LED + SSL, Research

A Look At The Color-Mixed White LED Future

In February 2022, the US DOE released its 2022 SSL Research & Development Opportunities report. While the report covers many promising directions for SSL R&D, one of the most significant evolutions predicted for LED light sources is the shift from phosphor-converted white LEDs (PC-LED) to color-mixed white LEDs (CM-LED):

  1. Image: US DOE 2022 SSL R&D Opportunities

    the PC-LED is based on a blue LED pumping yellow and red wavelength optical down-converters (typically phosphors) to produce white light, and

  2. the CM-LED approach uses primary colors that compose a red, green, blue, and amber (RGBA) LED combined to produce white light.

The PC-LED architecture is the dominant white light architecture used for LED lighting today. It has three major advantages: simplicity (only one LED type), temperature robustness (the InGaN blue LED and YAG phosphor down-converters can operate at relatively high temperatures), and color stability (the fractions of red, green, and blue source colors are determined during manufacture by the phosphor optical density and are relatively stable over time).

Over the past decade, luminous efficacies have more than doubled, from ~85 lm/W to approximately 185 lm/W. The principal reason has been improvement in blue LED efficiency, although progress has also been made in phosphors (efficiency and wavelengths to maximize spectral efficiency) and package efficiency (optical scattering/absorption). Despite these improvements, there is significant remaining potential for improved efficacy. Luminous efficacies of approximately 250 lm/W at the prescribed operating conditions are believed to be practically possible for PC-LEDs.

For the color-mixed architectures, an upper limit of 325 lm/W is considered achievable with greater breakthroughs in the technology. While the performance potential is high, today’s efficacies are much lower than the PC-LED approach due to the inefficient green and amber direct emission LEDs (known as the ‘green gap’).

While LED emitter materials have improved rapidly over the past decade, there are still key technological challenges that are limiting further improvement. The low efficiency of green and amber direct emission LEDs constrains the performance of color-mixed LED systems.

The full 2022 SSL R&D Opportunities report can be downloaded here.

Image: US DOE 2022 SSL R&D Opportunities


Image: US DOE 2022 SSL R&D Opportunities

  • Derek Cowburn November 4, 2022, 1:32 AM

    Yes, LumenCache supports RGBY fixtures with a 4ch card or the 5ch SIB.

    • Suelynn Shiller November 4, 2022, 2:52 PM

      Thanks Derek for the information and for being a LightNOW reader!

  • Kevin WIllmorth November 7, 2022, 6:12 PM

    Color mixed white with 5 to 7 source colors is certainly intriguing, and has been on the DOE roadmap from day one. Regardless of efficacy gains made, there is one issue that is going to stall progress – and that is quantum depreciation. Each color has a unique curve over its life, which means that a luminaire may start white, but over time, it will shift like a rainbow, as the sources degrade. At least with phosphor conversion, the decline is somewhat linear. Without a feedback loop and multiple channel drivers, there is no hope for a multi-colored LED product to remain consistent over time. Further, optical control and aberrations in beam patterns from individual dies interacting with lenses and reflectors, means that outside diffuse lighting products, the application of multiple colors for controlled optics is going to require the individual dies to be very small, and densely packed, to produce optical color uniformity. This applies also to etendue edge rainbow effects that current mixed color optics produce. The future of lighting is not about more high lumen diffuse source luminaire designs, it is going to become more and more about tightly controlled micro-optics that control brightness and glare, and improve fixture efficiency in putting light where we want it, and not where we don’t – something diffuse optics cannot do. This trend (that the DOE is not fully recognizing), is going to be a hurdle to overcome, on top of the color point maintenance issue – or it will never bear fruit. I personally believe that by 2050, there will be a new technology, perhaps based on graphene, or??? that will displace LED technology before the color mixing tech is mature. LED technology will be 82 years old by 2050 – about time for a fresh revolution to push it aside like LED has CFL, fluorescent and HID.


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