After that, advancement in home lighting more or less came to a halt. A century ago, incandescent lamps with tungsten filaments lasted about 1,000 hours (same as today’s), were only slightly dimmer and sold in the familiar varieties of 40, 60 and 100 watts. Edison didn’t worry about how many watts they consumed; after all, he also owned an electric company. Efficiency wasn’t an issue until the energy crisis of the 1970s, which inspired compact fluorescents, but they went over poorly and never made much of a dent in the incandescent’s market domination.

The compact fluorescent’s failings were a matter of price — the first ones sold for $25 to $35 a bulb — and taste. American consumers seem to prefer incandescence, for reasons connected to the science of light. “What we term ‘light’ does not exist without the human eye — it’s just radiation,” says Nadarajah Narendran, a professor at the Lighting Research Center at Rensselaer Polytechnic Institute. “Your eye is a detector that senses this energy coming to it at different wavelengths.” Those wavelengths are perceived as colors. Natural light combines all the colors of the visual spectrum. When people complain that fluorescent light is cold, what they’re really describing is an overload of radiation at the bluish wavelengths.

“I don’t think it’s cultural; I think it’s much deeper than that, that our reaction to long-wavelength light is warm and short-wavelength light is cold,” David DiLaura says. Humans don’t see all wavelengths equally well; DiLaura says the eye’s “sensitivity curve” is adapted to the spectral composition of light on the African savanna. The light that surrounds us can have psychological and physical effects. Research has suggested that altering wavelengths can affect students’ attention and that patients on the south side of a hospital, which gets more light, recover more quickly than those on the north. So it’s hardly surprising that the incandescent phaseout has prompted a visceral reaction.

Boosters say L.E.D.’s can be calibrated to create light that’s just as good as — maybe better than — natural. They have long been used for low-intensity applications, like the digits on your microwave, but it was only about a decade ago that a cadre of physicists began to awaken the industry to their wider potential. Roland Haitz, a scientist associated with Lumileds, argued that just as computer chips were becoming exponentially more powerful, L.E.D.’s were getting brighter and cheaper at a predictable rate, a proposition now known as Haitz’s Law. Transitioning to L.E.D.’s, Haitz forecast, would cut the amount of electricity used for lighting by more than 50 percent worldwide, eliminating some 200 million tons of carbon emissions a year.

Individual L.E.D.’s come in precise wavelengths — gradations of red, green, blue and so on — and can be combined to appeal to the way the eye assimilates light. Inside Philips’s L Prize bulb, 24 red and blue L.E.D.’s are divided into four quadrants and covered by a curved yellow shell. When they are turned on, they send a stream of red and blue photons through the casing, which contains a phosphor that converts some particles to yellow, and they mix to create white light that looks nearly identical to incandescent. The bulb runs on less than 10 watts of electricity.

Much of the crucial basic research behind the bulb was done by a specialized group of about 40 Lumileds scientists. They continually work to improve the L.E.D. performance by experimenting with the closely guarded “recipe” used to cook up the diodes by combining molecules of indium, gallium and nitrogen. “The material system is not very well understood,” says Ted Mihopoulos, who heads the department. Minuscule changes in temperature inside a reactor can yield significant variations in color and brightness. People sometimes say that L.E.D.’s are like diamonds; no two are exactly alike. When the time came to build an L Prize prototype, Mihopoulos said he culled the 24 brightest diodes from his lab’s private stash.

“The L Prize is the Rolls-Royce,” Christoph Hoelen, one of the bulb’s lead developers, says. “Then the question beyond that is, how do you make a good car that is affordable?” Philips recently brought out the AmbientLED, a clunkier version of its competition design, which Hoelen called his Honda. It incorporates fewer L.E.D.’s and is a bit dimmer and less efficient, but it’s still as bright as a 60-watt incandescent, and it is advertised to last 17 years. The bulb’s affordability is relative, though. At the Home Depot closest to Lumileds, I saw the AmbientLED marked at $39.97.