Researchers Revamp Incandescent Lightbulbs With Infrared-Reflecting Shell

A redesigned incandescent light bulb recycles heat radiation to emit visible light with an efficiency comparable to that of some fluorescent and LED bulbs.

The ubiquitous incandescent light bulb is a high-temperature thermal emitter, producing mostly invisible and, in the context of illumination, unwanted IR light. Now researchers from the Massachusetts Institute of Technology (MIT) have designed a bulb that mitigates wasted energy.

The incandescent bulb is more than a century old. They produce beautiful light by passing electricity through a tiny filament. The problem, however, is that 90 percent of their energy is wasted, escaping in the form of heat.

Physicist at MIT have solved this problem by creating a light bulb that prevents the thermal energy from dissipating. Their new light bulb encases a traditional light-emitting filament in a photonic crystal that reflects the escaping thermal energy back toward the filament where it is reabsorbed and converted to light.

The crystal is made of thin layers of Earth-abundant elements, stacked and deposited on a substrate. The crystal works to reflect a variety of wavelengths, arriving at an array of angles, but allows the necessary wavelengths of warm incandescent light to pass through.

“It recycles the energy that would otherwise be wasted,” lead researcher Marin Soljacic, a physics professor at MIT, told MIT News.

Computer models suggest the technology can eventually be perfected enough to achieve efficiencies as high as 40 percent. The best incandescent bulbs peak at 2 or 3 percent. Flourescents boast efficiencies between 7 and 15 percent, while compact LEDs range from 5 to 15 percent.

The first proof-of-concept prototype topped out well short of 40 percent, but its 6.6 percent efficiency is already on par with LEDs and CFLs.

“The results are quite impressive, demonstrating luminosity and power efficiencies that rival those of conventional sources including fluorescent and LED bulbs,” said Alejandro Rodriguez, an assistant professor of electrical engineering at Princeton University who was not involved with the research.

Rodriguez thinks the findings will inspire additional incandescent emission technologies. Soljacic says the true potential of the research — published in the journal Nature Nanotechnology — isn’t yet realized, and that unforeseen applications, beyond illumination, lie ahead.

“The ability to control thermal emissions is very important,” he said. “That’s the real contribution of this work.”

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