easily dimmed, their low current and driver electronics require special controls. National Electrical Manufacturers Association (NEMA) is working on a standard to address this issue (NEMA SSL 7-2012; Phase Cut Dimming for Solid State Lighting: Basic Compatibility). There is, at present, no standardized method for measuring the lifetime of SSL products, even though lifetime is a critical parameter in economically justifying SSL. Consequently, lifetime is a missing metric on the Lighting Facts label. DOE has instead recently incorporated a lumen maintenance metric, LM-80.6 This metric gives the number of hours of operation before the lumen output of the LED emitter degrades to 70 percent of its initial value (the so-called L70 point). This metric does not apply to product (luminaire) life, and if the durability of the balance-of-product does not match the expected 25,000-hour life of the LED emitter, the committee expects there will be negative consumer reactions.
The color of illuminated objects is also a key determinant of the perceived quality of lighting products, and in this regard the CRI of LEDs can be very high—comparable to high-CRI fluorescent lamps. There is consensus, however, that improved measures of color quality7 are needed to guide manufacturers, which, for SSL products, can be more numerous and much smaller in size compared to the incandescent lamp market. This diffuse supplier market compounds the problem of industry standardization.
ORGANIC LED-BASED SOLID-STATE LIGHTING
The OLED offers the possibility of unusual form factors by taking advantage of the inherent slim, flexible character of the device itself, and by leveraging its area-source characteristic to develop possible new applications. Although some OLED-based luminaires are commercially available, their present costs limit widespread adoption. The lifetime of an OLED is very sensitive to its exposure to both air and moisture, making the hermetic sealing of large, flat packages critically important. Both lifetime and efficacy are also negatively impacted by the high currents required to generate light of brightness sufficient for general purpose lighting, leading to the phenomena of current droop and thermal droop (a decrease in lumen output with increasing current or temperature). The committee recommends that the Department of Energy support research to understand the fundamental nature of efficiency droop at high currents in OLEDs and to seek means to mitigate this effect through materials and device architectural designs. Color consistency among OLED panels forming a luminaire is also a challenge. While OLEDs are employed extensively for displays, displays do not require the large area packages or high levels of illumination of general purpose lighting. Perhaps the largest efficiency gain that has yet to be achieved is improved outcoupling of light in OLEDs, made particularly difficult compared with LEDs by the large areal dimension and integrated form factor of the former. The committee recommends that the Department of Energy focus on efforts that result in significant light outcoupling enhancements that are low-cost to implement and are independent of both wavelength and viewing angle. While there is a manufacturing infrastructure for OLED displays, located almost exclusively in Asia, there is currently none for lighting products.
DOE LIGHTING PROGRAM
Solid-State Lighting has been funded in recent years at roughly $25 million per year, of which roughly $9 million was directed toward R&D in FY2011, emphasizing three interrelated thrusts: (1) core technology research and product development, (2) manufacturing R&D, and (3) commercialization support. The SSL Manufacturing Initiative was added to the SSL R&D portfolio in 2009 with the aim of reducing costs of SSL sources and luminaires, improving product consistency and maintaining high-quality products, and encouraging a significant role for domestic U.S.-based manufacturing.8 The DOE Lighting program also addresses issues related to commercialization. It supports independent testing of SSL products, supports exploratory studies on market trends and helps to identify critical technology issues, supports workshops to foster collaboration on standards and test procedures, promotes a number of industry alliances and consortia, disseminates information, and supports a number of other initiatives. It also conducts technical, market, economic, and other analyses and provides incentives to the private sector to innovate.
DOE has done a remarkable job of helping to advance SSL R&D and manufacturing and educating the lighting community, and the committee recommends that the Department of Energy’s SSL program be maintained and, if possible, increased. However, the committee notes that the percentage of matching funds from R&D grant recipients has declined in the past few years. The committee recommends that the Department of Energy seek to obtain 50 percent cost sharing for manufacturing R&D projects, as was done with the projects funded by the American Recovery and Reinvestment Act. In addition, the committee found that the Bayh-Dole waiver is discouraging some universities and small companies from participating in the program. The
6 Illuminating Engineering Society, IES LM-80-2008, Approved Method for Measuring Lumen Depreciation of LED Light Sources.
7 At present, the color rendering index, managed by the International Commission on Illumination (CIE), is the internationally accepted metric for the evaluation of a light source’s color rendering abilities and was developed in response to the advent of fluorescent lamps.
8 U.S. Department of Energy. 2011. Solid-State Lighting Research and Development: Manufacturing Roadmap. Washington, D.C.