By Neal Singer
The human eye is as comfortable with white light generated by diode lasers as with that produced by increasingly popular light-emitting diodes (LEDs), according to the results of tests conceived at Sandia.
A LIGHT TOUCH - Jeff Tsao examines initial setup used to test diode lasers as an alternative to LED lighting. Skeptics felt laser light would be too harsh to be acceptable. Research by Jeff and his colleagues suggests the skeptics are wrong. (Photo by Randy Montoya)
Both technologies pass electrical current through material to generate light, but the simpler LED emits lights only through spontaneous emission. Diode lasers bounce light back and forth internally before releasing it.
The finding is important because LEDs - widely accepted as more efficient and hardier replacements for century-old tungsten light bulb technology - show drops in efficiency at electrical currents above 0.5 amps. Meanwhile, the output of the sister technology - the diode laser - increases, providing even more light than LEDs at higher amperages.
"What we showed is that diode lasers are a worthy path to pursue for lighting," says Jeff Tsao (1120), who proposed the comparative experiment. "Before these tests, our research in this direction was stopped before it could get started. The typical response was, 'Are you kidding? The color rendering quality of white light produced by diode lasers would be terrible.' So finally it seemed like, to go further, one really had to answer this very basic question first."
Little work had been done to research (much less commercialize) diode lasers for lighting because of a widespread assumption that human eyes would find laser-based white light unpleasant. It would be composed of four extremely narrow-band wavelengths - blue, red, green, and yellow - and would be very different from sunlight, for example, which blends a wide spectrum of wavelengths with no gaps in between. Diode laser light is an order of magnitude narrower than that emitted by LEDs.
The tests - a kind of high-tech market research - took place at the University of New Mexico's Center for High Technology Materials. Forty volunteers were seated, one by one, before two near-identical scenes of fruit in bowls, housed in adjacent chambers. Each bowl was randomly illuminated by warm, cool, or neutral white LEDs, by a tungsten-filament incandescent light bulb, or by a combination of four lasers (blue, red, green, yellow) tuned so that their combination produced a white light.
The experiment proceeded like an optometrist's exam: The subjects were asked, Do you prefer the left picture or the right? All right, how about now?
The viewers were not told which source provided the illumination. They were instructed merely to choose the lit scene with which they felt most comfortable. The pairs were presented in random order to ensure that neither sequence nor tester preconceptions played roles in subject choices, but only the lighting itself. Alexander Neumann, a UNM doctoral student of professor Steve Brueck, wrote the computer program and created the set.
Each participant, selected from a variety of age groups, was asked to choose 80 times between the two changing alternatives, a procedure that took from 10 to 20 minutes, says Sandia scientist Jonathan Wierer (1123), who helped plan, calibrate, and execute the experiments. Five results were excluded when the participants proved to be color blind. The result was that there was a statistically significant preference for the diode-laser-based white light over the 'warm' and 'cool' LED-based white light, Jon says, but no statistically significant preference between the diode-laser-based and either the neutral LED-based or incandescent white light.
Results were not expected to start a kind of California gold rush of lighting fabricators into diode lasers, says Jeff, but merely to open a possible, formerly ignored, line of research. Diode lasers are slightly more expensive to fabricate than LEDs because their substrates must be made of lower-defect densities than those used for LEDs. Still, he says, such substrates are likely to become more available in the future, as they also improve LED performance.
Also, while blue diode lasers have good enough performance that the automaker BMW is planning their use in its vehicles' next generation white headlights, performance of red diode lasers is not as good, and yellow and green have still further to go before they are efficient enough for commercial lighting opportunities.
Still, says Jeff, a competition wouldn't have to be all or nothing. Instead, he says, a cooperative approach might use blue and red diode lasers with yellow and green LEDs. Or blue diode lasers could be used to illuminate phosphors – the technique currently used by fluorescent lights and the current generation of LED-based white light - to create desirable shades of light.
The result makes possible still further efficiencies for the multibillion dollar lighting industry. The so-called smart beams can be adjusted on site for personalized color renderings for health reasons and, because they are directional, also can provide light illumination where it's wanted.
Colorimetric and experimental guidance was provided by the National Institute of Standards and Technology.
The research was published in the July 1 Optics Express.
The work was conducted as part of the Solid-State Lighting Science Energy Frontier Research Center, funded by the DOE Office of Science. - Neal Singer
By Patti Koning
As Sandians enter the Micro and Nano Technologies Laboratory (MANTL) each morning, they will soon be greeted by Hydrogen Man, as depicted in the mural "Hydrogen Man versus Carbo."
"Hydrogen Man vs. Carbo," created by Jazmin Vital (on left) and Carlos Hernandez Reyes, caught the attention of many hydrogen researchers, including Tom Felter (8252), manager of hydrogen and metallurgy research. (Photo by Randy Wong)
Occupants of other buildings need not feel jealous, however - Hydrogen Man, along with four other clean energy-themed murals, will be rotated among the lobbies of MANTL (940), the Combustion Research Facility (904), the Combustion Research Computation and Visualization building (905), the Distributed Information Systems Laboratory (915), and Bldg. 911.
Local middle and high school students created the murals this summer through the Path to Picasso program, a partnership between Horizons Family Counseling, the city of Livermore, and the Livermore Police Department. The program, now in its fifth year, gives at-risk youth the opportunity to work with a local professional artist to create a large piece of art that is displayed publicly.
Horizons, a division of the Livermore Police Department, provides family counseling, case management, and parent training for Tri-Valley families. Last year Jacquie Reardon (8131) invited the organization to participate in a site SHARE (Sandia Helps and Reaches Everyone) event, which is where the idea for the Path to Picasso Sandia project first emerged.
"I noticed some blank walls and started to imagine the possibilities," says Horizons youth and family services manager Lynn Gardner. "Path to Picasso art has decorated City Hall, the Livermore Police Department, the Bankhead Theater Plaza, and the Wheels Transit Depot, so why not Sandia too? I knew that doing a project for a national laboratory would open the students' eyes to new concepts and maybe even give them enough understanding to consider new career opportunities they hadn't thought of before."
To kick off the project, Mike Janes and Allison Doughty (both 8529) shared with the Path to Picasso students Sandia's mission and many areas of work, including clean energy and transportation.
"The theme of clean energy was challenging, because there isn't a lot of 'clean energy' art out there," says Regina Levya, creative director of Path to Picasso. "They really had to be pioneers. When we first got started, many of these kids weren't sure if they could do this. Finishing a project like this and seeing the reaction of Sandians is a huge boost to their self-esteem."
When the murals were unveiled at a SHARE event Sept. 22, the artwork struck a chord with many Sandians. "I love this mural," said Glenn Kubiak (8600), looking at Hydrogen Man vs. Carbo. "I'm a chemist and I see so many clever embedded messages."
Artists Jazmin Vital and Carlos Hernandez Reyes were inspired by Sandia's research into hydrogen as a clean transportation fuel. They chose a comic book theme of good vs. evil, in this case "Carbo," who is trying to stop Hydrogen Man from making renewable energy. In the painting, Hydrogen Man stands on top of the periodic table.
In "Clues to Solutions," Sandra Cortez, Grecia Arias, and Jessica Santiago created an abstract painting in Picasso's cubist style depicting the world, solar panels, algae, and other areas of Sandia's research. Look hard enough and you'll find the botnet lurking near the lower left-hand corner.
Best friends Cianna Chavez and Brandon McCullough worked together on "Clean Energy versus Pollution," a painting that shows a street dividing two very different buildings. Jaidee Sandoval was inspired by Sandia's research into creating fuel from natural things to paint "Biomass Transit." Yvonne Nolasco used a tree as the unifying theme of her appropriately named painting, "Communi-tree."
"We are delighted with the art created by the Path to Picasso students. Sandia is very proud to support such an important community program," says Mike. "This is a great example of a community partnership that has been developed through SHARE."
At the Sept. 22 SHARE event, host Jacquie told her personal story of the impact that Horizons had on her life. "Years ago, my teenage daughter began making some very grave choices and we were dealing with matters of life and death on a daily basis. I was ready to send her to a teen boot camp, when I took to the recommendation of a counselor at Horizons to try something different," she explains. "Horizons gave me the ability to parent my child through it personally."
Jacquie also shared the happy news that her daughter is now transferring to California State University East Bay with a 4.0 grade point average. She added that a family's situation does not have to be as grave as hers was to benefit from Horizons.
"They are available for a myriad of challenges," she says. "We don't have to parent alone - it took an entire community to raise my daughter effectively."
For more information on Horizons Family Counseling, visit http://www.cityoflivermore.net/citygov/horizons/default.asp. -- Patti Koning
Sandia's FY10 electronics stewardship activities have received an award for reducing the environmental impacts of the computers, printers, and other office electronics it uses on a daily basis.
The US Environmental Protection Agency (EPA) and the Office of the Federal Environmental Executive, which jointly manage the Federal Electronics Challenge (FEC), gave Sandia a silver award for its progress in life- cycle electronics stewardship (purchasing, operations, and end-of-life management). Sandia was one of four DOE sites recognized at the silver level and was recognized at the bronze level in fiscal year 2008.
John Zepper, director of Sandia's Computing and Network Services Center (9300), accepted the award at a recent ceremony in Washington, D.C.
Sandia's Pollution Prevention program works on electronics stewardship with other Labs organizations, including procurement, computer support, and property management. Sandia's best practices in electronics stewardship include:
The FEC encourages federal facilities and agencies to purchase greener electronics, reduce the impact of electronics during use, and manage used electronics in an environmentally safe way.
Sandia has participated in the FEC since 2006. -- Stephanie Holinka