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The luminous efficacy of solid-state lighting (SSL) has surpassed previous lighting technologies and still has significant room to improve. Moreover, the LED technology platform also offers the opportunity to:

  • Advance beyond legacy form factors, which embody the limitations of the previous lighting technologies
  • Move past the legacy functionality of providing basic illumination
  • Enable energy savings beyond improved source efficiency to encompass more precise delivery of more suitable light at the appropriate time

The luminous efficacy of SSL, as measured in lumens per watt (lm/W), continues to advance toward the practical limit of 255 lm/W for phosphor-converted LED architectures. LED lighting technology is already saving significant and measurable amounts of energy and, if DOE performance projections are met (through ongoing advancements), will be on track to save about 5 quadrillion British thermal units (quad) per year by 2035. This equates to about $50B in annual energy savings and could account to about a 5% reduction in the total primary energy budget of the United States. The efficacy of LED lighting technology still has considerable room to improve. With greater breakthroughs, particularly for green and amber emitting LEDs, there is the potential to reach the ultimate theoretical limit of 325 lm/W for direct-emitting architectures that combine direct-emitting color LEDs to make white light.

LED lighting can improve the quality of lighting and comfort of building occupants, while simultaneously providing energy savings beyond improved source efficiency. The next generation of energy savings from SSL will come from improving lighting application efficiency (LAE), which characterizes the efficient delivery of light from the light source to the lighted task. LAE can also account for the effectiveness of the light spectrum for the lighting application and the ability to actively control the source to minimize energy consumption when the light is not being used. Improved optical design can allow more efficient delivery of light with the optimum optical distribution. Precise spectral control enables delivery of more suitable light for the application needs and building occupants. Instantaneous control over a wide range of intensity provides the ability to deliver the right amount of light on demand. Improvements in LAE can deliver substantial additional energy savings. However, a new LAE framework needs to be developed to understand and quantify these benefits to drive further innovations for energy savings.

LED technologies can enable new lighting functionality beyond basic illumination for vision and visibility. The inherent spectral tunability in SSL provides the potential to improve building occupant well-being and productivity by supporting healthy circadian rhythms. LED lighting can also improve roadway safety by providing more suitable lighting that can enhance visual acuity and discernment for different roadway situations. The LED lighting platform is also capable of providing outdoor lighting that reduces environmental and ecological impacts, while also increasing security. In addition, it can also improve the sustainability and resiliency of food production by providing light sources that enable indoor, optimized growing conditions.

Arc-shaped lighting technology.
Bendable OLED panels with efficacies >60 lm/W are commercially available and exemplify the technology’s flexible design possibilities. (Photo courtesy of OLEDWorks)

SSL offers the possibility of new form factors that cost less, deliver light more efficiently, use more sustainable materials, and more easily integrate into buildings. Another technology group within the SSL family is diffuse direct emitters, such as organic LEDs (OLEDs). This low-illuminance lighting has the potential to offer unique benefits complementary to LED lighting since, by its very nature, it is a diffuse light source, meaning it can be placed very close to the occupant or object being lit. Most other lighting technologies, including LEDs, require optical diffusion to protect occupants from glare by a bright light source. However, significant technology barriers remain for OLED lighting, with progress lagging behind LED performance and cost. Current commercial OLED panels provide an efficacy of approximately 90 lm/W. OLED lighting technology needs ongoing research and development (R&D) to translate lab scale efficiency and performance advancements to commercially practical approaches. Other diffuse direct emitter materials, such as electroluminescent quantum dots and perovskites can also provide this low-illuminance lighting and can be compatible with elements of the OLED architecture and manufacturing process.

Unlocking the next wave of advancements in SSL will require numerous and ongoing breakthroughs in fundamental, early stage R&D across the SSL value chain. To learn more, download the 2019 DOE Lighting R&D Opportunities document.