American scientists have adapted a technology now used for mobile phone display screens into a form that they say could be an efficient and flexible source of indoor lighting.
The technology is a cousin of the familiar LEDs - light-emitting devices - seen in many electronic products and traffic lights.
Stephen Forrest of the University of Michigan says organic LEDs, or OLEDs are better suited to production in sheet form. "These are devices that are comprised of organic materials, very thin films of organic materials. And organic materials are primarily carbon-containing. And it turns out [that] a lot of those have very good electrical properties," he says. "We can put them down in very, very thin films - just a few nanometers thick - and by putting electricity through those contacts we will generate light. And we can tune the color quite precisely by changing the composition of the various molecules that are used in these thin films."
Lighting uses a lot of energy. In the United States, for example, lighting accounts for one-fifth of indoor electricity usage. Traditional incandescent bulbs are particularly inefficient, with much of the electricity ending up as heat rather than light. Fluorescent lights are much more efficient, but they have other disadvantages, such as a harsh bluish color and a tendency to flicker. Forrest says OLED-based lighting doesn't have those problems, and unlike fluorescents, could take almost any shape.
"You can shape them like a light bulb, if you really want to be archaic," he says with a laugh. "Or you can make panel lighting, just make them, where your ceiling tiles are, replace it with a sheet of OLED, or you can put it around corners and make lamps and things like that. So it has any form factor that you want to apply."
Forrest says you could even replace a window with an OLED panel. It would let natural sunlight in during the day, and at night you flip a switch and the whole window turns into a light source, illuminating the room ... and even the garden outside. "We tried very hard to mimic the spectrum of the sun. So our device has a very pleasing white to it," he says. "It doesn't have the harsh bluishness that you see in some, but not all fluorescents."
Details of the new invention were published this week in the journal Nature.
Stephen Forrest, whose field is physics and engineering, worked on this project with Mark Thompson, a chemistry professor at the University of Southern California. Forrest says we can expect to see more of this kind of collaboration. "I think this is a trend in modern research, that you have to blend conventional disciplines to achieve new advances very often. So the whole scene of science is really changing a bit, and this is a nice example of that.
Lighting panels based on organic light emitting devices are still some years away, and will undoubtedly be expensive when they first hit the market. But their low operating costs, flexible design options, and pleasing color could be a challenge to traditional illumination sources.
