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IamN2pot
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Totally depends on the plants and environment. Some plants can handle more light than others. Will 400umole make better than 1300? Who knows, maybe you should do a side by side and see. I doubt you can draw a symmetrical curve.First, a HUGE thank-you to the THCF members that have enlightened me greatly about PAR and PPFD (yes, pun intended). That said, I may still have knucklehead ideas about what I think I've learned, so feel free to step in and correct me, again!!!.
All of the info I've been reading about how much light a cannabis plant needs goes along these lines. They need a minimum and 20 moles of light and up to 40 moles max per day, 18hr or 12hr, doesn't matter as long as it's a total of 20-40 moles a day. Total amounts of light "over 40 begins to hit a point of diminishing returns for your crop."
Now, I'm thinking that the 40 moles per day is the sweet spot and the term "diminishing returns" means a smaller total volume of flower, just like flowers that receive less than 40 moles per day will begin to render "diminishing returns". But then I wonder to myself, is that term being used commercially? Is it refering to a diminishing return more along financial lines of cost per gram to produce (profit margin diminishing)?
The reason I am asking that question is because IF the maximum amount of light is 40 moles, and bud size diminishes at light concentration over that, then I have questions and ideas about how LED lights are designed. In a perfect cannabis light, wouldn't ALL the PPFD measurements on a PPFD map read about 900umols? ..for a perfectly even maximum canopy coverage?
I think I must have something wrong because there are alot of PPFD maps that have the center area mapped at way over 900umols and the outside edges well under 450umols. Do both of those areas of the grow tent, over 900 and under 450umols, have equally diminishing returns?
TIA for your help and answers, N2
Go to you tube and look up Bruce Bughee. There is a video of him and in the cover of the you tube title he is in a lab coat. He explains the formula for changing u miles to molesFirst, a HUGE thank-you to the THCF members that have enlightened me greatly about PAR and PPFD (yes, pun intended). That said, I may still have knucklehead ideas about what I think I've learned, so feel free to step in and correct me, again!!!.
All of the info I've been reading about how much light a cannabis plant needs goes along these lines. They need a minimum and 20 moles of light and up to 40 moles max per day, 18hr or 12hr, doesn't matter as long as it's a total of 20-40 moles a day. Total amounts of light "over 40 begins to hit a point of diminishing returns for your crop."
Now, I'm thinking that the 40 moles per day is the sweet spot and the term "diminishing returns" means a smaller total volume of flower, just like flowers that receive less than 40 moles per day will begin to render "diminishing returns". But then I wonder to myself, is that term being used commercially? Is it refering to a diminishing return more along financial lines of cost per gram to produce (profit margin diminishing)?
The reason I am asking that question is because IF the maximum amount of light is 40 moles, and bud size diminishes at light concentration over that, then I have questions and ideas about how LED lights are designed. In a perfect cannabis light, wouldn't ALL the PPFD measurements on a PPFD map read about 900umols? ..for a perfectly even maximum canopy coverage?
I think I must have something wrong because there are alot of PPFD maps that have the center area mapped at way over 900umols and the outside edges well under 450umols. Do both of those areas of the grow tent, over 900 and under 450umols, have equally diminishing returns?
TIA for your help and answers, N2
Thanks for the Dr. B video input. There is a converter online to do that, here. 900umols per second adds up to 38.88 moles during 12 hours of light... so right around 900umols is the sweet spot, I think???Go to you tube and look up Bruce Bughee. There is a video of him and in the cover of the you tube title he is in a lab coat. He explains the formula for changing u miles to moles
Do both of those areas of the grow tent, over 900 and under 450umols, have equally diminishing returns?
Bizarre indeed. THanks for the info!I know it's bizarre but the real loss of efficiency in photosynthesis is not matched with an actual decrease in harvest, as grow experiments have shown a rather linear increase.
Now I see. If I'm reading that graft right, the "diminishing return" is a "smaller bang for your buck" commercially speaking. It is NOT leading to smaller buds or total weight. It looks like the total yield continues to increase up to around 1500umols or 60 moles in a 12/12 bloom cycle? Am I on the right track there?Here is a study showing nature of diminishing returns graphed out. You can see how the yield curve is still climbing at 450 and flattens after 900.
High light intensities can be used to grow healthy and robust cannabis plants during the vegetative stage of indoor production (2021)
Melissa Moher, David Llewellyn, Max Jones and Youbin Zheng
Abstract. Although the vegetative stage of indoor cannabis production can be relatively short in duration, there is a high energy demand due to higher light intensities (LI) than the clonal propagation stage and longer photoperiods than the flowering stage (i.e., 16 – 24 hours vs. 12 hours). … To determine the vegetative plant responses to LI, clonal plants of ‘Gelato’ were grown for 21 days with canopy-level photosynthetic photon flux densities (PPFD) ranging between 135 and 1430 μmol·m-2·s-1 on a 16-hour photoperiod (i.e., DLI daily light integrals of ≈ 8 to 80 mol·m-2·d-1). Plant height and growth index responded quadratically; the number of nodes, stem thickness, and aboveground dry weight increased asymptotically; and internode length and water content of aboveground tissues decreased linearly with increasing LI. … Generally, PPFD levels of ≈ 900 μmol·m-2·s-1 produced compact, robust plants that are commercially relevant, while PPFD levels of ≈ 600 μmol·m-2·s-1 promoted plant morphology with more open architecture – to increase airflow and reduce the potential foliar pests in compact (i.e., indica-dominant) genotypes.
View attachment 1284296
There was almost a 3-fold increase in DW (dry weight) over the 135 to 1430 μmol·m-2·s-1 APPFD range in the present study, although 90% of the maximum increase in DW was attained at an APPFD of only ≈ 900 μmol·m-2·s-1.
In contrast, plants were smaller at ≈ 900 vs. 600 μmol·m-2·s-1 but had ≈ 15% higher DW and ≈ 6% thicker stems (i.e., ≈ 13% higher cross-sectional area).
Since the number of nodes saturated at relatively low LI, a canopy-level PPFD target of about 900 μmol·m-2·s-1 may be most appropriate for producing robust but not overly compact plants while also minimizing lighting-related energy and infrastructure costs. Although not as common in commercial settings, production facilities that target more open plant architecture and greater energy conservation may opt for canopy-level PPFD target of ≈ 600 μmol·m-2·s-1.
Few contemporary recommendations suggest exposing vegetative cannabis plants to PPFDs higher than 800 μmol·m-2·s-1 in indoor production systems. The current study demonstrates that vegetative cannabis can be exposed to substantially higher LIs (than commonly-used in the industry) with positive morphological outcomes that can prime plants for the transition into the flowering phase.
Note: "Blurple light" spectrum LEDs used for study!
View attachment 1284297
F igure 1. Relative spectral photon flux distribution of blue (B) and red (R) LEDs used during the propagation and vegetative stages
Flowering study summary and links belowthe study you are refering to did only veg, not flower, plants.
I think that pretty well answers my question about a light saturation point and so called "diminishing return". Thank you to both @effexxess and @N1ghtL1ght for you patience with me and your knowledge. I really appreciate it!CONCLUSION. The results also indicate that the relationship between LI and cannabis yield does not saturate within the practical limits of LI used in indoor production. Increasing LI also increased harvest index and the size and density of the apical inflorescence; both markers for increasing quality. However, there were no and minor LI treatment effects on potency of cannabinoids and terpenes, respectively.
Reading my mind. I have to believe there is something wrong with my simplistic thinking. So why wouldn't one use a square bar design fixture to go into a square tent to get even PPFD readings across the map? It must be easier said than done. My idea is a design like this one, and of course, no PPFD map for it.IME, 900 - 1000umols is the sweet spot in veg and 1200 - 1600 umols in flower. 900umol is almost 40,000 Lux.
Of course much of this is also dependent on room environment. Pushing 1600umol is going to create a lot of heat regardless of the cooler running LED's. Anything higher in Umol will burn the canopy unless you have high air exchange rates and air conditioning that can cool down the environment to a workable temperature.
What I would like to see from lighting fixture companies is to use more LED's towards the edges of the lights so that you get a more uniform PPFD across the whole light fan.
For example, the SF4000...
Nominal run height would be around 18" so I will use the map provided. At center it is putting out close to 1400 ppfd. At the edge it is putting out around 450 ppfd. Adding more LED/psi at the edges would increase PPFD at those zones. Of course this would mean that COB manufacturers would have to construct and designate each panel in a specific configuration to correspond to where it is in the fixture. Not a big deal but much easier to just put an even amount on each panel and call it a day since each panel is the same and they don't have to make and track four different panels.
If there was a manufacturer that was willing to do this I would seriously consider buying their light.
I got to talk to some of the engineers at California Lightworks and asked them why the center is always the highest PPFD and the edges the lowest. They explained it to me this way.Reading my mind. I have to believe there is something wrong with my simplistic thinking. So why wouldn't one use a square bar design fixture to go into a square tent to get even PPFD readings across the map? It must be easier said than done. My idea is a design like this one, and of course, no PPFD map for it.
Light translates to sugar --> biomass, but not necessarily trichomes. High light mostly causes dense, swollen buds that weigh heavy, but its quality may already suffer from the 'Dilution-Effect'.
Most "bleaching" you see on top is actually a misdiagnosed deficiency. Light acts as a metabolic driver, high lights needs more nutes than lower. The PPFD affects a large number of variables that need to be considered.
It is just due to crosslighting, this is also dependant on distance to canopy. Once close up like 20-30cm it alleviates and homogenizes the light dustribution better.I got to talk to some of the engineers at California Lightworks and asked them why the center is always the highest PPFD and the edges the lowest. They explained it to me this way.
Each LED puts out the same amount of PPFD. Those LED's are either built with a refractor as part of the design or they augment it with a refractor that will spread the fan of the LED since raw LED's emit a single beam. Because each LED has a particular angle of fan the center ones get the benefit of the fan from the others which ups the PPFD readings. Essentially the center of the light is being showered with electrons while the edges don't have the advantage of the other diodes adding electrons into their light fan as much. That's why you see the PPFD go down exponentially as you move to the outer edge of the light.
You can remedy this by adding a light next to it or near it to supply the edge with enough crossover fan light but now you need more room and the outer edge of the added light still suffers the same issue. This is why I say that tailoring the light so that the output is as even as possible throughout the light footprint would be a boon to tent growers like me. With a light like this I can do a wall to wall SCROG in the tent and not have to accept that the farther out I go from the center of the lamp the smaller my yields will be.
A bar light like the SE5000 could be made to have the 2 end bars have double or triple the amount of LEDs while the bars inside next to the outer bars would have less and the center even less. Both ends of each of these inner bars would also have to have more LED's to be able to have the light power like the outside bars do so that all four walls are getting the same light coverage.
I'm no electrical engineer and I'm sure there is some sort of physics law that prohibits this but it seems that a light like this is what would be most beneficial to us tent growers.
Well, my last run did confirm that is not necessary. The plants were able to develop big buds even with almost no veg (cut >> root >> flower). In 3 months they are able to do that easily. Although it surely help to enter flower well-prepared. But then roots can only drink when they are new, so a plant's roots always grows.Yes, high PPFD will create dilution effect BUT that depends on earlier development of your nutrient delivery system, i.e. Branches, and your root system
and exactly this causes the dilution effect - pumping flowers to be heavy with nutes. I'm aiming to grow trichomes, not inert dry plant matter.being able to deliver the nutrients it needs to avoid the dilution effect and produce heavy , swollen DANK flower.
It is just due to crosslighting, this is also dependant on distance to canopy. Once close up like 20-30cm it alleviates and homogenizes the light dustribution better.
The solution thought out by SANlights system (to prevent the typical hotspot and increase ppfd uniformity) is to use 2 lamps (instead of one), place them a bit towards the sides, but slightly tilted/directed towards the center:
I was so sure that your solution was what I have been looking for but I ran into a few issues.It is just due to crosslighting, this is also dependant on distance to canopy. Once close up like 20-30cm it alleviates and homogenizes the light dustribution better.
The solution thought out by SANlights system (to prevent the typical hotspot and increase ppfd uniformity) is to use 2 lamps (instead of one), place them a bit towards the sides, but slightly tilted/directed towards the center:
LOL, N1L1, I completely agree. Between my e-nail that gets 95% of my usage and the S & B Plenty for the occasion when I feel like an hour long flower session, my lungs and bronchial tubes are seriously improved over when I smoked alot of plant matter.I'm aiming to grow trichomes, not inert dry plant matter.
Please elaborate with some additional tips. Canopy light intensity numbers? Hydro? Soil? Nute regime?Well, my last run did confirm that is not necessary. The plants were able to develop big buds even with almost no veg (cut >> root >> flower).
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