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BRILLIANT Researchers from the University of Illinois, Northwestern University, the Institute of High Performance Computing in Singapore, and Tsinghua University in Beijing report having found a better way of producing inorganic LEDs (ILEDs).
Image: © D. STEVENSON AND C. CONWAY, BECKMAN INSTITUTE, UNIVERSITY OF ILLINOIS
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Lights and video displays made with energy-efficient light-emitting diodes (LEDs) are already making strong inroads in consumer and industrial markets long dominated by fluorescent bulbs and liquid crystal displays (LCDs). Although the majority of these LEDs get their electroluminescence from layers of film made from carbon-containing organic compounds, such organic LEDs (OLEDs) may be superseded by LEDs made from inorganic compounds that shine brighter and last longer than OLEDs.
The life spans of inorganic LEDs (ILEDs) can be 100,000 hours or more, much longer than OLEDs. (Some television-makers promote sets with OLEDs lasting 30,000 hours or so—that's about 3.5 years of continuous run-time.) Now, an international team of researchers is reporting success developing a process for making ILEDs that could put them on equal footing with OLEDs, the latter of which currently can be made smaller, cheaper and in a larger number of configurations. (ILEDs have so far be used primarily in large outdoor digital displays that do not require high resolution.)
View a slide show of experimental ILED devices
The new approach to ILED-making offers a more effective means of fabricating and assembling smaller, thinner ILEDs, says John Rogers, a University of Illinois at Urbana–Champaign professor of materials science and engineering. Rogers and colleagues from Northwestern University, the Institute of High Performance Computing in Singapore, and Tsinghua University in Beijing describe their work—funded by Ford Motor Co., the National Science Foundation, and the U.S. Department of Energy—in the August 21 issue of the journal Science.
LEDs generally are made up of several layers of organic or inorganic compounds that emit light when an electric current flows through them. These layers include the emissive layer that gives off the light, a conductive layer and a substrate, along with anode and cathode terminals that provide the electric charge. ILEDs are used today to make large display screens but cannot easily be made small enough to be packed into arrays that work well for indoor lighting or for video screens (several different brands of televisions, computer monitors and smart phones already use OLEDs).
ILEDs are "ridiculously bright, with the strongest emitting the equivalent of about one tenth the brightness of the sun," says Ioannis Kymissis, an assistant professor of electrical engineering at Columbia University in New York City who is also studying ways to make ILEDs more practical, separate from Rogers's research.
Whereas OLEDs can be made atop relatively inexpensive materials such as plastic or glass, ILEDs must be created on top of more expensive crystal wafers (made from, for example, gallium arsenide or gallium nitride, both of which are semiconductors). For ILEDs, thin films are grown to generate crystals on the surfaces of these wafers, which are typically circular in shape, with thicknesses a little less than 0.5 millimeter and with diameters between five and 10 centimeters.
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9 Comments
Add CommentLEDs are the inexpensive energy-saving lights of the future. For several years we have all colors of LEDs out into the public domain, except inexpensive full spectrum white. Present LEDs for light bulbs available at about $10 & up depending on light level...price coming down fast. Most still use transformers but energy levels are around 4 watts for 60 watt equivalent and lifetimes of many thousands of hours....much longer life, more durable, half the wattage & better light balance, compared to the mercury-containing CFLs. Recent developments at Cambridge have produced inexpensive white light LEDs with no transformer, AC or DC use, and 110 or 220 volts. ,...especially useful for those off grid on solar and wind power. Even at $14 each, a local church is converting to the current white light LED recessed ceiling lights....one contribution at a time...
Reply | Report Abuse | Link to thisJames Beal
EMF Interface Consulting
Is there a spectral power distribution available for this device>
Reply | Report Abuse | Link to thisPete
Maybe we should be building houses with a low voltage power supply suitable for LED illumination. One more conductor and use the neutral line for return
Reply | Report Abuse | Link to thisThat picture is funny, it says "click to enlarge", but the new picture is actually smaller.
Reply | Report Abuse | Link to thisI always thought that the LED will be the future light source, it is very economical and use less electricity.
Reply | Report Abuse | Link to thisWith only a single ultra-bright white LED (3 watts) inside a small flashlight, this low energy consumption and highly emitting luminence flashligh that seems to be a useful toy for most people who need to walk in the darkness nights!
Reply | Report Abuse | Link to thisyes the 'bike lights' are the future, changes from metal halide and other flourescents are being made in many lighting applications.from flashlights to traffic lights, retail and residential this push for more and more sustainable options will lead to even more creative use. visual designers are replacing the colored gels for computer programmed LED effects proving more flexible and dynamic.. the latest home-ware sustainable option being the compact flourescent however given time i believe this will also turn electronic.
Reply | Report Abuse | Link to thisThe article doesn't talk about how to dissipate the heat from these new tiny LEDs. LEDs generate less heat for the amount of light they produce than other forms of lighting, but that heat is concentrated in a very tiny spot, sometimes requiring things like heatsinks to get rid of it. Will these new tiny LEDs be able to dump their heat somehow? The problem will become worse when those tiny LEDs are packed together in flat-screen displays.
Reply | Report Abuse | Link to thisCome to that, how do OLED displays dump their heat? Or is that an issue at all?
Lot's of interesting comments here. LED sources look very promising and they are approaching widespread viability very rapidly. They are not a panacea however. The best commercial white light LED's now offer about 40 lumens per watt and are very expensive compared to conventional sources. They are not viable in high wattage applications and most suffer color rendering indexes in the 70-80 CRI range and unfavorable monochromatic color temperatures. Fixture and lamp design is in it's infancy right now with many inelegant designs attempting to deal with the heat issue. But as many have stated, they are coming fast. They remind me of the first big screen TV's way before the flat screen revolution we have seen recently.
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