UPDATED January 14, 2016
The incandescent light bulb, maligned as an epic waster of energy, could be revived with a change in design that boosts their efficiency, university researchers said.
In a news release, the Massachusetts Institute of Technology said that researchers at MIT and Purdue University collaborated on a new design that could prove to be more efficient than either fluorescent lamps or LEDs.
The new bulb uses a metal filament, just like a conventional light bulb. But instead of allowing radiant energy to escape, as it does in a conventional bulb, the radiant energy is reflected back to the filament where it’s re-absorbed and re-emitted as visible light. MIT described these “secondary structures” surrounding the filament as a type of photonic crystal composed of abundant materials and made with conventional material-deposition technology.
In the U.S., conventional incandescent bulbs are being phased out under energy-efficiency regulations because as much as 95% of the energy they consume is wasted, mostly in the form of heat. Fluorescents and LEDs are rapidly taking their place, even as some consumers grouse about their cost or the quality of light they produce.
MIT said that one characteristic of a lighting source is luminous efficiency, a metric which takes the reaction of the human eye to light into account. The luminous efficiency of a conventional incandescent bulb is between 2% and 3%, with fluorescents measuring between 7% and 15% and most commercial LEDs between 5% and 20%. These new bulbs have efficiencies as high as 40%.
Results of the research were reported in Nature Nanotechology. (The report is behind a pay wall.)
Still in the lab
Don’t run out to the store quite yet. The first “proof-of-concept” bulbs produced by researchers don’t approach the 40% efficiency they believe the redesigned bulbs are capable of. Yet the measured 6.6% luminous efficiency is still three times as high as a conventional incandescent bulb, and as good as some fluorescents and LEDs.
The team is “not seriously contemplating” commercialization at this point. The point of the research, the team said, was to “understand the science of how (and to what extent) thermal emission from high temperature sources can be tailored through this concept of light recycling, which might have many potential applications for energy conversion.”
But the research is very promising. The team succeeded in designing a crystal that works for a variety of light wavelengths and angles. The stack of layers can be assembled so that the desired wavelengths pass through and out of the bulb, while the infrared wavelengths are reflected.
One of the researchers said the technology might be applied to a number of other products.
“LEDs are great things, and people should be buying them,” said Marin SoljaÄiÄ‡ of MIT, one of the researchers. “But understanding these basic properties” about the way light, heat, and matter interact and how the light’s energy can be more efficiently harnessed “is very important to a wide variety of things.”
Dr. Ognjen Ilic, one of researchers, added some information from the report comparing the experimental light bulb to a standard incandescent, a compact fluorescent lamps (CFL), and a LEDs lamp.
A typical incandescent produces about 15 lumens of light per watt (lum/W), compared to the 40-100 lum/W for a compact fluorescent (CFL) 40-140 for a replacement LED (state-of-the-art LED chips have higher ratings). The experimental bulb produced an estimated 45 lum/W.
In terms of the percentage of electricity that is converted into light, an incandescent is about 5% efficient, compared to 15% to 20% for CFL and 20% to 25% for an LED replacement lamp. The proof-of-concept bulb is about 16% efficient and in principle could go much higher.