Effects of Light Intensity on Plant Growth

Greetings, AFN members, OSP here. I’m a new AFN member moving in from another forum. After sneaking around a number of threads here looking for secret information, I’ve decided to start this thread. I want to evaluate the effects of light intensity on plant growth. More specifically, how lighting can be used to encourage or minimize plant stretch.
In the short time I’ve been a member here I’ve met a number of very knowledgeable growers, and I’m inviting each of you to participate or chime in as you see fit. Since I am new to AFN I’m sure I’ve missed a lot of interested parties. If you are reading this feel free to tag in anyone I’ve missed:
@fettled6 @912GreenSkell @bushmasterar15 @Waira @MedGrower @Son of Hobbes @Nosias @Screwauger @HemiSync @ChroToker @Need4Weed

I've grown photoperiods since forever under High Intensity Discharge (HID) lighting, and stretch has always been a thing to plan for. Several years ago I decided to experiment with an autoflower freebie, and since then I've completed (12) single-plant autoflower grows. To the point that I'm not doing photoperiods anymore. Maybe again one day. I have a Colombian Gold freebie that has brought back memories, but not today.
In the process of migrating from photoperiods to autoflowers, I also began a transition from HID to LED lighting. Over this period I began to see a pattern. With every one of my HID grows, all my autoflowers exhibited healthy stretch. It started quicker than photoperiods, but the overall effect was similar. Low Stress Training (LST) was effective, bud quality was very good and yield was very good to excellent. But with my LED grows, absolutely NONE of my autoflowers stretched. I had complete grows that never exceeded 10” in height.But with LED I can’t help but think much more is possible. Over 44+ years of growing I’ve seen well trained plants out-yield plants with no training every time. So I want the ability to encourage stretch in my plants.
For the sake of other AFN members, I believe the inverse of this stretch phenomena could be very beneficial to growers with a limited amount of grow space headroom. I want to prove or disprove, to some relative degree of certainty, that light intensity can be used to influence stretch when growing cannabis. But first I need to gather data on other growers’ experiences with plant stretch, and its association to light intensity during the plant’s lifecycle.

This is NOT an opinion piece of “is LED better than HID?” LED is certainly different, and in many respects (heat &efficiency) we all know it IS better. And this is NOT an attempt to compare LED lighting brands. There are numerous characteristics of LED lighting that determine light quality, and our most excellent site admin, @Son of Hobbes has started a thread on what parameters can be used to define those. His efforts may be reviewed here: https://www.autoflower.org/threads/what-should-be-on-a-grow-light-review.64857/ I’ve added a few well chosen thoughts on that topic - PAR watts, efficiency, most favored color spectrum, etc.. But I’m not smart enough to make that final differentiation so I’m happy to watch as SOH finishes that. The only facts I intend to present here are those I’ve experienced with my auto grows.

There are a number of other factors besides lighting that affect plant growth. In an effort to keep this thread focused on light intensity with no outside variables, I asked one of AFN’s most experienced members, MedGrower, for his input. His comments, and my follow up confirming those variables were addressed, can be found in his grow thread located at https://www.autoflower.org/threads/...-dwc-hs1-telos-0008.64718/page-2#post-1758834
In consideration to MedGrower, if you have any comments / questions, send them to me or post here. I don’t want to trash his grow thread with my conspiracy theory so I’m asking each of you to please share that consideration with me.

For the sake of this study I’d like to focus on the two main lighting factors that control intensity - light height throughout the grow cycle, and “power” of the light over the grow canopy; i.e. watts per sq.ft.. Light height is an easy factor to define as long as we document the variation during a plant’s growth cycle. Plant canopy area is an easy measure. Power consumption is an easy measure. I know, watts per sq.ft. is not the most meaningful measure of an LED’s efficiency. But until or if we ever reach consensus of an industry standard measure for all lighting types, I am using watts consumed at the wall, per square foot. No matter how much we insist this is not the best method (I agree), wattage consumed per square foot is the only readily available factor across all lighting types. And no matter how much we agree to disagree, it should provide a reasonable enough classification of small / medium / large lighting to support this study.

My light ratings are 62.5W/sq.ft. for HID and 65W.sq.ft. for LED. As to other influences on plant stretch, my grow techniques with HID and LED are as close to identical as one can get for environmental control and nutrient regimen. So enough intro, let’s kick this in the ass as I describe my experiences with autoflowers to date.

My starting system for HID is a 250W cooltube and batwing reflector with a metal halide bulb for veg and a high pressure sodium for bloom. The tent is a 4 sq. ft. system (2' X 2' X 5’3") by Secret Jardin. I configured it with (2) 4” 170CFM centrifugal fans, one for light cooling and the other for odor control through a 12” X 4” Phresh carbon filter). My nutrient regimen is General Hydroponics’ expert recirculating formula with some strength and slight ingredient tweaks. This regimen has not changed between HID and LED grows.
I grow hydroponically, and my system is configured for a single plant in a DIY 4 gallon Ebb ‘n Gro net pot with hydroton clay pebbles. The system floods automatically every two hours for 15 minutes. I call this DIY because I do not rely upon the complex valves and fittings normally associated with commercially available ebb and grow systems. Those systems rely upon multiple pumps, flow control valves and timers opening and closing with each flood cycle to deliver and recover nutrients to/from the plant. A strength of these commercial systems is they enable the reservoir to sit at the same height as the grow containers. Negatives are they are complex and expensive. My system relies upon a passive DIY manifold sitting on top of the reservoir, and the only moving part is an inexpensive and very reliable 170 gph hydro pump. Total ebb n’grow component cost with four net pot buckets was under $100. I bought four net pot buckets to simplify plant positioning changes throughout my grows, and to run parallel grows in separate tents. My DIY manifold does raise system height by the height of the reservoir, but the entire reservoir, tent and plant container system comes in under 7’ tall. It’s a quality system with all the right parts, and it fits in a closet if it has to (mine doesn’t).

I’m going to drift off topic for a moment as I’ve been known to do. I’ve used all types of hydro systems for many years and this is my favorite. It re-oxygenates the root zone after each flood every two hours. Supply to the net pot is positive pressure flow, while draining is passive / gravity, so aggressive root growth is pushed back into the net pot and will never cause a clog in the system’s hydro line. And even if a clog were to somehow mysteriously occur, overflow is not possible due to the design of the manifold. The system is fully automated - I recently took an eight day trip with no worries that the system would stay fully functional until I returned, and it did. A separate reservoir (I use 12 to 14 gallons) from the grow container makes nutrient changes and maintenance simple, and the added capacity gives me plenty of “headroom” in the nutrient mix as the plant drinks.
Here’s a pic of the original HID tent. The manifold is the white bucket to the left outside the tent. The ebb ‘n Gro bucket is slightly out of position on the shelf behind the tent:

IMG
 
I think the fact that they all stopped at the same time is due to light intensity and the spectrum your light has. Those leaves are starting to taco nearly with the edges turned up. Not horrible at all, but indicating the light is a touch intense.
 
I think the fact that they all stopped at the same time is due to light intensity and the spectrum your light has. Those leaves are starting to taco nearly with the edges turned up. Not horrible at all, but indicating the light is a touch intense.
Citris Noir is the only one really tacoing, and she is the most sensitive. SW maybe a little on the highest colas, Ruby not at all and could take more nutes but I'm trying to be kind to the Sativa's

I need a temp gun to get an actual handle on leaf temps!


f6
 
Here is a link to a really nice article about improving your terpene production. Most info in one place I have ever seen.
https://www.growweedeasy.com/how-to-improve-cannabis-smell
Hey MedCzech, finally got around to reading the section on Stronger Smelling Cannabis. Great article, and I agree, it had a wealth of info. Unfortunately I didn't really find anything I wasn't doing - at least within the realms of hydro, which I'm pretty well dedicated to.
I have all the supplements, light quality, temps and humidity is under control, drying and curing techniques are on par...
So after reading that section
I came away with a few possibilities:
1- Is organic really better for taste / smell? I've always admired those who have the patience and affinity for full organic / living dirt, but I left dirt behind when I moved inside right after the turn of the century. Enjoyed my dirt days but now I find myself needing and enjoying the automation that hydro gives me. And secretly, I've always been a bit suspicious that organic grows can do anything Hydro can't. But I have to wonder, is that just my ego? I do have to kick myself in the ass occasionally to keep being willing to learn.
2- Are there better supplements out there? The nutrient industry is full of snake oil... look at the wars between AN and GH. Everything in this marketplace has markups that are through the roof, and the only reason I stick to Gen Hydro is that I know the product line so well. Overpriced but worth the money for stellar results, so
I use them all.
But is there a better terpene enhancer than theirs?
3- Does this just come down to strain differences? I've never really thought about it a lot, but my photoperiod grows all seemed to smell and taste better than my autos. And within the realm of autoflowers, I'm up to 15 or 16 strains grown, and some have definitely been better than others.

Maybe I just bought some especially flavorful strains in Monterey.
Maybe I'm being too hard on myself. Or the price for hydro's better yield is less smell????? Damn, I hope not.
Maybe someone out there has discovered the secret pill? Come on, Boyz 'n Gurls, help a brother out.
 
Hey MedCzech, finally got around to reading the section on Stronger Smelling Cannabis. Great article, and I agree, it had a wealth of info. Unfortunately I didn't really find anything I wasn't doing - at least within the realms of hydro, which I'm pretty well dedicated to.
I have all the supplements, light quality, temps and humidity is under control, drying and curing techniques are on par...
So after reading that section
I came away with a few possibilities:
1- Is organic really better for taste / smell? I've always admired those who have the patience and affinity for full organic / living dirt, but I left dirt behind when I moved inside right after the turn of the century. Enjoyed my dirt days but now I find myself needing and enjoying the automation that hydro gives me. And secretly, I've always been a bit suspicious that organic grows can do anything Hydro can't. But I have to wonder, is that just my ego? I do have to kick myself in the ass occasionally to keep being willing to learn.
2- Are there better supplements out there? The nutrient industry is full of snake oil... look at the wars between AN and GH. Everything in this marketplace has markups that are through the roof, and the only reason I stick to Gen Hydro is that I know the product line so well. Overpriced but worth the money for stellar results, so
I use them all.
But is there a better terpene enhancer than theirs?
3- Does this just come down to strain differences? I've never really thought about it a lot, but my photoperiod grows all seemed to smell and taste better than my autos. And within the realm of autoflowers, I'm up to 15 or 16 strains grown, and some have definitely been better than others.

Maybe I just bought some especially flavorful strains in Monterey.
Maybe I'm being too hard on myself. Or the price for hydro's better yield is less smell????? Damn, I hope not.
Maybe someone out there has discovered the secret pill? Come on, Boyz 'n Gurls, help a brother out.

I agree with you on so many points, and a big point up front is the Auto versus photoperiod argument. The photoperiod plants are stronger and definitely create more resin I know from pressing, plus the hash yield was always at least 2 to 5% higher than with autos. So part of the issue, in both of our own minds here, is that we are trying to get the same exact flavor profiles we got from the photos. Genetics have improved for sure, that's the main reason I went to autos. Less hassle for me, it wasn't ever about perpetual grows or shorter grow seasons. I only grow two times a year,early spring and early fall.
Ok, but back to the subject of terpenes and the flavors we are looking for.
1- is organic better? I run advanced Hydroponics of Holland nute line complete, very similar to GH. I grow in coco-perlite-clay pebbles and Autopots, no air pumps anymore(hassle and more electric), and I don't even use the res anymore, as I like hand watering. I do water from the bottom still, but I am there usually lighting up some hash in glass or doing something in my shop anyway.
I have never tried to run organic indoors either, but I did run outdoor organics in big pots with dry amendments added only. Then I watered, but those were the photoperiod days, so I don't have much to compare. I am not sure if the organic thing will help, but in my next grow I will run dry amended coco-perlite-fert combo of a 2-3-2 and a 4-4-4 dry amendment, as well as adding a few more dry nutes throughout. Costs about $30 per plant to get set up for the entire grow. Check out that Canadian dude Canuck Grower on YouTube. That dude grows some seriously dank looking autos. He grows in dry organic amended coco as well. Another thing is that he grows in veg under basic blurple using veg lights(mostly blue), and then switches them to under the Electric Sky, wideband led lights. The unique thing about them is their radical spectrum profile that gives a shit ton of red, deep reds, and far reds. This is similar to some of the things I was noticing about in my grows that was getting better results, but by accident at first. Really focusing on more blue in veg and then transitioning them to more and more reds and then blast them hard with all the red I had through mid to late flower. I am just trying to get a little more clever with each grow and more precise with both spectrum and intensity.

2-nutes are nutes, it's all the same shit! Your Nitrogen is not better than my Nitrogen. I like the grow doctor dude on YouTube who jokes about that all the time. That dude also has some great knowledge.

3- hard to say how to really judge this whole auto endeavor we have taken on. Sometimes I think about going back to photos, but I believe the genetics are really catching up for sure. Nothing easier than just dropping that egg and then just water and go, so easy to grow. When we want easier, quicker version of our precious herb, something had to suffer a little. I do consider going back to photos just because of flavor alone, but I will fight a little longer. My last grow was very successful. The strain was Auto Night Queen from DP. I found the elusive pheno everyone wants, twice by using this method of spectrum manipulation.

I start with blue lights (veg switch) from my 600w blurple at 36" in the center of the tent and two cobs on opposite corners at 48". These cobs are 3500k Cree 3590 chips running at 65w from the wall. I am around 300 par with the blurple and only around 150 or so with the cobs.

I will then slowly increase the intensity throughout the veg stage, but keep the ratio. As soon as we see signs of flower, I turn on the other two lights I have, a 3000k 150w double cob light and a 180w Chinese QB knock off(but has great parts inside- meanwell drivers, etc.). This adds more reds and the QB adds nice IR and UV.

I am thinking of adding some light that emits the harmful UV-B rays to induce more terpene and trichome production in veg. I have read that that can help.

So this is a small insite into where I am heading with my grows. Spectrum and intensity. I can't think of much else we can do at this point.
Let's keep in touch and work at it together!
 
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@MedCzech , OUTSTANDING, well thought out summation that deserves a well earned :slap: my Friend!
Sometimes I stare at a problem, know the answer, but just can't accept it because it isn't what I WANT it to be.
And I really was comparing those top-shelf photoperiod grown strains I picked up in Monterey to my latest strain of TH Seeds Auto original BubbleGum. So yes, I have to accept what I've always known, that autoflowers have the Ruderalis gene which IS going to affect smell, taste and strength. However great or small, it does have an effect.
Knowing that because I've grown the photoperiod BubbleGum from TH Seeds and it IS a little better in all respects except single-plant yield. Same with Pineapple Express, Northern Lights / Big Bud, ChemDawg, and probably other strains where I've done the auto and photo versions over the years. I'm with you - auto's are getting better, but I will always be tempted to try photo's again - probably this winter. But I still love the auto's, it's a simpler grow style for me.
Soon as Fall is upon me and I hang up the canoe, kayak and backpacking gear for the year, I'll be coming back around to chase this with renewed vigor. Until then, stay tuned & I'll keep you posted as well.
My next stop is going to be Fast Buds' Rhino Ryder, their auto version of Mr. Nice's Medicine Man. Dropped the seed for an overnight soak two nights ago, dropped it into a rapid rooter yesterday. Mr. Nice's photo version was one of the best top shelf medical photoperiods I've ever grown, so it will be very interesting to see how Fast Buds' Auto version stacks up.
 
@MedCzech , OUTSTANDING, well thought out summation that deserves a well earned :slap: my Friend!
Sometimes I stare at a problem, know the answer, but just can't accept it because it isn't what I WANT it to be.
And I really was comparing those top-shelf photoperiod grown strains I picked up in Monterey to my latest strain of TH Seeds Auto original BubbleGum. So yes, I have to accept what I've always known, that autoflowers have the Ruderalis gene which IS going to affect smell, taste and strength. However great or small, it does have an effect.
Knowing that because I've grown the photoperiod BubbleGum from TH Seeds and it IS a little better in all respects except single-plant yield. Same with Pineapple Express, Northern Lights / Big Bud, ChemDawg, and probably other strains where I've done the auto and photo versions over the years. I'm with you - auto's are getting better, but I will always be tempted to try photo's again - probably this winter. But I still love the auto's, it's a simpler grow style for me.
Soon as Fall is upon me and I hang up the canoe, kayak and backpacking gear for the year, I'll be coming back around to chase this with renewed vigor. Until then, stay tuned & I'll keep you posted as well.
My next stop is going to be Fast Buds' Rhino Ryder, their auto version of Mr. Nice's Medicine Man. Dropped the seed for an overnight soak two nights ago, dropped it into a rapid rooter yesterday. Mr. Nice's photo version was one of the best top shelf medical photoperiods I've ever grown, so it will be very interesting to see how Fast Buds' Auto version stacks up.

Ooh, that Mr. Nice's Medicine Man sounds good. Rhino Ryder I have never done either. I have done some similar strains using that Low Ryder lineage.
Some of the new Mephisto stuff is looking good for terp action though.
Thanks for the rep! Always great to find like minded people just trying to enjoy the little things in life. I am looking forward to watching your grows and sharing knowledge. I have seen girls who just popped their heads above ground myslef. Fast Buds Green crack, two fast Buds GSC, Dr. Feelgood from Short stuff seeds(high cod strain -and super tasty), Auto Blueberry from Dopeseeds, and last is Fruit Punch and Massive midget from Haevyweight seeds. Nice variety of flavors for me to experiment on in this grow. I am working on the spectrum intensity and nutrient uptake all being delivered in ratio. Hopefully my precision in this grow will lay dividends. Simple to do as well. Just had to work out the math.
 
@Dinafem-Mark Hey Pal, haven't seen you around in recent days. Have a question for ya - our Blue Cheese is turning into quite a lovely young slut, and as Bob Seger best described her, with "... points all her own sitting way up high, way up firm and high". I literally can't count the number of bud sites she's putting out so I'm expecting great things from her for yield. But Man, ooooh Man, she's working my ass off keeping her bush trimmed. Not complaining, enjoying the work, but I don't recall ever seeing a girl this bushy since I quit watching 70's / 80's porno for the 21st century variety.
:crying:
Is this the norm for this strain?

x42olz.jpg


Oh... she's starting to stack on the trichromes as well, and showing a hint of blue along the edges of the newest top sugar leaves.
Pretty, sweet smelling, sticky. All things a Man wants in his Girls.

2q0vko3.jpg


And yes, I am a hopeless perv. Worked hard at it, proud of it.
 
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@Dinafem-Mark Hey Pal, haven't seen you around in recent days. Have a question for ya - our Blue Cheese is turning into quite a lovely young slut, and as Bob Seger best described her, with "... points all her own sitting way up high, way up firm and high". I literally can't count the number of bud sites she's putting out so I'm expecting great things from her for yield. But Man, ooooh Man, she's working my ass off keeping her bush trimmed. Not complaining, enjoying the work, but I don't recall ever seeing a girl this bushy since I quit watching 70's / 80's porno for the 21st century variety.
:crying:
Is this the norm for this strain?

2hf135t.jpg


Oh... she's starting to stack on the trichromes as well, and showing a hint of blue along the edges of the newest top sugar leaves.
Pretty, sweet smelling, sticky. All things a Man wants in his Girls.

2q0vko3.jpg


And yes, I am a hopeless perv. Worked hard at it, proud of it.

Yep, love me some bush, but if you trim it up nicely, their flowers will really open up for you!
 

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