Breakthrough Technology Accelerates Solid-State Lighting
|Photo courtesy of the Lighting Research
Scientists at Rensselaer's Lighting Research Center (LRC)
have developed a method known as "SPE" (scattered photon
extraction) 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
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.
Narendran's research group 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.
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.
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
"As LED components improve in efficiency, SPE will further
multiply those improvements and help catapult the industry
toward its goal," said Narendran.
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 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) and will be published in an
upcoming print edition of the journal.