LEDs have been commercially available since the 1960's, but in recent years there have been remarkable improvements in performance. These technology developments have enabled the use of LEDs in a variety of colored and white lighting applications. Colored LEDs have already become the technology of choice for traffic signals, much of interior and exterior vehicle lighting, signage of various types often as a replacement for neon, and other areas. LEDs are expected to become the dominant technology for most colored lighting applications. LEDs are beginning to penetrate white lighting markets such as flashlights and localized task lighting. With further improvement LEDs have the potential to become an important technology for large area general illumination. White LED products already have performance of over 30 lumens/watt which is nearly 3x better than incandescents. White LEDs with outputs of more than 100 lumens are already available commercially, and higher power devices can be expected in the near future. LEDs can be used as point sources, or can be used with light guides of various types to provide distributed illumination. Developments that will need to occur for LEDs to be viable for large area general illumination are discussed.
This paper describes the status and trends of visible LED (light-emitting diode) technology. LED technology is compared to conventional incandescent and fluorescent lighting technology. Performance and cost, the key issues which need to be improved to enable LEDs to substantially penetrate the illumination market are discussed.
Jonathan Wierer, Jerome Bhat, Chien-Hua Chen, G. Christenson, Lou Cook, M. Craford, Nathan Gardner, Werner Goetz, R. Scott Kern, Reena Khare, A. Kim, Michael Krames, Mike Ludowise, Richard Mann, Paul Martin, Mira Misra, J. O'Shea, Yu-Chen Shen, Frank Steranka, Steve Stockman, Sudhir Subramanya, S. Rudaz, Dan Steigerwald, Jingxi Yu
High-power light-emitting diodes (LEDs) in both the AlInGaP (red to amber) and the AlGaInN (blue-green) material systems are now commercially available. These high-power LEDs enable applications wherein high flux is necessary, opening up new markets that previously required a large number of conventional LEDs. Data are presented on high-power AlGaInN LEDs utilizing flip-chip device structures. The high-power flip-chip LED is contained in a package that provides high current and temperature operation, high reliability, and optimized radiation patterns. These LEDs produce record powers of 350 mW (1A dc, 300 K) with low (<4V) forward voltages. The performance of these LEDs is demonstrated in terms of output power, efficiency, and electrical characteristics.
Michael Krames, G. Christenson, Dave Collins, Lou Cook, M. Craford, A. Edwards, Robert Fletcher, Nathan Gardner, Werner Goetz, William Imler, Eric Johnson, R. Scott Kern, Reena Khare, Frederick Kish, Chris Lowery, Mike Ludowise, Richard Mann, M. Maranowski, Steven Maranowski, Paul Martin, J. O'Shea, S. Rudaz, Dan Steigerwald, J. Thompson, Jonathan Wierer, Jingxi Yu, David Basile, Ying-Lan Chang, Ghulam Hasnain, M. Heuschen, Kevin Killeen, Christophe Kocot, Steven Lester, Jeffrey Miller, Gerd Mueller, Regina Mueller-Mach, S. Jeffrey Rosner, Richard Schneider, Tetsuya Takeuchi, Tun Tan
Currently, commercial LEDs based on AlGaInN emit light efficiently from the ultraviolet-blue to the green portion of the visible wavelength spectrum. Data are presented on AlGaInN LEDs grown by organometallic vapor phase epitaxy (OMVPE). Designs for high-power AlGaInN LEDs are presented along with their performance in terms of output power and efficiency. Finally, present and potential applications for high-power AlGaInN LEDs, including traffic signals and contour lighting, are discussed.
Mari Ochiai-Holcomb, Michael Krames, Gloria Hofler, Carrie Carter-Coman, Eugene Chen, Patrick Grillot, Kwang Park, Nathan Gardner, Jen-Wu Huang, Jason Posselt, David Collins, Steve Stockman, M. Craford, Frederick Kish, I. Tan, Tun Tan, Christophe Kocot, Mark Hueschen
High power light emitting diodes (LEDs) are of interest for many lighting applications. Flux improvements can be achieved by scaling conventional chips to larger dimensions. However this scaling results in a decrease in extraction efficiency. These penalties can be offset by modifying the chip geometry such that the number of internal reflections is reduced, thereby increasing the probability of photon escape. LEDs with a truncated-inverted-pyramid (TIP) geometry have been fabricated and packaged. Peak efficiencies exceeding 100 lm/W have been measured (100 mA dc, 300 K) for orange ((lambda) p approximately 610 m) devices. In the red wavelength regime ((lambda) p approximately 650 nm), peak external quantum efficiencies of 55% (100 mA dc, 300 K) have been achieved. Flux exceeding 65 lumens from a single 594 nm device has also been demonstrated. These characteristics match and/or exceed the performance of many conventional lighting sources.
Steven Maranowski, Michael Camras, Changhua Chen, Lou Cook, M. Craford, Dennis DeFevere, Robert Fletcher, Gloria Hofler, Frederick Kish, Chihping Kuo, A. Moll, Tim Osentowski, K. Park, Michael Peanasky, S. Rudaz, Dan Steigerwald, Frank Steranka, Steve Stockman, I. Tan, J. Tarn, Jingxi Yu, Mike Ludowise, Virginia Robbins
A new class of LEDs based on the AlGaInP material system first became commercially available in the early 1990's. These devices benefit from a direct bandgap from the red to the yellow-green portion of the spectrum. The high efficiencies possible in AlGaInP across this spectrum have enabled new applications for LEDs including automotive lighting, outdoor variable message signs, outdoor large screen video displays, and traffic signal lights. A review of high-brightness AlGaInP LED technology will be presented.
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