Beating LED droop

Scientists have been working frantically to create better LEDs to meet the ever-increasing demand for energy-efficient lighting, but one thing stands in the way: ‘droop’.

Droop refers to the fact that LED efficiency falls as operating currents rise, making the lights too hot to power in large-scale applications. Many scientists are working on new methods for modifying LEDs and making progress towards cooler, bigger and brighter bulbs.

Researchers at the University of California, Santa Barbara, led by material scientists Kristin A Denault and Michael Cantore, have devised an alternative means of creating high-power white light by using a different excitation source: a laser diode in combination with inorganic phosphors, instead of the traditional LEDs.

Their laser-based lighting options are high in efficiency and high in performance metrics, according to their study, described in the journal AIP Advances, which is produced by AIP Publishing.

“We found two ways to create high-intensity ‘cool’ white light,” said Denault.

“In one we used a blue laser diode and yellow-emitting phosphor powder with a luminous flux of 252 lumens, which is comparable to current high-brightness white LEDs. For our second method, we used a near-ultraviolet laser diode and a combination of red-, green- and blue-emitting phosphors.”

They also achieved a variety of other colour temperatures with high colour rendition, broadening the range of applications for these new lights, Denault said.

The article, ‘Efficient and stable laser-driven white lighting’ by Kristin A Denault, Michael Cantore, Shuji Nakamura, Steven P DenBaars and Ram Seshadri, is available here.