Scientists struggle to solve engineering mystery as they work to improve LED efficiency

Scientists struggle to solve engineering mystery as they work to improve LED efficiency

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News & Events - Engineering News

February 23, 2012

The light emitting diode (LED) has become increasingly popular over the past few years, and engineers are hoping to augment its functionality as they work to overcome a previously insurmountable obstacle in its architecture.

Researchers at Sorra Inc., a California-based company, are at the forefront of LED research in the U.S. The push toward energy efficiency has prompted a renewed interest in the light bulb, which is based on semiconductor technology that was invented in the mid-20th century. Still, while the Obama Administration and scores of private companies have embraced the LED, their allure is still largely relegated outside of the consumer space.

If engineers have their way, that could soon change.

LEDs are currently able to operate at low currents using only one-tenth of the electricity incandescent light bulbs require to run. Though highly efficient when operating at such levels, LEDs' effectiveness drops off precipitously when they are placed in high current outlets, such as those used in a majority of homes. This quandary has prevented LEDs from replacing the incandescent.

While consumers have been loath to embrace the LED, the implementation of energy efficiency laws – the first phase of which occurred at the onset of 2012 – will likely lead to an uptick in household installations, experts say. Passed in 2007 with bipartisan support, the regulations preclude U.S. manufacturers from producing 100-watt incandescent light bulbs that do not adhere to strict efficiency standards. The manufacturing of lower-wattage iterations of the lighting solution will similarly be prohibited over the coming years.

Sorra engineers are hoping to revolutionize the way LEDs perform in high currents, a goal they said would bolster the light bulb's cache among consumers and spur installations. Overcoming the so-called efficiency droop, though, is exceedingly difficult, and has frustrated scientists.

"The efficiency droop is one of the most severe and most interesting problems and controversies in science and engineering," Renesselaer Polytechnic Institute electrical engineering professor E. Fred Schubert told The New York Times. "Considering that LEDs are the winning future in lighting," he said that it is essential "for industry and society that the efficiency droop be understood and solved."

The diodes in modern LEDs enable a current to flow readily in one direction, while electrons travel through a junction embedded in the lighting solution. When electrons, or charge-carriers as they are also known, reach voids they are transported to a lower energy level. The process ultimately generates photons of light, with the simplicity and elegance of its design lending LEDs a lifespan that exceeds 10 years.

Nonetheless, engineers are at odds over how to improve LED efficiency. Experts are still puzzled by the LED because they do not always emit photons. Though solving that conundrum will ultimately lead to the development of a virtually flawless light bulb, researchers have already achieved a significant amount of progress in boosting LED efficiency. Just this month, Sorra engineers announced they had reached a turning point in their research, although they have not elaborated.

Scientists have posited a number of conflicting theories to explain the efficiency droop, but they have heretofore been unable to agree upon the science that underlies it. University of California, Santa Barbara scientists last year published the results of a study they conducted in which they suggested that the Auger recombination was responsible for the efficiency droop.

Other researchers contend that carrier leakage is responsible for the phenomenon. Backers of such a hypothesis assert that electrons ultimately are not able to find a paired hole at high electric currents because they are driven from the region of the LED where they are designed to recombine and produce photons.

Regardless of the science underlying the LED droop, scientists said that efficiency gains are already helping improve performance and functionality. Some experts even predict LEDs will become cost competitive with incandescent and fluorescent lighting within the next 10 years.


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