[delta9nxs]

I have been studying the “daily light integral” lately and have a few questions that I hope someone can answer or provide a reference to answers.

Since our plant is a mole counter on a diurnal basis it follows that there is a “reset” mechanism. Is the mechanism reset by light or the absence of light? Or is it reset chemically or hormonally? Or maybe a combination of these things? People using a 24/0 veg cycle are not getting a “dark” cycle but is the production of photosynthate rolling off at some point, perhaps allowing the plant to reset?

Each species of plant has a maximum daily light integral beyond which photosynthesis ceases or slows down. What is this figure for cannabis?

We know that few greenhouses get more than about 30 moles/day. Dr Elsohly's research was done at 24/25 moles/day.

It has been mentioned by Spurr that 46-48 moles/day might be the maximum usable but I don't know where he got the figures.

I have been doing exhaustive searches on this subject and I am running into a wall trying to get more info.

Any help would be greatly appreciated.

Later, d9

[grow101]

Far red (740nm) resets any red light exposure, which would inhibit flowering in short day plants when given as last light before the dark period. Red flashes at night will inhibit flowering, unless they are followed by far red light.

Ch25, p730ff, Plant Physiology, Taiz, Zeiger, 5th edition.

Originally Posted by itzaplant

reallt guy is it that complicated

Well hell, man, if you got the answer let's hear it! Or are you just being a sarcastic troll? [Edit] Nevermind, I see you're just turbo-posting. Kinda lame, bud.

I wish I had something constructive to add to the conversation, but I am subscribed in hopes of learning more

[delta9nxs]

hi, grow101, thank you for the link, every piece of the puzzle helps!

mugenbao, hey buddy, looks like one of the mod types got wind of mr itzaplant's trolling and yanked his stuff. thank you!

d9

[spurr]

Originally Posted by delta9nxs

I have been studying the “daily light integral” lately and have a few questions that I hope someone can answer or provide a reference to answers.

Since our plant is a mole counter on a diurnal basis it follows that there is a “reset” mechanism. Is the mechanism reset by light or the absence of light? Or is it reset chemically or hormonally? Or maybe a combination of these things?

What do you mean by "reset mechanism"? Resetting what? And resetting it when?

Originally Posted by delta9nxs

People using a 24/0 veg cycle are not getting a “dark” cycle but is the production of photosynthate rolling off at some point, perhaps allowing the plant to reset?

I am not sure what you mean by "reset", some so-called "dark reactions" are now more correctly called "light-independent reactions". So some functions that are at optimum under darkness can be carried out under light.

Of interest, plants can tell when it's 'midnight' when the plant is given a stable day/night schedule.

If by "reset" you mean "the point when the plant senses 24 hours have passed", in terms of plants grown under 24 hours of light (24/0), AFAIK it is due to the natural circadian rhythm (24 hours).

One point about growing 24/0, is the rate of photosynthesis will dip throughout the day; it won't stay high during light like it does when a night time is used.

Originally Posted by delta9nxs

Each species of plant has a maximum daily light integral beyond which photosynthesis ceases or slows down. What is this figure for cannabis?

I do not believe anyone knows, or that anyone has even studied. Most studies on cannabis and irradiance (brightness of light) relative to rate of photosynthesis (Pn) used red light and used 60 minute irradiation periods before finding rate of photosynthesis. No studies I am aware of, have looked at long term rate of photosynthesis over hours of irradiation for cannabis (Pnnet).

In cannabis "steady-state" Pn is achieved after about 30-40 minutes under bright light (within PAR range), IIRC.

Originally Posted by delta9nxs

We know that few greenhouses get more than about 30 moles/day. Dr Elsohly's research was done at 24/25 moles/day.

If you are referring to the DLI for Dr. Elsohly, from what I posted in another thread, it's an approximation, a best guess of mine. AFAIK Dr. Elsohly hasn't studied DLI, or has he and I am unaware?

Depending upon where the greenhouse is located, DLI (def: mol/meter^2/day) can exceed 30; ex., > 30 mol/area^2/day.

Originally Posted by delta9nxs

It has been mentioned by Spurr that 46-48 moles/day might be the maximum usable but I don't know where he got the figures.

I'll post an explanation with links and math, etc., tomorrow. It was formed using my best guess in some areas. I have been using my quantum sensor for much testing and found some (crude, incomplete) data/opinion about quantity of light (photons).

Originally Posted by delta9nxs

I have been doing exhaustive searches on this subject and I am running into a wall trying to get more info.

Any help would be greatly appreciated.

This info was presented in the 24 hour light thread, a link is in m sig. It's buried somewhere on page 10-20ish ...

I am planning on finding it tomorrow to post more.

[aggregatebuzz]

my control is last run was a progressive light watt increase from 500w(30dayveg/24-0) to 1000w, yielded 18oz finished 4 plants,5Gal. pots, in 2x4x8:Sunmaster MH/HPS...Quantum push
this time 400w veg 600w flower(30dayveg/24-0) Ushio Red M.H. Horti. HPS.. Next Gen push

all the rest same,seeds too(AK-48 and Ice)
see if this light level is better

[spurr]

---------------------
PPFD:

One point about PPFD as used below, the definition of PPFD is "Photosynthetic Photon Flux Density". That is a label for the number of photons (particles of light) that hit an area of a meter squared (three-feet squared) in one second; but only photons that are within a range that best drives rate of photosynthesis (Pn), called the PAR range (Photosynthetically Active Radiation) of 400-700 nanometers. However, when one measures PPFD one does not measure the instantaneous irradiance (as umol/area^2/second) over a whole meter squared, to find PPFD. To measure PPFD (i.e., instantaneous irradiance as micromoles per area squared per second) one uses a quantum sensor, but they are only about an inch squared.

When the concept of measuring (quantifying) photons within the PAR range (per second; instantaneous) that best drives Pn, was being developed, it was (mostly) developed to be used for outdoor and greenhouse growing, when used for whole-plant application. AFAIK, the designers did not take irradiance foot-print of a horizontal lamp in a reflector into consideration, only an ideal situation of point-source light from the sun or greenhouse lamps far from the plants. Granted, the scientists who came up with PPFD used single leafs, at times, when measuring effect of irradiance on rate of photosynthesis.

The calculation of PPFD is based upon at least one big assumption: all spots (ex., plants) within the area of a meter squared get the same instantaneous irradiance. Ex., all the plants in a meter squared outside in a field the get the same 'amount' of sun light (photons; if they are no shaded); so one measurement in any spot within the meter^2 will show the PPFD of the meter^2. That means to find PPFD outdoor or in a greenhouse, one measurement is taken within a meter^2 with a quantum sensor and the assumption is made that all other areas within the meter^2 will have the same instantaneous irradiance as the original spot. Thus one measurement of a small area (about an inch or 2 squared) is used to find PPFD for a whole meter^2. But indoors under a reflector with a horizontal lamp, not all plants in a meter squared get the same 'amount' of lamp light (photons). That means using PPFD is not representative of the real-world irradiance per smaller-than-a-meter^2 area, within that meter squared. Also, the PPFD from a horizontal lamp in a reflector can't be found by just a single measurement, many measurements must be taken to account for un-even light distribution over the meter squared (and light side the meter^2).

Along with the reasons above, un-even irradiance over many areas of measurement within a meter^2 is another reason PPFD is not ideal for our use case; IMO anyway. By Definition PPFD is fixed at a meter squared, which works fine for outdoor and greenhouse growing, but indoors canopies are often smaller than 3'x3' or not shaped in a square, as well as the flaws/limits above.

What all the means, in my opinion, is using the term PPFD is not ideal, mostly because the area is fixed. I think it may be better if PPFD was not fixed in area, but required one to report the area measured for irradiance; no assumption made. So PPFD could mean umol/1"^2/second or umol/12"^2/second; as long as area is defined.

Anyway, in the post below when I write PPFD I mean "umol/any-area-^2/second"; not necessarily "umol/meter^2/second". Likewise, DLI means "mol/area^2/day"; not necessarily "mol/meter^2/day".
---------------------

[spurr]

Originally Posted by delta9nxs

It has been mentioned by Spurr that 46-48 moles/day might be the maximum usable but I don't know where he got the figures.

DLI is rarely found much higher than 60 mol/m^2/day outside and in a natural greenhouse.

To find a possible goal DLI for flowering cannabis I tried to mimic what would happen in nature (re PPFD bell curve and DLI), using natural PPFD bell curve found in Hawaii that provided peak PPFD of ~1,500-1,800 (because that PPFD has been studied for cannabis). I did my best to create a goal flowering DLI of ~48, using the data from Hawaii and working backwards (ex. for 12 hours) to find PPFD that is both high enough to keep Ph in the 'high' range (ex., > 1,000), and high enough but not too high, to mimic a DLI naturally found during very bright and long days (re Hawaii).

If one used 1,500 PPFD all day (ex. 12 hours, 18 hours, etc) it could be too much DLI, and hinder rate of photosynthesis and cause photoinhibition (ex., midday depression of photosynthesis, (increased) photorespiration, etc.).

Using peak PPFD of 1,500 adjusted with an average PPFD bell-curve (over the whole daylength) from a high irradiance location (ex. Hawaii on relatively cloudless day maxing out at 1,500-2,000 PPFD) to find DLI is the best method I could think of at my disposal to easily guesstimate a possible goal DLI for flowering cannabis. That is, short of using PPFD per wavelength weighted with K.McCree's quantum yield.

1,500 PPFD fits into my DLI model because that irradiance level was found to provided near peak Pn in four different studies on cannabis, with variables such as temp, Co2, etc. And IIRC > 1,000 PPFD could be considered a benchmark for high(est) Pn. However, I didn't want to use 1,500 PPFD to find DLI because IMO 1,500 PPFD is too much instantaneous irradiance for every second over greater than 12 hours. Outside there is a PPFD bell curve, it starts low, gets high, ends low; and outside peak PPFD can be found about and just above 2,000.

I wanted to try and mimic the DLI a plant like cannabis (a 'sun loving' type) could experience outside, naturally, respective to the PPFD found to provide peak Pn for cannabis. So I found a long set of spectroradiometer graphs for PPFD every X minutes over a (nearly) cloudless day in Hawaii in summer; used to find DLI of that spot in Hawaii. I used Hawaii because (a) it has very high irradiance, a good example for what cannabis likes; and (b) I have grown cannabis in Hawaii (halfway up a big mountain, when I had my med card there) and saw first hand the effect of long days and high irradiance.

I think I am making it sound more complicated than it really is, it's quite simple but I think I may be over explaining in an attempt to explain enough.

Basically it's like this:

I used a natural PPFD bell curve from high irradiance location (Hawaii) that peaked at ~1,800 PPFD around noon; about the same PPFD that offers highest rate of photosynthesis for cannabis. Then I worked backward starting with the DLI from Hawaii, using 12 hour daylength (ex., for flowering) to find PPFD. And the PPFD was > 1,000, which is kind a benchmark for high(est) Pn.

My model for flowering (12 hour day) puts DLI at 46-48 (mol/area^2/day); that is achieved using ~1,000-1,100 umol/area^2/second (specifically ~1,065 to ~1,111 umol/area^2/second).

However, in reality most grow rooms will not provide over 1,000-1,100 umol/area^2/second to any plant; unless there is for example one small plant below a good lamp/reflector. For example, under a Blockbuster 8", with 1,000 watt Digilux HPS and Galaxy select-a-watt set to 'super lumens' (supposed to be 10% increase in radiance from 1,000 watt) -- with an Equalizer hot-spot diffuser -- the peak irradiance under about plumb center of lamp (while keeping irradiance high at the range of 3'x3') is ~920-975 umol/6"^2/second (10 second average to account for lamp flicker).

Most grow rooms will probably provide somewhere around 40-44 mol/area^2/day for flowering; those that are 'bright'. Very well designed rooms, esp. with respect to canopy size relative to size of reflector and light mover, can have over 50 mol/area^2/day for 12 hours.

(... nuts and bolts in next post ...)

[spurr]

(much of below was taken from other posts I have made on this topic in the past)

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.

[spurr]

Here is a good web article on this topic, and the source of PPFD data from Hawaii I used above:

"A Different Look at Lighting: Effects of Prolonged Photoperiod, Spectral Quality, and Light Dosage"
Pomacanthus Publications, Inc.
https://www.advancedaquarist.com/2009/5/aafeature