Breakthrough Technology Accelerates Solid-State
Scientists at the Lighting Research
Center (LRC) at Rensselaer Polytechnic Institute have developed a method known
as "SPE" to get significantly more light from white LEDs (light-emitting diodes)
without requiring more energy.
"We have developed a technology based on a new scattered photon extraction (SPE)
method that will speed up the progress of solid-state lighting and help secure
our nation's energy future," said Nadarajah Narendran, Ph.D., director of
research at the LRC. "The new technology dramatically increases light output and
efficacy of white LEDs, and could play a fundamental role in the evolution of
white LEDs for lighting in homes and offices."
Commercially available white LEDs combine a light-emitting semiconductor with a
phosphor, a rare earth compound, to produce visible white light. However, more
than half of the light, or photons, produced by the phosphor is diverted back
toward the LED where much of it is lost due to absorption. This reduces the
LED's overall light output.
A research group, led by Dr. Narendran, developed a method to extract the
backscattered photons by moving the phosphor away from the semiconductor and
shaping the LED lens geometry. When combined, these changes allow the photons
that would typically be absorbed inside the LED to escape as visible light. The
new technology is patent pending.
"Demonstration of this new 'remote phosphor' concept by Rensselaer's Lighting
Research Center is an exciting development for solid-state lighting," said Dr.
Jeffrey Tsao, principal member of the technical staff at Sandia National
Laboratories. "This advance has a number of significant implications, including
higher-efficiency extraction of photons."
Compared to commercial white LEDs, prototypes of the new SPE LED technology
produced 30-60 percent more light output and luminous efficacy—light output
(lumens) per watt of electricity. This means more visible light is produced
without increasing energy consumption. Further research into the SPE technology
could result in even higher levels of light output and greater luminous
efficacy, according to Narendran.
The industry has set a target for white LEDs to reach 150 lumens per watt (lm/W)
by the year 2012. The new SPE LEDs, under certain operating conditions, are able
to achieve more than 80 lm/W, compared to today's typical compact fluorescent
lamp at 60 lm/W and a typical incandescent lamp at 14 lm/W.
"As LED components improve in efficiency, SPE will further multiply those
improvements and help catapult the industry toward its goal," said Narendran.
"The possibility of solid-state lighting replacing traditional incandescent and
fluorescent lamps looks promising."
According to Narendran, his group is the first to use the SPE method to improve
white LED performance. The research was funded by the U.S. Department of
Energy's Building Technologies Program and the National Energy Technology
Laboratory through its competitive research and development program (cooperative
agreement no. DE-FC26-01NT41203), and is a collaborative effort with the
University of California, Santa Barbara.
The SPE research is published online in the journal physica status solidi (a),
published by John Wiley & Sons, and will be published in an upcoming print
edition of the journal.
Narendran joined Rensselaer's Lighting Research Center in 1996 and was named
director of research for the LRC in 1998. He is also an associate professor
within Rensselaer's School of Architecture. Narendran earned a doctorate in
physics in 1991 and a master's in physics in 1987 from the University of Rhode
Island, and a bachelor's in physics in 1983 from the University of Peradeniya,
LEDs are made of semiconductor chips and emit light when a current passes
through them. LED lighting offers many benefits, including safety, flexibility
and light quality. Since LED lighting systems have proved to be very effective
in applications where brightness, visibility and long-life are important, they
were typically used for exit signs and traffic signals, and then applications
expanded to include small-area lighting.
Lighting applications that use light-emitting diodes are referred to as
solid-state lighting (SSL). According to the U.S. Department of Energy, by 2025,
SSL could displace general illumination light sources such as incandescent and
fluorescent lamps, decreasing national energy consumption for lighting by 29
To learn more about the ground-breaking SSL research taking place at the LRC,
visit its SSL Web site at http://www.lrc.rpi.edu/programs/solidstate/.
ABOUT THE U.S. DEPARTMENT OF ENERGY'S BUILDING TECHNOLOGIES PROGRAM
The goal of the U.S. Department of Energy's Building Technologies Lighting R&D
Program is to develop viable technologies having the technical potential to
conserve 50% of lighting consumption by 2010. The Program partners with
industry, utilities, universities, and research institutions to create energy
efficient lighting technologies in pursuit of this goal.
ABOUT THE LIGHTING RESEARCH CENTER
The Lighting Research Center (LRC) is part of Rensselaer Polytechnic Institute
of Troy, N.Y., and is the leading university-based research center devoted to
lighting. The LRC offers the world's premier graduate education in lighting,
including one- and two-year master's programs and a Ph.D. program. Since 1988
the LRC has built an international reputation as a reliable source for objective
information about lighting technologies, applications, and products. The LRC
also provides training programs for government agencies, utilities, contractors,
lighting designers, and other lighting professionals. Visit http://www.lrc.rpi.edu.
ABOUT RENSSELAER POLYTECHNIC INSTITUTE
Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest
technological university. The university offers bachelor's, master's, and
doctoral degrees in engineering, the sciences, information technology,
architecture, management, and the humanities and social sciences. Institute
programs serve undergraduates, graduate students, and working professionals
around the world. Rensselaer faculty are known for pre-eminence in research
conducted in a wide range of fields, with particular emphasis in biotechnology,
nanotechnology, information technology, and the media arts and technology. The
Institute is well known for its success in the transfer of technology from the
laboratory to the marketplace so that new discoveries and inventions benefit
human life, protect the environment, and strengthen economic development.
Lighting Research Center (LRC)
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