor.

Trends in the computer chip industry are described by Moore’s law, which states that the number of transistors that can be placed on an integrated circuit doubles every two years. The LED industry is driven by Haitz’s law, named for Roland Haitz, a retired engineer who led the optical engineering program at HP for much of his 32-year tenure at the tech company. Haitz’s law predicts that the performance of LEDs — the amount of light that can be produced per diode — increases 20-fold every decade, while the cost of that light decreases 10-fold.
The $100 billion global lighting industry is undergoing radical change: New office buildings and retail outlets are abandoning fluorescent lighting in favor of LEDs, or light-emitting diodes, those tiny, energy-efficient, long-lasting, and blindingly bright points of light. Giants such as GE (GE) and Philips are shifting production from incandescent bulbs to LEDs. Even the local Home Depot (HD) — which today probably stocks only a couple of LED lighting products — will soon carry a bouquet of LED bulbs, ultimately edging out fluorescents and halogen lamps. By the end of the decade, analysts predict, LEDs will be the dominant source for commercial and residential lighting.

LEDs, which are based on a technology similar to that of computer chips, have more in common in their design and manufacture with your laptop than with the incandescent bulb that Thomas Edison patented almost 130 years ago. As lighting goes digital, the industry is likely to encounter some of the same upheaval that took place when television, music, and other businesses shifted away from analog technologies.

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