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Image credit: MIT/Ognjen Ilic.

Image courtesy of the researchers under CC BY-NC-ND 3.0

research & development

Incandescent bulbs

could make an energy-efficient comeback US researchers have developed a way to combine the warm look of traditional light bulbs with 21stcentury energy efficiency. Published in the journal Nature Nanotechnology, their study features a new type of filter that ‘recycles’ the infrared photons in incandescent bulbs.

T

he way incandescent lights work is that you

much less electric power than would ordinarily

heat a filament to a certain temperature and

be required.”

it emits a broad band of light,” explained As-

Commercially available fluorescent lighting

sistant Professor Peter Burmel, from Purdue

has an efficiency range from 7–15% and LED

University’s School of Electrical and Computer

lighting products range from 5–15%, while more

Engineering. “But only about one in 20 photons

advanced LED lamps under development may

or so is actually visible to the human eye; the other 19 photons

range as high as 29%. The efficiency of the

are essentially just wasted as heat.”

new lighting method already approaches that

Burmel and fellow Purdue researchers recently joined with

of some fluorescent and LED bulbs, achieving

Massachusetts Institute of Technology (MIT) to develop a way to

around 6.6% efficiency (a threefold improvement

recycle these wasted photons. Their method features a conven-

over the efficiency of current incandescents),

tional heated metal filament surrounded by secondary structures

and could one day reach 40%.

made of alternating layers of Earth-abundant elements such as

The filter also could have applications in a

silicon dioxide and tantalum dioxide, each with thicknesses less

new type of solar technology called thermopho-

than 1/100th that of a human hair.

tovoltaics, which could improve the efficiency

The secondary structures enable the passage of visible photons

of solar cells. Assistant Professor Bermel ex-

Image credit: Purdue University-MIT/Peter Bermel

but not infrared photons; instead, these are reflected back to the

plained, “In thermophotovoltaics you have a radiating heat source,

incandescent source. They are then reabsorbed by the incandescent

not unlike an incandescent filament, and then you shine that light

filament, causing its temperature to rise. The method is said to

on a photovoltaic cell to generate electricity. The filter can be

improve incandescent lighting efficiency by 10 times.

used to select only photons with energy levels corresponding to

“You can send those infrared photons back to the emitting source as many times as you need until they get reabsorbed,”

the semiconductor band gap of the material in the solar cell for maximally efficient conversion.”

Assistant Professor Bermel said. “Each photon has a certain

Assistant Professor Bermel acknowledged that further research

amount of energy associated with it, so you can reclaim that

is needed to measure the long-term performance and production

energy as heat. The net effect when you do that many times is

costs of the new devices. “Fortunately,” he said, “the basic ma-

that you can maintain a higher temperature and brightness using

terials used in our experiment are both abundant and non-toxic.”

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Sustainability Matters Feb/Mar 2016  

Sustainability Matters is a bi-monthly magazine showcasing the latest products, technology and sustainable solutions for industry, governmen...

Sustainability Matters Feb/Mar 2016  

Sustainability Matters is a bi-monthly magazine showcasing the latest products, technology and sustainable solutions for industry, governmen...