Boffins switch on pinchfist incandescent bulb

An efficient new spin on old school tungsten tech

Scientists at MIT have been dabbling with some tech which could see the incandescent lightbulb make a comeback at energy efficiencies far exceeding current LED and compact fluorescent (CFL) alternatives.

The venerable incandescent bulb simply uses electricity to heat a tungsten filament to around 2,700°C, at which temperature it emits visible light and an awful lot of waste heat - some 97-8 per cent of the energy input.

This profligacy has led to the bulb's gradual replacement by LED and CFL units, which boast an efficiency of between 4-13 per cent, and 5-10 per cent, respectively.*

Now, though, a team of boffins has taken the humble glowing filament and surrounded it with a "cold-side nanophotonic interference system" - basically a sandwich of "common oxides of various refractive indices" - which allows visible light to pass while reflecting infrared energy back for reabsorbtion by the emitter.

The proof-of-concept version comprised a "thin sheet of polished tungsten, laser machined into a closely-packed, radiator-like structure that maximises the planar surface while allowing for resistive heating".

Around that was an interference system made up of 90 layers of silicon dioxide and tantalum pentoxide. This system achieved a "luminous efficiency of around 6.6 per cent", although the researchers reckon a more complex interference structure of 300 layers, incorporating other oxides, might hit 40 per cent.

That's an impressive figure, although the challenge in one day creating a lean, mean incandescent bulb is making the interference design simple, reliable and economical to manufacture, much as Thomas Edison did with the original tungsten filament technology.

The MIT research is published in Nature Nanotechnology. ®


*Figures provided by MIT.

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