Very interesting info. I appreciate you posting it.
Last point first - if your PPFD is in range, there's no reason to no use 100% red. Traditionally, growers used blue heavy lights in veg (was it CMH?) and then red heavy (HPS) in flower. Blue keeps plants short, limited internodal space, strong branches, and small leaves. Red (660nm) doesn't have any specific impact on morphology (plant shape and structure) but red diodes are electrically efficient. (It's far red, at 730nm, that causes cell expansion).
Below are the spectra for a Mars LED from ad and the spectrum for an HPS light.
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And these that I grabbed from random hits from Google.
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This graphic is from the YTY video at the bottom of the image. Though you can't see the % from the HPS spectra, the numbers for the different lights are shown here and the HPS spectrum has 4% red. Interestingly, that same 4% values the value that Bugbee talks about in one of his videos as being the least amount of blue needed to ensure that plants don't grow with deformities.
A huge amount of cannabis has been flowered with very nigh % of red and almost no blue. Given that fact, I can't see an argument to not use more red.
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One advantage of using more red is that you get more photons for a given amount of electrical input. I added a pair of Vipar R80's to my grow a grow weeks back. I'm getting about 300µmol of 660nm light from them. They draw 80 watts of power but I've been able to turn down the dimmer on my Growcraft X3 from 300 watts to 170 watts.
Here are spectra for my Growcraft:
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Even though it's a "flower" light, there's a fair amount of blue. But I'm adding 300µmol of 660. Per below, the deep red diodes are electorally efficient so I'm using less power, getting more photons, and the temperature in my tent is down about 2°.
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The latter point is very important. And here's why:
Another screenshot from the Westmoreland video. He recommends that growers use temps up to 85° in veg and in the early stages of flower. In those phases of plant growth, the goal is to create the maximum amount of infrastructure and so going up to 85 (or maybe 87) will maximize vegetative growth.
Once growth stops (vegetative growth continues up to about the second week of "flower"), keep temps below 78° in order to stop secondary metabolites from being "obliterated". That's pretty much the phrase that he used in his 2021 video but he doesn't go there in the videos that he put out last year. If you check for the old videos (he looks like a wet behind the ears kid just there years ago!). you'll see him talk about the research that he did back then.
Lotsa info to substantiate my recommendation but, as far as I can tell, it's based on the best research that we have on cannabis.
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And it
is the path that I followed.
Earlier this summer, I decided to retire my Growcraft flower light because it's an older design and the PPFD map isn't as flat as I'd like. I spent a lot of time looking for lights and even bought, tested, and returned a Mars SP 3000R which is their (flamethrower), pure red greenhouse flower light. The PPFD map is unsuited for use in a 2' x 4' tent and the heat output was very high so back it went.
I was resigned to making do with my Growcraft until someone raised the idea of using supplements lighting. I had given them a pass when they first came out because they were being sold without PPFD maps and I have little interest in a light that doesn't have a PPFD map.
Fortunately, vendors are publishing PPFD maps and, as soon as I saw what the Spider R80 would do, I bought them. Per the photo below. the R80's are nestled between the light bars of the X3. (The light on the left is a Mars SP3000 that I retired when I bought the Growcraft. It's running at 60watts, just enough to light up the front part of the plant.)
All in all, get the PPFD up to 1k± and as you use more red, your electricity bill with tend to drop. you'll get more photons, and more growth.
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