The incandescent lightbulb is a miracle of modern engineering. It requires a vacuum inside, blown glass and special filaments to work. Yet despite more than a century of refinements, an average bulb emits just 15 lumens of light for every watt of electricity it consumes. As a result, simple lighting accounts for 22 percent of the electricity used by buildings in the U.S. Now a team of engineers and chemists has created a carbon-based series of light-emitting diodes (LEDs) that operate at the pinnacle of efficiency while emitting a strong white light.

Electrical engineer Stephen Forrest of the University of Michigan, chemist Mark Thompson of the University of Southern California and their colleagues created the so-called organic LED by combining two layers of phosphorescent diodes--to release green and red wavelength light--and one layer of a fluorescent diode to supply blue wavelength light. Together, they produce white light much more efficiently than current incandescent or fluorescent bulbs. "A 100-watt bulb is about 15 lumens per watt and we're at about 25 lumens per watt just on the lab bench," Forrest says.

The diode also requires a lower voltage than purely phosphorescent devices do thanks to its fluorescent component, the researchers note in the paper presenting the finding in today's Nature. Furthermore, because the organic layers are only 10 nanometers thick, and transparent when turned off, they can be built into walls, furniture or even windows.

Challenges remain before light-emitting ceilings can become common. Among other things, scientists will need to find a material to encase the sensitive diodes. "This doesn't need a vacuum but it does need a moisture barrier and that can be expensive," Forrest explains. "The biggest barrier to large scale production is simply cost. It costs very little to make a light bulb today." Nevertheless, the development of the novel LED may well signal the dimming of the lightbulb era.