DOE researcher solves part of lighting riddle

A federal researcher has taken a big step toward revolutionizing the energy-efficient lighting market with his recent work on organic light-emitting diodes, or OLEDs.

Formulated into a flat, screen-like panel, OLEDs are expected to use far less energy than traditional incandescent bulbs. Engineers love that aspect, while product designers focus on the freedom OLEDs offer from traditional bulb shapes.

But white OLED lights are limited by weaknesses in blue diodes, said Asanga Padmaperuma, a research scientist at the Energy Department's Pacific Northwest National Laboratory and technical leader for the lighting program there.

"The weakest link, that's a stable and efficient blue OLED," Padmaperuma explained in an interview. His work, presented Sunday at an American Chemical Society meeting, has focused on how to improve the efficiency of blue OLEDs using novel semiconducting materials to improve electrical flow.

Blue diodes are important in two ways, Padmaperuma explained. White light can be created either by blending the output of three diodes -- one each in red, blue and green -- or it can be made by using a blue diode and filtering out certain wavelengths to leave white.


Padmaperuma thinks the latter approach may turn out to be simpler, but in either case, perfecting today's troublesome blue lights will be key.

The scientist said his research, which has been funded by DOE's Building Technologies Program and the National Energy Technology Laboratory, has yielded a far more efficient diode.

"We have achieved the efficiency part," he said. "We have attained the efficiency milestones that we like."

He added, "What's left in this blue OLED is the lifetime metric," a reference to a DOE target that an OLED device should last 40,000 hours.

"That's going to be my focus in the future -- to take my efficient blue OLED and improve the lifetime," Padmaperuma said.

DOE has set a 2015 target date to have OLED products available, with an eye to widespread market adoption by 2025 -- goals that Padmaperuma described as "a reasonable expectation."

So far, it is unclear whether Padmaperuma's program, which supports a dozen researchers working on a range of challenges associated with light-emitting diodes, will benefit from new science funding available through the recent stimulus package.

In Padmaperuma's eyes, the benefits of cracking the OLED challenge are two-fold.

First, running a more efficient light reduces energy use at the user level -- OLEDs are expected to produce about 160 lumens of light per watt of electricity, orders of magnitude more productive than the 5 lumens per watt produced by incandescent light bulbs, and even more impressive than the roughly 50 lumens per watt available from compact fluorescent bulbs today, he said.

Second, and just as important, energy conservation has a strong multiplier effect, he said. "Half of the electricity produced in a power plant doesn't reach our home," he said, pointing to losses in production and distribution systems.

"That means if we can save one unit at our houses, we actually save more than that in production," he said. "It's not only the power you save, but the power that you don't even need to manufacture."

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