Welcome to our SSLS EFRC
Sandia National Laboratories is home to one of the 46 multi-million dollar Energy Frontier Research Centers (EFRCs) funded by the U.S. Department of Energy Office of Science. These Centers integrate the talents and expertise of leading scientists in a setting designed: to accelerate basic and advanced discovery research; and to establish the scientific foundation for a fundamentally new U.S. energy economy that enhances U.S. energy security and protects the global environment in the century ahead.
Our own EFRC is focused on solid-state lighting science. Solid-state lighting (SSL) is simply the use of solid-state devices, like light-emitting diodes, or like the lasers which are illuminating the frosted white post in the left graphic shown above, to produce white light for general illumination. The goal of our SSLS EFRC is to help build the scientific foundation that enables solid-state lighting to produce the most light for the least energy, both in the U.S. and, as a side-benefit, throughout the world.
As discussed in “Light Emitting Diodes (LEDs) for General Illumination, Update 2002, An OIDA Technology Roadmap” (co-sponsored by the U.S. Department of Energy, the National Electrical Manufacturers Association, and the Optoelectronic Industry Development Association), artificial lighting technologies are substitutes for sunlight in the 425-675 nm spectral region where sunlight is most concentrated and to which the human eye has evolved to be most sensitive. The history of lighting can be viewed as the development of increasingly efficient technologies for creating visible light inside, but not wasted light outside, of that spectral region.
The three traditional technologies are Fire, Incandescence, Fluorescence; Solid-State Lighting constitutes a new, fourth technology. These four technologies can be differentiated by the type of material (gas or solid) that emits the light, by the spectral bandwidth (broadband blackbody or narrowband) of the light emission, and by the fuel (chemical or electrical) used to create the light. These differences, in turn, have consequences on the fundamental efficiencies of the technologies.
Semiconductor electroluminescence was first reported by H.J. Round in 1907, and the first light-emitting diode (LED) was reported by O.V. Losev in 1927. Not until the birth of semiconductor physics in the 1940s and 1950s, however, was scientific development of technologies for light emission possible.
For solid-state lighting, the use of semiconductor electroluminescence to produce visible light for illumination, the seminal advances were: first, the demonstration of red light emission by N. Holonyak in 1962; and, second, the demonstration of a bright blue LED by S. Nakamura in 1993, along with earlier materials advances by I. Akasaki and H. Amano. Here, we briefly discuss these two advances and their subsequent evolution; more details can be found in “Light Emitting Diodes” and in “Solid-state lighting: ‘The case’ 10 years after and future prospects.”
The graphic on the left shows the anatomy of a state-of-the-art white solid-state lamp; and the graphic on the right shows in the black curve the spectral power density of the light that it emits. The lamp is basically a blue LED coated with green and red phosphors. Some of the blue light leaks through the phosphors, so you see this relatively narrower peak here in the blue part of the spectral power density. But some of the blue light is absorbed by the phosphors and is re-emitted as green and red light, so you see these two relatively wider peaks here in the green and red parts of the spectral power density. The combination of blue, green and red gives a white light that renders fairly faithfully colors of objects in the environment around us.
The efficiency of this state-of-the-art SSL lamp is about 20-25%, slightly better than that of a fluorescent lamp, but far from the 50-100% efficiency that is in principal possible. Why is this? We can see why by looking at the three sub-efficiencies associated with the lamp.
The goal of our SSLS EFRC is not to work on advancing the technology itself; that is something that industry is extremely good at. Our goal instead is to help advance the scientific foundation that underlies current and potential-future SSL technology so that all of these sub-efficiencies can be improved. We do this through seven Scientific Research Challenges discussed in more detail elsewhere in this website. Very briefly, these are:
These Scientific Research Challenges, again as discussed in more detail elsewhere in this website, have as common themes:
- Researching the fundamental mechanisms that limit energy efficiency in the current generation of SSL technology
- Exploring new, nanophotonic routes, such as nanowires, quantum dots, and lasers, to the conversion of electricity to light with the potential for much higher efficiencies.