David Kirkpatrick

September 2, 2010

Improvements in LED lighting coming?

Looks pretty promising. I haven’t blogged about alternative lighting in a while, but I remain very fascinated about the potential for LED lighting. I have two LED bulbs right now, and as cool as they are (figuratively and literally) they suffer from the main complaints against LEDs right now — they are quite dim (albeitly by design in these particular bulb’s case) and they are very unidirectional and suitable only for spot lighting applications.

Here’s the latest news in LEDs and looks to be quite ambitious and very interesting. I’m looking forward to being able to replace all my residential lighting with crazy long-lasting and cheap-to-run LEDs.

From the link:

Researchers from the Nichia Corporation in Tokushima, Japan, have set an ambitious goal: to develop a white LED that can replace every interior and exterior light bulb currently used in homes and offices. The properties of their latest white LED – a luminous flux of 1913 lumens and a luminous efficacy of 135 lumens per watt at 1 amp – enable it to emit more light than a typical 20-watt fluorescent bulb, as well as more light for a given amount of power. With these improvements, the researchers say that the new LED can replace traditional fluorescent bulbs for all general lighting applications, and also be used for automobile headlights and LCD backlighting.

The history of luminous efficacy in different types of lighting shows the rapid improvements in white LEDs. The years in which the white light sources were developed are also shown. Credit: Yukio Narukawa, et al.

August 9, 2010

A meeting of the photonic minds

Experts from three major photonic fields — solar photovoltaics, infrared (IR) photovoltaics and light emitting diode (LED) — met at the 2010 International Symposium on Optoelectronic Materials and Devices held on July 12 and 13, 2010, in Chicago. The conference was put together by the Quantum-functional Semiconductor Research Center of Dongguk University, the Microphysics Laboratory of the University of Illinois at Chicago (UIC) and Sivananthan Laboratories Inc. The symposium gave photonics leaders the opportunity to get together and discuss the current and future state of the industry and its materials and devices.

About the conference, Dr. Chris Grein, Professor of Physics and Director of Graduate Studies at the University of Illinois at Chicago, said, “The fields of solar and infrared photovoltaics and light emitting diodes have many common technical elements yet few conferences bring together experts from all three. One of the goals of the symposium was to facilitate the cross-pollination of many ideas that will benefit these technologies.”

The entire photonic space is rapidly evolving and conferences that put the different disciplines together can spur innovation from unseen sources. A material that imrpoves LED lighting could possibly improve solar cells, or a production technique lowering the cost of solar photovoltaics might also be applicable to IR photovoltaics. Another benefit of this meeting is it puts industry leaders, top researchers, students and other members of this business sector together in one place for a couple of days to speculate and share ideas.

Symposium topics included:

  • thin film solar cells
  • very high efficiency tandem solar cells
  • heteroepitaxial growth
  • antimonide- and HgCdTe-based infrared sensors
  • ZnO nanorods
  • The featured speakers were Dr. Martha Symko Davies of the National Renewable Energy Laboratory and Mr. Minh Le of the Solar Energy Technologies Program at the U.S. Department of Energy. This year’s conference was seventh in an ongoing series

    April 7, 2009

    The latest in LEDs

    It’s been far, far too long since I’ve had a reason to blog about LED lighting. I’ve been champing at the bit for this tech to become a viable option for home lighting. Right now the actual products just aren’t quite there, and they are very expensive for the most part.

    I received two 40 watt equivalent LED spots from an enthusiast friend at the holidays. They aren’t ideal, but I’m damned excited to have them burning daily. Cool to the touch, even with 24 hour a day use, and throwing off a bluish, broad spectrum of light. Someday soon these things will be ready for prime time.

    Here’s the latest in LED research news:

    Cheap and efficient white light LEDs new design described in AIP’s Journal of Applied Physics

    IMAGE: Light produced by a new type of light emitting diode (LED) made from inexpensive, plastic-like organic materials.

    Click here for more information. 

    COLLEGE PARK, MD, April 7, 2009 — Roughly 20 percent of the electricity consumed worldwide is used to light homes, businesses, and other private and public spaces. Though this consumption represents a large drain on resources, it also presents a tremendous opportunity for savings. Improving the efficiency of commercially available light bulbs — even a little — could translate into dramatically lower energy usage if implemented widely.

    In the latest issue of Journal of Applied Physics, published by the American Institute of Physics (AIP), a group of scientists at the Chinese Academy of Sciences is reporting an important step towards that goal with their development of a new type of light emitting diode (LED) made from inexpensive, plastic like organic materials. Designed with a simplified “tandem” structure, it can produce twice as much light as a normal LED — including the white light desired for home and office lighting.

    “This work is important because it is the realization of rather high efficiency white emission by a tandem structure,” says Dongge Ma , who led the research with his colleagues at the Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences.

    Found in everything from brake lights to computer displays, LEDs are more environmentally friendly and much more efficient than other types of light bulbs. Incandescent bulbs produce light by sending electricity through a thin metal filament that glows red hot. Only about five percent of the energy is turned into light, however. The rest is wasted as heat. Compact fluorescent bulbs, which send electricity through a gas inside a tube, tend to do much better. They typically turn 20 percent or more of the electricity pumped through them into light. But compact fluorescents also contain small amounts of mercury vapor, an environmental toxin.

    LEDs on the other hand, are made from thin wafers of material flanked by electrodes. When an electric current is sent through the wafers, it liberates electrons from the atoms therein, leaving behind vacancies or “holes.” When some of the wandering electrons and holes recombine, they create a parcel of light, or photon. These photons emerge from the side of the wafer as visible light. This turns 20 to 50 percent, or even more, of the input energy into light. LEDs also concentrate a lot of light in a small space.

    Producing LEDs that can compete with traditional light bulbs for cost and efficiency is one thing. Making LEDs that consumers want to use to light their homes is quite another. One of the main barriers to the widespread use of LED lights is the light itself. LEDs can easily be manufactured to produce light of a single color — like red — with applications such as traffic lights and auto brake lights. Indoor lighting though, requires “natural” white light. This quality is measured by the color-rendering index (CRI), which assigns a value based on the light source’s ability to reproduce the true color of the object being lit. For reading light, a CRI value of 70 or more is optimal. LEDs can produce white light by combining a mixture of blue, green, and red light, or by sending colored light through a filter or a thin layer of phosphors — chemicals that glow with several colors when excited. However, these solutions increase costs. To reach a larger market, scientists would like to make inexpensive LEDs that can produce white light on their own.

    The authors of this paper report important advances towards this goal. First, they built LEDs from organic, carbon-based materials, like plastic, rather than from more expensive semiconducting materials such as gallium, which also require more complicated manufacturing processes. Second, they demonstrated, for the first time, an organic white-light LED operating within only a single active layer, rather than several sophisticated layers. Moreover, by putting two of these single-layer LEDs together in a tandem unit, even higher efficiency is achieved. The authors report that their LED was able to achieve a CRI rating of nearly 70 — almost good enough to read by. Progress in this area promises further reduction in the price of organic LEDs.

     

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    The work of Dongge Ma and colleagues was funded by the Hundreds Talents program of Chinese Academy of Sciences, the National Science Fund for Distinguished Young Scholars of China, the Foundation of Jilin Research Council, Foundation of Changchun Research Council, Science Fund for Creative Research Groups of NSFC, and the Ministry of Science and Technology of China.

    The article “A high-performance tandem white organic LED combining highly effective white units and their interconnection layer” by Qi Wang et al. was published online on April 6, 2009 [J. Appl. Phys. 105, 076101 (2009)]. The article is available at http://link.aip.org/link/?JAPIAU/105/076101/1.

    ABOUT THE JOURNAL

    Journal of Applied Physics, published by the American Institute of Physics (AIP), is an archival journal presenting significant new results in applied physics. The journal publishes original and review articles that emphasize understanding of the physics underlying modern technology. See: http://jap.aip.org/.

    ABOUT AIP

    The American Institute of Physics (AIP) is a not-for-profit membership corporation chartered in 1931 for the purpose of advancement and diffusion of the knowledge of physics and its application to human welfare. An umbrella organization for 10 Member Societies, AIP represents over 134,000 scientists, engineers and educators and is one of the world’s largest publishers of physics journals. A total-solution provider of publishing services, AIP also publishes 12 journals of its own (many of which have the highest impact factors in their category), two magazines, and the AIP Conference Proceedings series. Its online publishing platform Scitation (registered trademark) hosts more than 1,000,000 articles from more than 175 scholarly journals, as well as conference proceedings, and other publications of 25 learned society publishers. See: http://www.aip.org.

    December 17, 2008

    More nanotech transistor news

    Just blogged on a Technology Review story a few minutes ago, and here’s a press release on another nanotech transistor breakthrough. Bonus because this one even involves LEDs.

    The release:

    USC researchers print dense lattice of transparent nanotube transistors on flexible base

    Low-temperature process produces both n-type and p-type transistors; allows embedding of LEDs

    IMAGE: See-through circuit makers: Hsaioh-Kang Chang, left, and Fumiaki Ishikawa, with their transparent, flexible transistor array.

    Click here for more information. 

    It’s a clear, colorless disk about 5 inches in diameter that bends and twists like a playing card, with a lattice of more than 20,000 nanotube transistors capable of high-performance electronics printed upon it using a potentially inexpensive low-temperature process.

    Its University of Southern California creators believe the prototype points the way to such long sought after applications as affordable “head-up” car windshield displays. The lattices could also be used to create cheap, ultra thin, low-power “e-paper” displays.

    They might even be incorporated into fabric that would change color or pattern as desired for clothing or even wall covering, into nametags, signage and other applications.

    A team at the USC Viterbi School of Engineering created the new device, described and illustrated in a just-published paper on “Transparent Electronics Based on Printed Aligned Nanotubes on Rigid and Flexible Structures” in the journal ACS Nano.

    Graduate students Fumiaki Ishikawa and Hsiaoh-Kang Chang worked under Professor Chongwu Zhou of the School’s Ming Hsieh Department of Electrical Engineering on the project, solving the problems of attaching dense matrices of carbon nanotubes not just to heat-resistant glass but also to flexible but highly heat-vulnerable transparent plastic substrates.

    The researchers not only created printed circuit lattices of nanotube-based transistors to the transparent plastic but also additionally connected them to commercial gallium nitrate (GaN) light-emitting diodes, which change their luminosity by a factor of 1,000 as they are energized.

    “Our results suggest that aligned nanotubes have great potential to work as building blocks for future transparent electronics,” say the researchers.

    The thin transparent thin-film transistor technology developed employs carbon nanotubes – tubes with walls one carbon atom thick – as the active channels for the circuits, controlled by iridium-tin oxide electrodes which function as sources, gates and drains.

    Earlier attempts at transparent devices used other semiconductor materials with disappointing electronic results, enabling one kind of transistor (n-type); but not p-types; both types are needed for most applications.

    The critical improvement in performance, according to the research, came from the ability to produce extremely dense, highly patterned lattices of nanotubes, rather than random tangles and clumps of the material. The Zhou lab has pioneered this technique over the past three years.

    The paper contains a description of how the new devices are made.

    “These nanotubes were first grown on quartz substrates and then transferred to glass or PET substrates with pre-patterned indium-tin oxide (ITO) gate electrodes, followed by patterning of transparent source and drain electrodes. In contrast to random networked nanotubes, the use of massively aligned nanotubes enabled the devices to exhibit high performance, including high mobility, good transparency, and mechanical flexibility.

    “In addition, these aligned nanotube transistors are easy to fabricate and integrate, as compared to individual nanotube devices. The transfer printing process allowed the devices to be fabricated through low temperature process, which is particularly important for realizing transparent electronics on flexible substrates. … While large manufacturability must be addressed before practical applications are considered, our work has paved the way for using aligned nanotubes for high-performance transparent electronics “

     

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    Ishikawa and Chang are the principal authors of the paper. Viterbi School graduate students Koungmin Ryu, Pochiang Chen, Alexander Badmaev, Lewis Gomez De Arco, and Guozhen Shen also participated in the project. Zhou, an associate professor, holds the Viterbi School’s Jack Munushian Early Career Chair.

    The Focus Center Research Program (FCRP FENA) and the National Science Foundation supported the research. The original article can be read at: http://pubs.acs.org/doi/abs/10.1021/nn800434d

     

    March 31, 2008

    Tiny projectors and space elevators

    From KurzweilAI.net today — tiny digital projectors for cell phones and other portable media devices, and outlining a potential problem with the space elevator concept.

    Coming Soon, to Any Flat Surface Near You
    New York Times, Mar. 30, 2008Tiny digital projectors for cellphones and portable media players are in the works, able to project video on any smooth surface.

    The microprojectors, still in prototype, use light-emitting diodes, lasers or a combination of the two to cast a display of up to 50 or 60 inches, or perhaps even wider, in darkened spaces and 7 to 20 inches or so when there is ambient light.

    Later, the projector modules will be directly embedded in cellphones and other devices.
    Read Original Article>>

    Space elevators face wobble problem
    New Scientist news service, Mar. 28, 2008A Czech Academy of Sciences study suggests that building and maintaining a space elevator would be an bigger challenge than previously thought, because it would need to include built-in thrusters to stabilize itself against dangerous vibrations.
    Read Original Article>>

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