Scientists may have found a way to make light bulbs far more efficient. They've discovered a way to recycle light that could potentially optimize emission at useful wavelengths.
The incandescent bulb is an example of a high temperature thermal emitter. It's very useful, but only a small fraction of the emitted light-and therefore energy-is actually used. In fact, most of the light is emitted in the infrared, which is invisible to the human eye. That's why researchers decided to find a way to recycle this infrared light and potentially help light at visible wavelengths.
In this latest effort, the researchers built a more energy-efficient incandescent light bulb. The approach that they used to create it could also be used to improve the performance of other hot thermal emitters, including thermo-photovoltaic devices.
"For a thermal emitter at moderate temperatures one usually nano-patterns its surface to alter the emission," said Ognjen Ilic, the lead author of the new study, in a news release. "At high temperatures, such nanostructures deteriorate and it is impossible to alter the emission spectrum by having a nanostructure directly on the surface of the emitter."
The researchers solved this problem by surrounding the hot object with special nanophotonic structures that spectrally filter the emitted light, meaning that they let the light reflect or pass through based on its color. Because the filters are not in direct physical contact with the emitter, temperatures can be very high.
The researchers also redesigned the incandescent filament from scratch. In this case, they turned it into a piece that was laser-machined out of a flat sheet of tungsten, which makes it completely planar. Since a planar filament has a large area, it's efficient at re-absorbing the light that was reflected by the filter.
In the new-concept light bulb prototype, the efficiency approaches some fluorescent and LED bulbs. This could be huge for the future of light bulbs.
The findings are published in the journal Nature Nanotechnology.
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