By Jeremy Faludi, posted on May 10, 2006.
We've been saying that LED's are the future of energy-efficient lighting. What if we're wrong? Organic light-emitting diodes (OLED's) have been emerging for years, but they are gradually getting more and more exciting, starting to give traditional LED's a run for their money. In a few years you might be able to wallpaper your home in light-emitting sheets, or maybe turn all your windows into heads-up displays. Why you'd want to do this might be a different question, but there are obviously useful applications, too, such as flexible displays (the roll-up computer or the e-ink newspaper; there's also talk about sewing them into clothing, too, but no one's done it yet like they have with LED's.) Cambridge Display Technology and Epson have also used OLED's to make color printers faster, higher-resolution, and smaller. OLED's also promise to ubiquitize displays: already a keyboard has been prototyped whose keys change according to what alphabet you want to use, or what program / game you have running. When any surface can become an interactive display, what will we want to display where?
One recent myth that's popped up is that OLED's are more efficient than normal LED's. They have higher quantum efficiencies (up to 100%), but this is not the same thing as total device efficiency. A device's efficiency (or efficacy, for the truly anal) is measured in how many lumens of light you get from so many watts of power input; OLED's have at best about 30 lumens per watt, while LED's have 30 - 60 lm/W. (For comparison, an incandescent light bulb has an efficiency of about 15 lm/W and a fluorescent has 60 - 100 lm/W.) OLED's efficiencies are increasing, but so are normal LED's; I wouldn't hazard a guess which will win in the long run.
However, as we mentioned before, OLED's are greener to manufacture than LED's or fluorescents, and can even be printed by inkjet, instead of requiring vacuum chambers, high temperatures, and bevies of toxic chemicals like lead or mercury. This is a big reason to keep an eye on them for the future. Because of these facts, they will also end up cheaper to make than today's technologies.
For now, though, the main advantage OLED's have is not brightness or efficiency as a light source, it's the extremely high resolution and fast switching, which make for good displays. They are already better for displays than LCD's, because they're emissive displays (i.e. they give off light, rather than blocking light coming through them from a backlight), and because they switch faster than LCD's. But it will be some time before they can compete as an illumination source with other home / office products, especially until manufacturing cost comes down from economies of scale. OLED's also don't stack up to LED's in terms of robustness: they are shorter-lived, and are easily damaged by moisture. People are of course working on this, but it remains a vulnerability.
If you're wondering how OLED's are different from normal LED's, How Stuff Works has a good article on them, more readable than Wikipedia's, though there are one or two mistakes in both. (For instance, it says OLED's are more efficient than fluorescent lights; and both say blue OLED's don't last long, which used to be true, though that problem is now largely solved.)
The next revolution after flexible lighting, if you ask me, will be paintable lighting. OLED's basically work by having a phosphorescent layer of material between two charged electrodes. Why not have five layers of paint, where the bottom and top layers are insulators (transparent), the second and fourth layers are conductive (also transparent), and the middle is the phosphor? Put a voltage across the conductive layers of paint, and the entire surface of your room/object/whatever can glow uniformly.
(image from Blaine Brownell)
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