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Purple-emitting LEDs Get Closer to the Sun

6/27/2017 00:01 AM EDT
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TanjB   6/28/2017 11:53:12 AM
"others have high CRI, but our spectrum is like the sun".  Oh really?  As if that is not the point of a high CRI, to fill out a black body spectrum?   What is their CRI?

The phosphor mixes have been around for a long time, since at least flourescents, so the principles are well understood.  In practice there is a tradeoff of efficiency to fill in the spectrum with an accurate mix, and this one makes that trade (they say 10% less efficient).  The key point appears not to be the use of violet, where they are using what appears to be the standard frequency, but also adding a phosphor which can absorb violet and produce blue at minimal spectral shift - that is indeed a good trick.  They are correct that a cheap LED light with a poor CRI will just allow the violet to pass through for a pseudo-blue effect.

There are other approaches.  Soraa have for a few years been producing efficient lights with an invisible ultraviolet at 365 nm which, due to the larger shift, has some easier choices for blue phosphor chemistry.  They have CRI around 95% this way, and any residual UV can be blocked but (just as in this new device) the efficiency incentive is to absorb it with the phosphors.  The 365 nm LED is also one of the most efficient types.

Cree also have high CRI lamps which must similarly pay attention to detail in the phosphor mix.  I do not know any other details of how they do it, they don't have the same kind of technical publications on their website (afaik) as Soraa do.

It is great to see another high CRI (?) LED enter competition.  When you install LED lighting it is for a lifetime so you should think about your quality and color temperature choices.  But, perhaps EETimes could have a little more engineering care and attention to detail when transcribing the marketing blurbs for us, not just accept low-content hype?


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Purple is Worthless!
GSKrasle   6/27/2017 12:42:18 PM
And besides, shouldn't it be 'Violet"?

There are two issues with Violet:

For PLANTS (irrelevant here, but interesting anyway), photosynthesis needs that the light be absorbed by chlorophyll, and that its hv be high enough to do more than make heat. Blue is the colour of peak conversion efficiency, but there's another peak in the red. So 'grow lights' for best energy efficiency are made of red and blue LEDs. The extra energy to make violet would not be worth it, and any yellow-green is just inefficiency. Since (I believe) the photosynthetic reaction is quantized, any photon energy greater than the threshold of the reaction energy (or maybe some multiple?) is wasted. Besides, violet, being more energetic, appears to be damaging, a limiting factor in a plant's tolerance to natural light intensity: omitting it APPEARS to allow higher insolation levels and higher peak photosynthetic rate than otherwise tolerated.

Home Furnishings fade from light. Art fades from light. Again though, the secret is in the hv. Museums are careful to prevent UV, and violet, from impinging their treasures (and they prohibit you from blasting them with your Xenon emissions). If a "natural enough" colour-rendering is obtained without the highest-energy part of the spectrum, we all benefit.

But a non-phosphor 'Purple' LED would be cool.

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Nice Post
Online Loans Near Me   6/27/2017 2:30:52 AM
Nice Post

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