On spectrum - do plants care about the emission source spectrum or the overall spectrum?

[HomerPepsi]

Hey everyone, just tuning my room and started thinking, what is the source of the spectrum the plants care about? Is it the spectrum of the emission source? Or the over all spectrum of the room?

Ie: are plants looking at red leds and blue leds as individual sources? Or the spectrum of the combination of the two?

Cheers

[TEKNIK]

Plants want a combination of not just red and blue but everything else also. A heavier red during flowering stage always seems to work better. My advice is to look at how nature works

[The_Mouse_Police]

Everything from UVB to IR, typically. Narrower spectrum lights work out OK, though, because the same receptors and pigments responding to some extreme wavelengths also respond to those within visible light. I don't have the exact values handy, but the one responsible for a protective UVB response also has additional peaks around I think 420 and 470nm (though that might be off by a little), allowing strong blue from LEDs to elicit the same response, just to a lesser degree for the amount of light put out. Likewise, there is a lot of action in the red range around 630nm or so, so most LEDs being weak past about 650nm isn't a big deal. You would ideally want more deeper red, plus blues nearer 400nm, but then cost and complexity start to get in the way.

Look up the McCree action curve/spectrum, for a starting point.

[HomerPepsi]

Thank you both for your answers, but that is not what I am seeking to understand. I get the range of EMS that plants photosynthesize with and understand they want the full spectrum. Perhaps I wasn't clear in my original post. Tougher to conceptualize and describe than I thought.

For example, in the sense that say I have one 445nm LED, one 660nm LED, one 3000k LED and one 5000k LED in a room with all other variables equal.

1) do the plants get both a pure 3000k, 5000k, 445nm and 660nm stream of photons because they are "looking" at the emission source (glowing LED surface)?

2) or do plants care about the overall spectrum of the room ie. if just running the 3000k LED and 5000K LED, is the resulting spectrum the plant "sees" is 4000k?

3) given a true answer to question 2, what would be the point of adding 445nm AND 660nm if the room's spectrum always works as one? Unless spectrum mixing only applies to full spectrum LED's?

Thanks for your patience with more poor wording of questions

[TEKNIK]

1.If you have your leds close to each other the colors will blend together. I am not sure of the effects of having them spaced apart so the plant only sees bits and pieces of color.
2/3. By blending different colors depending on what they are the results are often positive, using 450nm with white LEDs is usually pointless at most whites already have 450nm and adding more blue in most cases just increases the color temperature. Adding 660nm is generally beneficial to mixing with white LEDs as most white LEDs have little 660nm, this is one reason why many like to use cri90 as it has more 660nm than a standard led.

[The_Mouse_Police]

1. https://www.reddit.com/r/microgrowery/c ... for_a_4x4/ PFD seems to have totally disappeared, but he already did basically that, adding 440 and 460 to Samsung LEDs with their own pump at 450nm, plus 660nm diodes, and had the measurements for it, too. Result: a wider, smoother blue bump, instead of the narrow spike. Those things made tastier more aromatic lemon and common thyme, oregano, and dark purple opal basil, than the sun itself, IME. The 660 comes in right where most whites start to drop off, filling it in. As long as there are enough emitters spread out enough, you basically get blanket coverage. At 120 degrees (typical bare white LED), you want a distance to canopy of no less than 2/3 the widest horizontal distance between LEDs, FI. 445nm might be a good add on to 460nm or longer blue pump, but most are 450 or 440. If you want to try going down that road, try to keep the added blues 10-15nm off, so that they don't just make for a bigger main spike - that can result in a lot more waste heat inside the leaves, and could also signal to the plant that there's too much light, retarding leaf growth.

2. Generally yes, though there are exceptions. With some series, the CCTs are different enough. FI, if you look at the new Bridgelux EB gen 3 data sheets, you'll see they are clearly using a very different phosphor recipe, and I would guess a different pump, from 4000k to 5000k, though 3000k to 4000k is just the typical change in blue/green/red balance. With 80 CRI Samsungs, you'd need to include most CCTs from 2700k to 6500k to really get something different.

3A. Those add to the output in spectral ranges where whites are usually weak, but where plants still show a good bit of response. Going back to the linked page, note the 660nm spike. Without the added LEDs, it would follow the gentle drop off that begins around red-orange, instead. Blue and red are also pretty efficient as single color LEDs, while cyan and green don't tend to be. In addition, sub-480nm blues, right down through UV-B, can cause plants to perform expensive actions like making secondary pigments, much more efficiently than just blasting them with more overall light. Since sunlight comes with strong blue during intense mid-day sun, and that usually comes with UV, more nearer-UV blue can get some nice stress responses going.

3B. Down to around 400nm or so, there is still a pretty strong photosynthetic response, so it can also add to PPF efficiently. If you look at most data sheet graphs, from about 10nm shorter than the pump, and then around 640nm on up, output is often negligible, despite there being receptors, pigments, and chlorophyll peaks below ~450nm and above ~640nm. Even high CRI only go so far, in this regard, often still having little in the 660-700 range, where the McCree curve shows a strong response, there is a second red chlorophyll peak, and where there can be some synergistic effects with the shorter wavelength blues, and far red (it seems 5-10% far red is plenty for the Emerson Effect, and even 80 CRI emitters often get into that range, now).

3C. Having said all that, while there isn't anything super conclusive quite yet, plants seem to adapt well to artificial lighting, with wonky spectrums, when it comes to photosynthesis. So, while different added wavelengths can be good for use with triggering desired morphology, improved spectrums of light sources don't improve growth/weight by a significant amount, once a, "good enough," point is reached. If you have enough blue, red, and far red for the Emerson effect, PPF is more or less PPF. Plankton have more research on that, since knowledge of their environmental light changes predates white LEDs (effects of water depth). While not directly applicable to plants, they adapt to varying amounts of blue and green, including shifting peak sensitivity in chlorophylls a and b (or at least the related photosynthetic action) for longer blue and cyan wavelengths, as shorter wavelengths got filtered out. Plants are unlikely to be so dynamic, but similar adaption when grown from seedlings under artificial light would seem like a reasonable hypothesis.

[unkle_psycho]

I think there's a lot to explore in the blue region. I wish I could get to a region where I would not need to worry so much about plant counts... Cutter has interesting wide blue elements, and it seems to me that combining the 97cri 5000k with 80cri whites would create a really even spectrum for the blue end. The 97 cri has a bump at 420, and a dip at 450.

Seems varieties have very different reactions though. Just hooked up my 280nm diodes, and blasted an almost finished El Chapo for 30min, and she changed color. The Chapo's seem to react very violently, with leaves getting crimpled etc. My other varieties seem to take it like a champ, especially my hybrid Jack, that I blasted for 4h at close distance, without any signs of physical damage.

Now I have some NL5xhazes under 3500k 80cri white, and also in another space with 3000k/HID. The latter bulked triple, but barely have any odor... the ones under pure led are growing slower but have thee mint/haze odor that leaves people speechless.

[Futuregrow]

I haven't been active lately here, but I'm still kicking around. Here's an example of a spectrum blend I've been playing with using a few different diode combinations