The passing of Edison's bulb has already been decreed, and which of the two alternatives will replace it is at last becoming clear. It will be the LED.
The success of the light-emitting diode means curtains for the compact fluorescent light (CFL). This clunky, mercury-ridden, hard-to-dim, excessively white device has just two things going for it: It's more efficient than Edison's bulb and, right now, cheaper than the LED-based alternative.
But the LED's quality is rising and its price is dropping—fast. Even now you can pick up a 40-watt-equivalent LED bulb with an appealingly warm hue for just US $9.97. By the end of 2012, a 60‑W cousin could be available for about the same price, and within a few years for much less than that.
A glimpse of what's to come appeared this past August, when an LED lightbulb from Philips Lighting North America won the U.S. Department of Energy's $10 million Bright Tomorrow Lighting Prize, better known as the L Prize.
"Our L Prize bulb is essentially the Ferrari of lighting," boasts Todd Manegold, director of LED lamps marketing at Philips. "It does everything that any lightbulb could ever or should ever want to do."
In the beginning—perhaps in the first half of this year—the bulb will sell at a Ferrari price, perhaps $50 apiece. But the pressure to cut that premium will grow as early adopters buy up other brands of LED bulbs that trade efficiency for lower prices. And indeed, those prices are falling fast.
Philips had to design the bulb to hit a slew of engineering targets set by the DOE. First, the bulb had to put out at least 900 lumens—as much light as a 60-W incandescent bulb, the most common kind in the United States. Then it had to last for 25 000 hours, which is roughly 25 times as long as a standard incandescent. And it had to draw less than 10 W.
Philips built its bulb around the Luxeon Rebel, an LED radically different from those that backlit the keypads and displays of early handsets. In a conventional LED, most of the light bounces around within a stack of semiconductor layers, which have a far higher refractive index than air, so only a small proportion of the light goes out in the proper direction. In the Luxeon Rebel, a metallic mirror on the bottom of the chip keeps light from leaking out the wrong way, and the roughening of the top surface allows more of the properly directed light out of the box. As a result, the bulb needs just 9.7 W to yield 910 lumens, whereas an incandescent's 60 W yields only 800 lumens.
The L Prize bulb also features omnidirectional emission, a hallmark of the incandescent bulb. Simply putting a handful of white LEDs into a glass bulb will not lead to uniform illumination, because each device produces a beam. It would be like trying to illuminate a room with a dozen flashlights.