The traditional incandescent light bulb may have been a massive boon to humanity since its development in the 19th century, but its extremely low energy efficiency has seen an international phase-out in recent years in favour of more environmentally friendly alternatives.
That could one day turn around, however, thanks to a new kind of incandescent bulb developed by scientists in the US, which feeds upon its own waste heat to power itself, effectively recycling light in the process.
The researchers behind the new bulb say that if the technology reaches its potential, it could offer vast electricity savings over today’s conventional energy-efficient lights such as compact fluorescent bulbs (CFLs) and light-emitting diode bulbs (LEDs).
Incandescent bulbs work by heating a thin wire – usually tungsten – to an extremely hot temperature of about 2,700 degrees Celsius. The intense heat causes the wire to emit visible light, but that’s not all. It also produces lots of excess radiation we can’t see, including infrared, which ultimately means more than 95 percent of the energy that goes into incandescent bulbs is wasted, most of it as heat.
This is why more energy-efficient alternatives like CFLs and LEDs have increasingly replaced incandescent globes, but what if there were a way of harnessing that excess heat and energy and using it? That’s exactly what the researchers at the Massachusetts Institute of Technology have reportedly done, developing their “light recycling” light bulbs in a two-stage process.
The first stage involves making a regular incandescent light bulb with a conventional heated metal filament. In the second stage, the researchers create a structure that surrounds the filament. This structure, made from a form of photonic crystal, captures the excess radiation produced by the wire and reflects it back to the filament, where it becomes re-absorbed and re-emitted as visible light.
The challenge for the researchers was in finding a material capable of reflecting the infrared radiation while still allowing the visible light to shine through.
“The key advance was to design a photonic structure that transmits visible light and reflects infrared light for a very wide range of angles,” said one of the researchers, Ognjen Ilic. “Conventional photonic filters usually operate for a single incidence angle. The challenge for us was to extend the desired optical properties across all directions.”
The nanophotonic interference system developed by the researchers, described in Nature Nanotechnology, gives their preliminary incandescent bulbs almost a threefold improvement in energy efficiency over traditional bulbs, achieving 6.6 percent compared to between 2-to–3 percent in regular incandescent globes.
While this isn’t yet as effective as CFLs (between 7 and 13 percent) or LEDs (between 5 and 13 percent), the team believes the technology could reach efficiencies as high as 40 percent in the future, meaning the system might one day see a return of incandescent bulbs to supermarket shelves.
Until that point, today’s energy-efficient bulbs are the way to go, say the researchers. “LEDs are great things, and people should be buying them,” said one of the team, Marin Soljačić. “But understanding these basic properties [of light and heat] is very important to a wide variety of things.”