• Come join us as we welcome Horticulture Lighting Group to the Autoflower Network!

    We have an official representative from HLG that will be active on the forum to answer your questions, several units that are coming for our official product testing (grow and show's,) and we'll be working together to provide better information on lighting in general!

    Come say hello!
  • Do you LOVE AFN?? bighug We do too!! But we need your help to keep the servers running!

    If you feel like AFN has been useful in your journey and would like to help us pay some of the bills, we have a gofundme page setup for donations.
    Any amount that you can spare will be gratefully received

    Click [HERE] to donate to AFN

Effects of Light Intensity on Plant Growth

Slater

Flowery Twats
Joined
Sep 7, 2016
Messages
5,378
Reputation
0
Reaction score
27,360
Points
0
Age
46
So here’s where you can help. I’m asking for each of you who have had successful grows under LED lighting to provide some basic statistics on your grow. I’m not trying to be rude by restricting this to successful grows. But I do need to acknowledge MedGrower’s point that there are other factors affecting plant growth, and eliminate those from the equation. So if something went bad on your grow - heat, nutes, bugs, pH drift not controlled, your room mate smoked it all when you weren’t looking - whatever - please defer posting until you complete a successful grow. Here’s what I’m looking for:

What is the breeder & strain and final cured yield of the plant you are reporting

Watts per sq. ft. documented from wattage-at-the-wall of your light(s) and with size and square footage of your grow area (size to identify odd shaped areas). If you use multiple lights, list each with a total wattage consumed.

Finished height or plant length. Difference being a measure of training effectiveness to final height. For example, if you took a 30” tall plant and brought her down to 12” with LST, then report total plant length at 30”. Remember, I want to measure stretch, more so than final plant height. The simplest method to measure stretch of a trained plant is with a string following the contour of the main trunk from base to tip.)
If you did no training & allowed the plant to follow its natural form, report No Training and normal plant height.

And finally, the magic sauce –
What light heights did you maintain throughout veg, transition and bloom? Ranges fine, for example:
Veg – start @ 30”, down to 16”,
Transition – start @ 16”, down to 12” (I frequently skip this, feel free to as well)
Bloom –maintained at 12” throughout bloom.

I don’t care if you raised the light to finish final bloom.
And maybe I should care about at what age the plant stopped growing vertically? Of all the info I gathered during my auto grows, I never thought to document that. If you did, report it.

As your reports come in, I will try to summarize these on the next post in table form, and maintain a running average of light height to plant height. If I find that’s not working out or for unknown reasons just not making sense, I’ll find some way to summarize & report your results. I’ll attempt to maintain that table by editing my thread post immediately following this.

Thanks for bearing with me, I know it’s a long start for this thread. If you don’t know yet, there are two things about me – I won’t do anything half-assed, and I don’t know how to write short posts
:bighug::shrug:
Awesome have quite some experimentation in to this my self... I have height restrictions

01 - Maple Shurbet x pre 89 skunk (photo) by seedstockers

02 - on average about 40w per square foot

03 - No training just trellis netting with the odd tie down / super crop... I let them get to about 15" to 20" before I flower them, I go by % on the stretch, my findings are below.

04 - Veg...T5 up until 2 weeks before flower, then 50w of led COB's for the 2 weeks before moving into the flower tent
Flower... 380w led COB's, 2 lights, one at 1400ma and the other 1050ma.

05 - light hight... I let them grow towards it, they can reach 5" in places... super cropping is used


Just my thoughts on this subject... This has been something that has interested me from the start due to my hight restrictions and I've done quite a lot of experiments, not as science as yours, more observational. Both with "burple" LED's and full white spectrum LED's.

My stats -
Tent... 117cm x 87cm x 145cm
Light... about 380w of DIY COB power
system... run to waste feeding every 24hrs

So far my findings are that light intensity and hang hight make no difference to stretch, I've been playing around with this for 2 years now... what I have found out and makes a massive difference in stretch is heat. I've seen and come to the conclusion with clones over this summer (its been a hot one in my loft garden)... Your old HID lighting projects more heat down, LED project more heat up, something to consider in you findings.

3 grows in a row with the same clones, starting in spring and the third and final grow is now into week 5... first grow about 60% stretch ambient temps of 24-25c, they reached on average about 15" to 10" from the light... 2nd grow (peek of the summer), easy 100%+ stretch with plenty of super cropping, ambient temps of 29c -31c, on average 5" from the light with quite a few needing super cropping as they grew into the light... 3rd grow 60%, ambient temps 25c - 28c back to 12" to 8" ( I did scrog this grow due to the last being so out of control which did effect the stretch on a couple of the plants but didn't hinder others)... the lights have been in a fixed potions at the top of the tent for all 3 grows.

I also have another tent of the same size (clones) with 455w of COB / Quantum board power driven 1050ma and are seeing the same results in there with heat over light intensity.. that light is like the sun, super bright and way over powered for the space.

This is just a personal opinion and from my observations but I think genetics / ambient heat / RH make all the difference in stretch and not so much light hight... that's not saying spectrum doesn't play a part in all this as we know the burple LED's light like to make those nodes spacing tighter.
 

Slater

Flowery Twats
Joined
Sep 7, 2016
Messages
5,378
Reputation
0
Reaction score
27,360
Points
0
Age
46
Fact: my HID grows have ALWAYS stretched.
Fact: My LED grows have NEVER stretched.
just to help bolster my point of heat being the biggest factor in stretch next to genetics... HID projects more down, LED project more up... Its a heavy read this thread but I'm getting there.
 

Olde School Player

Celebrating 44th anniversary of my 1st grow
Joined
Feb 25, 2018
Messages
386
Reputation
0
Reaction score
1,386
Points
0
Currently Smoking
Dinafem Blue Cheese Auto, FastBuds' RhinoRyder (Medicine Man), FastBuds GorillaGlue
Mine were from a maverick breeder that's name comes up occasionally, all the FB I grew were top notch!

Hope the fix works, I recall it was only 4 days of 12/12 so that might save you a day. See how you go

Edit, actually iirc it was weird, they didn't stretch or do anything in preflower just slowly, and I mean slowly got bigger without producing flower, will not be growing his again although it was quite pleasent!



6
Thanx for the input, my Brother from a different Mother!
I started 48 hours of darkness at noon today, dropped feed cycle from every two hours to noon and midnight. Could probably get by with no feed cycles - ebb n' gro retains about an inch of water in the bottom of the container below the net pot that I fill with aquarium bio-balls to encourage beneficials. But each feed cycle forces fresh air throughout the root zone so that's enough reason to continue some flood cycles. That alone I believe is one main reason this setup is so effective - oxygenated roots.
I understand your description - didn't stretch... just slowly got bigger. This girl fooled me into thinking she would stretch - in 15 days from transplant she reached 16" tall. Day 16 I started LST which dropped her to 11". Day 18 I had pretty well finished LST, exclusive of fine tuning each branch tip, and added a second COB that day as well. By day 21 she was showing a few scattered pre-flowers, and like you said, she just kept growing without blooming. Not stretching, just a nice steady grow. By day 30 (three days ago) she had almost filled the tent with a good strong branch infrastructure that should produce some excellent colas IF I CAN GET THE BITCH TO BLOOM. Hoping your fix kick starts the changeover from veg to bloom. She's already on a transition nute formula in hopes of that encouraging her as well.

So Fall's here, and I'm slowly getting back into a bit more Forum time. Still got a couple of more day hikes and outdoors things to do before the snow flies, but I'm thinking I'll kick this Rhino Ryder project over to its own thread and save this Light Intensity thread for its original intended purpose. Hopefully the gang's all back soon to help with both projects!
 

Olde School Player

Celebrating 44th anniversary of my 1st grow
Joined
Feb 25, 2018
Messages
386
Reputation
0
Reaction score
1,386
Points
0
Currently Smoking
Dinafem Blue Cheese Auto, FastBuds' RhinoRyder (Medicine Man), FastBuds GorillaGlue
Awesome have quite some experimentation in to this my self... I have height restrictions

01 - Maple Shurbet x pre 89 skunk (photo) by seedstockers

02 - on average about 40w per square foot

03 - No training just trellis netting with the odd tie down / super crop... I let them get to about 15" to 20" before I flower them, I go by % on the stretch, my findings are below.

04 - Veg...T5 up until 2 weeks before flower, then 50w of led COB's for the 2 weeks before moving into the flower tent
Flower... 380w led COB's, 2 lights, one at 1400ma and the other 1050ma.

05 - light hight... I let them grow towards it, they can reach 5" in places... super cropping is used


Just my thoughts on this subject... This has been something that has interested me from the start due to my hight restrictions and I've done quite a lot of experiments, not as science as yours, more observational. Both with "burple" LED's and full white spectrum LED's.

My stats -
Tent... 117cm x 87cm x 145cm
Light... about 380w of DIY COB power
system... run to waste feeding every 24hrs

So far my findings are that light intensity and hang hight make no difference to stretch, I've been playing around with this for 2 years now... what I have found out and makes a massive difference in stretch is heat. I've seen and come to the conclusion with clones over this summer (its been a hot one in my loft garden)... Your old HID lighting projects more heat down, LED project more heat up, something to consider in you findings.

3 grows in a row with the same clones, starting in spring and the third and final grow is now into week 5... first grow about 60% stretch ambient temps of 24-25c, they reached on average about 15" to 10" from the light... 2nd grow (peek of the summer), easy 100%+ stretch with plenty of super cropping, ambient temps of 29c -31c, on average 5" from the light with quite a few needing super cropping as they grew into the light... 3rd grow 60%, ambient temps 25c - 28c back to 12" to 8" ( I did scrog this grow due to the last being so out of control which did effect the stretch on a couple of the plants but didn't hinder others)... the lights have been in a fixed potions at the top of the tent for all 3 grows.

I also have another tent of the same size (clones) with 455w of COB / Quantum board power driven 1050ma and are seeing the same results in there with heat over light intensity.. that light is like the sun, super bright and way over powered for the space.

This is just a personal opinion and from my observations but I think genetics / ambient heat / RH make all the difference in stretch and not so much light hight... that's not saying spectrum doesn't play a part in all this as we know the burple LED's light like to make those nodes spacing tighter.
Hey Slater, thanks for dropping by, and all the Likes in this thread, looks like you took the time to look at them all!!! I admire the patience.
Your (1) says photoperiod strains, and "...3 grows in a row with the same clones" so I assume your grows have not included autoflowers? This could be a significant difference for us. I never had any issues with lack of stretch in photoperiods; all my "problems" began in my transition to autoflowers under COB's. But still, interesting premise. I never tried growing photoperiods under anything but HID lighting, so I can't honestly think there's no similarities.
I never would have expected heat, as both my "old" HID tent grows and LED system-light grows maintained about the same heat range at the plant canopy. Then again, I have not recorded daily canopy temperatures, and this may be a difference of low 70's to high 70's (Fahrenheit, I can't think C clearly, sorry), or high 70's to mid 80's. I do recall some summer HID grows getting a bit warmer inside the tent, and they all stretched whether cooler or warmer. And then again, my first eight grows spanned over two years through all seasons (my indoor grows DO run cooler during Winter). Every one of my HID grows still stretched. As a matter of fact, I never saw a stretch difference between auto's and photoperiods until I went LED.
In spite of our photo VS auto differences, I have to give this some serious thought as to how I might experiment with this. It's an interesting premise that I've pretty much ignored until now, shame on me. I appreciate the viewpoint & experience. Stay tuned as we get this back on track over the coming weeks.
 

Dudeski

Auto Warrior
Joined
Apr 2, 2016
Messages
20,251
Reputation
0
Reaction score
86,837
Points
0
Age
58
Currently Smoking
Fairy Frost by Portal
I do think a strong LED too close to a canopy will prevent much stretch from happening. Some plants will not climb to the lights, others will. I had a green crack and fairy frost under my cobs that were dialed up more than I thought, and both stayed squat. Chunky assed buds but squat. I'm a rookie still. Raise the LEDs and see if the plants get height.
 

The Iconoclast

Auto Warrior
Joined
Oct 6, 2018
Messages
695
Reputation
35
Reaction score
1,677
Points
0
So if I go from 20" to 40", or 18" to 36", or 12" to 24", that would decrease intensity by a factor of four.
I'm only up to this page in the thread so it may have already be answered but, the answer is Yes. And the answer is also No. This is only true for a *point* light source, like the sun, because it radiates equally in all directions. For gravity the inverse square law is pretty straight forward because you cannot direct or focus gravity. EM also operates under the inverse square law, and the surface of a sphere increases as the square of the radius, however we are not dealing with a point light source. We are dealing with focused LED or focused COB's or banks of LED with different types of lenses, some spread at 90º some at 120º some just have a reflector. The reason light from the sun falls off at the inverse square of the radius, is simply that the light spreads out. So it's all a matter of how the light is spreading out.

Go and find your LED torch, the one with the adjustable focus ring, (or maybe you have a searchlight with a focussing lens in your backyard), position yourself a certain distance from the wall and as you focus the light it is brighter and as you cover more area it is dimmer, and you have not changed your distance. This is why laser pointers work because the light is tightly collimated it does not spread out so if the photons are not covering a larger area then the photo beam will stay bright,

So what you have to do is get a light meter and actually measure the light. There are apps that do this. Remember one ƒ stop equals a doubling or halving of the light. ƒ4, ƒ5.6 ƒ8 or you can use the EV reading in which case each number is one ƒ stop. So what if you get a reading of ƒ4.5, well square 4 and get 16, square 4.5 and get 20 (close enough), square 5.6 and get 32. IOW you can forget about trying to apply the inverse square law in the case of LED's. Just measure the amount of light. Now this will only give you a relative answer it.

Having said all that I don't believe that the distance of the light has anything whatever to do with stretching, it just has to do with how much light is reaching the plant the stretching is to create more room for bud sights. Think about it, you have a plant sitting in a field in the full sun and it's getting x amount of light, if we now have bright cloudy days for 3 months, the plant will get less light and it will not photosynthesise as much. BUT, would the plant stretch? Why, it is going to be closer to the sun, no. What would be the purpose of stretching. From what I understand plant stretch happens when plant senses it is getting covered by canopy, and I believe this is what the 730 nm wavelength is supposed to trigger, namely the plant is sensing infra red light and says to itself, holy mother of fuck I need to get above this canopy. It wasn't the lack of light it was the *quality* of light that triggered it.

Plants don't know where the light is (I mean it's vertical distance), they just sense the light that if falling on them. The plant doesn't go 'oh the light is dimmer it must be further away'. It goes 'oh infra red light that must be from light hitting the leaves and then getting transmitted as invisible lower energy wavelengths, I must be under a canopy'.

The only way you are going to make any sense of all this is not from anecdotal evidence where there are an unlimited mix of variables. The only way is to do the tests yourself using clones in identical conditions and then change a single variable. You'll need to test different balances of wavelengths.

Here's an idea, maybe build yourself a small LED bank that just uses the 730nm LED's and see if that induces stretch. But this is going to take years of testing. When I was doing photoperiods under Son T Agros, the light was always the same distance from the plants which was as close as I could get it without getting too hot. Stretch was a function of the plants switching to flower mode only. I don't even know for sure if cannabis actually responds like this to the infrared light anyway. Is it the kind of plant that can get caught under a canopy?

Maybe something like
Led World 10 PCS 3W High Power LED Lamp Infrared IR Light 730-740nm with 20mm Heat Sink Star

What I don't understand, (unless I read it wrong) is that you said you got 11 oz from one of your stubby plants, so isn't that a good thing?

Having said all that if the light is further away then the •difference• in intensity from the top of the plant to say 10 inches down, will be more gradual. Like tidal forces, the Earth is pulling on your head about the same amount it's pulling on your feet, but if the Earth was compressed to the size of a basket ball it would be pulling on your feet with many times more force than your head and you'd get stretched out, or spaghettified as some people like to say.

In at the end of week 4 in my grow and I'll put all the info in when I'm finished. I'm pretty pleased with the spectrum of the vipar, it's got some good spectrum spread as well as green which is in the two white banks a 3000K and a 7500K. At the moment it's pretty squat and bushy and I don't know what's going to happen.

COBs don't have to be white https://futurefarmtech.com/cob-grow-lights/
 

Attachments

Last edited:

The Iconoclast

Auto Warrior
Joined
Oct 6, 2018
Messages
695
Reputation
35
Reaction score
1,677
Points
0
If you want to test this 'canopy effect' stretch factor here's how to build it... I'm not saying it will work, and even if it does work I'm not saying the 730nm is the right wavelength. But it's worth investigating as you are trying to figure out how to stretch with LED's. But there's tons of grows that have plenty of stretch with LED's so I'm not really sure why *all* you plants are so short. As for me, all I'm interested in is growing a healthy plant with a decent yield however it does it.

 

gringuito98

On the way to moon
Joined
Aug 12, 2017
Messages
454
Reputation
10
Reaction score
1,396
Points
0
Currently Smoking
Homegrown organic weed.
INHO ... you can‘t compare the sun and artificial light when it comes to stretch.

With artificial light you have a short distance between plant and light ... changing the distance has a very big influence on intensity. Plants are guided by light and they don’t only „see“ and grow towards it, they also „feel“ the higher intensity of it.

Sun: the sun is quite far away (149.600.000km / 92.960.000 mi) from our little planet ... so why should a plant stretch when it‘s cloudy?... a 20 feet plant receives exactly the same light intensity as a 10‘‘ plant.
 
Last edited:

NorthernLights_420

Autoflower Cultivator
Cultivators Club
Joined
Aug 18, 2018
Messages
2,132
Reputation
138
Reaction score
3,849
Points
0
Currently Smoking
Zkittlez
I veg strictly under t5 until preflowers show or around a month for 2 reasons, to save on electricity and to keep them shorter and bushier, then they go under the 1000 watt hps HID and they stretch like crazy then. I top sometimes and lst sometimes or superscrop to help control stretching or height issues since I have height restrictions myself in my grow area
 

puggle6

HydroPotato!
Joined
Jun 8, 2016
Messages
5,719
Reputation
0
Reaction score
24,058
Points
0
I'm nearing the end of a grow with a far red 600w Ceramic HPS

Previous 860w CMH grow and before that 600w traditonal MH/HPS grow.

They all stretched! If anything the CMH best density, the Ceramic HPS is not exciting me but the girls under it are still finishing

f6
 
Top