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Summary Congress, recognizing the potential for energy savings tronic circuit to provide them with the proper form of electric in the use of general lighting for illumination, requested in power. Both LEDs and OLEDs and the luminaires based on the Energy Independence and Security Act of 2007 (EISA them are discussed below. 2007) that the Department of Energy (DOE) contract with The committee’s main findings and its key recommenda- the National Research Council (NRC) to conduct a study to tions for the Department of Energy are listed in Boxes S.1 assess the status of solid-state lighting (SSL) as a technology. and S.2, respectively. The contract requested that the National Academies provide an objective and independent assessment of the current state LED-BASED SOLID-STATE LIGHTING of solid-state lighting and its future potential for accommo- dating the new minimum efficiency standards for lighting. Technology and Lighting Products The NRC established the Committee on Assessment of Solid State Lighting (Appendix A) composed of diverse experts in Because a single LED emits light that is monochromatic, the fields of solid-state physics, electronics, lighting design, devices that emit white light must do so by combining the human perception of light, industrial commercialization, emissions of individual red, green, and blue (RGB) LEDs and policy. The statement of work directed the committee to or by using a single blue LED whose emission excites a review the development and future impacts of SSL, includ- phosphor, which in turn emits white light. This latter design ing projections of cost and research and development (R&D) is the more common. The efficacy3 of white LEDs has been necessary to overcome barriers to widespread adoption and increasing rapidly and is expected to approach 200 lumens/ the potential for unintended consequences of deployment. watt (lm/W) by 2020, greatly exceeding all other general Solid-state lighting consists of two technologies—the illumination technologies. The committee found that lumi- inorganic semiconductor-based light-emitting diode (LED) naires and lamps based on LEDs will be able to support the and the organic polymeric-based light-emitting diode lumen output standards Congress required to be promulgated (OLED). Both technologies are the subject of active research by DOE in Section 321 of EISA 2007. worldwide. The LED technology is currently in the early LED-based lighting products currently are available in stages of commercial deployment while OLEDs are in the two forms. The first consists of lamps that can replace, one- demonstration phase. All LED-based luminaires1 require for-one, the incumbent lamp (i.e., the lamp that is currently optics to distribute the unidirectional light emitted by the in use) without modification to the original fixture. The LED, LED and a large heat sink to maintain the LED temperature optics, heat sink, and electronic drivers are all packaged within limits. Furthermore, like fluorescent lamps,2 both in the replacement lamp, typified by the screw-in replace- LED and OLEDs require they be supplied through an elec- ment—now offered by Cree, Philips, OSRAM Sylvania, and others—for the familiar household incandescent bulb (the 1 “A-19”). A 60 W A-19 lamp produce about 850 lumens, for A luminaire consists of, minimally, a lamp holder, commonly called a socket, and the way to connect the socket to the electrical supply. Most an efficacy of 14 lm/W. The high-quality commercial LED fixtures also contain optical elements that distribute the light as desired, such equivalent produces 93 lm/W. For comparison, the equivalent as a reflector, lens, shade, or globe. When needed, fixtures and luminaires contain a ballast or a driver. 2 The term lamp is equivalent to the term light bulb in every-day usage, 3 Efficacy is a measure of the efficiency with which a lamp or luminaire i.e., the source of light that attaches to the luminaire by means of a screw- converts electricity to useful light. It is defined as the ratio of the luminous base or pins. flux to the total electrical power consumed and has units of lumens per watt. 1
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2 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING BOX S.1 Findings Finding 1: Luminaires and lamps based on LEDs will be able to support the standards for lumen output Congress required to be promulgated by DOE in Section 321 of the Energy Independence and Security Act of 2007. Finding 2: Cost is the biggest obstacle to the widespread deployment of SSL based on LEDs. Finding 3: The Bayh-Dole waiver is discouraging some universities and small companies from participating in the DOE program. Finding 4: On a lifecycle basis, warm and cool white LEDs are already cheaper than incandescent lighting and will likely be comparable to that of fluorescent lighting technologies in the near future. NOTE: The full text of all findings and recommendations in the report appear in Chapter 7. BOX S.2 Recommendations to the Department of Energy Recommendation 1: The Department of Energy should continue to make investments in LED core technology, aimed at increasing yields, and in fundamental emitter research to increase efficacy, including improvements in the controlled growth and performance of the emitter material. Recommendation 2: The Department of Energy and lamp manufacturers and retailers should work together to ensure that consumers are educated about the characteristics and metrics of these new technology options. Recommendation 3: The Department of Energy should 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. Recommendation 4: The Department of Energy should focus on efforts that result in significant light outcoupling enhancements for OLED that are low cost to implement and are independent of both wavelength and viewing angle. Recommendation 5: The Department of Energy SSL program should be maintained and, if possible, increased. Recommendation 6: The Department of Energy should 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. Recommendation 7: The committee recommends that the Department of Energy consider ending its waiver of Bayh-Dole for SSL funding. NOTE: All the findings and recommendations presented in the report are collected in Chapter 7, where the recommendations are double-numbered to indicate the chapter in the main text where they appear in context. spiral tube compact fluorescent light (CFL) has an efficacy The second product form is the retrofit luminaire, which is of 63 lm/W. LED lamps have also been developed as drop- similar to many existing non-SSL products and requires com- in replacements for lamps with other form factors, such as plete removal and replacement of the incumbent luminaire— 4-foot linear fluorescents, although the total light output is recessed troffers, high-bay fixtures, track lighting, and lower. pendant lights, for example. Two further applications in which LED-based luminaires have performed well are down
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SUMMARY 3 lighting, including recessed cans, where the directional qual- Cost of the LED device is primarily driven by two issues: ity of the emitted light is important, and roadway lighting, (1) the mismatch in thermal expansion between the sapphire in which a premium is placed on durability and low mainte- substrate on which the LED is grown5 and the nitride LED nance. In 2010 LED luminaires had achieved a 4.3 percent material, resulting in thermal stresses that decrease device penetration in this latter application. SSL products for yield; and (2) because of process variability, the variability downlighting have efficacies of 35 to 85 lm/W compared to in the emission characteristics (color) among individual 10 to 30 lm/W for fluorescent and halogen luminaires in the LEDs, which necessitates they be sorted (i.e., “binned”) and same application. grouped for consistency. The efficacy of the LED is limited by both physical mechanisms within the semiconductor material and the limited ability to access light trapped in the Role of Standards and Testing substrate and emissive layers (i.e., improved outcoupling). Because of the different spectral, electrical, and thermal Increasing efficacy not only improves energy savings, but characteristics of LEDs, OLEDs, and SSL products, existing also has a strong leveraging effect on the cost of LED lamps standards to measure the photometric properties (i.e., measures and luminaires because, as less heat is generated, smaller of perceived light intensity) and colorimetric properties (i.e., and less complicated thermal management and packaging measures of perceived color characteristics) of other lighting systems are required. The committee recommends that technologies frequently cannot effectively be employed. A the Department of Energy continue to make investments number of standards development organizations are involved in LED core technology, aimed at increasing yields, and in recommending test procedures for the measurement of in fundamental emitter research to increase efficacy, LEDs, OLEDs, and SSL products.4 The United States has including improvements in the controlled growth and taken early leadership on several influential standards, such as performance of the emitter material. IES LM-79-08 “Electrical and hotometric Measurements of P Solid-State Lighting Products,” which specifies the procedures Consumer Acceptance for measuring total luminous flux, electrical power, luminous efficacy, and chromaticity of SSL lamps and luminaires. In addition to cost, consumer acceptance of SSL will Despite rapid progress, a number of important test and mea- depend on an understanding of its unique characteristics surement standards still need to be developed for SSL to be and the new vernacular used to specify it. To this end DOE successful. For example, there is currently no way to measure has created the Lighting Facts label for SSL lamps, which or estimate the lifetime of SSL luminaires. provides specifications for luminous output (lumens), power (watts), efficacy (lumens per watt), color temperature, and color rendering index (CRI). The Environmental Protection Cost Agency (EPA) and ENERGY STAR® program are also The committee found that cost is the biggest obstacle engaged in developing informative labeling for SSL prod- to the widespread deployment of SSL based on LEDs. The ucts. But consumers must be made aware of the significance high cost relative to conventional light sources is due to a of label parameters, and to this end EISA 2007 authorized combination of costs associated with the LED device, heat $10 million a year to advance public awareness. This money sink, electronics, and packaging, each of which is the subject has yet to be appropriated. The committee recommends of substantial R&D activity. All categories of cost will need that DOE and lamp manufacturers and retailers work to be addressed along the value chain to improve the value together to ensure that consumers are educated about proposition of higher-quality light, longer product life, and the characteristics and metrics of these new technology overall lower life-cycle cost compared to current lighting options. products on the market. Thermal management is particularly Poor experience with spiral CFL lamps has made con challenging because the LED chip must be kept at a tempera- sumers skeptical of new lighting technologies. But unlike ture below 200°C. The small size of the chip means that even spiral CFLs, SSL turns on to full brightness instantly, is a watt or two of dissipation will raise its temperature well unaffected by low temperatures, has good color quality, beyond this limit if adequate heat sinking is not provided. and is inherently dimmable with properly designed light- ing controls. However, a number of SSL performance characteristics may jeopardize consumer acceptance if not 4 These include, but are not limited to, the following: the Illuminating addressed. The most significant of these is the incompat- Engineering Society of North America (IES or IESNA), a professional organization; the International Electrotechnical Commission (IEC), an ibility of SSL lamps with many existing dimming controls, international consensus standards organization for electrotechnology; the precluding a simple SSL retrofit, particularly in residential International Commission on Illumination, an international standards body; applications. Although unlike CFLs LEDs are in principal the National Electrical Manufacturers Association; and the Underwriters Laboratory, which sets safety standards. The American National Standards Institute also provides accreditation and serves as the U.S. national member 5Some devices are grown on a silicon carbide (SiC) substrate, which organization to the IEC. some manufacturers believe to be a better, albeit more expensive, alternative.
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4 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING easily dimmed, their low current and driver electronics this effect through materials and device architectural require special controls. National Electrical Manufacturers designs. Color consistency among OLED panels forming a Association (NEMA) is working on a standard to address luminaire is also a challenge. While OLEDs are employed this issue (NEMA SSL 7-2012; Phase Cut Dimming for extensively for displays, displays do not require the large area Solid State Lighting: Basic Compatibility). There is, at packages or high levels of illumination of general purpose p resent, no standardized method for measuring the lifetime lighting. Perhaps the largest efficiency gain that has yet to be of SSL products, even though lifetime is a critical parameter achieved is improved outcoupling of light in OLEDs, made in economically justifying SSL. Consequently, lifetime is a particularly difficult compared with LEDs by the large areal missing metric on the Lighting Facts label. DOE has instead dimension and integrated form factor of the former. The recently incorporated a lumen maintenance metric, LM-80.6 committee recommends that the Department of Energy This metric gives the number of hours of operation before the focus on efforts that result in significant light outcoupling lumen output of the LED emitter degrades to 70 percent of its enhancements that are low-cost to implement and are initial value (the so-called L70 point). This metric does not independent of both wavelength and viewing angle. While apply to product (luminaire) life, and if the durability of the there is a manufacturing infrastructure for OLED displays, balance-of-product does not match the expected 25,000-hour located almost exclusively in Asia, there is currently none life of the LED emitter, the committee expects there will be for lighting products. negative consumer reactions. DOE LIGHTING PROGRAM Color Quality Solid-State Lighting has been funded in recent years at The color of illuminated objects is also a key determinant roughly $25 million per year, of which roughly $9 million of the perceived quality of lighting products, and in this was directed toward R&D in FY2011, emphasizing three regard the CRI of LEDs can be very high—comparable to interrelated thrusts: (1) core technology research and product high-CRI fluorescent lamps. There is consensus, however, development, (2) manufacturing R&D, and (3) commer- that improved measures of color quality7 are needed to guide cialization support. The SSL Manufacturing Initiative was manufacturers, which, for SSL products, can be more numer- added to the SSL R&D portfolio in 2009 with the aim of ous and much smaller in size compared to the incandescent reducing costs of SSL sources and luminaires, improving lamp market. This diffuse supplier market compounds the product consistency and maintaining high-quality products, problem of industry standardization. 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 ORGANIC LED-BASED SOLID-STATE LIGHTING testing of SSL products, supports exploratory studies on The OLED offers the possibility of unusual form factors market trends and helps to identify critical technology issues, by taking advantage of the inherent slim, flexible character supports workshops to foster collaboration on standards and of the device itself, and by leveraging its area-source char- test procedures, promotes a number of industry alliances and acteristic to develop possible new applications. Although consortia, disseminates information, and supports a number some OLED-based luminaires are commercially available, of other initiatives. It also conducts technical, market, eco- their present costs limit widespread adoption. The lifetime nomic, and other analyses and provides incentives to the of an OLED is very sensitive to its exposure to both air and private sector to innovate. moisture, making the hermetic sealing of large, flat pack- DOE has done a remarkable job of helping to advance SSL ages critically important. Both lifetime and efficacy are R&D and manufacturing and educating the lighting commu- also negatively impacted by the high currents required to nity, and the committee recommends that the Department generate light of brightness sufficient for general purpose of Energy’s SSL program be maintained and, if possible, lighting, leading to the phenomena of current droop and increased. However, the committee notes that the percentage thermal droop (a decrease in lumen output with increasing of matching funds from R&D grant recipients has declined current or temperature). The committee recommends that in the past few years. The committee recommends that the Department of Energy support research to under- the Department of Energy seek to obtain 50 percent cost stand the fundamental nature of efficiency droop at sharing for manufacturing R&D projects, as was done high currents in OLEDs and to seek means to mitigate with the projects funded by the American Recovery and Reinvestment Act. In addition, the committee found that 6 Illuminating Engineering Society, IES LM-80-2008, Approved Method the Bayh-Dole waiver is discouraging some universities and for Measuring Lumen Depreciation of LED Light Sources. small companies from participating in the program. The 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 8U.S. Department of Energy. 2011. Solid-State Lighting Research and in response to the advent of fluorescent lamps. Development: Manufacturing Roadmap. Washington, D.C.
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SUMMARY 5 committee recommends that the Department of Energy The committee prepared a first-order comparison of the consider ending its waiver of Bayh-Dole for SSL funding. consumer life-cycle costs of lighting consumption in a fur- ther two scenarios for daily usage of lights: 3 hours per day (h/day) and 10 h/day.11 These two scenarios are representa- BENEFITS OF DEPLOYMENT OF SSL PRODUCTS tive of average daily usages in the residential and commercial The committee estimated the prospective benefits of sectors, and the results are found to be very sensitive to the reduced energy consumption from the deployment of SSL number of hours of use. The committee found that on a lighting products. The committee calculated benefits in two life-cycle basis, warm and cool white LEDs are already scenarios, each measured against a counter-factual baseline cheaper than incandescent lighting and will likely be in which there were no impacts from EISA 2007. The first comparable to that of fluorescent lighting technologies scenario calculated the savings that would accrue based on in the near future. For applications where the daily usage the lamp efficacy standards in EISA 2007 Section 321, and is larger than 10 h/day, cool, white LEDs now have a simi- it is estimated that electricity consumption for lighting would lar consumer life-cycle cost to that of CFLs or T12 linear be reduced by 514 terawatt hours (TWh9) in the residential fluorescent tubes. sector and 60 TWh in the commercial, cumulative from 2012 With continued U.S. government support and funding and to 2020. In a scenario with more aggressive assumptions DOE leadership, the promise of low-cost and very efficient on the improvements in the efficacies of LED luminaires, solid-state lighting could be realized, lowering U.S. energy cumulative savings in the residential sector over the same needs and allowing the United States to be a significant time period were 939 TWh and in the commercial sector solid-state lighting manufacturer and technology provider. 771 TWh.10 11 The following assumptions were used: a retail electricity price of 9 The assumed lamp efficacies were as follows: 96 lm/W in 2010; 141 0.11 $/kWh and a 10 percent discount rate, reflecting the implicit discount lm/W in 2012; 202 lm/W in 2015; and 253 lm/W in 2020. rate of the consumer. It is further assumed that a 60 W incandescent light 10 A typically sized electric power plant of 500 megawatt capacity, operat- bulb would be replaced by another lighting technology providing the same ing 5,000 hours, would generate 2.5 TWh in a year. energy service (approximately 850 lumens).