Sunnyvale, CA--Developers at Osram Opto Semiconductors have succeeded in increasing the efficiency of red thin-film LEDs by 30%, a new record.
While white-light LEDs (most of them based on a blue-LED/yellow-phosphor combination) have been grabbing headlines, red-emitting LEDs are very important for illumination. They are used in projectors, traffic lights, and automobile tail lights; they can also be also added to standard blue-source/yellow-phosphor white-light LEDs as a way to improve the color-rendering index (CRI).
The latest generation of thin-film red LED chips benefit from an optimized chip platform that has potential for further improvements. This boost in efficiency is opening up new LED applications in general illumination, in projection, and in the industrial sector.
119 lm/W at 350 mA
The record efficiency for a red LED of 119 lm/W at an operating current of 350 mA (136 lm/W at 70 mA) was achieved for the latest generation of red indium gallium aluminum phosphide (InGaAlP) 1 mm2 thin-film chip. The chip is packaged in a "Golden Dragon Plus" LED and emits at a central wavelength of 615 nm. At present, there is not an LED with higher efficiency at this wavelength. The efficiency has been measured at 44% at 350 mA (49% at 70 mA), and exceeds 50% efficiency at 350 mA for a device emitting a longer wavelength of 642 nm.
One benefit is that fewer chips are needed for the same output requiring less space. In addition, there is 50% less wasted thermal heat needed to be removed which, in turn, reduces the required cooling. As brightness increases, the light sources can be made smaller and smaller.
The 30% increase in the efficiency of the diode results from improved material properties, further development of the thin-film platform and greater output efficiency. Unencapsulated chips benefit even more from the improvements, says Osram.
