An incandescent lighting device that reuses some of the infrared light it emits could be as efficient as an LED light but contribute less to carbon emissions.
Lighting accounts for about 20 per cent of the world’s electric use and more than 10 per cent of its carbon emissions. LEDs contribute less to this, as they tend to be more energy-efficient than incandescent bulbs, but they don’t always reveal objects’ true colours. Kehang Cui at Shanghai Jiao Tong University in China and his colleagues set out to build an incandescent lighting device that does not have to make this trade-off.
Incandescent lights traditionally work by running electrical current through tungsten filaments inside a glass bulb. In the new device, the researchers used a filament that had two layers: one made from a roll of atomically thin carbon called a carbon nanotube, and another made from a ceramic material that contains boron and nitrogen. Instead of encasing it in glass, they placed it in a ceramic box made with a window made of a special kind of quartz.
The researchers ran a current through the two-layer filament, which then radiated both visible and infrared light. Unlike the glass in light bulbs, the quartz slab didn’t just let all this radiation shine through, says Cui – made of of extremely thin layers of the mineral, it was designed in such a way that it redirected the infrared radiation back to the filament.
This recycling of infrared light pushed the device’s efficiency to 25.4 per cent – that is on par with common LEDs, but more than a tenfold improvement over conventional light bulbs. Because it was still incandescent, the device had a higher so-called colour rendering index than an LED, which means that the colours of objects it illuminated looked nearly identical to what they would look like in natural light.
Cui says that his team’s analyses also showed that because the lamp is made of relatively simple and accessible materials, and could work for over 60,000 hours before breaking, carbon emissions across the lifetime of one device could be as low as a quarter of that for a comparable LED light.
“The efficiency of the device is impressive, but this is a much more complex device than a traditional incandescent light bulb. It would probably not be cheap to mass produce it,” says Jonathan Wierer at North Carolina State University. It could find some niche uses, but it would be a big challenge for it to catch up to LEDs without being able to perform a function that an LED absolutely cannot, he says.