MAXIMIZING FLOWER YIELD: CO2/Temps & HOW TO AVOID: too much Lux/PPFD?

I am working to maximize my yield in flower. Today I picked up a 3rd White Light 3000K 240 Watt Quantum Board for my 4x4 ft. chamber. I have been running 1100 PPM Co2, and keep the room around 29.5 C.

My questions (first two are simple, 3rd is more important and difficult):

1. Do I keep this 1,100 PPM - 1,500 PPM level for the rest of flower (of course stop 2 weeks before harvest) and is it worthwhile to bump up to 1,500 PPM?

2. Shall I keep 29.5 C as my temps (which is said to be ideal for Co2-enhanced grows) or slowly decrease (simulating autum season)?

3. The more complex question:

I am running max 750 watts of Quantum Boards (3,000K and 3,500K and 3,500K including one with with UV+IR). Total I have about 3,300 PPFDμmol/(m2·s) if considering the 2x 1000 PPFDμmol/(m2·s) lights and 1x 1300 PPFDμmol/(m2·s) UV+IR light. When not dimmed.

I think this is quite a lot for a 4x4. And likely too much light in the center (which would reduce yield). Does that sound correct? Now like most people, I don't have a PPFD meter but I can measure Lux with my phone easily. I've read that cannabis maxes out at 1500 PPFD or 80,000 LUX even with CO2.

If I have all the lights on full blast, it can get up to 200,000 LUX in the middle of the canopy! I've turned the middle light down 50% and so lux in the center comes to just around 100,000. It is the right move to dim, by half, the middle light or not?

I wouldn't put all your faith into the lux measurements since they are made to measure how humans perceive light and not the PAR that the plants care about. If you're gonna run on the bleeding edge of co2 and DLI it probably warrants investing in a quantum meter. Ultimately though you're gonna be reading the plants reaction.

I mean from what I've read a lot of the benefit from CO2 falls off around 1,200 ppm. Also the ability for the plant to utilize the CO2 is based on the intensity of the light. I believe keeping it around 1,200 ppm throughout the flowering period will be fine. Although a higher temperature does increase the absorption rate in the plant there is a difference between ambient temperature and leaf temperature. Once the leaf temperature goes past 27 degrees Celsius the reverse happens. Since the leaf temperature tends to be slightly higher than ambient temperature I would said you're already pushing past the optimal conditions sitting at 29 degrees Celsius. I would try and get the temperature back down to around 25 degrees Celsius. I mean you can try dimming the light and see how the plants respond. As long as you're not bleaching any of your buds I don't actually know what the adverse effects would be from blasting the center of the canopy.

Leaf temperature should be lower than ambient due to transpiration. Your plants look happy I wouldn't dim just when they're gonna start putting on weight unless you see taco leaves, end of day droop or bleaching.

all coco said:

Leaf temperature should be lower than ambient due to transpiration. Your plants look happy I wouldn't dim just when they're gonna start putting on weight unless you see taco leaves, end of day droop or bleaching.

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That's true, but certain lights can raise the leaf temperature higher which happens with HPS. I don't know how close your lights are to your plants so the leaf temperature could be higher, the same, or lower. Even if the lights aren't that warm the difference in temperature would only be 1-2 degrees Celsius and anything past 27 degrees starts to negatively effect the plant. Since you're sitting at 29 degrees Celsius I believe lowering the temperature would be the best first step.

SomethingToDo said:

That's true, but certain lights can raise the leaf temperature higher which happens with HPS. I don't know how close your lights are to your plants so the leaf temperature could be higher, the same, or lower. Even if the lights aren't that warm the difference in temperature would only be 1-2 degrees Celsius and anything past 27 degrees starts to negatively effect the plant. Since you're sitting at 29 degrees Celsius I believe lowering the temperature would be the best first step.

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Something to do with the leaves absorbing infrared light I believe. Also gotta take into account different strains tolerances and thermometer accuracy. I've let my grow area get up to 30C in veg and the plants didn't seem to care. I've read a research paper where they grew tomatoes at 40C with co2 and the yield wasn't affected too much.

all coco said:

Something to do with the leaves absorbing infrared light I believe. Also gotta take into account different strains tolerances and thermometer accuracy. I've let my grow area get up to 30C in veg and the plants didn't seem to care. I've read a research paper where they grew tomatoes at 40C with co2 and the yield wasn't affected too much.

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I mean sure different strains have different tolerances but the plant biology is the same. I've flowered in non-ventilated spaces that hit 40 degrees Celsius and came out with weed that got me high but it was far from optimal. I thought the goal of these questions was because you wanted to maximize your yields? Even in the tomato studies I've read discussing CO2 enrichment, and high temperature stress they always kept their greenhouses at 25 degrees Celsius or cooler. https://ucanr.edu/blogs/NurseryFlower/blogfiles/55783.pdf

Either way I am merely giving suggestions and ultimately you can do whatever you want.

SomethingToDo said:

I mean sure different strains have different tolerances but the plant biology is the same. I've flowered in non-ventilated spaces that hit 40 degrees Celsius and came out with weed that got me high but it was far from optimal. I thought the goal of these questions was because you wanted to maximize your yields? Even in the tomato studies I've read discussing CO2 enrichment, and high temperature stress they always kept their greenhouses at 25 degrees Celsius or cooler. https://ucanr.edu/blogs/NurseryFlower/blogfiles/55783.pdf

Either way I am merely giving suggestions and ultimately you can do whatever you want.

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I didn't start the thread I just wanted to talk about some Bruce Bugbee shit

all coco said:

I didn't start the thread I just wanted to talk about some Bruce Bugbee shit

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Oh interesting, I have never heard of this guy before and I am now watching some of his Youtube videos. I love hearing educated people speak about the biology of cannabis! I'll report back once I'm done with this hour long video, lol.

I am using LED lights and 15-24 inches distance. The leaf temps are 2-4 degress C lower than the room temp. So at 29 leafs are already around 26. Yes the temps are fine. I think I will keep it as such.

Noted about 1200 PPM.

The more complex question is how to avoid the over-dosing on light which can reduce yield. I did a search for Quantum Sensors and not much came up. Yes Lux is pretty useless in this front but nevertheless helpful. PAR or PPFD or μmol is pretty confusing for me! Wtf

I love Bruce Bugbee and will be using his recommened medium for my next run. His talk about lighting is a bit over my head however.

Overgrowtho said:

I am using LED lights and 15-24 inches distance. The leaf temps are 2-4 degress C lower than the room temp. So at 29 leafs are already around 26. Yes the temps are fine. I think I will keep it as such.

Noted about 1200 PPM.

The more complex question is how to avoid the over-dosing on light which can reduce yield. I did a search for Quantum Sensors and not much came up. Yes Lux is pretty useless in this front but nevertheless helpful. PAR or PPFD or μmol is pretty confusing for me! Wtf

I love Bruce Bugbee and will be using his recommened medium for my next run. His talk about lighting is a bit over my head however.

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Here is a nice experiment using a thermal camera to show the surface leaf temperatures of cannabis under varying kinds of lights. You might be surprised by the results! https://www.blackdogled.com/lst#Evidence

The only way you're going to know for sure how much light is being put out at the distance they're currently hanging is to invest in a lux meter.

You mean invest in a Quantum Meter for PPFD? Lux meters are so cheap.

I read that study which basically says that LED can allow for higher temps in the room since it has less effect of heating the leafs.

So if with Co2 the optimal temp is 29 degrees then I should target 29 for my LEAF temps not my ROOM temps???

Overgrowtho said:

You mean invest in a Quantum Meter for PPFD? Lux meters are so cheap.

I read that study which basically says that LED can allow for higher temps in the room since it has less effect of heating the leafs.

So if with Co2 the optimal temp is 29 degrees then I should target 29 for my LEAF temps not my ROOM temps???

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I would say Lux meter since it's cheap the quantum meters can be like $300+ where you could grab a lux meter for $50 off Amazon to give you a rough idea.

Lol, I must be stoned because I was completely negating the CO2 in the room. Your temperatures should be more than fine if you're running 1200 ppm of CO2. For some reason I was thinking about ambient levels of CO2, not CO2 being pumped into the room, woops...

Lux meters are free with an App on your phone bro.

But I should target 29 for the ambient not leaf temp. Right?

Overgrowtho said:

I am working to maximize my yield in flower. Today I picked up a 3rd White Light 3000K 240 Watt Quantum Board for my 4x4 ft. chamber. I have been running 1100 PPM Co2, and keep the room around 29.5 C.

My questions (first two are simple, 3rd is more important and difficult):

1. Do I keep this 1,100 PPM - 1,500 PPM level for the rest of flower (of course stop 2 weeks before harvest) and is it worthwhile to bump up to 1,500 PPM?

2. Shall I keep 29.5 C as my temps (which is said to be ideal for Co2-enhanced grows) or slowly decrease (simulating autum season)?

3. The more complex question:

I am running max 750 watts of Quantum Boards (3,000K and 3,500K and 3,500K including one with with UV+IR). Total I have about 3,300 PPFDμmol/(m2·s) if considering the 2x 1000 PPFDμmol/(m2·s) lights and 1x 1300 PPFDμmol/(m2·s) UV+IR light. When not dimmed.

I think this is quite a lot for a 4x4. And likely too much light in the center (which would reduce yield). Does that sound correct? Now like most people, I don't have a PPFD meter but I can measure Lux with my phone easily. I've read that cannabis maxes out at 1500 PPFD or 80,000 LUX even with CO2.

If I have all the lights on full blast, it can get up to 200,000 LUX in the middle of the canopy! I've turned the middle light down 50% and so lux in the center comes to just around 100,000. It is the right move to dim, by half, the middle light or not?

View attachment 4792807

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1. Ramp up to 1500 by mid flower (a bit excessive, but will max it out). Yes stop 2 weeks before harvest
2. Check out this chart provided by cultured solutions, it really breaks down desired temps and co2 levels throughout flower


3.(disclaimer-i know lux is not very accurate at all, but I have the app on my phone also so I know what your talking about) have you actually tested 200,000 lux?? How far from the light was that? Thats a crazy amount of light if thats what you measured at the canopy (12-20" from the light) cannabis would max out around 82,000 lux in flower. Veg the max you would want to see is 45,000 lux if you were running 18/6
I am about 4 weeks veg from seed currently and my phone reads 25,000 lux
(Granted the inaccuracies here)
That would translate to roughly 450 PPFD and a DLI of 30. (You need a minimum of 20 for growth, max out at 55-60 or so with co2)
I like to keep my DLI a bit lower during early veg to help me LST
What I'm getting at is... I find it hard to believe you can be pushing 200,000 lux as that would be 3,500 ppfd.
Long story short, if thats ACTUALLY what your pushing, its too much. Peak flower, the plant can only withstand maybe 1,500 ppfd with CO2

Hi thanks for your reply. No I did not keep running 200k Lux. I was smart enough to know that would be insane and hurt yield! So I turned my middle light down to 50%. Thius staying at around a max of 100 Lux for the moment.

The chart you showed from Cultured Solutions seems wrong, the temps are really too low compared to research on this. I think I will disregard that chart.

However I had a look at this video about hacking LUX meters on your phone to determine PPFD. (see conversion chart in text below video on youtube.com) which seems legit.

According to that, while running 3500k I should max out at an average of 140,000 LUX with the phone app (really it is 100,000 LUX based on the Vlog's calibration chart when using 3500K) to reach the 1400 PPFD. This would give me a DLI of 60.

I hope this all sounds correct and fine. It sounds like I've got it all sorted now, but anyone please chime in and let me know if something sounds incorrect.

This is not an exact science since I also have 3000 and UV+IR lights in there, but I think it is as close as I can come to a good maxed-out-but-not-too-much lighting for bloom.

Overgrowtho said:

The chart you showed from Cultured Solutions seems wrong, the temps are really too low compared to research on this. I think I will disregard that chart.

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I'm sure your must not be reading the chart correct
This shows day temperature, night temperature, and water temperature for hydroponics throughout a plants life.
This is a really good chart, and I would reccomend to not disregard it.
The only change I make from this chart is a higher EC

Overgrowtho said:

Lux meters are free with an App on your phone bro.

But I should target 29 for the ambient not leaf temp. Right?

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I believe 29 for the ambient should be fine and as you said earlier even upward of 35-40 degrees Celsius the plants were still fine with when at 1,500 ppm of CO2. I don't believe adverse effects come until after 40 degrees Celsius. Some say if you're running LEDs that a higher ambient temperature is better anyways so the leaf temperature can get a little higher. So if you're going to be pumping 1,200-1,500 ppm of CO2 it should be okay if the temps even jump up a few degrees.

Overgrowtho said:

Hi thanks for your reply. No I did not keep running 200k Lux. I was smart enough to know that would be insane and hurt yield! So I turned my middle light down to 50%. Thius staying at around a max of 100 Lux for the moment.

The chart you showed from Cultured Solutions seems wrong, the temps are really too low compared to research on this. I think I will disregard that chart.

However I had a look at this video about hacking LUX meters on your phone to determine PPFD.

(see conversion chart in text below video on youtube.com) which seems legit.

According to that, while running 3500k I should max out at an average of 140,000 LUX with the phone app (really it is 100,000 LUX based on the Vlog's calibration chart when using 3500K) to reach the 1400 PPFD. This would give me a DLI of 60.

I hope this all sounds correct and fine. It sounds like I've got it all sorted now, but anyone please chime in and let me know if something sounds incorrect.

This is not an exact science since I also have 3000 and UV+IR lights in there, but I think it is as close as I can come to a good maxed-out-but-not-too-much lighting for bloom.

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Thanks for showing me that video, I haven't seen that before and Shane does good stuff.
His measurements are sure off from mine though, and I feel like I'm severely under lighting my veg now if thats the case lol
I'm only reading 23,000 lux on my 4000k. So only 255 ppfd?? I find that hard to believe

Overgrowtho said:

Hi thanks for your reply. No I did not keep running 200k Lux. I was smart enough to know that would be insane and hurt yield! So I turned my middle light down to 50%. Thius staying at around a max of 100 Lux for the moment.

The chart you showed from Cultured Solutions seems wrong, the temps are really too low compared to research on this. I think I will disregard that chart.

However I had a look at this video about hacking LUX meters on your phone to determine PPFD.

(see conversion chart in text below video on youtube.com) which seems legit.

According to that, while running 3500k I should max out at an average of 140,000 LUX with the phone app (really it is 100,000 LUX based on the Vlog's calibration chart when using 3500K) to reach the 1400 PPFD. This would give me a DLI of 60.

I hope this all sounds correct and fine. It sounds like I've got it all sorted now, but anyone please chime in and let me know if something sounds incorrect.

This is not an exact science since I also have 3000 and UV+IR lights in there, but I think it is as close as I can come to a good maxed-out-but-not-too-much lighting for bloom.

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Hey I was doing some messing around with the app after you shared this video, and I'm stumped
If I am supposed to be taking my LUX from the app, and dividing by 90 to get my PAR for my 4000k LED, then that would mean my spiderfarmer sf4000 is only putting out 745 PAR at its focal point. And I know it should be doing a minimum on 1000
But thats means I would have to be reading 90,000 lux
At 100% power its only reading 67,000