Warm- to cool-white tunable LED package has high CRI, luminous efficacy

In the quest for ever-better performance of white LEDs for illumination, researchers at Kookmin University (Seoul, South Korea) and PSI Co. (Kyungki-Do, South Korea) have created a series of multipackage LEDs that have luminous efficacies of around 100 lm/W and, at the same time, high Ra color-rendering indices (CRIs) of around 95. What’s most remarkable about the new multipackage LEDs, though, is that these luminous efficacies and CRIs hold while the LEDs are tuned from a warm white (2700 K) color to a cool white (6500 K) color—the entire range of hues needed for most white-light illumination uses.

The package contains four individual LEDs. A cyan phosphor-converted (pc) blue LED allows some of the blue light to leak through the phosphor to adjust the cyan hue. The other three are monochromatic red, amber, and green pc-LEDs that are capped with long-pass dichroic filters to block the blue pump light. The researchers experimented with different cyan phosphor paste concentrations (20wt%, 22.5wt%, 25wt%, and 27.5wt%) for the blue/cyan LED; in general, the lower the wt% of the cyan phosphor, the higher the luminous efficacy and the lower the CRI (although both figures remained very high). The hue-tunable white LED could lead to very high color-quality smart lighting systems. Contact Y.R. Do at[email protected].