A team in the Research Triangle has spent much of the past five years combining physics, chemistry and nanotechnology to build what could be tomorrow's light bulb.
The scientists work in a lab on the sprawling campus of RTI International, a research institute that has long been involved in green technology efforts. It's about a mile from Cree, the Durham manufacturer of light-emitting diodes that was in the national spotlight last month when it hosted Vice President Joe Biden and Secretary of Energy Steven Chu.
The prototype for the new light bulb uses a Cree LED, but the light it produces is softer and easier on the eye than the intensely bright light an LED emits.
Lynn Davis, director of RTI's nano scale materials program, came up with the idea for the nanotech light bulb and is overseeing its development. He estimated it will take another three to five years to get a commercial version ready.
"It's not a product; there's still a lot of work to do," Davis said, showing off the prototype. "It's very much a research project."
It's also another step researchers are taking toward producing light that comes close to sunlight without producing the sun's heat.
Electricity has been used to light everything from homes to spaceships in the past century. Incandescent light bulbs are the oldest and cheapest source of electric light. They're easy to replace, and the light the tungsten filament produces inside the vacuum-filled glass bulb is similar to sunlight. But traditional light bulbs convert only 2 percent to 5 percent of the electric energy they consume into light. The rest is lost as heat, which is why they are more appropriately called "bright heaters."
Several technologies that are more energy-efficient are available for inside and outside lighting, including halogen and fluorescent lights. Compact fluorescent light bulbs are more than twice as energy-efficient as incandescent light bulbs, but they produce light that can be very harsh and unflattering.
"It's been worked on for years," said Ron Kelley, founder of Green Gap Solutions in Rockville, Md., and an alternative energy consultant who specializes in lighting technologies. "Companies have spent a lot of time and money on filament and coating just to eke out a little more light and color."
LEDs have been around since the 1960s. They are semiconductors, like computer chips, and shine when an electric current is forced through them and their electrons jump around. The semiconductor material determines the color of the LED. The first LEDs were red. Next came green ones. In 1989, Cree introduced blue LEDs, which are best for making white light.
LEDs are tiny, produce little heat and convert 10 percent to 20 percent of the electric energy they consume into light. So far, they have been used in appliances, electronics, traffic lights and lights for parking lots and buildings. Many tail lights on trucks and cars are LEDs, and they are showing up as headlights, too. They are also starting to appear in residential lighting but at a retail price of $10 or more, LED light bulbs are pricey. The U.S. Department of Energy supports development of LED technology in hopes that efficiency will rise and prices will fall. Widespread adoption of LEDs could reduce greenhouse gas emissions and save an estimated $120 billion in energy costs over 20 years, according to a department report released in February.
All the heavy hitters in the international LED market, including General Electric, Osram Sylvania and Philips, are working on next-generation LEDs, Kelley said. But much of the research is still in its infancy. Davis' team at RTI, whose work is funded by the U.S. Department of Energy, has a head start on the competition, he suggested.
Davis, a chemist who has worked in the electronics industry, is keenly aware of the competitive pressure and RTI's intentions to attract a partner that will bring the technology to market. He lets outsiders into the lab, explains how the nanotech light bulb is put together and allows photographs of the prototype. But some of the production equipment remains locked away.
The key component of RTI's technology is a white material that is slightly sticky and peels off of a blue, fabric-like sheet like skin after a sunburn. The material is made of plastic fibers that are 1 millimeter or longer but so thin that a powerful electron microscope is needed to see them. David Ensor, an expert on filtration and indoor air quality at RTI, developed the nanofibers.
Robert Yaga is the member of the RTI team responsible for making the nanofiber material.
Initially, he used an electrospin chamber, a glass cylinder the size of a small tree trunk that sits in the middle of the lab. He would squeeze a solution with nanofibers through a needle on top of the cylinder, which was filled with electrically charged air.
The charge initiated a tornado-like funnel of fibers and lightning inside the cylinder, Yaga said. Like cotton candy, the fibers twirled toward a grounding plate on the bottom of the cylinder, where they were collected in sheets.
Now that the team has built a prototype of the nanotech light bulb, Yaga uses another piece of equipment that makes bigger sheets of nanofabric. That piece of equipment sits in a secure part of the building outside the lab.
The prototype resembles a cupped hand with a blue LED mounted where the hand meets the wrist. A piece of nanofabric covers the opening. Some of the blue light bleeds from the LED, but the nanofabric glows with a pleasant white light.
It is covered with a blend of variously sized crystals: large ones made of phosphorus and nanocrystals made of semiconductor materials such as cadmium selenide and indium phosphide. The nano crystals - called quantum dots - can be sprayed or printed onto the nanofabric.
The crystal blend absorbs the blue light and emits white light, and it determines what the white light looks like.
"Good light sources are a perception of color," Davis said. "The eye is most sensitive to green light and less to red and blue, but you need all colors for the full spectrum." Good quality white light, he said, "is a matter of blending [the colors] in the right proportions."
To make sure the crystal blend is right, Yaga or one of his teammates, Kim Guzan, Karmann Mills and Li Han, sticks a prototype nanotech light bulb into a test chamber the size and shape of a basketball. The chamber is attached to a computer screen, where test results are displayed in two-dimensional diagrams. One diagram shows the color spectrum by wavelength and eye sensitivity.
A black, curved line that runs through the middle of the diagram represents the spectrum of white light. The curve, called a Planckian locus, represents an international standard set in 1931.
"This is one of the key tests," Davis said. White light looks most natural to the human eye when the test result is on a particular spot of the curved line, he said.
To get the right test results, the RTI team has to work together like clockwork.
At one time during the lab visit, Davis stood on the sidelines, watching team members at their work stations and commenting on their roles.
"Kim on the printer and the keyboards, Karmann on the cutting board, Li Han on the sprayer and Bobby on the spinning chamber," Davis said and started laughing. "Sounds like a rock group: The Nanofibers. But they make light instead of music."
Sabine Vollmer: email@example.com