Since the publication of the 2013 National Research Council1 (NRC) report Assessment of Advanced Solid-State Lighting (NRC, 2013), the penetration of solid-state lighting (SSL) has increased dramatically, with a resulting savings in energy and costs that were foreshadowed by that study. What was not anticipated then is the dramatic dislocation and restructuring of the SSL marketplace, as cost reductions for light-emitting diode (LED) components reduced profitability for LED manufacturers. At the same time, there has been the emergence of new applications for SSL, which have the potential to create new markets and commercial opportunities for the SSL industry. This report will discuss these aspects of change—highlighting the progress of commercialization and acceptance of SSL and reviewing the technical advances and challenges in achieving higher efficacy for LEDs and organic light-emitting diodes (OLEDs). The report will also discuss the recent trends in SSL manufacturing and opportunities for new applications and describe the role played by the Department of Energy (DOE) Lighting Program in the development of SSL.
In 2014, approximately 15 percent of all retail electricity used in the United States was consumed by lighting. Since that time, the commercialization of lighting products utilizing LEDs has grown dramatically. Projections suggest that LED products will account for 48 percent of installed lighting service in 2020 and 84 percent in 2030—with lighting expected to consume 14 percent of electricity in 2020 and 11 percent in 2030. However, only 6.4 percent of U.S. general illumination, measured in number of installations, was provided by LEDs in 2015.
Solid-state lighting is an ever-expanding technology that is now widely accepted within the design and commercial building industries and growing in popularity with the general public. During the early stages of commercialization, the most common SSL products have been LED lamps and luminaires that replicated existing legacy form factors, such as general service “A-lamps” (the familiar “light bulb”), recessed troffers, and cobra-head-style luminaires for street and roadway lighting. These have been used in applications similar to their legacy lamp predecessors. One might characterize these early stages as constituting a first wave of commercialization, with key acceptance factors being cost and potential energy savings.
In recent years, there has been evidence of a second wave of commercialization emerging—that is “smart” and feature-rich—in which new applications for SSL leverage factors beyond efficacy alone, focusing on the quality and form factors of lighting, their connectivity, “smartness,” and controllability. Embracing these new applications can provide new markets and thus sustained growth for SSL.
COMMERCIALIZATION AND ACCEPTANCE OF SSL
The penetration of LED-based SSL has increased dramatically since the 2013 NRC report. There remains, however, a large opportunity for SSL products worldwide: in 2010 there were about 4 billion incandescent and halogen lamps installed in the residential sector. Within the United States, DOE has regulated traditional lighting products (incandescent reflector lamps, fluorescent and high-intensity discharge [HID] lamps and ballasts, as well as HID luminaires), and it is expected that future rulemakings would have the effect of accelerating the transition to SSL by making lower performing traditional lighting products obsolete through regulation. Although the annual installation of residential LED bulbs increased six-fold from 13 million to 78 million between 2012 and 2014 (there were fewer than 400,000 installations in 2009), LED bulbs account for only 3 percent of the installed base of indoor lighting and 14 percent of outdoor lighting. However, the installed base of outdoor lighting is
1 Effective July 1, 2015, the institution is called the National Academies of Sciences, Engineering, and Medicine. References in this report to the National Research Council are used in an historical context identifying programs prior to July 1.
only 5 percent of that for indoor lighting. There remains a great deal of interest in OLED-based lighting because of the diffuse quality of light (compared to LEDs as directional, “point-sources”) and the possibility of integration with flexible substrates, allowing a variety of form factors for OLED lighting.
Truly widespread consumer acceptance of this technology will require products to consistently deliver high-quality light and meet consumer expectations regarding reliability and interoperability with control systems. The determinants of light quality have been continually under re-evaluation; however, essential elements include color quality (chromaticity and color rendering), light intensity, and visual comfort, relating to factors such as the absence of glare, flicker, and disruptive shadows. Expectations for color quality and light intensity are highly context dependent, yet consumers have expectations of equal or better performance of SSL technology compared to legacy lamps and luminaires. Users expect smooth, flicker-free dimming and, in some applications, a warmer color appearance as the lamps dim. However, some newer SSL applications, such as agricultural lighting, require quality parameters that are quite different from the conventional ones used for illumination.
Designers still have relatively little knowledge and information about power supplies or drivers, relying on the luminaire manufacturers for compatibility coordination with the specified control systems. Frustration over the lack of driver standards and choices is evident. Despite the increased penetration of SSL into the commercial sector, there remains a need to educate consumers so that they are aware of the advantages of these new bulbs. The committee recommends that the Department of Energy, in partnership with industry, states, and utilities, should develop and implement a public outreach program in support of deployment of SSL. (Recommendation 2-1)
LIGHTING EFFICACY AND PROGRESS IN SSL TECHNOLOGY
Widespread adoption of LED products has the potential to result in a 40 percent savings in the energy consumed by lighting by 2030, relative to the use of other lighting technologies, but these projections are contingent on technology developments that achieve the DOE goal of 200 lumens per watt (lm/W) luminaire efficacy by 2025. In fact, values of 200 lm/W for LED luminaires have already been achieved in the laboratory. To make further progress at the level of luminaires and lighting systems, some fundamental core technological challenges must be addressed. LEDs continue to suffer from the droop in efficiency at high operating currents, as well as the lower efficiency of green LEDs (the so-called “green gap” that makes certain white-light architectures requiring the presence of green light infeasible). Although there is a better understanding of the underlying mechanisms and possible solutions, the costs of implementing those solutions may be too expensive for industry to consider action. Similarly, efficient light extraction and the reduced lifetime of blue OLED emitters remain key technological issues for OLEDs, although there is enough basic understanding of these issues to make progress in these areas. The committee recommends that DOE should continue to make investments in core technology improvements for SSL technologies, both LED and OLED, and should also consider solutions that will ultimately allow low-cost implementation and embody risks that industry is not likely to take. Early-stage investment in disruptive technologies represents high risks that industry is not likely to take. (Recommendation 3-1)
MANUFACTURING AND COST
There has been a considerable decrease in the price of LEDs and an increase in their quality—the result of about a 90 percent product cost reduction since 2008 (see Figure S.1). Nonetheless, LEDs are still, and probably will remain, more expensive than incandescent lighting technology. Thus, cost is still a determinant of the continued penetration of LED SSL and the eventual success of OLED SSL. Cost-effective approaches may lie in improvements in the manufacturing processes, as well as in the development of SSL within new integrated applications. For example, packaging LEDs in larger packages, such as “chips on board,” makes use of lowered die costs and produces an effective increase in light output. Somewhat ironically, improvements in LED manufacturing processes since the 2013 NRC report, resulting in the drop of component prices and thus profits, have caused some manufacturers to leave the business. This trend, in turn, provides a negative incentive to address the challenge of further improving SSL performance metrics, such as efficacy.
APPLICATIONS AND SYSTEMS
Product designers, as well as lighting designers, are exploring new ways of using SSL products in innovative, dynamic lighting designs, which include features such as changeable spatial distribution of emitted light, spectral tuning, intensity variation, and schedule programming. The development of connected lighting systems, also referred to as “smart lighting,” has also been facilitated by SSL. These systems collect and process data from the illuminated environment and offer additional features to consumers and end users. One example is visible light communication, which can provide local high-speed communications, thus increasing the functionality of lighting that is also used for illumination. Thus, the committee notes with interest the development of new, feature-rich products that provide additional benefits with functions beyond illumination and that may promise higher margins and higher penetration opportunities for products made by U.S. manufacturers.
Lighting can be used for other purposes, some of which are becoming more widespread. Strictly speaking, some of these applications, such as visible light communication, are unlikely to reduce energy consumption and have the potential to do the opposite. However, if growth of these applications is inevitable, DOE may wish to consider ways of maximizing efficiency. DOE does set targets for light utilization for advanced luminaire systems in its research and development program, but its approach is still product-focused. The committee recommends that DOE should develop strategies for supporting broader research that enables more efficient use of light in such a way that the application efficacy is maximized, with attention to both the lighting design process and the design of lighting products. (Recommendation 4-3)
LIGHTING PROGRAM OF THE U.S. DEPARTMENT OF ENERGY
DOE received $24 million in its fiscal year 2016 appropriation for lighting programs focusing on improvements in energy efficiency and light quality. Forty-one percent of the funding is for multiyear R&D programs. The funding is split approximately 2:1 between LEDs and OLEDs over the multiyear duration of the programs.
Since DOE began funding SSL research in December 2000, more than 230 cost-shared R&D-funded projects have resulted in more than 245 patents. Recently, commercial SSL products (i.e., luminaires) have efficacies as high as 125 to 135 lm/W and laboratory demonstrations reaching 200 lm/W. Thus, DOE’s goal of having 200 lumen/W for LEDs available by 2025 has already been demonstrated in the laboratory. The committee recommends that DOE continue investments in cost-effective solutions at 200 lm/W at the luminaire level, while also considering reliability and quality of light. Quality of light needs to be defined with the help of all relevant stakeholders, including—but not necessarily limited to—regulators, manufacturers, efficiency advocates, and consumer advocates. (Recommendation 2-2)
The lighting industry is very much aware of the market pressures and requirements for products with good lighting quality, in addition to high luminous efficacy. The various stakeholders (regulators, industry, academics, and the Illuminating Engineering Society [IES]) all agree that color rendering, minimal flicker, the ability to dim the lights, and choice of color temperature are elements of good lighting quality, but the exact requirements for these performance features have not been agreed upon. The measurement of color rendering remains controversial, and several alternative metrics have been proposed. The IES has recently published a new color rendering metric, typically referred to by its document number, TM-30 (IES, 2015). There is some, albeit limited, research on the effects of light source spectrum on circadian rhythms and ecological consequences of certain wavelengths during periods of darkness. Evidence on the effects of duration, wavelengths, and intensity is still being researched, while broad assumptions on these effects are already being addressed in voluntary standards. Some research may be needed in order to achieve consensus in these areas.
IES (Illuminating Engineering Society). 2015. Method for Evaluating Light Source Color Rendition. TM-30-15. New York. https://www.ies.org/store/product/ies-method-for-evaluating-light-source-color-rendition-3368.cfm.
NRC (National Research Council). 2013. Assessment of Advanced Solid-State Lighting. Washington, D.C.: The National Academies Press.