LED/OLED lighting shines at SPIE meeting
Since the introduction and initial commercial availability in the 1960s, the luminous efficacy of LED illumination has increased and the cost of LED illumination has decreased, both by about an order of magnitude per decade, according to plenary comments by George Craford, CTO of Lumileds (San Jose, CA) during the 5th International Conference on Solid State Lighting at the Annual Meeting of the SPIE (July 31-August 4).
SAN DIEGO, CA - Since the introduction and initial commercial availability in the 1960s, the luminous efficacy of LED illumination has increased and the cost of LED illumination has decreased, both by about an order of magnitude per decade, according to plenary comments by George Craford, CTO of Lumileds (San Jose, CA) during the 5th International Conference on Solid State Lighting at the Annual Meeting of the SPIE (July 31-August 4). And the continuing exponential rate of change in LED technology is in large part what makes it unique and highly promising among other lighting technologies, he added.
Specific focus areas that are currently crucial to moving forward in general white light illumination include an improvement in green LED internal efficiency by a factor or 3 or 4 to match current levels of red and blue efficiency. The development of green will ultimately be a big factor in determining whether RGB color combinations as opposed to phosphor stimulated white light from blue or ultraviolet sources become more important sources of white LED illumination, Craford said. The phosphor approach tends to be simpler but loses some quantum efficiency in the conversion process. The RGB approach, while not sacrificing quantum efficiency, does require the additional complexity of feedback circuitry to maintain color mixture. Ideally, combining a phosphor approach with RGB can not only yield high color rendering index (CRI) values, on the order of 96, but also provide tunable white light that could be adjusted through the day, for instance, to match daylight conditions.
While difficult engineering challenges to achieving these goals remain there don’t appear to be any barriers to overcome in terms of the fundamental physics, he added. In addition to development efforts related to chip substrates and growth conditions, new areas of study that may yield significant efficiency and cost improvements include quantum dot sources and phosphors as well as photonic crystal LEDs to provide higher light outputs, while also focusing the light output entirely in a forward direction. The current U.S. performance goal is 150 lumens/Watt by 2012, even though it is difficult to predict exactly when general LED illumination will actually happen.
With a primary focus on significant energy savings over the long term (lighting accounts for 21% of U.S. energy consumption) the Department of Energy is currently funding 42 solid-state lighting projects with a cumulative contract value of $63.6 million, according James Brodrick, who spoke after Craford and described the solid state lighting R&D effort in the DOE Building Technologies Program. Of the 42 funded projects, 23 account for $29.8 million in total funding ($23.5 million from the DOE and $6.3 million from applicants) and concern LED technology. The remaining 29 projects account for $33.8million in funding ($23.3 million from DOE and $10.5 million from applicants) and concern OLED research.
Current major OLED R&D projects include a materials and devices designs project at Los Alamos National Laboratory (Los Alamos, NM) focused on key materials challenges for OLED use in general illumination. Also with DOE funding, the Pacific Northwest National Laboratory (Richland, WA) is exploring state-of-the-art phosphorescent organic light emitters to increase the power efficiency of blue OLEDs in order to ultimately integrate a UV or blue OLED with a thin film phosphor and demonstrate 30 lumens/Watt white light with CRI in excess of 85 at 800 cd/m-squared. The University of California Santa Barbara is working on surface plasmon enhanced phosphorescent organic colored and white light emitting diodes to demonstrate high efficiency at large injection current densities, operational lifetimes in excess of 10,000 hours and true daylight color temperature and luminous efficiency close to (LED levels of) 50 lumens/W (for white OLEDs). General Electric (Fairfield, CT) is working with Dow Chemical (Midland, MI) to develop polymer OLEDs with CRI greater than 90, correlated color temperature (CCT) between 3000 and 6000 K, luminous efficacy in excess of 45 lumen/Watt and fabricated in a manner consistent with high speed processing.
Following Brodrick’s talk, Juni Kido described a 3-year (2004-2006), collaborative university-industry project at Yamagata University (Yamagata, Japan) funded by the Ministry of Economy, Trade and Industry (METI; Tokyo, Japan) for $8 million US to produce white light emitting OLEDs for lighting applications. In addition, Sven Murano described Novaled’s (Dresden, Germany) achievement, in collaboration with Philips (Eindhoven, The Netherlands) and the Institute for Applied Physics at the Technical University of Dresden, of 25 lumens/W at 1000 cd/m-squared and a CRI of 76, in an alkali- and metal-free OLED based on a proprietary phosphorescent, stacked layer technology (see related newsbreak). He also discussed the company’s roadmap for ultimately achieving an efficacy of 100 lumens/W.
Nearly 6000 people attended this year’s annual meeting, according to SPIE. Other highlights included:
- The Atmospheric Communication, Control, and Imaging program, chaired by Jennifer Ricklin, DARPA/ATO. One of the better attended talks in this group of presentations on “free-space optics” was an invited paper given as part of the Systems Design and Analysis session cochaired by David Voelz, New Mexico State Univ., and Jennifer Ricklin, DARPA. Titled “DARPA Free-Space Optics” and presented by Steven Griggs, DARPA, this paper highlighted some of the novel ways researchers at DARPA are trying to provide the desired bandwidth and the desired reliability for mobile links.
- The Organic Photovoltaics conference, chaired by Zakya Kafafi, Naval Research Lab. With California set to become a worldwide leader in photovoltaic power, the work being done by the scientists, engineers and researchers presenting their findings in Kafafi’s conference, particularly those pioneering the use of thin film deposition to make possible the mass production of cheap, flexible highly efficient solar arrays, has gained more importance than ever.
- The Quantum Communications and Quantum Imaging conference. Now in its third year as part of Optics & Photonics 2005 and chaired by Ronald Meyers, Army Research Lab., and Yanhua Shih, Univ. of Maryland/Baltimore County, the conference features some of the latest research by those attempting to leverage the indistinct and shifting states between matter typified by quantum physics to create new and much more powerful “quantum” transistors for use in computing, communication cryptography and imaging.
- The strong emphasis on nanotechnology at Optics & Photonics 2005 in San Diego continued with the Nanotechnology Plenary Session. Comprisung seven plenary sessions, most of the topics in these presentations focused on much of the current materials research driving advances in nanotechnology. Larry Dalton, Univ. of Washington, for example, in his presentation on nanoparticle engineering, covered efforts to create more effective organic electro-optic materials. The importance of these materials, Dalton said, lies in their ultrafast response times compared to inorganic compounds. Organics have very large electro-optic coefficients, up to 10 times that of lithium niobate.
-Hassaun A. Jones-Bey