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SPIE Professional July 2008

LED Landscape from a Department of Energy Perspective

The DOE partners with the solid-state lighting industry and others to create energy savings in general illumination.

By James Brodrick

In the last few years, the pace of solid-state lighting technology progress has picked up rapidly. Laboratory announcements promise LED efficacies of 120 lm/W and greater. New products coming to market are beginning to demonstrate performance levels that can rival traditional light sources. These solid-state lighting advances are built on years of innovative research and development, much of it made possible by the U.S. Department of Energy (DOE) and its partners from industry, research and academic institutions, and national laboratories.

The Energy Independence and Security Act of 2007 defines a number of energy-efficiency initiatives for the United States, and moving solid-state-lighting products into the marketplace is among them. As a nation, we use about one-quarter of our electricity for lighting, at a cost of more than $50 billion annually. Much of this energy is wasted; only 10 percent of the energy used by an incandescent bulb produces light. Recent energy legislation sets rigorous future lighting efficiency standards that will require far superior lighting solutions.

Solid-state lighting has the potential to reduce lighting energy use by 50 percent and to transform the lighting landscape. Spurred in part by DOE's R&D program, the energy efficiency of solid-state lighting has improved dramatically. But DOE is well aware that to realize the potential energy savings, commercialization support is also needed. Solid-state lighting is poised to deliver on its performance promise, and DOE and its partners are driving the R&D advances and market introduction activities needed to make that happen.

Partners in Progress

Designing a replacement lamp using LEDs is challenging. It requires integration of dense LED packaging, thermal management, and a robust driver, among other features. The product design shown here was created in a DOE-funded joint project between Philips Solid-State Lighting Solutions and Cree, Inc.

Collaborative, cost-shared DOE research and development projects combine the technical resources of research institutions and national laboratories with the product development, manufacturing, and commercialization expertise of industry leaders. DOE is currently a partner in more than 50 ongoing solid-state lighting R&D initiatives.

Guiding the DOE solid-state lighting portfolio is a comprehensive Multi-Year Program Plan, developed in cooperation with industry and academic partners. This plan defines specific goals for solid-state lighting technology development and for market introduction, and it is used to guide development of DOE's annual funding opportunities for solid-state lighting R&D. To keep pace with the rapidly developing technology, the plan is updated every year through discussions with DOE's industry partner, the Next Generation Lighting Industry Alliance, and participants at DOE's annual R&D workshop.

LED Priorities

A number of key events in 2007 guided the latest updates for the DOE plan. LED efficacies far surpassed projections, and several high-quality LED luminaires appeared on the market (along with some low-performance products, too). As a result, the 2008 plan includes higher near-term performance targets for LEDs and a new emphasis on luminaire performance.

For example, poor thermal design can significantly degrade energy efficiency or shorten the life of an otherwise perfectly good LED. LEDs do not radiate heat, which can be an advantage, but LED luminaires must be designed to conduct heat away from the package or to enhance thermal convection. In the current plan, tasks related to stable packaging materials, lifetime and reliability, and stable, efficient power electronics were all moved to a higher priority.

Luminous efficacy remains a high priority for DOE. One long-standing high-priority LED task is to increase the efficiency of deep green LEDs. Although most products today use phosphor conversion (PC) to produce white light from a blue LED, having a good green source could lead to color-mixed white sources that would avoid the losses associated with the PC approach. DOE-funded research at Rensselaer Polytechnic Institute (RPI) has shown the importance of both the epitaxial structure and the substrate material in improving green light efficiency. The RPI team is working on non-polar epitaxial multi-quantum well LEDs on gallium nitride substrates that produce deep green light directly. So far, they have been able to produce excellent low-dislocation material and to replicate substrate quality throughout the active region, leading to a doubling of green light output for a given input power.

OLED Products

OLED research at Universal Display Corporation targets improvements in internal quantum efficiency, outcoupling efficiency, device voltage, and lifetime of white OLEDs.

For organic light emitters, cost and longevity are difficult issues, so low-cost encapsulation and packaging tasks are raised to a higher priority in DOE's 2008 plan. There are no commercial OLED products available yet, and there is no widely accepted "best" architecture, so finding the right design for OLEDs also remains a high research priority for DOE.

Progress has been made in many areas, as evidenced by DOE-funded research conducted by Universal Display Corporation (UDC). UDC researchers have addressed many OLED high priority tasks and have demonstrated a 45 lm/W white light efficacy at 1000 cd/m2, bringing OLED performance to a point well above incandescent sources and approaching some compact fluorescents. They also have demonstrated lifetimes of 100,000-plus hours for green- and red-emitting materials; the lifetimes for blue light remain a challenge.

DOE's goal, of course, is to realize energy savings through products on the market, so another near-term milestone for OLED development in the 2008 plan challenges engineers and scientists to introduce the first product offerings in the next year or so.

R&D Opportunities

A non-polar homoepitaxial multi-quantum well LED on a bulk GaN structure shows tenfold stronger green peak emission than the same growth on sapphire. The research team at RPI will continue this work to further improve green lighting efficiency.

DOE partnerships—with researchers, chip makers, fixture manufacturers, designers, specifiers, energy program managers, utilities, and other organizations—are accelerating advances in solid-state lighting and helping to ensure that solid-state lighting products succeed in the market.

The annual DOE Solid-State Lighting R&D Workshop, held in January, provides a forum for industry, research organizations, universities, and national laboratories to share updates on research progress and strategies to move solid-state lighting products to market. The annual DOE Market Introduction Workshop, held in July, brings together efficiency programs, utilities, the design community, and industry to identify ways to work together to shape markets for high-performance SSL products.

SSL Plenary Sessions at SPIE Optics+Photonics, 12 August
  • Why the Developing World is the Perfect Market Place for SSL, 8:30-9:15 a.m., Dave Irvine-Halliday, University of Calgary, Canada.
  • Use of Heavy Metal Complexes in Solid State Light Sources (OLEDs), 9:15-10 a.m., Mark E. Thompson, University of Southern California.

Path to Market for SSL Products

Anyone who owned an 8-track player understands that sound research and high quality are only part of a product's market success. As the federal government's lead organization for solid-state lighting market introduction activities, DOE supports targeted strategies to ensure that its investments in solid-state lighting R&D-and our energy future-pay off.

DOE CALiPER testing of commercially available products provides reliable, unbiased product performance information to foster the developing market for high-performance solid-state lighting products. DOE GATEWAY demonstrations provide experience and data on product performance and cost effectiveness in commercial and residential applications.

Bright Tomorrow Lighting Contest

DOE's Bright Tomorrow Lighting Prize (L Prize™) competition is an initiative defined by recent energy legislation that challenges industry to develop innovative, high-performance solid-state lighting products to replace inefficient products. The legislation authorizes up to $20 million in cash prizes, and DOE is working with utility partners and other government agencies to arrange for federal purchasing agreements, utility programs, and other incentives for the winning products.  

DOE Energy Stars

Look for the first DOE ENERGY STAR® solid-state lighting products on the market. The ENERGY STAR label is a widely recognized mark of energy efficiency that helps guide purchasing decisions.

Have a question or comment about this article? Write to us at SPIEProfessional@spie.org.

James Brodrick

James Brodrick, manager of the U.S. Department of Energy Solid-State Lighting Portfolio, is the DOE's industry liaison for research, development, and market introduction of advanced solid-state lighting technologies. His PhD in mechanical engineering is from the University of Illinois at Champaign-Urbana. For information on DOE workshops or to receive regular program announcements regarding funding opportunities for solid-state lighting R&D, reports, events, and other activities see the DOE Solid State Lighting Web site.

DOI: 10.1117/2.4200807.09

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