I have seen the light … have you?


lightbulbs A proof-of-concept device built by MIT researchers demonstrates the principle of a two-stage process to make incandescent bulbs more efficient. This device already achieves efficiency comparable to some compact fluorescent and LED bulbs.

A proof-of-concept device built by MIT researchers demonstrates the principle of a two-stage process to make incandescent bulbs more efficient. This device already achieves efficiency comparable to some compact fluorescent and LED bulbs.

I have seen the light, or to be a tad precise, everybody in the UK has been having a bit of a lack of a lightbulb moment. Back in 2007 the UK government announced that they would be phasing out sales of the classical incandescent bulbs with the aim that they would no longer be sold after 2011, and so that is what happened.

Well, not quite, because you can still get them, it is just a bit more difficult.

No Incandescent Lightbulbs … Why?

It is of course very understandable because about 5% of the energy consumed was light and the rest was heat, so that caused a considerable degree of waste. The move was a worldwide initiative to nudge us all in the direction of the far more energy efficient alternatives. The result might perhaps bring both joy and despair because while we might indeed embrace with relish a lower power bill, the actual illumination was not as it once was. Banished was the more natural lighting and instead we bathe in a rather unnatural cold blue from these newer more efficient bulbs, oh and lets not forget that the instant-on experience was also banished and replaced with a noticeable delay as the energy efficient one wakes up from what appears to be hibernation and slowly builds up.

No doubt as you might guess, it created a demand for the good old days and some are able to capitalise on that …

“It’s only a small thing, but people get intensely upset about it,” says Jonathan Wright, the owner of two lighting shops in south-east England and the purveyor of dwindling stocks of filament lightbulbs (“We strive to provide what the public wants regardless of European bans,” proudly proclaims its website). He sells lightbulbs under a loophole that allows the sale of “industrial” bulbs, which are essentially the same as domestic, but tougher and slightly more expensive. He says people travel miles to buy them. “People want them. The colour rendering is good, it’s soft. The fact they come on instantly.”

All is not lost in darkness

The UKs Guardian reports that MIT has now come up with a rather interesting solution …

a group of researchers at the Massachusetts Institute of Technology (MIT) have had a bit of a lightbulb moment.

… well yes, apparently the author could not resist that pun …

The fondly remembered, but extremely inefficient, old-fashioned tungsten bulb could soon be modified to reuse its wasted energy. This would make it even more efficient than the new types of energy-saving LED and compact fluorescent bulbs to which we’ve switched in recent years.

Almost all the energy used by old filament bulbs is converted to heat, with only around 5% given off as light. In their paper, poetically entitled “resurrection of the incandescent source”, the MIT team describe how infrared radiation, which would otherwise be wasted, can be reflected and reabsorbed through a structure of up to 300 layers around the filament, using nanotechnology. “It is not so much the material you make the surrounding structure from, it is how you arrange the material to create the optical filtering property that will recycle infrared light and let the visible light through,” said Ognjen Ilic, from MIT’s research laboratory of electronics. This research could lead, one day, to the introduction of a high-tech lightbulb with an old-world glow.

Ooooh interesting indeed, and so being the curious person that I am, I went to have a look at what MIT have to say themselves …

The key is to create a two-stage process, the researchers report. The first stage involves a conventional heated metal filament, with all its attendant losses. But instead of allowing the waste heat to dissipate in the form of infrared radiation, secondary structures surrounding the filament capture this radiation and reflect it back to the filament to be re-absorbed and re-emitted as visible light. These structures, a form of photonic crystal, are made of Earth-abundant elements and can be made using conventional material-deposition technology.

That second step makes a dramatic difference in how efficiently the system converts electricity into light.

… and also the actual paper itself …

Here, we show that a plain incandescent tungsten filament (3,000 K) surrounded by a cold-side nanophotonic interference system optimized to reflect infrared light and transmit visible light for a wide range of angles could become a light source that reaches luminous efficiencies (∼40%) surpassing existing lighting technologies, and nearing a limit for lighting applications. We experimentally demonstrate a proof-of-principle incandescent emitter with efficiency approaching that of commercial fluorescent or light-emitting diode bulbs, but with exceptional reproduction of colours and scalable power. The ability to tailor the emission spectrum of high-temperature sources may find applications in thermophotovoltaic energy conversion and lighting.

It would be a huge leap forward, not just because it might be even more efficient than the prevailing solution, but also because it would give us back the far more natural instant-on experience that so many miss. Alas, this is just a proof-of-principle and so you will not be able to rush out and buy one tomorrow, but it does bring the hope that such a day might not be too far away and that there is some light at the end of the tunnel here (OK, yes, I just had to crowbar in that pun).

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