Cool tube vs. bare bulb test, just for kicks

[DHF]

Thanks for the thoughts guys! Good point Mister_D about the value of increased yield, but not all are medical/commercial growers. The "cost" I was trying to optimize was efficiency, not profit.

Speaking of which, if profit is your motive, wouldn't it be better to go way beyond 50 watts per sq. foot? I'd imagine that once you have temps and RH under control, you're always best pumping up the watts to as much as our space will allow in terms of increasing profits.

Increasing wattage beyond 50 per sq ft has NEVER increased yields in ANY garden I`ve ever seen online or up close and personal Flat......

What increased wattage does is create constant environmental issues from excess transpiration to light bleaching/heat scorching and many other issues once you start chasing watts instead of settling for dialed everything runnin in sync and pumpin out the nuggage consistently.....

My 2 cents from all them yrs....

Peace....DHF.........

 

[farmari]

I've read plenty of growers going beyond 50 per sq ft and getting near linear increases in yield.

Yes if you're scorching your plants and creating environmental issues with high watts then you're not going to get much any yield increase. (possibly a decrease) Generally it gets more and more difficult to dial things in the higher w/sq ft you go and going +100w/sqft can be very difficult if not impossible depending on the space and circumstances you have.

It misses the big picture to go by simple gpw anyway because if you double the watts and get 50% more yield, you need 50% less space and labor in your grow to get the same yield with 50% bigger buds. And either plant count or veg can be reduced for the same result because plants will grow significantly larger during the stretch at high w/sq ft.

DHF I guess you haven't seen grows by Texas Kid, foaf, doubleds, etc...

I've been at 130w/sqft for the last 5 grows and have been far from dialed in, am just a newbie grower, made a lot of mistakes and problems unrelated to the wattage, and still get over 0.5gpw if I don't completely screw up. For example I've grown a number of plants 3ft diameter or less that were 1-2lbs.

a couple icmag links to high watt per sq ft discussions:

https://www.icmag.com/ic/showthread.php?t=45767
https://www.icmag.com/ic/showthread.php?t=112351

 

[DHF]

I've read plenty of growers going beyond 50 per sq ft and getting near linear increases in yield.

Yes if you're scorching your plants and creating environmental issues with high watts then you're not going to get much any yield increase. (possibly a decrease) Generally it gets more and more difficult to dial things in the higher w/sq ft you go and going +100w/sqft can be very difficult if not impossible depending on the space and circumstances you have.

It misses the big picture to go by simple gpw anyway because if you double the watts and get 50% more yield, you need 50% less space and labor in your grow to get the same yield with 50% bigger buds. And either plant count or veg can be reduced for the same result because plants will grow significantly larger during the stretch at high w/sq ft.

DHF I guess you haven't seen grows by Texas Kid, foaf, doubleds, etc...

I've been at 130w/sqft for the last 5 grows and have been far from dialed in, am just a newbie grower, made a lot of mistakes and problems unrelated to the wattage, and still get over 0.5gpw if I don't completely screw up. For example I've grown a number of plants 3ft diameter or less that were 1-2lbs.

a couple icmag links to high watt per sq ft discussions:

https://www.icmag.com/ic/showthread.php?t=45767
https://www.icmag.com/ic/showthread.php?t=112351

Hey Farm....I`ve prolly seen every setup TK`s ever done even over at the farm , well maybe not EVERY 1 , but I was never aware of him using crazy watts per sq ft and his claims that it increased yields....and....

I helped groom that nuthin ass Doubleds @HG yrs and yrs ago with Heath Robinson , and I assure yas you couldn`t believe a fuckin word that self-indulged asshole said from 1 day to the next.....

Claimin he "invented" a "big-plant" system when ALL he did was copy Krusty buckets and Heath`s RDWC designs for his bullshit waaaay too many bells and whistles "recirculating death without cause" behemoth that killed more plants than it grew....and damn if I ever remember him runnin more than 50 watts per sq ft either Farm , but maybe I missed it and never noticed ?....again....dunno...and then....

FOAF....He runs 1 plant in a closet with nuthin but cfl`s all wrapped around , up and down , or have I again missed somethin.....regardless....

Increased mega wattage may INDEED penetrate deeper into either a horizontal OR vertical canopy allowing yas to THINK yields are increased since less lollypoppin lowers and insides are necessary to prevent larfy popcorn bullshit , but I assure yas ...

Mega wattage is waaaay harder to control environment in a grow area , and environment is 1000 times more important than slingin light at there ass guaranteed.....

Proper watts per sq ft is paramount in importance for hardening nuggage and all those other scientific chemical and hormonal changes as the plants progress through their cycle , but I stand by what I`ve seen and done over the yrs as good solid info for optimum returns on investment...and for the record....

I`ve never been part of those higher wattage discussions and threads cuz trust me....back in the day at the old dead sites , every OG grow guru tested ALL conceivable possibilities for yield AND quality increasage , and when all the smoke cleared it was just too costly to chase environment tryin ta shove buncha lumens up the plants asses for very little to ANY difference in bottom line results across the board.....but in retrospect.....

Show me I`m wrong and I`ll eat my words , cuz solid info that works for EVERYONE that I`m not aware of means more than what I`ve tried to preach for 20 yrs , and hey.....the times they are a changing technology wise and anything`s possible , and I`m ALWAYS willin ta learn.....but again.....I don`t think so IME.....

Peace....DHF........

 

[farmari]

Well those are just examples off the top of my head. Texas Kid for example preferred and used over 100w/sq ft in tents and recommended it. Soquick was near 100w sq ft and getting near a gpw in his last grow thread if I recall right. I don't think it's fair to dismiss Foaf's grows as "CFLs in a closet" as they're pretty clear examples of very high w/sq ft allowing for greater results in a limited space. LOL about doubleds, I wouldn't be surprised if he was lying about yields but the photos weren't photoshopped. I'm just saying, I spent a lot of time reading about others high w/ sq ft grows online before changing my setup. The info is out there for anyone who wants to look. The most common experiences are those going up to 1000w in a 3x3 or 1m^2 tent and getting significant yield increases if their environment is sound.

To give an example of what is capable, after growing for a couple years 30-50 w/sq ft I switched to +100 and on my first attempt I not only had a 3ft diameter plant that yielded 2 lbs but there were two plants that were only a foot wide when put under 12/12 and they both yielded over 12 ounces. (they were both different strains from seed so it's not like this was a monocrop of a high yield clone) Good luck putting a 1ft plant under 12/12 with 50 w/sq ft and getting such results!

Visualizing the results it's easy to see 1gpw (which is almost 5 ounces a square foot!) being possible, especially by a skilled SOG grower. Wish me luck at showing ya wrong I'll try to get up there this year. I do hear what you're saying, and think that as a general rule 50w/sq ft is an ideal number to recommend. I just thought I should put the perspective out there, that for any grower who wants to try much higher light intensity, try setting it up, and if the environmental conditions can be handled properly, give it a go, then report to us your results please!

 

[Gert Lush]

With ANY room big enough to utilize bare bulbs , guaranteed they squash the shit outta any reflector on the market , horizontal OR vertical....witnessed it first hand and have 1000`s of testimonies from folks I`ve brought into the light so to speak over the yrs....

That's very useful to know, thanks!

I'm trying my first ever vert at the moment, in a very small space, so the cooltube was inevitable, but I will certainly consider bare glass if/when I decide to scale this style up.

 

[DHF]

Well those are just examples off the top of my head. Texas Kid for example preferred and used over 100w/sq ft in tents and recommended it. Soquick was near 100w sq ft and getting near a gpw in his last grow thread if I recall right. I don't think it's fair to dismiss Foaf's grows as "CFLs in a closet" as they're pretty clear examples of very high w/sq ft allowing for greater results in a limited space. LOL about doubleds, I wouldn't be surprised if he was lying about yields but the photos weren't photoshopped. I'm just saying, I spent a lot of time reading about others high w/ sq ft grows online before changing my setup. The info is out there for anyone who wants to look. The most common experiences are those going up to 1000w in a 3x3 or 1m^2 tent and getting significant yield increases if their environment is sound.

To give an example of what is capable, after growing for a couple years 30-50 w/sq ft I switched to +100 and on my first attempt I not only had a 3ft diameter plant that yielded 2 lbs but there were two plants that were only a foot wide when put under 12/12 and they both yielded over 12 ounces. (they were both different strains from seed so it's not like this was a monocrop of a high yield clone) Good luck putting a 1ft plant under 12/12 with 50 w/sq ft and getting such results!

Visualizing the results it's easy to see 1gpw (which is almost 5 ounces a square foot!) being possible, especially by a skilled SOG grower. Wish me luck at showing ya wrong I'll try to get up there this year. I do hear what you're saying, and think that as a general rule 50w/sq ft is an ideal number to recommend. I just thought I should put the perspective out there, that for any grower who wants to try much higher light intensity, try setting it up, and if the environmental conditions can be handled properly, give it a go, then report to us your results please!

Bro......I`d NEVER discount Friend of a friend`s setup using cfl`s cuz light is light , but growing 1 plant surrounded by mega bulbs up , down , and all around 1 plant ain`t exactly what we`re talkin bout now is it...and.....I`ve never seen a TK grow in tents , so that may be where I missed it......

God Knows I`ve seen him grow monsters in kiddie pools and every other setup under the sun , but again I re-iterate....Increased wattage DEMANDS waaaay more environmental control than what it`s worth for the returns I`ve seen WELL experienced growers over the yrs attempt to produce....that`s all I was tryin ta get across Farm....and....

I watched EVERY setup SoQuick ran back in the day , cuz Krusty and he stayed tooth and neck as rivals for the "GPW" CLUB KING for several yrs , and again.....

Not once was it said or let be known that he was runnin 100 watts per sq ft with his increased plant number setups that were AWESOME , cuz Krusty would`ve bashed the SHIT out of it on how he was controlling environment in the meantime......anyways....

Farm....Dial that shit and let us know how things progress "consistently" , cuz consistent returns run in and run out are what matters across the board IME , and 1gpw with 100 watts per sq ft seems like a feat un-reachable on a consistent level , but I`ve been wrong before......

Peace....DHF........

 

[BredForMeds]

agreed.. cool tubes and air cooled are ment for areas that u cant keep your temps down.. or for those hot summers.. so u don't need to run as big a AC..

 

[Mister_D]

Thanks for the thoughts guys! Good point Mister_D about the value of increased yield, but not all are medical/commercial growers. The "cost" I was trying to optimize was efficiency, not profit.

Speaking of which, if profit is your motive, wouldn't it be better to go way beyond 50 watts per sq. foot? I'd imagine that once you have temps and RH under control, you're always best pumping up the watts to as much as our space will allow in terms of increasing profits.

Efficiency is exactly what I'm talking about. Be it for profit or personal use, growing the most bud per watt of power should be the goal of any grower. My point was simply that even if it cost you an extra 5-10 bucks a month to run a bigger fan/ac to cool your lights, the quarter ounce or whatever per light of extra bud more than makes up for the added cost. In the case of a personal grower this means they can go longer between harvests/ grow less often. Thus saving more power/money, increasing efficiency. As for increasing past 50wpsf, this again comes back to efficiency. As noted above you hit a point of diminished returns shortly after 50wpsf (cost becomes too high for the added return)

 

[flat9]

Efficiency is exactly what I'm talking about. Be it for profit or personal use, growing the most bud per watt of power should be the goal of any grower. My point was simply that even if it cost you an extra 5-10 bucks a month to run a bigger fan/ac to cool your lights, the quarter ounce or whatever per light of extra bud more than makes up for the added cost. In the case of a personal grower this means they can go longer between harvests/ grow less often. Thus saving more power/money, increasing efficiency. As for increasing past 50wpsf, this again comes back to efficiency. As noted above you hit a point of diminished returns shortly after 50wpsf (cost becomes too high for the added return)

Seems like you and I actually agree roughly but with different goals in mind. In other words, as an example, if you looked at Heath's tree grow thread, he was using some strategy in which he didn't have all the bulbs running during flower at once. The layout was something like:

o - o
- x -
- o -
- x -
o - o

with the o's being 600s and the x's the trees. He didn't have all bulbs running at once, and his reasoning was that he didn't care about total yields and more about making the grow more efficient in terms of GPW. Could he have gotten more from the grow by running all 600s at full power? Sure. But it seems he was trying to maximize his GPW rather than just get the largest yield, maximizing revenue, or even maximizing profit.

Which brings me to your other point. As for 50 watts per square foot being ideal for either a revenue or profit maximizing strategy, well, I don't quite buy it. All we have is anecdotal evidence, which can be useful but is not definitive. To do this properly, we need an experiment in which we use the same strain, same media, same nutes, same environment (try to control for all possible confounding variables), and gradually increase the watts and note the differences in yield. Certainly there will be some breakeven point (from a microeconomics perspective in which profit maximization is the goal, the optimal point is where marginal revenue = marginal costs), but unless marginal (gains in) yield rapidly drops off a friggin cliff after 50 watts per square foot, I doubt we're even close.

I mean just think about it: each additional hour using a 1kw bulb costs us roughly an additional 10 cents, or roughly an additional $125 over the course of a 3 month grow w/ 1 month veg time (using 18/6 here). Presuming we got just an extra half pound from said bulb (or 0.225 grams per watt), you'd still get almost ten times that extra cost in revenue. In short, we're not even close to that break-even point. In fact, you'd have to get just about 1 oz. extra (or a measly 0.028 gpw) to reach that break-even point.

Caveats: of course if the environment isn't controlled in adding that extra bulb, then things can go awry. But if the environment is dialed in, and you can afford it (either financially or from a rather curious electric bill perspective), why not add more watts?

 

[DHF]

Well Flat......As I stated earlier about running the same strain for 12 yrs outside under the big metal halide in the sky , and then another 8+ yrs inside with only 34 watts per sq ft , BEFORE I was finally talked into 50 watts per sq ft , once implemented yields did NOT increase at all , but rather the finished plant nuggage was as different as night and day with waaaay pronounced trichome formation , bud density , smell , taste , and flavor off the charts from ALL previous dialed to the tits runs.....now.....

As I`ve also expressed to you I know at least once if not twice in other threads is that , MANY and I mean MANY WELL experienced old head growers experimented and experimented at the old dead sites with FAR increased wattage over 50 , 75 , 100 , and.....

On up into the 200 watts per sq ft ranges with never ONCE any yield increases , but rather diminished returns BECAUSE dialed environment and VPD issues weren`t known about back then as much as we know about it today , and mostly heat stress , foxtailing , scorching , and light bleaching were the dominant factors during said quests......but again....

Far be it from me to discourage a true side by side experiment with all things being equal EXCEPT watts per sq ft to come to YOUR own conclusions , and for the record.....

Heath`s "shit`s and giggles" thread where he checkerboarded those lights and each set on the ends turned off and on every 6 hrs was not for ANY reason whatsoever other than shit`s and giggles trying to learn absolutely nothing other than how much larf would be left on the lowers and outer extremities of the plants as a whole WITH decreased wattage....and....

I was there through the whole thread , and although both plants pulled nice numbers , they did turn out leafier and less dense compared to the proper 50 watts per sq ft runs that he practiced and preached for so many yrs......anyways...

Handle it and come back with updates....

Peace....DHF.........

 

[flat9]

Thanks for your input DHF! I'm running 67 per sq ft so perhaps I'm just trying to talk myself into justifying it. At any rate, it's only grow #2 for me, but I think at least from a conceptual standpoint we agree that there'd be diminished returns... just questioning how much.

 

[DHF]

Thanks for your input DHF! I'm running 67 per sq ft so perhaps I'm just trying to talk myself into justifying it. At any rate, it's only grow #2 for me, but I think at least from a conceptual standpoint we agree that there'd be diminished returns... just questioning how much.

Bro....EVERY horizontal flat grower with 2-1K`s over 4 x 8 flood tables are rockin 66.66 watts per sq ft as well , but with reduced light from glass in air-cooled hoods , or even un-cooled reflectors of any shape still haveta deal with lumens lost out and away from the plants on said tables......IOW....

Running bare bulbs eliminates lumen loss by covering all surfaces including ceilings to make the room itself it`s own air-cooled reflector , and guaranteed with increased wattage , as long as yas keep environment under control , you`re gonna pull some rock hard dense dank nugs.......but......

Yield increase.....naaaah.....just don`t work that way , but hey I applaud your efforts and fully expect yas ta come back and update us on your findings........

Peace....DHF..........

 

[flat9]

Will do DHF. Thanks for your input.

 

[farmari]

The last Heath grow thread I saw was a horizontal DWC SOG 75w/sqft setup that was yielding him over 1gpw.

Which brings me to your other point. As for 50 watts per square foot being ideal for either a revenue or profit maximizing strategy, well, I don't quite buy it. All we have is anecdotal evidence, which can be useful but is not definitive. To do this properly, we need an experiment in which we use the same strain, same media, same nutes, same environment (try to control for all possible confounding variables), and gradually increase the watts and note the differences in yield. Certainly there will be some breakeven point (from a microeconomics perspective in which profit maximization is the goal, the optimal point is where marginal revenue = marginal costs), but unless marginal (gains in) yield rapidly drops off a friggin cliff after 50 watts per square foot, I doubt we're even close.

The effect of electrical lighting power and irradiance on indoor-grown cannabis potency and yield.

The floral development and potencies [Δ(9) -tetrahydrocannabinol (THC) contents] of cannabis plants were compared when grown indoors under high-pressure sodium lamps consuming electrical power at three densities (270, 400, and 600 W/m(2)). After a 3-week vegetative phase, plants were grown for 8 weeks, with lamps maintaining an artificial day length of 12 h. Foliar and floral yields were measured. Gas chromatography was used to measure the content of the psychoactive cannabinoid THC. Mean yields per unit of electrical power in each lighting regime ranged from 0.9 to 1.6 g/W, the highest being achieved in the lowest irradiance regime. The individual potencies of the separated leaf and flower materials were not affected by increasing irradiance. However, there was a corresponding increase in the overall potency of the aerial plant tissue. This was because of the plants in brighter conditions producing a higher proportion of floral material.

Best gpw result in this study at 1.6gpw was at only 25w/sq ft.

The pdf of this study might be available for download on this site or others but I don't know.

 

[DHF]

Thanks for the input Farm....and see...That`s how gpw`s are "increased" , as wattage "decreases"....IOW.....

Heath started really bustin the gpw`s when he ran increased plant numbers wrapped around single or double stacked 600`s with his recirculating NFT setups.....Hell.....

The first time I saw him in a breeding experiment , he ran 2-600`s side by side in a small 4 x 6 area with shelves all the way round the room , and put seeds straight 12/12 as a pheno hunt , and then filled in the rest of the canopy with rooted cuts , and pulled lil over 4 lbs from if memory serves , 87 plants.....now....

I didn`t read the study in the link cuz I don`t go offsite from weedsites , but what was stated stands to reason in that the plants exposed to more light would produce more foliage as once again , a defense mechanism and survival trait to insure seed production and proliferation of the plant...in the wild as a species , of course....anyways....

Knowledge is power.....Puttin it to use in practical application takes time and many runs before dialage occurs.....thanks again Farm...

Peace....DHF........

 

[flat9]

T
I didn`t read the study in the link cuz I don`t go offsite from weedsites , but what was stated stands to reason in that the plants exposed to more light would produce more foliage as once again , a defense mechanism and survival trait to insure seed production and proliferation of the plant...in the wild as a species , of course....anyways....

Actually the article found that there was no increase in foliage but only an increase in floral mass. I'll write a more detailed post here soon...

 

[flat9]

Wow farmari! Now this is what I'm talking about -- proper experiments. Here's a link to the PDF I found on someone's Google Docs:

https://docs.google.com/file/d/0ByW-RytTeYMQMTc3M2MxYzMtNjUxZi00ZGZhLTg0YWMtYjAzMzNjNGY5NDEw/

Haven't read all the details yet. But note that they were using 25, 37, and 56 watts per square foot. It seems that there indeed was diminishing returns in terms of grams per watt as the watts/sq-ft increased...

... but as I was saying above, I don't buy that the yield just drops off a cliff enough that you don't get more profit. If you're a med or commercial grower, grams per watt isn't the goal; quantity is, with the knowledge that every 1 kw costs you roughly another $125 of the grow. Speaking of which, Farmari's own result of 0.7 g/w is interesting in that even had he got 1.3 g/w w/ 50 watts per square foot instead of 110 watts per square foot, in terms of profits assuming 2 large per pound, he'd be better off running more watts (as the latter result would yield roughly a little under an extra pound whereas the former would only save about $250 in leccy costs over the grow).

Unfortunately the paper didn't delve into the regime which we're more interested in (60, 70, 80, etc. g/w), but I'll email the authors to see if I can extract the regression equation and ask about the validity of using it to predict in these regimes. Nevertheless, interesting quotes:

Increasing the power of the electrical lighting during the flowering phase had no significant effect on the mass of foliage produced or the total mass of THC within the foliage. However, as power
levels were raised, plants exhibited a significantly increased floral mass (linear regression, p < 0.0001) and a corresponding significant increase in flower leaf ratio (p < 0.0001) (Table 1). The total quantity of THC produced by the floral material showed a significant increase as power was increased (p < 0.0001). The total mass of THC produced by the combined foliar and floral materials similarly showed a significant increase (p < 0.0001).

Anyway, absolutely awesome post Farmari. Thanks for dropping in and sharing that one.

 

[flat9]

Here are some tables and figures from the paper for quick reference...

 

[flat9]

Hey Farms, while you're dropping knowledge in here, why didn't you go bare bulb w/ your grow? It seems like you're not using ducting anyway through the hoods so heat isn't the issue....

 

[flat9]

http://link.springer.com/article/10.1007/BF00195075

Equation for growing weed? Loving this google scholar thing. Abstract:

The shapes of photosynthetic light-response curves for leaves of Eucalyptus maculata (Hook) and E. pauciflora (Sieber ex Sprengel) were examined. Three different methods were used to measure photosynthesis: CO2 and H2O-vapour exchange, O2 evolution at a 5-kPa CO2 partial pressure, and chlorophyll fluorescence. The three methods were compared and gave good agreement when measured under equivalent conditions. However, O2 evolution was inhibited by high CO2 partial pressures. A non-rectangular hyperbolic curve has been used widely to describe photosynthetic light-response curves. It has three variables which define the maximum quantum yield (photosynthetic rate divided by absorbed irradiance at very low irradiances), the maximum capacity and the curvature (Θ). We found that Θ was affected by the CO2 partial pressure, declining to a minimum of about 0.6 as CO2 partial pressure increased to 100 Pa. Further increases in the CO2 partial pressure began to inhibit the rate of O2 evolution at 2000 μmol quanta · m−2·−1 and Θ increased back to 0.95 by 5 kPa CO2 partial pressure. At low irradiances, photosynthesis is limited by the rate of electron transport while at high irradiances, photosynthesis is frequently limited by the activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco). The dependence of Θ on CO2 partial pressure arises because the transition between limitations changes as a function of the CO2 partial pressure. The light-response curve is truncated by the transition to a Rubisco limitation and the lower the irradiance at the transition, the higher the value of Θ. There is a gradient in light absorption through the leaf which influences the photosynthetic capacity of different layers within the leaf. The gradient in photosynthetic capacity can be demonstrated by the fact that the shape of the light-response curve changes when the leaf is illuminated unilaterally onto either the adaxial or abaxial surface. We compared two Eucalyptus species which had either isolateral or dorsiventral leaf anatomy. Leaves were able to reverse completely the gradients in photosynthetic capacity following inversion of the leaves for a week, irrespective of their anatomy.

Granted, not cannabis, but someone out there must have found the photosynthetic response curve for cannabis....

... speak of the devil (thank you Google scholar):

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3550641/

Effect of different photosynthetic photon flux densities (0, 500, 1000, 1500 and 2000 μmol m−2s−1), temperatures (20, 25, 30, 35 and 40 °C) and CO2 concentrations (250, 350, 450, 550, 650 and 750 μmol mol−1) on gas and water vapour exchange characteristics of Cannabis sativa L. were studied to determine the suitable and efficient environmental conditions for its indoor mass cultivation for pharmaceutical uses. The rate of photosynthesis (PN) and water use efficiency (WUE) of Cannabis sativa increased with photosynthetic photon flux densities (PPFD) at the lower temperatures (20–25 °C). At 30 °C, PN and WUE increased only up to 1500 μmol m−2s−1 PPFD and decreased at higher light levels. The maximum rate of photosynthesis (PN max) was observed at 30 °C and under 1500 μmol m−2s−1 PPFD. The rate of transpiration (E) responded positively to increased PPFD and temperature up to the highest levels tested (2000 μmol m−2s−1 and 40 °C). Similar to E, leaf stomatal conductance (gs) also increased with PPFD irrespective of temperature. However, gs increased with temperature up to 30 °C only. Temperature above 30 °C had an adverse effect on gs in this species. Overall, high temperature and high PPFD showed an adverse effect on PN and WUE. A continuous decrease in intercellular CO2 concentration (Ci) and therefore, in the ratio of intercellular CO2 to ambient CO2 concentration (Ci/Ca) was observed with the increase in temperature and PPFD. However, the decrease was less pronounced at light intensities above 1500 μmol m−2s−1. In view of these results, temperature and light optima for photosynthesis was concluded to be at 25–30 °C and ∼1500 μmol m−2s−1 respectively. Furthermore, plants were also exposed to different concentrations of CO2 (250, 350, 450, 550, 650 and 750 μmol mol−1) under optimum PPFD and temperature conditions to assess their photosynthetic response. Rate of photosynthesis, WUE and Ci decreased by 50 %, 53 % and 10 % respectively, and Ci/Ca, E and gs increased by 25 %, 7 % and 3 % respectively when measurements were made at 250 μmol mol-1 as compared to ambient CO2 (350 μmol mol−1) level. Elevated CO2 concentration (750 μmol mol−1) suppressed E and gs ∼ 29% and 42% respectively, and stimulated PN, WUE and Ci by 50 %, 111 % and 115 % respectively as compared to ambient CO2 concentration. The study reveals that this species can be efficiently cultivated in the range of 25 to 30 °C and ∼1500 μmol m−2s−1 PPFD. Furthermore, higher PN, WUE and nearly constant Ci/Ca ratio under elevated CO2 concentrations in C. sativa, reflects its potential for better survival, growth and productivity in drier and CO2 rich environment.

Whelp. I'm gonna have to read through this and find some online calculators to see what PAR rating of 1500 umol per ... whatever ... means in terms of watts/ft-sq.