Physics professors Marin Soljačić, John Joannopoulos, and Peter Mermel, along with professor of power engineering Gang Chen, principal MIT research scientist Ivan Celanovic, and post-doctorate Ognjen Ilic, came together for the project. The team published the results of their work in Nature Nanotechnology.
The solution they came up with was a casing that keeps radiation from escaping the familiar metal filament. The casing is made of photonic crystal, which is earth-abundant. The crystal layers reflect a wide scope of infrared wavelengths that would otherwise dissipate as heat and turns them into visible light, hence the “recycling” name for the technique.
This not only increases the energy efficiency, but the luminous efficiency as well. Luminous efficiency describes the way the human eye responds to a given light source. Conventional incandescent bulbs are about two to three percent efficient, while compact LEDs are about 5 -15 percent efficient. Incandescents that use the new nanophotonic technology could hit 40 percent efficiency, according to the research.
The proof-of-concept units haven’t yet hit that number, instead peaking at about six to seven percent. That is, however, a significant upgrade over old incandescents. This development has broad implications for things other than bulbs. “The ability to control thermal emissions is very important,” Soljačić told MIT News. “That’s the real contribution of this work.” Devices that could use thermo-photovoltaic technology, like generators, could also be improved using the understanding of properties developed here.
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