So the 40-45 is ppf not ppfd, correct?
What is the sq meters this is over? In other words, what is the ppfd?
What do you think, for cannabis, is the minimum far red ppfd for emerson (assuming 2:2:1 ratio r:dr:fr)? For initiator?
As for time length of eod initiator treatment on stretch, i run that far red bar for full 15 min at beginning of lightsout, since end of stretch. No apparent stretch at all, expect it would be different before stretch.
To make a final recommendation for C. I need more far-red experience.
I've just a bit over 9sft; 0,875m² to be exact (125x 70cm or 50x 28", height is 165cm or 66") so ppfd is ~50μMol/s -20% wall/driver loss = ~40μMol/s/m².
I have now 185w CRI80 and 105w CRI90 and calculate the far-red part with only 6% or 6,3w. With only 50% efficiency (COBs run at 450mA) this would be ~3,15PAR/w or ~19μMol/s PPF. I've just rounded up to 20...
Its probably more than 6%(700-780nm) cuz COB efficiency is more like 53%. With the 20μMol/s far-red trigger it sould be at least 40μMol/s/m² PPFD incl driver and wall loss. And the 185w CRI80 adds another 3% far-red to the spectrum.
I can not recommend a specific value for cannabis. Last run I've used maybe 20-25μMol/s/m² because of the defective driver and I got the impression that they loved it and want even more.
This time I have 40-50μmol/s/m² depending on the distance and I'm pretty sure they'll like it even more. When I look at the sun spectrum, summer day, clear sky the red to far-red ratio is 55:45 (5700°k). For me that means plants can handle a lot more far-red when the main light is on and it should not cause much more stretch.
Only when the ratio changes to a far-red dominant spectrum with 40: 60 or 30:70 ratio red : far-red the plants would "think" they grow in the shade. SAS or shade avoidance syndrome is triggered and In this case you would see a lot more stretch as long as they don't stopped growing vertically.
Is the stretch finally done and they get still too much far-red you would get less dense buds(like from HPS), less branching, much bigger but fewer leaves and less yield.
So from my point of view the additional stretch depends mostly on the deep-to far-red ratio and as long as the plants get more deep- than far-red one should no see much additional stretch. In the pdf mentioned above they used 800-1000μMol/s PPFD and up to 90μMol/s were in far-red. So roughly 10% of the total output.
When I should make a recommandation, I would say start with 5% far-red and when you think it could be still more add another few % and see if you still like the results.
