LED Droop Mystery Solved
April 23, 2013

Mystery Of LED ‘Droop’ Solved – Future Looks Bright For Alternative Lighting

Lee Rannals for redOrbit.com - Your Universe Online

Researchers have identified what causes light emitting diodes (LEDs) to be less efficient at high drive currents, opening up the door for the energy efficient lighting alternative to be better implemented.

Previously, scientists had only theorized about the cause behind LED "droop," which refers to a mysterious drop in the amount of light produced when a higher current is applied to the lights. This phenomenon has helped hold LED technology back as a viable replacement for incandescent bulbs for all-purpose commercial and residential lighting. However, now that the cause has been identified, LEDs may finally take off on a large scale.

Researchers wrote in the journal Physical Review Letters that their findings may provide new ways to design LEDs to have significantly higher light emission efficiencies. The US Department of Energy recently estimated that the widespread replacement of incandescent and fluorescent lights by LEDs could save electricity equal to fifty 1GW power plants.

“Rising to this potential has been contingent upon solving the puzzle of LED efficiency droop,” said James Speck, professor of Materials and the Seoul Optodevice Chair in Solid State Lighting at University of California, Santa Barbara (UCSB). “These findings will enable us to design LEDs that minimize the non-radiative recombination and produce higher light output.”

Claude Weisbuch of the Center for Energy Efficient Materials at UCSB said their experiment was very complex, but it illustrated the benefits of teamwork and international collaboration.

For the study, Weisbuch and Speck teamed up with other UCSB colleagues as well as with scientists from the prestigious École Polytechnique in France. In 2011, UCSB professor Chris van de Walle and colleagues theorized that a complex non-radiative process known as Auger recombination was behind the LED droop. This droop took place when injected electrons lose energy to heat by collisions with other electrons rather than emitting light. Speck and colleagues helped to make a definitive measurement of Auger recombination in LEDs.

During the team's experiment, they used an LED with a specially prepared surface that allowed the scientists to directly measure the energy spectrum of electrons being emitted by the light. The results unambiguously showed a signature of energetic electrons produced by the Auger process, opening up the door for LEDs to one day be implemented even more efficiently.

NPD DisplaySearch reported last week that demand for LED lighting applications will double in 2013 and nearly triple by 2016. Researchers say that demand for all LED lighting products will reach 90 million in 2016, increasing the global penetration for LED lighting applications to 26 percent in 2016, up from just 5 percent in 2012.

“LEDs are playing a leading role in the lighting industry, driven primarily by government incentive policies and consumer demand for more efficient light sources with advanced technologies such as wireless and color control,” noted Steven Sher, an analyst with NPD DisplaySearch. “This increased demand will manifest over the next three years, as consumers look to replace their traditional light bulbs with more efficient LED lighting options.”