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So I was sold on the fugeray planted+ because I study biology and was fascinated with their "true red 660nm- which studies have found to be one of the most efficient wavelengths for plant photosynthesis" LEDs. As I recall however, Photosystem I functions optimally at 700nm and photosystem II functions optimally at 680nm. So where is this 660nm spectrum coming from? I would really like to know the methodology and research supporting this optimal red spectrum claim.
 

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Related follow up questions, not trying to hijak the thread. With the Planted+ having the primary red/white lights and also the blue moon lights, how do the blue lights effect plant growth? Would it be best to run the red/white and the blue together, or just the red/white?
 

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Chlorophyll A and B both have a red peak and a blue peak.

A ~ 430 & 660nm
B ~ 450 & 640nm

The blue LEDs on the planted+ are about 450nm, but this is also the same as the blue peak of the 7000k white LEDs (I can compare them myself this evening with a cheap spectroscope). Thus, the blue leds can be used, but aren't going to add anything that isn't already there. Regardless, the 450nm matches well with the blue peak of chlorophyll B, thus will be used efficiently.

Plants actually grow off a wide range of light anywhere between roughly 400nm and 700nm. They absorb green light around 520-600nm less efficiently, but they'll even absorb that light and use it too.

That said, plants grown in all-blue light tend to form leggy growth. All-red light tends to promote denser growth. AFAIK, as long as they are getting a decent amount of red, adding blue does not cause leggy growth. There's lots of studies of this in terrestrial plants, and I would assume the same applies to most aquatic plants as well.

Bump:
Ah, so it's going by chlorophyll absorbance and not photo-systems. Interesting, thanks.
In part that, and in part because nobody makes a cost-effective 680nm LED... 660nm is as close as it gets, and is still well used by plants. The next commonly available step up is 730nm.
 

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So I was sold on the fugeray planted+ because I study biology and was fascinated with their "true red 660nm- which studies have found to be one of the most efficient wavelengths for plant photosynthesis" LEDs. As I recall however, Photosystem I functions optimally at 700nm and photosystem II functions optimally at 680nm. So where is this 660nm spectrum coming from? I would really like to know the methodology and research supporting this optimal red spectrum claim.
Based on the "action spectrum"..

and quantum efficiency.



That along w/ "white" LED's in the range of 6000-on up are "short" in lower red..
6500k example:


Colored LED choices:
 

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Honestly water absorbs red light so effectively that above 660nm you are probably losing 75% of the PAR to the water anyways.
At typical aquarium depths of 10-24"? Not likely... Even at 700nm and a full meter of water depth you're around 60% absorption in pure water.

Source:
http://icecube.berkeley.edu/kurt/ice2000/papers/Pope_Fry_Applied_Optics_36_(1997)_8710.pdf

(Graph on page 8720, 700nm has an absorption coeficient of 0.6 m^-1)

So yeah, if you've got a large tank that's a bit over a meter deep and are using 700nm light, you might be loosing 75% of it.

My tank isn't nearly that deep.
 

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Oh, I totally agree that red is much more rapidly absorbed than blue.. but 75% is an exaggeration of the effect, at least at common aquarium depths.

If you've got a really deep tank, then maybe. But you're certainly not going to loose 75% at 18" deep.

As for comparisons, perhaps better is to compare these two:

All 660nm
http://www.bmlcustom.com/custom-report-details?partNo=PS1290S201TTTTTTTTTTTTTTT

vs all 450nm
http://www.bmlcustom.com/custom-report-details?partNo=PS1290S201LLLLLLLLLLLLLLL

And yes, BML does have higher loss rates for red than the study I quoted above.. they've got 69% loss at 24" for 660nm, and 82.5% at 36". Perhaps the difference amounts to some nominal "aquarium water" vs pure water differences.

Regardless, how many of us have tanks deep enough to put over 24" of water between the light and substrate (needed see a 75% loss)? Some, yes.. but not many.
 

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Ok, I promised a comparison falcooo between the blue LED and the white LED on the planted+...

Attached are two shots.

One with a blue LED and a white LED entering the spectrometer at the same time. Here you can see the "blue blob" to the left edge of the white LED output is quite similar to that of the blue LED alone. It might be a few nm lower, but it is really close (hard to judge with the slightly crooked shot, sorry). The white LED just has a bunch of extra spectrum in the green-yellow-orange-red range.

I also took another shot of the white-vs-660nm red. This one I was a more careful about lining the LEDs up, and the red LED is brighter than my prior attempt. I may have ended up cropping the red LED somewhat last time I did this.
 

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