Partnership for Solid-State Lighting Report of a Workshop (2002) / Chapter Skim
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Panel II: LED Lights: Emerging Opportunities
Panel II: LED Lights: Emerging Opportunities
Pages 48-65
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From page 48... ...
Today, he said, the efficiency of LED s has increased by two orders of magnitude and the auto industry is embracing them rapidly. THE EVOLUTION OF LED LIGHTS George Craford LumiLeds Lighting The Heart of the LED Dr.
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From page 49... ...
In practice today the highest light extraction efficiency is about 50 percent. There are many practical barriers to higher extraction efficiencies, including internal reflection and absorption at the metallic contacts, within the semiconductor layers, or in the encapsulation/package.
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From page 50... ...
Now a bigger chip, 0.5 mm square, emits tens of lumens. In the newer gallium nitride technology the trend is similar, from smaller to larger, from low to high power; GaN chips now emit up to 50 lumens, and in some research devices, over 100 lumens.
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From page 51... ...
They will also be increasingly used for low-power applications, especially where reliability is paramount or bulb changing is difficult, as in tunnel lighting. Before LED s can penetrate the general illumination market, they need major performance improvements, cost reductions, and better reliability.
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From page 52... ...
Gallium nitrate technology, which led to the development of blue LEDs, now makes it possible to create both white light and high brightness green light. The more recent development of ultraviolet emitters adds a new way to produce white and very deep ultraviolet sources.
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From page 53... ...
It would also bring the United States into compliance with the Kyoto environmental accord. The Complexities of Nitride Technology Thinking about the place of solid-state lighting in the future, he predicted that nitride sources would be used to generate ultraviolet and blue light, but enormous work was still required to understand the gallium nitride (GaN)
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From page 54... ...
The major target market of halogen and incandescent bulbs, however, can be penetrated only after substantial technical breakthroughs. The major challenge is to raise the luminous output by at least an order of magnitude.
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From page 55... ...
Another potentially enormous market is the backlights for computer notebook displays, where LED s promise great power savings and extended battery life. Two Major Challenges: Cost and Performance Dr.
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From page 56... ...
In describing a series of efforts under way, she noted that while the lumen is based on a well defined measurement of the photopic response of the eye, the perception of color and the quality metrics of color temperature and color rendition are based on measurements using broadband emitters. These metrics are being questioned as combinations of narrow band emitters, qua LEDs, are being created to provide white light.
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From page 57... ...
. In addition, the CIE has established technical committees to develop uniform standards; NIST participates in this process, representing the interests of U.S.
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From page 58... ...
Improving Chip Technology The big LED cost driver today is the LED chip. One major challenge is that the substrates are very small, and many of them are needed to make large quantities of chips.
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From page 59... ...
Better light extraction requires innovative fabrication techniques, such as chip shaping. This possibility has been understood since the first LED s were made in the 1960s, but more effective shaping is needed.
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From page 60... ...
At the same time, chip efficiency must be increased by three to five times through improved structure design, higher efficiency in materials systems regardless of wavelength, and novel fabrication devices and new structures for better light extraction. Problems of LED Packaging An area that is frequently overlooked in high-efficiency LEDs is the package.
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From page 61... ...
Here the major effort must come from industry, with a smaller contribution from academia and minor input from government labs. The Importance of Design Finally, he compared LED lighting with traditional lighting and emphasized the importance of design.
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From page 62... ...
Karlicek, "is that we need major breakthroughs in lighting paradigms to be able to use solid-state lighting and achieve the energy saving benefits they offer." DISCUSSION Charles Trimble observed that if one looks at successful partnerships between academia, government, and industry in the computer, semiconductor, and Global Positioning System arenas, one finds several common threads. First, the government invested seed capital in precompetitive research.
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From page 63... ...
From this plateau the industry still has to improve chip efficiency from three to five times, depending on the color. He said that he had not considered where to draw the line in defining precompetitive technologies, but genuine breakthroughs in efficiency "certainly must happen to allow this lighting technology to take off." Better Physics Steven DenBaars stressed the need for better understanding of the physics of light emission, including the characteristics of nanostructures, the role of defects, and the high voltages seen in the nitrides related to p-doping.
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From page 64... ...
The same is true for 4-inch silicon carbide wafers, whose development received substantial government funding that helped drive costs down. He suggested that if the industry had a government partner, it might reach its goals of efficient, effective, low-cost lighting in 5 to 10 years instead of 30 years.
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From page 65... ...
A second area would make use of Vertical Cavity Surface Emitting Lasers (VCSELS)
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