When amber LEDs are combined with phosphor-converted blue LEDs, warm white light with both high CRI and high efficacy can be attained simultaneously. Mark Dyble, product marketing manager of SSL products at Osram Opto Semiconductors discussed the potential of mixing monochromatic LEDs with phosphor-converted LEDs (PC-LEDs) to achieve high CRI and high efficacy at the same time. He presented this approach at the LED Show in Las Vegas last week.
Dyble stated that color mixing, marketed as Brilliant Mix by Osram Opto, provides an alternative method of achieving high CRI for applications such as high-end retail. He explained that typical approach today to attaining warm/neutral white light with LEDs and high CRI (>90) comes with a penalty of luminaire efficacy in the 75 lm/W range. Instead, if a combination of monochromatic LEDs (amber) are placed alongside phosphor-converted blue LEDs either in a multichip chip-on-board or multichip array, luminaire efficacy in the 90 lm/W range (up to 110 lm/W at the LED level) can be attained at 2700K.
High CRI image with color mixing.
Dyble noted that there are some caveats to taking this approach. For instance, an optical mixing chamber may be required to obtain the necessary color consistency. In addition, the correlated color temperature (CCT) over temperature may vary. To improve stability, light and temperature sensors can be installed and compensation circuitry can be implemented.
However, Dyble contends that a color mixing approach should definitely prove better than methods that overdrive the LEDs and lead to early luminaire failure. In addition, from a user standpoint a tradeoff can be made between efficiency and color rendering by adjusting the monochromatic to PC-LED driving ratio. "One of the reasons we've been able to do this is because we've been able to linearize the efficiency of monochromatic LEDs," said Dyble.
He added that Osram Opto and Cree have cross-licensing agreements in the area of color mixing.
