LED and Calmag issues.

[Covetsculitvars]

Eggshells lol

Simplicity at its finest!

 

[ChiefRunningPhist]

HPS, MH, CMH and even T5 have similar heat radiation like sun light. They all increase the leaf surface temps more like CRI80 LED's. Plant have addapted to sun light millions of years so one coulpd say, they are used to a certain ratio of light and heat. With LED its like they get a new type of light. A light that doesn't contains 15-30% heat radiation. For this reason the leaf temps are almost the same like the ambient temps with LED's. But plants are used to light thats heats up the LST more like that. They are used to light that heats up their leaves higher like LED's and because they don't get it the transpiration runs out of balance. CRI90 works already much better than CRI80 because it has twice as much far-red. A friend have switched from 3k/CRI80 F-strips to 3k/CRI95 Nichia boards and even with higher amounts of light there is no bleaching anymore and the plants look much better and less stressed. In many tests CRI90 has shown a signicicant reduce in flowering time without much loss in yield. To me that means something and I add far-red to my light spectrum since 4 years now.

I'm no prof and can only explain it to a certain degree. Not all species can handle heat and dry conditions in the same way.
Fact is, the missing far and infra red makes it neccessary for us to control transpiration manually by keeping the VPD in a healthy range.
If you maintain lets say a VPD of 0,4-0,8kpa for the seedling stage, 0,8-1,2kpa for vegging and 1,2-1,6kpa in the flowering stage you should not see calmag issues. If you still get issues it must have another reason.

You need also to keep in kind that we usually use a higher intensity now since we have such powerful LED's. No one tries to keep only 500-700μMol/s but that's the range we have used for years with HPS or MH light. When you keep 1000μMol/s/m² with HPS its also more difficult to keep the plants happy. The whole metabolism runs much higher and deficits occur much faster. So IMO the different nutrient demands with LED have also to do with the higher intensity.

Just for reference...

Sun..


MH...


LED...


T5HO...


HPS...


I don't think T5HO puts out more heat per cm2 than LED (referring to the heat:light correlation), nor do I think MH is similar to the sun like HPS is similar to the sun.

They are used to light that heats up their leaves higher like LED's and because they don't get it the transpiration runs out of balance.

In which way? More or less transpiration? Increasing LST increases transpiration, can we agree on that? If ambient temps used to increase LST have a positive effect, then it supports the hypothesis that it doesn't matter how the leaf is heated, just that it is. It's thermally regulated but spectrally triggered.

The HPS and sun with higher LSTs should transpire more, not less! Yet we increase VPD to decrease a higher transpiration rate for a plant with lower LST, but tons of red. Most LED SPDs are skewed only 12-20% blue (I think you told me that).

CRI90 works already much better than CRI80 because it has twice as much far-red. A friend have switched from 3k/CRI80 F-strips to 3k/CRI95 Nichia boards and even with higher amounts of light there is no bleaching anymore and the plants look much better and less stressed. In many tests CRI90 has shown a signicicant reduce in flowering time without much loss in yield. To me that means something and I add far-red to my light spectrum since 4 years now.

This could be due to other variables, no? Seems more than just red WVs increased from those different CRI SPDs. Although it does contradict my EMF hypothesis, unless perhaps he didn't have drivers mounted on lights, or changed driver location between chip upgrade? Hmmm dam lol i thought I was on to something.. Curious to know if any changes like that were made?

When you keep 1000μMol/s/m² with HPS its also more difficult to keep the plants happy. The whole metabolism runs much higher and deficits occur much faster. So IMO the different nutrient demands with LED have also to do with the higher intensity.

I agree.



****

I'm spent lol, I'm not satisfied with the explanation (god Dammit! lol) but I do see where you're coming from and hear what you're saying. I think the search is still on, if you come across some studies demonstrating high transpiration rates in low LST I'd be interested in seeing them. Thanks for the courteous back & forth.

 

[3rd Monkey]

Just for reference...

Sun..
View attachment 4302422

MH...
View attachment 4302423

LED...
View attachment 4302426

T5HO...
View attachment 4302425

HPS...
View attachment 4302424

I don't think T5HO puts out more heat per cm2 than LED (referring to the heat:light correlation), nor do I think MH is similar to the sun like HPS is similar to the sun.


In which way? More or less transpiration? Increasing LST increases transpiration, can we agree on that? If ambient temps used to increase LST have a positive effect, then it supports the hypothesis that it doesn't matter how the leaf is heated, just that it is. It's thermally regulated but spectrally triggered.

The HPS and sun with higher LSTs should transpire more, not less! Yet we increase VPD to decrease a higher transpiration rate for a plant with lower LST, but tons of red. Most LED SPDs are skewed only 12-20% blue (I think you told me that).


This could be due to other variables, no? Seems more than just red WVs increased from those different CRI SPDs. Although it does contradict my EMF hypothesis, unless perhaps he didn't have drivers mounted on lights, or changed driver location between chip upgrade? Hmmm dam lol i thought I was on to something.. Curious to know if any changes like that were made?


I agree.



****

I'm spent lol, I'm not satisfied with the explanation (god Dammit! lol) but I do see where you're coming from and hear what you're saying. I think the search is still on, if you come across some studies demonstrating high transpiration rates in low LST I'd be interested in seeing them. Thanks for the courteous back & forth.

Funny, just yesterday I started trying to make my conditions more equal so I can check pot weights under HPS and LED, see which transpires more.

I can already tell you that I have to water more frequently in the tent with the LED, but it's about 5-7 degrees warmer in there with an average ballpark of 10-15 percent more humid in there as well.

So, if I can duplicate conditions and then measure pot weight in 24hrs, the lighter pot should have transpired more, right? All factors being equal?

 

[ChiefRunningPhist]

Funny, just yesterday I started trying to make my conditions more equal so I can check pot weights under HPS and LED, see which transpires more.

I can already tell you that I have to water more frequently in the tent with the LED, but it's about 5-7 degrees warmer in there with an average ballpark of 10-15 percent more humid in there as well.

So, if I can duplicate conditions and then measure pot weight in 24hrs, the lighter pot should have transpired more, right? All factors being equal?

Ya I think that you could get some interesting data, and could be relevant.

Variables needing to be controlled for...
PPFD
Plant types
Plant sizes
Ambient
Pot temp
RH
Driver location
PAR SPD
Growth stage



If all those are controlled for I think your data would be definitely interesting and depending on results worthy of further repetitions.

Is it a possibility the pots could evaporate water from medium instead of being consumed by plant? I don't know how you have it set up but some sort of cover would eliminate this possible interference. You'd have to try to match SPDs as best you could, otherwise you couldnt isolate if it was from a different technology or not. High blue HPS vs low blue HPS, or high blue LED vs low blue LED. That way you could single out SPD as the cause or not. You could have 2 exact same HPS setups, and add an EMF source to one of the tents and measure any differences.

Its interesting you say your HPS area has decreased RH compared to your LED. In my experience when I ran (4) 1000w HPS I saw humidity go outrageous (was on a flood table though), much much more than my QBs seem to make. But could have been the size of the plants and the recirc on flood table (there were no "LED" or Ca-Mg issues). I'd be interested in seeing those results, I may try it as well but don't have a PPFD meter.

 

[3rd Monkey]

Ya I think that you could get some interesting data, and would be relevant.

Variables needing to be controlled for...
PPFD
Plant types
Plant sizes
Ambient
Pot temp
RH
Driver location


If all those are controlled for I think your data would be definitely interesting and depending on results worthy of further repetitions.

Is it a possibility the pots could evaporate water from medium instead of being consumed by plant? I don't know how you have it set up but some sort of cover would eliminate this possible interference.

Its interesting you say your HPS area has decreased RH compared to your LED. In my experience when I ran (4) 1000w HPS I saw humidity go outrageous (was on a flood table though), much much more than my QBs seem to make. Which is contradictory to what should be happening, but could be the size of the plants and the recirc on flood table because there were no "LED" or Ca-Mg issues. I'd be interested in seeing those results, I may try it as well but don't have a PPFD meter.

My HPS is in an open room, the LED is in the tent with a T5 (for seedlings and warmth).

Yea, that's a lot of data to try to control for me with my schedule lol.

I'm just going to take the same 10 plants and run them in the tent a week, checking pot weight each day, watering in the morning and recording percentage of weight drop at night.

Then switch to HPS with the same plants for a week and log that. I'm figuring root mass in each pot with the same humidity and temp should then put the ball in the lighting court.

I know that as the roots grow, percentage of water used will go up, but I figure I should be able to gauge a pattern and rough percentages. Maybe enough to prompt others with more scientific backgrounds to exploit it?

 

[Randomblame]

Here's what I've noticed, and I'm no science whiz, so bare with me a moment lol.

In my space, temps are too low and humidity is too low under my LED which is 287W true.

The conditions are actually slightly worse under the 600W HPS, with temps being lower and humidity being slightly lower.

In the tent, it's easy to light burn with the LED at less than 20". I can put plants at around 14" under the HPS with no ill effect.

So, it appears to me, that the LED spectrum is too strong for those temps, photosynthesis is low and transpiration is high, causing burns and over nutrition because of the increase in uptake but reduction of processing that uptake. Hits the top of the plant first.

Under HPS, the temps are lower than the tent EXCEPT on the canopy, increasing photosynthesis and therefore using up the increased nutritional uptake which reduces the importance of humidity in comparison.

Hope that makes sense.

Yeah, good found. Do you have and IR laser thermometer to compare the leaf temps in both tents with the same ambient temps? The leaf temps should be higher on the HPS side and for this reason the metabolism runs a little higher. All parts of the plant receive enough nutes and they can handle the light properly.
The LED side has even more light but the metabolisms run at a lower level and they grow slower for this reason. As soon as you add a heater and increase the ambient temps so that you have the same LST in both tents they would outperform the HPS side. Of course only when you maintain a healthy humidity..

This chart is calculated with -1°C LST so you're on the save side when using it. Set to ±0 the humidity values would be 2 or 3% lower but I'm rather on the safe side.


And this one is more like a general standard..


and this one is from fluence, a LED company that creates the SipderX or Spider2i LED growlight.



As you can see in all charts, the healthy range get smaller the hotter it is. For this reason it goes faster. I've two sensors measuring the humidity. One directly above the canopy next to one of the top colas and the 2nd one directly below the canopy. A thermometer on the wall is use less because directly under the light is much drier, up to 10% and more depending where you have mounted it.

 

[3rd Monkey]

Yeah, good found. Do you have and IR laser thermometer to compare the leaf temps in both tents with the same ambient temps? The leaf temps should be higher on the HPS side and for this reason the metabolism runs a little higher. All parts of the plant receive enough nutes and they can handle the light properly.
The LED side has even more light but the metabolisms run at a lower level and they grow slower for this reason. As soon as you add a heater and increase the ambient temps so that you have the same LST in both tents they would outperform the HPS side. Of course only when you maintain a healthy humidity..

This chart is calculated with -1°C LST so you're on the save side when using it. Set to ±0 the humidity values would be 2 or 3% lower but I'm rather on the safe side.

View attachment 4302416
And this one is more like a general standard..
View attachment 4302417

and this one is from fluence, a LED company that creates the SipderX or Spider2i LED growlight.

View attachment 4302419

As you can see in all charts, the healthy range get smaller the hotter it is. For this reason it goes faster. I've two sensors measuring the humidity. One directly above the canopy next to one of the top colas and the 2nd one directly below the canopy. A thermometer on the wall is use less because directly under the light is much drier, up to 10% and more depending where you have mounted it.

The HPS is in an open room, the whole house lol. The LED is in the tent.

I don't have any special thermometers. Going by feel though (lips and back of hand), I would say HPS definitely feel warmer than the air. LED feels cool to the touch, almost cooler than tent temp, real scientific, I know lol.

Speaking of growth rate, I did some different stuff already after the other day when we talked. I raised the LED and started misting the plants. It's only been a day or 2, but I see the difference already.

I have established coleus in there and I can already see a difference in growth with the LED backed off. It's better. The plant is growing more bushy and pushing nodes like crazy. Previously with the light closer, the leaves felt rigid and papery, now they have some flexibility back.

The cannabis on the other hand, is growing very similar to under the HPS. I can't notice a difference anyway, and I've been swapping them back and forth since the beginning, a day here and a day there, then a week in both environments back and forth.

On to the misting, I quit. The plants were droopy like they were overwatered, didn't come back to "attention" until I stopped. So, my humidity is still low, but the misting doesn't help.

 

[Capn-Crunch]

The HPS is in an open room, the whole house lol. The LED is in the tent.

I don't have any special thermometers. Going by feel though (lips and back of hand), I would say HPS definitely feel warmer than the air. LED feels cool to the touch, almost cooler than tent temp, real scientific, I know lol.

Speaking of growth rate, I did some different stuff already after the other day when we talked. I raised the LED and started misting the plants. It's only been a day or 2, but I see the difference already.

I have established coleus in there and I can already see a difference in growth with the LED backed off. It's better. The plant is growing more bushy and pushing nodes like crazy. Previously with the light closer, the leaves felt rigid and papery, now they have some flexibility back.

The cannabis on the other hand, is growing very similar to under the HPS. I can't notice a difference anyway, and I've been swapping them back and forth since the beginning, a day here and a day there, then a week in both environments back and forth.

On to the misting, I quit. The plants were droopy like they were overwatered, didn't come back to "attention" until I stopped. So, my humidity is still low, but the misting doesn't help.

This is a great thread. It explains some of the issues I've been having in my LED tents with the dry winter air we're having. My rooms are upstairs in a 2 story farmhouse. 2 tents in 1 room are running about 88° and 32% RH, while another room with 2 400w HPS is running about 77° and 52% RH.
I've been chasing what appears to be multiple deficiencies on all the plants in the 2 tents, but none in the HPS room.
The last 3 weeks have been driving me nuts!

 

[ChiefRunningPhist]

Well I've found some data.

Rt vs LST, seems pretty universal over the plant kingdom...



Rt vs VPD, which likewise seems pretty universal throughout the plant kingdom...


T vs VPD...


Increased LST increases Rt.
Increased VPD decreases Rt.
Increased T increases VPD.
Rt = Rate of transpiration
WUE = water usage effeciency
Pn = Rate of photosynthesis
Canopy depression = Ambient temp - LST

(Canopy depression) vs (Rt)...


So all this would leave me to believe that hotter LST, or hotter ambient are going to increase transpiration. This phenomenon can be described using VPD as well, (because they are related). The temp goes up and the air expands and VPD goes up. Leaf transpiration rates, when dealing with external temp stimuli, are being ultimately effected by how easy it is for the water to evaporate.

If we look at the initial environmental conditions provided by the 2 types of light, LED and HPS, we see it's actually HPS needing the close attention to VPD, not LED. This is contradictory to reality. Thus why I have a hard time excepting that if decreasing VPD helps with LED, that its solving a high transpiration rate problem other than something else.

None of this data was controlling for SPD, so the different SPDs between LED & HPS could very well be causing the increased Rt, but I can't yet find any data demonstrating that.

I did find some info about people actually treating water with EMF though, as its supposed to help or have some beneficial factors lol so that's probably a dead hypothesis.. Oh well..

 

[ChiefRunningPhist]

This is a great thread. It explains some of the issues I've been having in my LED tents with the dry winter air we're having. My rooms are upstairs in a 2 story farmhouse. 2 tents in 1 room are running about 88° and 32% RH, while another room with 2 400w HPS is running about 77° and 52% RH.
I've been chasing what appears to be multiple deficiencies on all the plants in the 2 tents, but none in the HPS room.
The last 3 weeks have been driving me nuts!

Exactly what I've experienced! HPS is higher RH, because its transpiring more. At least my reasoning.

LED is lower RH because its transpiring less. At least my reasoning.

But why is the LED transpiring less than the HPS if it's at a hotter ambient?

Can you check LST?

 

[ChiefRunningPhist]

I've been wondering if some how the LED is disssociating the H2O into H2 and O2 gasses which is keeping RH low?

 

[ChiefRunningPhist]

This is interesting, and looks like it's demonstrating what people are saying...


Seems like at high VPDs, SPD had a greater effect on transpiration. Would be nice to see a comparison between a 10% blue vs a 20% blue or something along those lines, considering other light sources have as much blue as LED and don't have issues. The SPD comparison in the study is between 10% blue & 0% blue.

 

[Randomblame]

I agree with you about good grow conditions.

All things being equal, LED requires an increased VPD compared to HPS, and historically, on this site at least, its been defined as HPS being hotter thus they reduce transpiration, and thus why LED would need higher VPD, but.... we see that's not the case, in fact this temperature relationship is reversed.

Could you post that blue light stomatal correlation data for me?

If the blue light is triggering transpiration, ie LED, why does increasing ambient help?

Furthermore, how are the HPS triggered to open?

And finally (ties into the previous question), if the sun isn't hot, ie <40C, why isn't the blue from the sun causing over transpiration? MJ grows in the mountains in arrid climates too.

View attachment 4302398

@Randomblame I'm not trying to refute the fact it works, if it does, but I think the current explanation has many inconsistencies and I can't help but think there's something different at play. At the very least you have to admit these are compelling questions. Ive thought it could be EMF generated by drivers or lights considering the close proximity, but just a guess...

HPS runs hotter and has IR radiation therefor we set ambient temps to 25-26°C to get leaf temps near the optimum(~28-30°C). With 25-26°C 50-55% is okay and that's the level you find normally in a well ventilated area.

With LED you set ambjent temps to 28-30°C to get the desired leaf temps. At that temperature you need around 60-65%, in veg 70-75% and that's not the level you find in a well ventilated area. It gets much drier under the light and we have to reduce ventilation by at least 50% or more.

HPS runs hotter and thus they reduce transpiration is not true. You need less ambient temps because the heat up the leaves more. With 25°C 55% under HPS you find the same transpiration rate like with 28°C/60% under LED. Same leaf temps same transpiration rates and with the same intensity you would see similar growth rates too.

The whole problems are caused by the 3°C difference in leaf temps. As a said before, with HPS and 25°C the humidity is coincidally in a good range cause we set it to only 25°C and 55% are enough. Would HPS require 30°C ambient temps or better would it not heat up the leaves you would get the same issues like with LED. It's not the heat causing this issues its the too low humidity you typically find under LED's with ambient temps of 30°.

Growers not having issues with LED know what the VPD is and many use some kind of ambient controller for temp, humidity and VPD to keep it in check and often you see humidifiers in their grooms. With LED a too high VPD is a common issue, with HPS not and for this reason there are lots of hobby growers out there having to learn what it is, how it works and how to deal with it. Most of the time they realize it too late(incl. myself). I've also though I would do something wrong or that the LED's require another nutrient strength until I found out what the VPD is and how important it is. It's actually more important like heat and a good VPD is neccessary for the plants to feel good no matter how hot it is. You could maintain 35°C when you add 1500ppm CO2 and keep the humidity at 75% with lights on and the plants would grow like crazy without getting nutrient issues.

 

[Randomblame]

Just for reference...

Sun..
View attachment 4302422

MH...
View attachment 4302423

LED...
View attachment 4302426

T5HO...
View attachment 4302425

HPS...
View attachment 4302424

I don't think T5HO puts out more heat per cm2 than LED (referring to the heat:light correlation), nor do I think MH is similar to the sun like HPS is similar to the sun.


In which way? More or less transpiration? Increasing LST increases transpiration, can we agree on that? If ambient temps used to increase LST have a positive effect, then it supports the hypothesis that it doesn't matter how the leaf is heated, just that it is. It's thermally regulated but spectrally triggered.

The HPS and sun with higher LSTs should transpire more, not less! Yet we increase VPD to decrease a higher transpiration rate for a plant with lower LST, but tons of red. Most LED SPDs are skewed only 12-20% blue (I think you told me that).


This could be due to other variables, no? Seems more than just red WVs increased from those different CRI SPDs. Although it does contradict my EMF hypothesis, unless perhaps he didn't have drivers mounted on lights, or changed driver location between chip upgrade? Hmmm dam lol i thought I was on to something.. Curious to know if any changes like that were made?


I agree.



****

I'm spent lol, I'm not satisfied with the explanation (god Dammit! lol) but I do see where you're coming from and hear what you're saying. I think the search is still on, if you come across some studies demonstrating high transpiration rates in low LST I'd be interested in seeing them. Thanks for the courteous back & forth.

In all these spectrum charts the range between 780 and 1000nm are missing but most of these bulbs have another spike in the range between 800 and 850nm which is almost only heat. So those SPD's doesn't show the whole spectrum the only show the plant usable spectrum.

More than 12% blue would probably only keep the plants smaller and because you get less photons from blue its counter productive to add more blue. With red you get twice as much plant usable photons and 8-10% blue is enough for healthy growth. The blue is not bad at all but using too much is simply inefficient when you try to create as much photons as possible with a minimum of energy.

When you compare CRI80 and 90 CRI80 is more efficient in creating photons so normally you would expect better yield with CRI80. But its not the case. If you compare the spectrums CRI80 peaks at 605nm and CRI90 ~630nm. Under the mccree curve you see both frequencies are used to almost the same degree(maybe 98 vs 99%) which means plants can use both photons in the same way with almost the same efficiency.
Whats left are the wavelength outside the PAR range(+700nm) and here you see a significant difference cuz CRI90 has almost twice as much far-red. Far-red not only heats the leaves up more it has also other beneficial effects.(Emerson effect, shortened flowering stage, evens out PS-I and PS-II, ...) Believe me, its the far-red which makes the difference.

Unfortunately, I do not have enough time to discuss here and also via pm's. There are many others who ask me questions and only to discuss with you would be unfair. If you break up each answer apart and ask 10 new things we will not get any further. As I said, I'm not a professor, I do not even have a higher education. I've worked hard for my knowledge and I'm happy to share it, but at some point it has to be good.

Don't feel pissed, bro! I've simply not enough time for that.

 

[ChiefRunningPhist]

50-55% is okay and that's the level you find normally in a well ventilated area.

I disagree with that statement. In lower than 55%RH climates you will have lower than 55%RH in your grow area, especially if well ventilated.

The whole problems are caused by the 3°C difference in leaf temps. As a said before, with HPS and 25°C the humidity is coincidally in a good range cause we set it to only 25°C and 55% are enough. Would HPS require 30°C ambient temps or better would it not heat up the leaves you would get the same issues like with LED. It's not the heat causing this issues its the too low humidity you typically find under LED's with ambient temps of 30°.

I think the difference between ambient and LST is where a lot of these LED symptoms can be blamed.


If you look at the graph, you see a huge spike in transpiration after a 2°C temperature difference is noticed between ambient & LST.

With HPS you heat the leaves with IR, and so if ventilated, the CTD (canopy tempertaure depression) is probably under 2C, and within normal transpiration ranges.

With LED you lack IR, so when leaves are full of water and no IR to heat them they are more than 2°C cooler than ambient (regardless of comparative ambient temps). Which is why we see the spiking. I highly doubt increasing ambient increases LST at a greater rate, so I refute that increasing ambient is effecting CTD.

If this hypothesis is correct, if you cooled your LED room down or ventilated it more, it should help with the CTD and have same effect as increasing VPD.

In conclusion, one could lay the blame of LED issues in a many different places, but a very popular choice of managing symptoms of CPD, is VPD.

 

[ChiefRunningPhist]

In all these spectrum charts the range between 780 and 1000nm are missing but most of these bulbs have another spike in the range between 800 and 850nm which is almost only heat. So those SPD's doesn't show the whole spectrum the only show the plant usable spectrum.

More than 12% blue would probably only keep the plants smaller and because you get less photons from blue its counter productive to add more blue. With red you get twice as much plant usable photons and 8-10% blue is enough for healthy growth. The blue is not bad at all but using too much is simply inefficient when you try to create as much photons as possible with a minimum of energy.

When you compare CRI80 and 90 CRI80 is more efficient in creating photons so normally you would expect better yield with CRI80. But its not the case. If you compare the spectrums CRI80 peaks at 605nm and CRI90 ~630nm. Under the mccree curve you see both frequencies are used to almost the same degree(maybe 98 vs 99%) which means plants can use both photons in the same way with almost the same efficiency.
Whats left are the wavelength outside the PAR range(+700nm) and here you see a significant difference cuz CRI90 has almost twice as much far-red. Far-red not only heats the leaves up more it has also other beneficial effects.(Emerson effect, shortened flowering stage, evens out PS-I and PS-II, ...) Believe me, its the far-red which makes the difference.

Unfortunately, I do not have enough time to discuss here and also via pm's. There are many others who ask me questions and only to discuss with you would be unfair. If you break up each answer apart and ask 10 new things we will not get any further. As I said, I'm not a professor, I do not even have a higher education. I've worked hard for my knowledge and I'm happy to share it, but at some point it has to be good.

Don't feel pissed, bro! I've simply not enough time for that.

I agree with you about the IR. Less so on the blue.

Your good man im not upset. You've contradicted yourself a few times about this issue and I normally take what you say to the bank, so that's why all the questions. It didn't make sense. I know you value real data and objectivity and so was having a hard time with this one, considering it wasn't adding up for me.

I chose to talk here instead of privately because I thought that many could benefit from the discussion. Never feel pressure to respond. I don't want that, nor am I meaning to imply that.

I'm a machine gun questioner lol I'm sure I'm annoying, but if people can get over my annoying demeanor (sorry man im just that way), I think they would find sound logic in my comments.

 

[3rd Monkey]

I just want to take this moment to thank everyone who has contributed to the thread.

Logic or no logic, the struggle is real lol. I'm already seeing an improvement in my LED tent based on what was provided here.

Thank you.

 

[Capn-Crunch]

I just want to take this moment to thank everyone who has contributed to the thread.

Logic or no logic, the struggle is real lol. I'm already seeing an improvement in my LED tent based on what was provided here.

Thank you.

I got my tent temp down to 78° and my RH up to 60% at the moment and will try and get it a little higher tomorrow.
I'm seeing an improvement in my LED tent as well and it's only been a little over a day since the change.
When I started growing indoor in Oct everything was fine, then as winter progressed so did my plant issues.
I've always liked my LED's because it gave me really tight internode growth and flowered well, but mid winter when I started to
have problems I bought a couple MH/HPS lights and my problems went away, so I was ready to ditch my LED's.
Never realized VPD was that big of a deal, guess it is!
On another note, was good having a discussion without any fights, pissing contests, or trolls!
Thanks everybody.

 

[Randomblame]

I disagree with that statement. In lower than 55%RH climates you will have lower than 55%RH in your grow area, especially if well ventilated.



I think the difference between ambient and LST is where a lot of these LED symptoms can be blamed.
View attachment 4303031

If you look at the graph, you see a huge spike in transpiration after a 2°C temperature difference is noticed between ambient & LST.

With HPS you heat the leaves with IR, and so if ventilated, the CTD (canopy tempertaure depression) is probably under 2C, and within normal transpiration ranges.

With LED you lack IR, so when leaves are full of water and no IR to heat them they are more than 2°C cooler than ambient (regardless of comparative ambient temps). Which is why we see the spiking. I highly doubt increasing ambient increases LST at a greater rate, so I refute that increasing ambient is effecting CTD.

If this hypothesis is correct, if you cooled your LED room down or ventilated it more, it should help with the CTD and have same effect as increasing VPD.

In conclusion, one could lay the blame of LED issues in a many different places, but a very popular choice of managing symptoms of CPD, is VPD.

Under white LED the typ. leaf temp stabilzed is almost the same like the ambient temps. It takes a while and after 2h you can still measure -1 less but another few hours later the difference is less than 1°C in my cab. If you cool your room down to 25°C you would also get leaf temps ~24-25°C and you could stay with the 55% but what happens?
Lets say it with a picture..
I'm sure you've seen it already and have just forgot it but if you look closer it makes clear why we want LST near 30°C.

As you can see, a plant getting 1500μMol/s/m² at 20°C grows slower like the same plant getting only 500μMol/s/m² at 30°C. That means that leaf temps and ambient temps are important factors for plants to run their metabolisms at a higher rate. With only 25°C you would slow down the grows rates. You would probably not even beat HPS results because of the blocked growth potential. At 1500μMol/s there is a huge difference between 25 and 30°C and you would waste light and energy with only 25°C.
HPS light heats up the plants so even with 25°C ambient you get the leaf temps where you want them. To grow at 25°C with LED's is simply not as efficient as to work with 30°C because of the lower metabolism.
I would rather use less light with higher ambient temps as the opposide but to reach canopy temps of 28-30°C alone with my LED light I need at least 700-800μMol/s/m² across the canopy(30-35w/sft.). Only in the summer month I need less.
I can say it again and again ..
You want the LST or better the temperature of the whole plant as close to 30°C as possible to allow her to make use of all the light. A plant getting 1500μMol/s ppfd with 20°C can simply not use all the light cuz their metabolism is just running too low. You would see slow growth and probably bleaching or other signs of saturation when you do is nevertheless.

 

[Randomblame]

I agree with you about the IR. Less so on the blue.

Your good man im not upset. You've contradicted yourself a few times about this issue and I normally take what you say to the bank, so that's why all the questions. It didn't make sense. I know you value real data and objectivity and so was having a hard time with this one, considering it wasn't adding up for me.

I chose to talk here instead of privately because I thought that many could benefit from the discussion. Never feel pressure to respond. I don't want that, nor am I meaning to imply that.

I'm a machine gun questioner lol I'm sure I'm annoying, but if people can get over my annoying demeanor (sorry man im just that way), I think they would find sound logic in my comments.

Yeah, problem is I understand plant processes to a certain degree and for many issues I know the solution but when it comes down to homones, receptors and molecules, to why, what and when I often run out of knowledge myself. So when it comes down to the molecule level and all the different processes inside plants it's often over my head. I usually store only the informations I need to have the best success as possible. It's not so important for me to know the exact reasons, I need only to know how to deal with it. VPD, temps and so are pretty simple to understand. Less humidity = higher VPD, high humidity= low VPD. The VPD could be called the happiness meter cause plants are only happy when the ratio of temps and humidity results in a VPD siutable for the according plant stage.