daily light integral

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

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.

itzaplant said:

reallt guy is it that complicated

Click to expand...

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

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

delta9nxs said:

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?

Click to expand...

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

delta9nxs said:

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?

Click to expand...

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.

delta9nxs said:

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

Click to expand...

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.

delta9nxs said:

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

Click to expand...

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.

delta9nxs said:

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.

Click to expand...

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).

delta9nxs said:

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.

Click to expand...

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.

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

---------------------
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".
---------------------

delta9nxs said:

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.

Click to expand...

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 ...)

(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.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.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.

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

First, thank you for your time and effort. A lot of work went into your response.

Quotes by Spurr.

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

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).”


Since beginning this thread I have been studying the plant circadian clock and now see what you mean about my use of the term “reset”. The mechanism is more of an “on/off” than a reset. This on/off cycle is mostly entrained by light although other forces such as temperature can come into play. I also have a better understanding of how the “clock” translates external stimuli into internal reactions by use of the phytochrome and cryptochrome receptors and the oscillator.


“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.”


i've been using 8 on 4 off 8 on 4 off each 24 hours in veg and the plants are reaching the same size they reached under 24/0, 20/4, or 18/6. this is approx. 30-32” in 4 weeks using a bare vertically oriented 1k hortilux hps at 14” to the nearest part of the plant. I have a quantum meter and it shows 1500 umols at 14” so theoretically I am delivering 43.2 moles per period or 86.4 per day to at least the front of the plant.


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


this I believe I have observed. The device i'm growing in now is fed in part by a sub-irrigation system that has a level controlled by a float valve. When the lights first come on there is virtually no drip occurring. At ten minutes there is a slow drip. At 20 it is faster. At 30 minutes even more volume. By the end of an hour it is dripping at over 100 drips per minute and stable. This is in flower with 8-9 large plants.


“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?”


in figure 1a on page 3 of Dr El Sohly's paper there is a graph and I think I misinterpreted part of it to mean that he used 25 moles per day. Upon rereading it I don't see moles/day clearly indicated anywhere. You might take a look and see what you think.


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


yes, but rarely does in practice. Those giant hydroponic tomato greenhouses in arizona report 48 moles/day regularly. But they located there for that reason. I think specmeters bases their program on 30 moles/day. All their literature is geared towards this level. I have a set of the “dli 100 lightscout” light meters and you can peg them at 30 moles/day. They measure accumulation only.

I don't believe that 30 moles is the max that can be used, but i'm thinking of a light array that hits each side of the plant in flower with 30 moles at alternating times. 6 hours per side.


“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".”


so, with sunlight, because of the great distance from the sun to the earth, the photon stream must appear almost as paralell and therefore nearly equal. indoors using fixed emitters close to the plant the stream must appear more like spokes of a wheel and therefore will be unequal applied to a flat surface. My meter shows that just 2” further from the light, for example, means the difference between 1500 umols and 1200 umols in free air. To me this means that foliage “penetration” indoors is all but nonexistant. We are really growing premium bud only on the periphery of the plant canopy.


“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.”


I gotcha. I use my lights in flower with cooltubes and I can get 1500 umols at 12” but of course that is only part of the plant.



“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.”

my thinking exactly. I'm wondering whether the 30 moles per side at the closest point of foliage that I described above can deliver 60 moles/day to the whole plant without causing inhibition. This also has me thinking about how photosynthate partitioning will work in this scenario. I'm wondering whether there is a threshold of light that turns a plant part into a producer instead of a sink. Say 2-300 umols or more. Could you provide links to the studies showing ideal ppfd? I have dr el sohly's.

“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 ~1,200 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 think I can determine the approx max dli relative to my own light and plant arrangement by using the drip rate of my system. As photosynthesis rolls off I should get a noticeable decrease in drip rate. I'll have a test plant set up for this soon.
Thank you for your thoughts and all the number crunching, it all helps.

d9

delta9nxs said:

spurr said:

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

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).

Click to expand...

Since beginning this thread I have been studying the plant circadian clock and now see what you mean about my use of the term “reset”. The mechanism is more of an “on/off” than a reset. This on/off cycle is mostly entrained by light although other forces such as temperature can come into play. I also have a better understanding of how the “clock” translates external stimuli into internal reactions by use of the phytochrome and cryptochrome receptors and the oscillator.

Click to expand...

Yup, sound like you understand it well

delta9nxs said:

spurr said:

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.

Click to expand...

i've been using 8 on 4 off 8 on 4 off each 24 hours in veg and the plants are reaching the same size they reached under 24/0, 20/4, or 18/6. this is approx. 30-32” in 4 weeks using a bare vertically oriented 1k hortilux hps at 14” to the nearest part of the plant. I have a quantum meter and it shows 1500 umols at 14” so theoretically I am delivering 43.2 moles per period or 86.4 per day to at least the front of the plant.

Click to expand...

Interesting. It's neat how plants aren't fixed to 24 hour circadian period. It can take a little as a couple of days for "photo-adaptation" to take place. I have flowered with a light regime of 16/12, and plan to further test flowering with 16 hours on (as well as 18 hours on) and 12 hours off (as well as 10 hours off).

I like flowering for longer daylengths to increase DLI, yields increase when I increase daylength; but some does time to harvest.

Do you notice any loss of chlorophyll (Chl A or Chl B) from leafs at ~1,500 umols? I notice loss of Chl once instantaneous irradiance exceeds ~1,000 umols for > 12 hours (I haven't tested shorter than 12 hours yet); but that's with a HPS (SPD rich in yellow/orange).

I would find it very interesting, if you do not see loss of Chl at 1,500 umols. I assume the shorter and more frequent daylengths may be the reason for no loss of Chl, re much less DLI at 8 hours of light vs 18 hours of light.

I have been testing a lamp with high green lately, the Digilux MH (1,000 watt). The higher green should mean higher daily net rate of photosynthesis for plants grown with high irradiance, after many hours each day. I notice (much) reduced loss of Chl when using a lamp with high green vs high yellow/orange; when both are near 1,000 umols.

What brand and model quantum sensor do you use?

FWIW, I recently came across a few uber great advanced lab experiments for finding Pn of plants, as well as Co2 fixation, etc. Finding Pn is very useful, even though the methodology is less than perfect. So one could test 8/4 vs 18/6 vs 20/4 vs 24/0 in terms of tracking Pn, Pnnet, irradiance and DLI, for less than ~$3,000-5,000. The lab and tools are from Qubit Systems, out of Canda. At time of writing, the lab (for a Unvierity in Canada) setup cost was ~$3,000 total. Today I assume the cost has gone up, as well product quality. Quibit Systems specializes in environmental, plant and animal science studies for Universities at an affordable price.

If I (or a group of us) could get good sized donations/grants, or rent the needed equipment, there would serous science on cannabis taking place ...

delta9nxs said:

spurr said:

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

Click to expand...

this I believe I have observed. The device i'm growing in now is fed in part by a sub-irrigation system that has a level controlled by a float valve. When the lights first come on there is virtually no drip occurring. At ten minutes there is a slow drip. At 20 it is faster. At 30 minutes even more volume. By the end of an hour it is dripping at over 100 drips per minute and stable. This is in flower with 8-9 large plants.

Click to expand...

Interesting thanks. One can also watch the movement of leafs for ~45 minutes after daylight with time-lapse camera, to see the 'wake up' time for plants. In fact, I have a "Plant Cam" time-lapse camera I bought to use for my grow, but it's hard to focus so I haven't used it (and HID glare ruins pics). I bet I can make a time-lapse video of leaf movement over the day, or at least the first 45 minutes of the day. I could note DLI a certain points if making a video of the whole day, etc.

delta9nxs said:

spurr said:

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?

Click to expand...

in figure 1a on page 3 of Dr El Sohly's paper there is a graph and I think I misinterpreted part of it to mean that he used 25 moles per day. Upon rereading it I don't see moles/day clearly indicated anywhere. You might take a look and see what you think.

Click to expand...

Will do, which paper should I read?

delta9nxs said:

spurr said:

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

Click to expand...

yes, but rarely does in practice. Those giant hydroponic tomato greenhouses in arizona report 48 moles/day regularly. But they located there for that reason. I think specmeters bases their program on 30 moles/day. All their literature is geared towards this level. I have a set of the “dli 100 lightscout” light meters and you can peg them at 30 moles/day. They measure accumulation only.

Click to expand...

Yes, ~30 mols/day is the common average in the U.S.

You use a Light Scout? From SpecMeter? Not to knock your quantum sensor, but the quantum response is pretty far from ideal. That means the data you present is useful, but is not very accurate, sorry to say.

The quantum response of the Light Scout (and Field Scout) is pretty much like that of the Lux meter (which is weighted to green/yellow), albeit the Light Scout is more like an inaccurate quantum yield curve. A PAR range quantum sensor for plants should try to not weight photons in PAR range.

Below is the quantum response of your meter, and here is a post I made about this topic with good info about ideal quantum response, plant usage of wavelengths within PAR range, etc:


Quantum Reponse of all FieldSout models:
http://www.specmeters.com/pdf/3415F Quantum Light Meters.pdf

delta9nxs said:

I don't believe that 30 moles is the max that can be used, but i'm thinking of a light array that hits each side of the plant in flower with 30 moles at alternating times. 6 hours per side.

Click to expand...

Sounds interesting.

delta9nxs said:

spurr said:

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".

Click to expand...

so, with sunlight, because of the great distance from the sun to the earth, the photon stream must appear almost as paralell and therefore nearly equal. indoors using fixed emitters close to the plant the stream must appear more like spokes of a wheel and therefore will be unequal applied to a flat surface. My meter shows that just 2” further from the light, for example, means the difference between 1500 umols and 1200 umols in free air. To me this means that foliage “penetration” indoors is all but nonexistant. We are really growing premium bud only on the periphery of the plant canopy.

Click to expand...

Yes, agree completely. That is why I grow in a stadium style horizontal garden with big plants for a full canopy that is not deep (~12-18"). I also like to use HID with sufficient green for various reasons, one being greater reflectance into canopy for higher irradiance lower and intra-canopy. That is also why I prefer to use strong air movement and a light mover, to increase "sunfleck".

In terms of lower and intra-canopy light, blue and red have highest rate of absorptance by leafs and lowest reflection, also low transmittance. That means blue and red photons get 'used' by the top leafs (or lost a heat) and not many blue and red photons make into the lower intra-canopy (besides from sunfleck). Green photons, when top leafs are not near blue and red light saturation, are reflected at the rate of about 50% by leafs; transmittance is lower than far-red but higher than blue and red, so the other ~50% is mostly absorptance. That means lower and intra-canopy has more green photons than blue and red. Far-red light has a high degree of transmittance through leafs, and very low absorptance as well as low reflectance, so lower and intra-canopy photons (in shade) is comprised of mostly far-red photons.

Here are spectroradiometer graphs of sunlight and under-canopy sunlight:

delta9nxs said:

spurr said:

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.

Click to expand...

I gotcha. I use my lights in flower with cooltubes and I can get 1500 umols at 12” but of course that is only part of the plant.

Click to expand...

Yea, same here. But if I want to irradiate a larger canopy area I need to use lower peak irradiance.

delta9nxs said:

spurr said:

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.

Click to expand...

my thinking exactly. I'm wondering whether the 30 moles per side at the closest point of foliage that I described above can deliver 60 moles/day to the whole plant without causing inhibition. This also has me thinking about how photosynthate partitioning will work in this scenario. I'm wondering whether there is a threshold of light that turns a plant part into a producer instead of a sink. Say 2-300 umols or more. Could you provide links to the studies showing ideal ppfd? I have dr el sohly's.

Click to expand...

Yea, I have posted them in the 24 light thread, I'll find the post and put it here.

delta9nxs said:

spurr said:

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 ~1,200 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.

Click to expand...

I think I can determine the approx max dli relative to my own light and plant arrangement by using the drip rate of my system. As photosynthesis rolls off I should get a noticeable decrease in drip rate. I'll have a test plant set up for this soon.
Thank you for your thoughts and all the number crunching, it all helps.

d9

Click to expand...

No worries, you have an interesting game plan, keep us updated.

I do not have the background to work numbers correctly, but have an intuitive grasp of what is going on, I think.

Even light over the canopy is attempted by using 7 HID's in a hex pattern. 23" lowbay white reflectors spaced 26" apart (3" between edges). Plants are 16" from lights. HPS was killing my chlorophyll and got banned six years ago, red HID (3), blue HID (2), and ceramic HID (2). All 400 watt inside a reflectix cyllinder 7' across.


I found green HID's but do not have room to hang them, since the lower leaves are the ones to normally get green light, would bottom lighting with green be a silly idea or might it help?

Phaeton said:

I do not have the background to work numbers correctly, but have an intuitive grasp of what is going on, I think.

Even light over the canopy is attempted by using 7 HID's in a hex pattern. 23" lowbay white reflectors spaced 26" apart (3" between edges). Plants are 16" from lights. HPS was killing my chlorophyll and got banned six years ago, red HID (3), blue HID (2), and ceramic HID (2). All 400 watt inside a reflectix cyllinder 7' across.


I found green HID's but do not have room to hang them, since the lower leaves are the ones to normally get green light, would bottom lighting with green be a silly idea or might it help?

Click to expand...

Bottom lighting of green light would help, but bottom lighting of red and blue light would probably help more.

I'm curious what you mean by "since the lower leaves are the ones to normally get green light". Why do you suggest lower leafs get more green light?

I suggested red light to increase the red:far-red ratio intra-canopy closer to 1 than 0.1. I suggested blue light beuase old leafs tend to use blue light as well, or better than red light, for photosynthesis.

I am also curious what you mean by 'red, blue and green HID', I assume you mean with respect to SPD. Correct?

All my HID have that blue mercury streak, but otherwise:

red is 590 nm, looks pinkish than red. EDIT: PlusRite put violet in with 590 YELLOW so it looks pink to my eye and they called it red, 590 is yellow, prisms don't lie, no actual red, the blue HID's have more red than the red ones. Darn.
blue is 450 nm, very similar to 420/460 nm T5 aquarium lights I also have.
green is available at 535 nm.
rated for 5000 hours, have only reached 2300 hours, so far so good.

I did say the inner leaves normally got more green light, that was an assumption on my part. My green sensitive eyes see the green bouncing all through the plant when I stick my head inside the canopy, I took the answer I would like to work 'cause I'm itching to get some green HID but need some justification.

And since my red has some blue it is the logical choice from the information I now have, the green will wait for another time. Thanks for the input.

The procedures and product usage backed by experience and study by members of this forum have increased the quality and quantity of my growing. Mostly an accumulation of small things that just work better or easier. Sometimes it involves major changes.

:kitty:
Daily Light Intregal. I'm autistic and sometimes I just have to know. DLI, never heard of it but it made sense. I purchased lights, I purchased fans, I built a new veg room to house them. I cranked up the lights, keeping a good spectrum until the plants tapped out in under 17 hours. It took 180,000 lumens, which I do understand is not a good unit of measure, over 26 square feet to achieve this. No HPS.
:kitty:

I used this information to rebuild my current budroom, not long enough for taste testing any finished product, but visually health and growth has increased over the previous rate.

Big items take work to effect, all the smaller hints save work. Many members, many grows, several ways to do it right, just had to pick and choose all the ones I liked.

This is a thank you to those who spend time and effort learning and then just give it to me free to use.
I thank you again.


ps: spurr, I put 2700K CFL's, big, fat, cool surface, 45 watt, T4 coils, under the canopy of the 2 newer trays.
The tray almost ready to come out got 6500K as the leaves are older.

Pheaton,

You’ve made a good choice on the MH over the HPS. Resin and THC has shown an increase with MH and the use of UVB. CA growers are finding this out as many Co-ops now want testing and the HPS guys are falling behind on the numbers. HPS guys have to be almost perfect to make the 20%+ that many top shelf Co=ops want for their top buds. Bag appeal is still number 1, but numbers are now right on it’s tail.

On your green light, it’s not that important. It’s available through most light bulbs and is not that important to cannabis and most plants. It’s used but not a major player in the game.

For lighting, the addition of UVB along with your MH will produce the most resin for any given lighting. Down side is it does inhibit growth. The smart guys figured this out years ago but it seems to still be a secret to most for some reason. So the secret is how to increase the resin without the incurring of growth stunting for a higher resin yield.

The UVB increase in resin requires two things. First the plant must take a set. Set being the reaction the plant makes to counter UVB damage. Second the plant must be exposed during the bloom stage so that the plant is forced to produce extra resin to protect itself.

Many know of using UVB through the whole growth/bloom process. They also know of the growth reduction this way. Some know of the benefits of using it for the first few weeks of growth and then using it after the second week of bloom to harvest. Still there is a bud growth penalty that must be paid, although the growth part is pretty much overcome this way. The most current and successful way seems to negate most if not all of the stunting.

Keep your mothers under a UVB regimen their whole lives. This will take the set process offline and you don’t have the growth penalty. Your clones will have the set programmed into them. They are already reacting to UVB but you do not expose them to it during the growth process. You can maintain the set by the use of MH lights which contain some UVB. UVB is very variable in the wild. It changes drastically during the day and changes during the year, so just a mild exposure will maintain the set.

The final and most important exposure is timing, technique and very strain dependent to reach the height of maximum gain. What appears to be the best method at this time is to start this exposure at the first recognition of the second growth cycle of the buds. Once you have noticed this, you should be 3-7 days into this growth spurt. This timing activation tends to help with the variation in strain issue. The plant will be telling you when it is ready. After several successful grows you will be able to fine tune more to your strain but don’t expect a huge change over this method already given.

This timing takes some inherent advantages the plant naturally has anyway. Resin is produced mainly from the start of this growth cycle to the end of harvest. Most plant growth is over by this time and the buds are just filling out so we don’t restrict growth as much this way. We are just working on the item that we seek the most, resin. And we are not restricting the growth factor as much. One technique, two wins.

This should help anyone who has a basic understanding of UVB usage. If you haven’t used it yet, study UVB and also PLANT STEERING through light manipulation. It will give you a pretty good understanding about what is needed but not bog you down with the science that really won’t help you much. Don’t let OCD tie you down picking up pennies when $100 bills are flying around your head.

This system works the best that I’ve seen and used. There may be others out there that people have not brought forward yet. So don’t stop looking. With what you have and add this, you should be on to hormones and PGRs for the next big increase.

Hello Sabertooth Phar,

Sabertooth Phar said:

Pheaton,

You’ve made a good choice on the MH over the HPS. Resin and THC has shown an increase with MH and the use of UVB. CA growers are finding this out as many Co-ops now want testing and the HPS guys are falling behind on the numbers. HPS guys have to be almost perfect to make the 20%+ that many top shelf Co=ops want for their top buds. Bag appeal is still number 1, but numbers are now right on it’s tail.

Click to expand...

I do agree that there is strong evidence UV-b (esp. < ~300 nanometers) can increase THC-A, from various studies and reports, as well as my own (less valid) testing with thin layer chromatography and spot density scanning. That is, if the daily UV-b integral is sufficient, ex., 6-14 kJ/area/day UV-bbe. The "be" stands for "biologically effective", and is weighted strongly at, and less than, 300 nm. However, I am unaware of any studies showing blue range light increases THC. That would be very interesting to read about, can you please post the references? (I'm familar with various cryptochrome responses)

I am also unaware of studies and evidence showing UV-b and blue light increase resin. What do you mean by "resin"?

Sabertooth Phar said:

On your green light, it’s not that important. It’s available through most light bulbs and is not that important to cannabis and most plants. It’s used but not a major player in the game.

Click to expand...

Green light is important for various reasons, ex., grater irradiance intracanoy, reduced stretch of plants, about 50% of incident leaf photons are used for photosynthesis under non-saturated conditions (re blue and red photon at upper chloroplasts of leaf), and under saturated conditions green light can drive rate of photosynthesis better than blue and red (ex., a long day of high irradiance increases chance of saturation).

Green light isn't necessary, but providing green light (either by HID or LED) is certainly beneficial. The caveat is green light, at high level, esp. with respect to blue and red, can reduce openness of stomas and slow plant growth.

Sabertooth Phar said:

For lighting, the addition of UVB along with your MH will produce the most resin for any given lighting. Down side is it does inhibit growth. The smart guys figured this out years ago but it seems to still be a secret to most for some reason. So the secret is how to increase the resin without the incurring of growth stunting for a higher resin yield.

Click to expand...

A grower can use UV-b without stunting growth of plants while providing the level of UV-bbe shown to increase THC-A. I have been providing a known daily dosage of UV-b (weighted with near UV-bbe profile just recently) for some years, close to 10-13 kJ/10"^2/day (I use lower instantaneous irradiance over longer hours per day). My plants never suffer. The key is providing sufficient PAR and UV-a range photons, to prevent harm from UV-b photons.

Using UV-b and UV-a is good for reasons besides THC increase (from low end UV-b), such as cryptochrome responses, increase in some flavonoids (ex., purple color pigmentation), reduced internode length and plant stretch, etc. (there is a lot of research that has been conducted and published in peer-reviewed journals on these topics).

Sabertooth Phar said:

The UVB increase in resin requires two things. First the plant must take a set. Set being the reaction the plant makes to counter UVB damage. Second the plant must be exposed during the bloom stage so that the plant is forced to produce extra resin to protect itself.

Click to expand...

What do you mean by "set"? How is it quantified for each plant?

FWIW, IME and AFAIU, all plants can and should be given UV-b, well, at least all cannabis plants (and most other indoor plants, too). I have been using UV-b on many different cannabis plants (cultivars of various genetic heritages), and other plants too (non-cannabis). I have yet to find one that didn't benefit from the proper amount of daily UV-b, when under sufficient PAR and UV-a range light, too.

In all studies I have found, and in my testing, starting UV-b irradiation from seedling/clone stage provide good results in terms of plant growth and THC yield. However, I would be interested in reading about that variables/parameters and testing done, on the grows you are describing. The more info we get the better. That said, maybe the Uv-b thread would be a better place for this discussion?

In the end, all we're really doing is replicating ideal outdoor conditions (re UV-b), indoor. P.S. how did we come to be discussing UV-b in a thread about DLI?

Sabertooth Phar said:

Many know of using UVB through the whole growth/bloom process. They also know of the growth reduction this way. Some know of the benefits of using it for the first few weeks of growth and then using it after the second week of bloom to harvest. Still there is a bud growth penalty that must be paid, although the growth part is pretty much overcome this way. The most current and successful way seems to negate most if not all of the stunting.

Click to expand...

Measured variables are the key to figuring out why those grows you are describing are suffering (they should not be). Ex., what was the UV-b irradiance (uW/cm^2) and daily dosage of UV-b (minutes of irradiation)? What was the temp at canopy and RH, any water stresses, etc.? What was UV-a and PAR range irradiance? Etc.

This should help anyone who has a basic understanding of UVB usage. If you haven’t used it yet, study UVB and also PLANT STEERING through light manipulation. It will give you a pretty good understanding about what is needed but not bog you down with the science that really won’t help you much. Don’t let OCD tie you down picking up pennies when $100 bills are flying around your head.

Click to expand...

I'm sorry, but most of what you wrote is incorrect/inaccurate, or not proven, so I would disagree with the above quote. Any problems you have had, or have been reported to you, are not due to use of any amount UV-b per se; it's other variables that are not under control (incl. providing too much UV-b).

Damn. I just fixed many more typos and increased clarity and accuracy of my post above. I shouldn't post when I'm very tired and very high!

.