Probably in the 800-1000 range, Ive been reading any higher and you need co2, theres a good thread that worth checking out over at icmag about DLI, ill paste some of the important stuff here,
We can use PPFD to find DLI (Daily Light Integral), and use DLI to find PPFD:
- DLI (mol/area^2/day) = (PPFD*3,600*daylength)/1,000,000
- PPFD (umol/area^2/second) = ((DLI*1,000,000)/daylength)/3,600
There are no studies looking at DLI for cannabis, AFAIK. DLI depends upon hours per day and PPFD. However, there are many studies looking at ideal PPFD* for cannabis. We could take the ideal PPFD for cannabis, ~1,500, and simply use that to find DLI for a plant providing 1,500 PPFD all day, but if we did that we would be over-saturating the plant with photons over the whole day, and in turn, cause photoinhibition.* these studies used single leaf photosynthesis chambers, ex., from Li-cor, to study effect of red light irradiance (from a red LED from Li-cor) upon rate of photosynthesis (Pn), in some cases as effected by Co2 and temp increases. IIRC Pn was founder afer steady-state Pn was achieved, I believe Pn was found after 60 minutes of irradiation of leaf with red light at 1,500 umol/area^2**/second (in the case of peak Pn, that is).** An area of maybe a couple of inches squared (a few dozen millimeters squared), the size of a not-very-large leaf. Regardless, the instantaneous irradiance was termed 1,500 PPFD (i.e., 1,500 umol/meter^2/second) because of reasons I wrote above, but it's really something like 1,500 umol/~30 mm^2/second)Considering once PPFD (for cannabis) drops below ~1,000 the rate of photosynthesis (Pn) drops a bit, using at least ~1,000 PPFD all day seems to be a good (max?) goal. I think using ~1,000 to ~1,2000 PPFD all day is good (max?) goal. I plan to test that DLI on Pn and net rate of photosynthesis (Pnnet), etc., for cannabis this coming year.
I already wrote about how/why I found the 46-48 DLI (using natural PPFD bell curve data from
HERE), for a 12 hour day. 48 DLI equals ~1,111 PPFD in 12 hours. In nature, DLI can be as high as 60, but that kinda seems high for flowing and I wouldn't use suggest it, until I or someone else had a chance to test it.
During veg and pre-flowering plants often have a higher rate of photosynthesis due to more and younger leafs. Younger leafs photosynthesize better than older leafs, and older leafs use blue light more efficiently for photosynthesis than younger leafs; in general IIRC. During flowering rate of photosynthesis is often reduced due to the changing needs of the plant, going from growth (veg/pre-flowering) to reproduction (flowering). Flowers themselves also photosynthesize, but not as well as leafs.
In the following example we can see that using ideal PPFD for cannabis (~1,500), all day, gives a very high total light (DLI). That is why I used a natural bell curve of daily PPFD found in nature (peaking at ~1,800 PPFD around noon) to come up with 48 DLI for flowering.
(DLI data is rounded):
- 1,500 PPFD for 12 hour daylength = ~65 DLI
- 1,500 PPFD for 18 hour daylength = ~97 DLI
- 1,500 PPFD for 20 hour daylength = 108 DLI
- 1,500 PPFD for 24 hour daylength (no dark period) = ~130 DLI
In the following example I work backwards from the highest DLI commonly found (~60), and from 48 DLI (my current-claim for cannabis in flowering) using various daylengths.
(PPFD data is rounded):
- 60 DLI for 24 hour daylength (no dark period) = ~695 PPFD
- 60 DLI for 20 hour daylength = ~833 PPFD
- 60 DLI for 18 hour daylength = ~926 PPFD
- 60 DLI for 12 hour daylength = ~1,389 PPFD
- 48 DLI for 24 hour daylength (no dark period) = ~556 PPFD
- 48 DLI for 20 hour daylength = ~667 PPFD
- 48 DLI for 18 hour daylength = ~741 PPFD
- 48 DLI for 12 hour daylength = ~1,111 PPFD
After looking at all those figures, it seems to me 1,000 to 1,200 PPFD is a good goal being that less than 1,000 PPFD can reduce Pn more than would be ideal. But as I noted above, I doubt most plants in most grow rooms are getting > 1,000-1,100 PPFD.My current grow has very few plants getting > 900 umol/area^2/second, most are getting > 600 umol/area^2/second; and that annoys the crap out of me. I never used my current set-up before, it's all brand new and it's a Cadillac, configured using a quantum sensor. Yet even with everything 'ideal' I can't seem to get my canopy into the ideal range for all plants (not even for a majority of plants). My next grows will be back to a light mover and rectangle canopy with moveable reflective walls, to keep irradiance high for all plants, ex. > 900 umol/are^2/second ...Below is some data for veg, mothers, etc. I have tested 16/8 and 17/7, and both worked very well when I kept PPFD high. Thus with 16/8 or 17/7 one can get the best of three worlds: high PPFD, high DLI and a dark period (with less electricity usage).
Looking back to the four studies on cannabis and PPFD, as well as PPFD bell curve under the sun, going over 1,300 PPFD for cannabis seems high, in my opinion. But that's not backed up by testing because I have yet to grow plants at higher than ~1,200 PPFD all day.
- 1,300 PPFD for 16 hour daylength = ~75 DLI
- 1,300 PPFD for 17 hour daylength = 80 DLI
- 1,300 PPFD for 18 hour daylength = ~84 DLI
- 1,300 PPFD for 20 hour daylength = ~94 DLI
- 1,300 PPFD for 24 hour daylength (no dark period) = ~112 DLI
- 1,000 PPFD for 16 hour daylength = ~58 DLI
- 1,000 PPFD for 17 hour daylength = ~61 DLI
- 1,000 PPFD for 18 hour daylength = ~65 DLI
- 1,000 PPFD for 20 hour daylength = 72 DLI
- 1,000 PPFD for 24 hour daylength (no dark period) = ~87 DLI
Looking the info above, I think ~65-70 DLI for veg (~1,300 PPFD for 16 hours and ~1,000 PPFD for 18 hours; respectively) are goals worth consideration.
