Electronics

Cheap, ultra low-power light source runs on just 0.1 Watts

Cheap, ultra low-power light s...
A new low-cost flat panel light source with extremely low power consumption could lead to brighter, cheaper and greener lighting (Photo: Tohoku University)
A new low-cost flat panel light source with extremely low power consumption could lead to brighter, cheaper and greener lighting (Photo: Tohoku University)
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Transmission electron microscope picture of dispersed carbon nanotubes (Photo: Tohoku University)
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Transmission electron microscope picture of dispersed carbon nanotubes (Photo: Tohoku University)
The coating surface is scratched by sandpaper to improve the rate at which electrons are emitted (Photo: Tohoku University)
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The coating surface is scratched by sandpaper to improve the rate at which electrons are emitted (Photo: Tohoku University)
Overview of three-dimensional scratched surface morphology of the light source (Image: Tohoku University)
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Overview of three-dimensional scratched surface morphology of the light source (Image: Tohoku University)
A new low-cost flat panel light source with extremely low power consumption could lead to brighter, cheaper and greener lighting (Photo: Tohoku University)
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A new low-cost flat panel light source with extremely low power consumption could lead to brighter, cheaper and greener lighting (Photo: Tohoku University)

Researchers at Tohoku University in Japan have developed a new low-cost flat panel light source that could pioneer a new generation of brighter, cheaper and greener lighting devices to rival LEDs. The device uses arrays of highly conductive carbon nanotubes to deliver evenly-distributed illumination with high efficiency and a power consumption as low as 0.1 Watts – about 100 times lower than that of light-emitting diodes.

LED lights are renowned for their high efficiencies, but the fact that only a fraction of the photons they produce actually ends up illuminating the surrounding environment suggests that there is still much room for improvement. One alternative approach explored by Prof. Norihiro Shimoi and colleagues was to build a structure based on carbon nanotubes, one-atom thick layers of carbon folded into a cylindrical shape.

This state-of-the-art device has a diode-like structure like LEDs but, curiously enough, the way in which it produces light is actually closer to the cathode ray tubes used in the TVs and computer monitors of the past century. Under the influence of a strong electric field, each carbon nanotube acts as a tiny cathode ray tube that releases a high-speed beam of electrons from its tip. These electrons then hit a phospor screen kept under vacuum and, in the process, release a small amount of energy that causes the phospor to glow.

Building the device was a fairly simple, low-cost process. The researchers started by mixing highly crystalline single-walled carbon nanotubes with an organic solvent and a surfactant compound. They then painted the mixture on the cathode and scratched the surface with sandpaper, which allows the electrons to more easily separate from the tip of the nanotubes.

Overview of three-dimensional scratched surface morphology of the light source (Image: Tohoku University)
Overview of three-dimensional scratched surface morphology of the light source (Image: Tohoku University)

Their test device needs a high voltage of 5 kV to produce the strong electric field that makes the electron emission mechanism work, but the researchers say the power consumption of the device is actually very low – as little as 0.1 W, which is two orders of magnitude less than LEDs require. This is partly because of the very low resistance posed by carbon nanotubes, and partly because the electron emission mechanism generates beams that are about 1,000 times denser than those in an incandescent light bulb, while also being much more directional and easy to control.

"Many researchers have attempted to construct light sources with carbon nanotubes as field emitter," said Shimoi, "but nobody has developed an equivalent and simpler lighting device."

The scientists say their simple, unoptimized device already achieved a good brightness homogeneity and fairly high lighting efficiency of 60 lumens per watt, which compares to around 100 lm/W for LEDs and 40 lm/W for organic LEDs, or OLEDs. With further development, this holds promise for cheaper, greener, and eventually, brighter devices that could compete with or surpass the performance of LEDs.

The development of the device is described in the latest issue of the journalReview of Scientific Instruments.

Source: American Institute of Physics

8 comments
Gadgeteer
So basically a nanoscale version of field emission cathodes. Neat. Hopefully, this will make it to market since that older technology never made it out of the lab.
Mr T
The Fifth Estate got this all wrong as well, and you have made some of the same mistakes. For example: “a power consumption as low as 0.1 Watts – about 100 times lower than that of light-emitting diodes.” LEDs vary in rated power from a few milliwatts to hundreds of watts, so the second part of that sentence is just rubbish and completely meaningless. And, of course, there’s “a 100 times lower” which is nonsensical. Nothing can be 100 times lower or 100 times smaller, it is 1/100th of the size/power/whatever, or 1% or some other sensible term, but not 100 times lower. I realise that this is a common error with many journalists, many of whom have seemingly had little or no science education, but it is nonsensical rubbish. That device is a lot more complicated than a LED, which is simply a chip mounted on a metal or ceramic substrate and enclosed in a protective case. LEDs are very cheap and extremely efficient, this device doesn’t even come close on any front. The best laboratory LEDs are over 300 lumens per watt (http://www.cree.com/News-and-Events/Cree-News/Press-Releases/2014/March/300LPW-LED-barrier) and commercially available devices at 200 L/W (Cree XP-L series), and this improves constantly with their continual development. Of course, this is early days for the device in this article, but they seem to be reinventing the wheel. Which is the biggest problem with many researchers – they come up with new ways to do things that are already done very well simply to keep themselves in research grants. I know that sounds cynical, but it is very common practice, it’s a pity journos can’t filter out this stuff…
Sven Ollino
Great comment Mr T
piperTom
My thanks, also, to Mr T. I came here to say that, but he said it better and with references.
SpotandJerome
With LED's, much of the energy is wasted due to non-radiative recombination. In addition, it is impossible to construct and LED in such a manner that all of the photons are actually emitted into space. Much of the light never leaves the device. Both of these inefficiencies are eliminated by the physics of a carbon nanotube structure. Consequently, the potential exist to create a significantly more efficient light source with a much higher photon density than that of an LED. However, as with any new technology, it will require research to optimize its implementation and discover any unforeseen limitations.
Riaanh
@Mr T, it is not that simple, we cannot just say let's stop al research, because we already have a similar working solution. These guys happen to be chasing a more efficient light source, which at the moment may not be a viable replacement for LED's, but in the meantime science is benefiting from their experience. They are for example getting valuable experience on manipulating nano tubes. Yes, this may eventually turn out to be a dead end, but one of the researchers will then take his knowledge gained and enrich another project. There are countless examples of dead-end research leading to a completely different solution. One of the famous examples was the microwave oven, which came about from radar research. All research should not be about trying to make money with a sellable product and aiding consumerism. With this brilliant work they are enriching our collective scientific knowledge.
Jay Finke
Seems to me LED's give off allot of heat, if that could be fixed my guess is the would be very efficient ? and I'm surprised they haven't made a LED water heater yet, i attempted to make a small version in 1977. but I was a little green and never succeeded.
Mugsman
This technology is the same as what Vu1 tried to commercialize - http://www.vu1corporation.com/products/ (good luck trying to buy a Vu1 product). Mr T has it right, there is no way this technology can match LEDs in terms of efficiency (or efficacy). You have to get the photons out of the phosphor with this approach also and you also have phosphor conversion losses as you convert higher energy electrons to lower energy photons. Any light emitting technology could be 1/100th of the power, even an LED run at low current, but that does not mean it is more efficient. It just means you will be getting less than 1/100th of the light output. The fact that the efficacy of the output is not mentioned in the article is telling. LEDs are by far the most efficient converters of electrical power to light with unmatched efficiency levels. With the best LEDs 90% of the light gets out, 90% of the electrons are converted to photons, the voltage efficiency is above 90% (the voltage is very near the blue emission band gap), and the phosphor efficiency is 80-90%. Sure, when these efficiencies are stacked up you end up with a system efficiency of ~50%, but this beats the heck out of any other light emitting technology. OLEDs can actually get pretty close but not at the same cost per lumen. Don't let these type of articles fool you, it will be very difficult and probably not worth the effort to surpass LED efficiency for lighting.