Ideal Light Intensity For Different Stages Of Flower Using High Power LEDs

[Davidjreimer]

Hi all,

I’m fairly new to growing, and I’m looking for your input on the ideal light intensity for the different stages of bloom when using high power LEDs (Fluence, Gavita, Blackdog etc)

I have a few Fluence Spydr 2i and use a TrolMaster, so I can dial in the power from 1 to 100.

According to Fluence, at 100% power the lights produce 1700 umol/s at 6-8 inches above the canopy, which is crazy high.

On FloraFlex website they have a guide on “How to grow” (link: https://floraflex.com/default/how-to-grow )

As you can see from the link, and the following pictures, they only recommend having the lights producing >1200umol/s during mid-late flower. Early flower and during flushing they recommend turning it down.

I’m aware it’s meant to be a general guide, so I wanted to get your personal feedback if you use these LED, or other high power LEDs.

What strength (percentage wise) do you find works best through the different stages? I have read that keeping the light intensity too high at the end of flower can cause the plant stress and foxtail etc.

Additionally, if you have any links I can read which talk about this topic please send in the thread.

Any feedback is welcome

 

[RootsRuler]

 

[SSgrower]

Am I right that over 1,200 U/moles require CO2 for better uptake? Otherwise it's just a waste.

 

[Davidjreimer]

View attachment 1289851View attachment 1289852

Thanks for the resource. I got the light meter app, and read through their site.

This is the only chart of its kind I found that talks about the DLI needed week to week during bloom.

They say it’s “based on research and experience” but offer no source, and don’t explain the “research”.

I wonder how they arrived at these specific numbers instead of having DLI at 50 from week 4-6 for example.

I’m in full agreement that the general trend of starting at lower DLI and ramping it up, before decreasing at the end is correct, but without proof I’m not sure if I believe their exact numbers

 

[Davidjreimer]

Am I right that over 1,200 U/moles require CO2 for better uptake? Otherwise it's just a waste.

Yes you are right. It’s lower than 1200 umol actually. You can read more here: https://fluence.science/wp-content/uploads/2018/11/Fluence-Photobiology-Guide-2019.pdf

 

[N1ghtL1ght]

Maybe they took PPFD readings at the top of the plants to calculate the DLI. Now the plants stretched towards the lamp, increasing PPFD. Then, towards ripening, the colas toppled down.

 

[Davidjreimer]

Maybe they took PPFD readings at the top of the plants to calculate the DLI. Now the plants stretched towards the lamp, increasing PPFD. Then, towards ripening, the colas toppled down.

Dont think so and doesn’t sound very scientific to me. The lights can be raised and lowered as needed, or turned up or down in strength

 

[RonnieB2nd]

View attachment 1289851View attachment 1289852

I use true 500 watt growcraft chilled tech lights, during veg I run them at 30% and about 15 inches maybe 12 from the canopy, then when I see pistils I take it to about 55%, then 65 for early flower, then 100% at flower

 

[N1ghtL1ght]

Dont think so and doesn’t sound very scientific to me. The lights can be raised and lowered as needed, or turned up or down in strength

I'd like to see any scientific DLI evidence for Cannabis :)

Who knows, maybe the 3 weeks are ment to throttle stretch or whatever

 

[Its420anytime]

There are so many light companies that basically cut copy and paste other manufactures info, graphs, and distort their lights capabilities. How many light manufactures use independant testing? Very, very few! Why wouldn't they want a 3rd party independant test to substantiate their claims?
Use the guy on a forum who doesn't push brands on most light discussions. Use the guy who has shown years of successful grows. Word of mouth from veteran grommies goes along way when I purchased first led.

There are alot of lights that do both, veg and flower without having to add different light in mid cycle, good lights don't normally have flip the switch to change to bud or grow.
The diy light kits are cheaper, I'd rather have professional I could point the finger at incase of fire and I don't want to be responsible loss of anything due to me being up late trying to finish solder joints just to show what I did.
A dimmer eliminates or facilitates controlling heat and intensity levels without having to adjust height all the time.

Again, proof is in the pudding, lots of lights work. For 45+ years one light fixture, I did change a bulb once every grow cycle, mh to hps, now with led light, I dont do anything other than control dimmer w 9 settings and two easy adjustable pulleys for heighth. Leds do give off heat and too close burns just like ballasts do, I'd say from personal experience that my 300 w led is similar in heat as to my 150w ballast.
Never grew for profit, light bill was very cheap with 150w, that light grew sea of green, 20 six inch pots on top of 2x3 motar mixing tub from hardware store. 20 spear chucker cola and tons of off shoots.

 

[delps8]

Thanks for the resource. I got the light meter app, and read through their site.

This is the only chart of its kind I found that talks about the DLI needed week to week during bloom.

They say it’s “based on research and experience” but offer no source, and don’t explain the “research”.

I wonder how they arrived at these specific numbers instead of having DLI at 50 from week 4-6 for example.

I’m in full agreement that the general trend of starting at lower DLI and ramping it up, before decreasing at the end is correct, but without proof I’m not sure if I believe their exact numbers

You hit it on the head. I've tested Korona/Photone (won't use it) and have traded emails with their programmer (I've been a professional programmer for > 30 years). Earlier this year, I emailed Dominik and asked him where he got the info for the light charts. At the time, they didn't have anything on autos so I asked him about that, as well.

His reply was to check their site for links to sources and he said that autos should have a DLI of 45.

Last time I checked that site, there were no citations. And, as I'll detail below, that's because the published research tell a very different story.

I've gone through a bit of a journey re. light since I started growing back in early 2021. Like so many growers, I followed the recommended light values for seedlings, veg, and flower. What was confounding was that all research re. light levels was very different than what the cannabis industry was recommending.

What really stood out was Bugbee's statement that almost all of the growers with whom he consults were "leaving money on the table" by not giving their plants enough light. When I read his research plus the Chandra paper and a few other papers by researchers, they were giving cannabis far more light than most growers.

About ⅔ the way through my last grow, I listened to one of the DeBacco (YouTube) videos of the Nth time and finally got my head out of my ass about light. Below is the light information for my Gorilla Glue grow. Those two plants yielded 740 grams. One of the contributing factors is that the X3 is a Growcraft full cycle light which is a red heavy grow light with very little blue. That's important because blue photons in flower reduce yield. Other than that, I did nothing special - two Gorilla Glue autos in a big res (holds 28 gallons of nutes), Jack's 3-2-0, keep VPD in range (0.8 seedling, 1.0 in veg, and 1.4 in flower), and I have very little desire to cut healthy leaves off my plants so the only pruning I did was to trim away dead/dying from the undercarriage as well as buds and their branches that could not grow into consumable product.

The mistake that I made was not giving the plants more light in the early parts of the grow. I've changed that in my current grow and those light values are shown below. The light values are averages of the canopy area. In many cases, parts of the canopy are receiving > 1100 µmols or a DLI of > 70. I've had two instances of light stress over the course of the grow and the solution has been to reduce the PPFD by 50-1000 µmols.

My reason for taking this approach is the research that has published (Bugbee, Chandra, Zheng, and Moher were leads on most of the papers) and all of it makes it very clear and, assuming that there aren't other limiting factors, more light = more weed.

Bugbee and Chandra have published research that shows that the photosynthesis yield curve starts to roll off at 500µmols. That's sort of a bummer because you want 1 more unit of input to result in 1 more unit of output. I think it's in this paper ("Cannabis yield increased proportionally with light intensity, but additional ultraviolet radiation did not affect yield or cannabinoid content") that the authors reviewed that issue and demonstrated that the photosynthesis yield curve drops off but the plant yield curve does not. Their conclusion - plant quality, plant yield and crop quality and crop yield increase in a linear manner to an increase in light input.

In short, there are a lot of sources that recommend, for example, that autos get 45 moles of light and there's no question that growers have grown a lot of great weed at that light level. Light manufacturers seem, for the most part, to err on the side of caution, understandably. And Shane @ Migro, though I think he makes good lights, give recommendations that are very much on the low side. You won't go wrong using those recommended values but we know that cannabis will handle up to about 1k µmols — why not turn up the light levels and get more weed?



Grow "2201", 2 Gorilla Glue autos

The numbers are a little blurry. Wilma yielded 139 grams, Chris yielded 590.

Grow 2202 - 2 Strawberry Pie autos:

 

[Moshmen]

You hit it on the head. I've tested Korona/Photone (won't use it) and have traded emails with their programmer (I've been a professional programmer for > 30 years). Earlier this year, I emailed Dominik and asked him where he got the info for the light charts. At the time, they didn't have anything on autos so I asked him about that, as well.

His reply was to check their site for links to sources and he said that autos should have a DLI of 45.

Last time I checked that site, there were no citations. And, as I'll detail below, that's because the published research tell a very different story.

I've gone through a bit of a journey re. light since I started growing back in early 2021. Like so many growers, I followed the recommended light values for seedlings, veg, and flower. What was confounding was that all research re. light levels was very different than what the cannabis industry was recommending.

What really stood out was Bugbee's statement that almost all of the growers with whom he consults were "leaving money on the table" by not giving their plants enough light. When I read his research plus the Chandra paper and a few other papers by researchers, they were giving cannabis far more light than most growers.

About ⅔ the way through my last grow, I listened to one of the DeBacco (YouTube) videos of the Nth time and finally got my head out of my ass about light. Below is the light information for my Gorilla Glue grow. Those two plants yielded 740 grams. One of the contributing factors is that the X3 is a Growcraft full cycle light which is a red heavy grow light with very little blue. That's important because blue photons in flower reduce yield. Other than that, I did nothing special - two Gorilla Glue autos in a big res (holds 28 gallons of nutes), Jack's 3-2-0, keep VPD in range (0.8 seedling, 1.0 in veg, and 1.4 in flower), and I have very little desire to cut healthy leaves off my plants so the only pruning I did was to trim away dead/dying from the undercarriage as well as buds and their branches that could not grow into consumable product.

The mistake that I made was not giving the plants more light in the early parts of the grow. I've changed that in my current grow and those light values are shown below. The light values are averages of the canopy area. In many cases, parts of the canopy are receiving > 1100 µmols or a DLI of > 70. I've had two instances of light stress over the course of the grow and the solution has been to reduce the PPFD by 50-1000 µmols.

My reason for taking this approach is the research that has published (Bugbee, Chandra, Zheng, and Moher were leads on most of the papers) and all of it makes it very clear and, assuming that there aren't other limiting factors, more light = more weed.

Bugbee and Chandra have published research that shows that the photosynthesis yield curve starts to roll off at 500µmols. That's sort of a bummer because you want 1 more unit of input to result in 1 more unit of output. I think it's in this paper ("Cannabis yield increased proportionally with light intensity, but additional ultraviolet radiation did not affect yield or cannabinoid content") that the authors reviewed that issue and demonstrated that the photosynthesis yield curve drops off but the plant yield curve does not. Their conclusion - plant quality, plant yield and crop quality and crop yield increase in a linear manner to an increase in light input.

In short, there are a lot of sources that recommend, for example, that autos get 45 moles of light and there's no question that growers have grown a lot of great weed at that light level. Light manufacturers seem, for the most part, to err on the side of caution, understandably. And Shane @ Migro, though I think he makes good lights, give recommendations that are very much on the low side. You won't go wrong using those recommended values but we know that cannabis will handle up to about 1k µmols — why not turn up the light levels and get more weed?



Grow "2201", 2 Gorilla Glue autos
View attachment 1294312
The numbers are a little blurry. Wilma yielded 139 grams, Chris yielded 590.

Grow 2202 - 2 Strawberry Pie autos:

View attachment 1294316

Ok I need pics I read all that bullshit and some I believe is true. But each plant is different and each one handles light different , healthy plants - there’s so many variable here , I have a meter and hardly ever use it! The plants speak to me and say hey turn that shit down ! Would ya! Lol - now seedlings and clones it may help as they can’t really talk very well yet

 

[delps8]

Ok I need pics I read all that bullshit and some I believe is true. But each plant is different and each one handles light different , healthy plants - there’s so many variable here , I have a meter and hardly ever use it! The plants speak to me and say hey turn that shit down ! Would ya! Lol - now seedlings and clones it may help as they can’t really talk very well yet

If you have questions about the plant biology aspects of my posting or can make constructive criticisms, that would be great.

If you want to check my grow journals, log in to 420magazine.com. I'm using the same screen name there so it will be easy to check things out.

"But each plant is different and each one handles light different , healthy plants - there’s so many variable here , I have a meter and hardly ever use it! The plants speak to me and say hey turn that shit down ! Would ya! Lol - now seedlings and clones it may help as they can’t really talk very well yet"
Agree 100% about seedlings (never dealt with clones) - I'd guess that by the time they do a light avoidance move, it could be their last earthly act. Using a light meter helps remove the guesswork. And, as you say, the plants will tell you to turn that shit down. That's happened twice during this grow but at pretty high light levels. Check the last two photos - they were taken on Monday at 2:44 PM and then at 10:35 PM. I think that qualifies as "turn that shit down"

"turn that shit down" - no question. In my last grow, I hit a couple of the tallest colas with about 970µmols and they bent about a couple inches from the top. Very strange. I moved them a little bit to get them to lower light but they never straightened up.

I'd posted some photos from the grow.

This is from the "Yield" tab in my grow journal (Excel):

There was more weed left on Wilma that I didn't chop - no more than an ounce. And what's hanging in the photos is from Chris and what was left of Wilma. I had already taken some from Wilma and had it drying in the fridge. This is documented on 420magazine if you want to read up on it.

This grow turned out well but I did pull almost 25 ounces from my grow in January, per below. It's all documented at in the same place. BTW, "late harvest" works for grapes/wine but not so much for weed. :-).

Jeff fox tailed so I "harvested" by cupping my hand and pulling the stems through it. After a while, I just gave up and have never smoked any of it. That 15 oz went into Grove bags and I ended up giving it to my neighbor who have back pain so bad that he needs cannabis to go to sleep.

 

[Aqua Man]

spectrum, media, nutrients, every single environmental factor, genetics, co2 etc all play a role in how much light a plant can effectively handle and utilize…. There is no one set number but rather guidlines as to the ppfd that a cannabis plant can handle.


long story short a plant can handle what a plant can handle

 

[Anthem]

If you have questions about the plant biology aspects of my posting or can make constructive criticisms, that would be great.

If you want to check my grow journals, log in to 420magazine.com. I'm using the same screen name there so it will be easy to check things out.

"But each plant is different and each one handles light different , healthy plants - there’s so many variable here , I have a meter and hardly ever use it! The plants speak to me and say hey turn that shit down ! Would ya! Lol - now seedlings and clones it may help as they can’t really talk very well yet"
Agree 100% about seedlings (never dealt with clones) - I'd guess that by the time they do a light avoidance move, it could be their last earthly act. Using a light meter helps remove the guesswork. And, as you say, the plants will tell you to turn that shit down. That's happened twice during this grow but at pretty high light levels. Check the last two photos - they were taken on Monday at 2:44 PM and then at 10:35 PM. I think that qualifies as "turn that shit down"

"turn that shit down" - no question. In my last grow, I hit a couple of the tallest colas with about 970µmols and they bent about a couple inches from the top. Very strange. I moved them a little bit to get them to lower light but they never straightened up.

I'd posted some photos from the grow.

This is from the "Yield" tab in my grow journal (Excel):

View attachment 1294369

There was more weed left on Wilma that I didn't chop - no more than an ounce. And what's hanging in the photos is from Chris and what was left of Wilma. I had already taken some from Wilma and had it drying in the fridge. This is documented on 420magazine if you want to read up on it.

This grow turned out well but I did pull almost 25 ounces from my grow in January, per below. It's all documented at in the same place. BTW, "late harvest" works for grapes/wine but not so much for weed. :-).

Jeff fox tailed so I "harvested" by cupping my hand and pulling the stems through it. After a while, I just gave up and have never smoked any of it. That 15 oz went into Grove bags and I ended up giving it to my neighbor who have back pain so bad that he needs cannabis to go to sleep.
View attachment 1294377


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View attachment 1294373View attachment 1294374

I am really not impressed by your work. I realize these are autos and typically grow a large central cola, so I see you showing off those specific cola's. But when I see your buds up close they look like they have been over feed and the fox tailing got out of control. I see am not seeing shining buds common in a well managed indoor grow with lighting being provided at the amount the plant can handle while not over doing to the point of destroying the fan leaves. I see your excel speed sheet with your inputs for each day and such but I am not seeing the quality or quantity you feel you have. I am a well rounded grower using state of the art equipment and environment but again I do not mean to sound degrading but your work is not up the the quality we see here on the farm.
@Moshmen you are correct. I have an apogee quantum sensor and I never use the thing. You can pretty much look at the plant and it will give you visual cues to what it wants and needs. This is just a matter of an individual trying to use equipment and the experience of others to elevate their work. While you and others are trying to become better growers by understanding the plant. The experience of a person that has really been growing for years and has 50 or more grows under their belt is priceless. You have to understand the plant and its needs to truly bring out the best the genetics have to offer. Sure someone can follow a recipe and get good results but the same plant and equipment in the hands of someone with the experience listed will produce better results every single time. It gets down to the Journeymen VS. Apprentice.

 

[delps8]

I am really not impressed by your work. I realize these are autos and typically grow a large central cola, so I see you showing off those specific cola's. But when I see your buds up close they look like they have been over feed and the fox tailing got out of control. I see am not seeing shining buds common in a well managed indoor grow with lighting being provided at the amount the plant can handle while not over doing to the point of destroying the fan leaves. I see your excel speed sheet with your inputs for each day and such but I am not seeing the quality or quantity you feel you have. I am a well rounded grower using state of the art equipment and environment but again I do not mean to sound degrading but your work is not up the the quality we see here on the farm.

Funny, you sound very credible but you're wrong on a number of counts.

"I am really not impressed by your work." what an obnoxious lead in. It really poisons the rest of what you've written.

When a plant is topped there is no central cola - so do I think that you have any idea of what you're talking about when you say something that is so fundamentally wrong? Well, it's tempting - after all, that's a fundamental piece information that what happens when you top a plant? Nah, just a brain cramp.

Those were the 20± secondary colas that were flopping all over the place.

"Overfed" - wrong again. The EC never got over 1.6 and was closer to 1.2 at the end of the grow. The only time there was any indication of nute burn was in early veg when I dropped some res water on one leaf.

Foxtails - Wrong again. Those colas were a very similar size, were round, and almost incompressible. I've seen fox tailing. That happened to my second grow and was definitely an issue with too much light. These two plants produced large, dense nugs.

"the quality or quantity you feel you have." - until the above statement, I have mentioned nothing about "quality" so you know nothing about how I "feel" about it.
There's no "feeling" about the quantity. Everything was measured and accounted for to 1/100 gm. As with my statement about quality, since I've never discussed the quantity aspect, so you have no basis to state that you have any insight whatsoever about my "feelings" about those issues.

So, about 90% of what you wrote is utter bullshit but, heh, there's a ray of sunshine down here.

"I do not mean to sound degrading but your work is not up the the quality we see here on the farm." Thank you for that feedback.

 

[Anthem]

Funny, you sound very credible but you're wrong on a number of counts.

"I am really not impressed by your work." what an obnoxious lead in. It really poisons the rest of what you've written.

When a plant is topped there is no central cola - so do I think that you have any idea of what you're talking about when you say something that is so fundamentally wrong? Well, it's tempting - after all, that's a fundamental piece information that what happens when you top a plant? Nah, just a brain cramp.

Those were the 20± secondary colas that were flopping all over the place.

"Overfed" - wrong again. The EC never got over 1.6 and was closer to 1.2 at the end of the grow. The only time there was any indication of nute burn was in early veg when I dropped some res water on one leaf.

Foxtails - Wrong again. Those colas were a very similar size, were round, and almost incompressible. I've seen fox tailing. That happened to my second grow and was definitely an issue with too much light. These two plants produced large, dense nugs.

"the quality or quantity you feel you have." - until the above statement, I have mentioned nothing about "quality" so you know nothing about how I "feel" about it.
There's no "feeling" about the quantity. Everything was measured and accounted for to 1/100 gm. As with my statement about quality, since I've never discussed the quantity aspect, so you have no basis to state that you have any insight whatsoever about my "feelings" about those issues.

So, about 90% of what you wrote is utter bullshit but, heh, there's a ray of sunshine down here.

"I do not mean to sound degrading but your work is not up the the quality we see here on the farm." Thank you for that feedback.

I think you suffer from a small unit and need to degrade others to allow yourself to feel like John Homes Junior.

 

[delps8]

I think you suffer from a small unit and need to degrade others to allow yourself to feel like John Homes Junior.

Why the ad hominem. You opened your statement with some that was pretty harsh. That set the tone but I put that aside. You've made statements that indicate either a brain cramp (my thinking) or that really don't know that topping removes the apical cola, and then you tell me that it was over fed (which is ridiculous) and that it was fox tailed due to light levels being too high and I stated that your conclusion was wrong because the colas are extremely large and all solid and hard, unlike the almost 1 pound of fox tails that I had in my previous grow.

So you did give one piece of feedback that wasn't assholish - it's not up to the standards on your farm and I have no problems with that feedback. And that does not surprise me. It's not "gorgeous" weed like I see in some dispensaries. It's middle of the road weed and I'm quite happy with it but I do know that has nothing to do with the statements I made about growing cannabis at the light saturation point.

It's about sharing information and discussing things like adults. Instead you take my statements about what you wrote and reply with a juvenile attack on me. That's just sad.

 

[Aqua Man]

Weez all in the same team here. Honesty is great but lets keep the personal insults out of the sandbox… after all we can all learn and teach eachother something of value from our own experiences to better our skills. Much stronger as a community that way

 

[Anthem]

Why the ad hominem. You opened your statement with some that was pretty harsh. That set the tone but I put that aside. You've made statements that indicate either a brain cramp (my thinking) or that really don't know that topping removes the apical cola, and then you tell me that it was over fed (which is ridiculous) and that it was fox tailed due to light levels being too high and I stated that your conclusion was wrong because the colas are extremely large and all solid and hard, unlike the almost 1 pound of fox tails that I had in my previous grow.

So you did give one piece of feedback that wasn't assholish - it's not up to the standards on your farm and I have no problems with that feedback. And that does not surprise me. It's not "gorgeous" weed like I see in some dispensaries. It's middle of the road weed and I'm quite happy with it but I do know that has nothing to do with the statements I made about growing cannabis at the light saturation point.

It's about sharing information and discussing things like adults. Instead you take my statements about what you wrote and reply with a juvenile attack on me. That's just sad.

Oh the take the high road approach now. This is typically called the 180. I am very well aware of how this is implemented. You get called out for posting your bragging in someone else's thread than you try to turn things around and become the good guy. First of all, if you are running Jacks per the formula it is not 3-2-0. it is 3.79, 2.52 and .99. This is the current recommended dose. if you want to keep this going I will respond when I have time but I stand by my words and options. I understand they can be harsh but sometimes the truth hurts.