Does the color of my LED bulbs matter?

[Canachris]

I have some LED bulbs 100 watt 27 k (15 actual watts) when I grew with CFL bulbs I used 65 k for veg and 27 k when I switched to flowering same when I grew with MH/HPS. now that I'm using LED, at the time I bought them my option was 3000 k or 4000 k. A year later I got a 3000 r spec full spectrum. Does it matter all that much the color spectrum? is 65k during flowering hurt or make no difference, same question about using 27k for flowering, will it help or not

 

[Wastei]

6500k doesn't hurt but will produce less yield then 2700k. 4000k is the most affordable diod on the market but not the most effective for flowering plants.

You should ease up a little on the nutrient strength, she looks nute burned. Cheers!

 

[safeman]

As mentioned veg or flower lighting can use in any cycle Sorry to say that the lighting isn't the cause of your plants issues. What type of nutrients are you using and how many x's a week do you feed ? any "dry"times or just water times ?

 

[Delps8]

Light color has a direct impact on plant shape ("morphology") and, to a lesser extent, yield.

Blue heavy lights have been used in veg because blue light tends to produce plants that are short, compact, and have a lot of foliage. Some blue light is needed in flower but blue light also reduces yield.

Red heavy lights are used in flower because red light tends to promote cell expansion.

If you're using a typical "white" LED, you have no control over the spectrum but it is something you may want to consider when purchasing a grow light. If your grow is in a confined space and/or you grow sativas, which tend to grow taller, a light with more blue in the spectrum will help keep plants from growing too tall.

On the other hand, a red heavy light will get taller plants and will give you a greater yield but those plants will tend to have a larger internodal space.

Yield is primarily a function of light quantity. Cannabis loves light//cannabis requires a lot of light and, assuming that the other aspects of your grow are well done, you plants should thrive up to the light saturation point which is 800-1000µmols.

 

[safeman]

Light color has a direct impact on plant shape ("morphology") and, to a lesser extent, yield.

Blue heavy lights have been used in veg because blue light tends to produce plants that are short, compact, and have a lot of foliage. Some blue light is needed in flower but blue light also reduces yield.

Red heavy lights are used in flower because red light tends to promote cell expansion.

If you're using a typical "white" LED, you have no control over the spectrum but it is something you may want to consider when purchasing a grow light. If your grow is in a confined space and/or you grow sativas, which tend to grow taller, a light with more blue in the spectrum will help keep plants from growing too tall.

On the other hand, a red heavy light will get taller plants and will give you a greater yield but those plants will tend to have a larger internodal space.

Yield is primarily a function of light quantity. Cannabis loves light//cannabis requires a lot of light and, assuming that the other aspects of your grow are well done, you plants should thrive up to the light saturation point which is 800-1000µmols.

Great information - also use 12by12 blue led panel 33watt for veg - and then red 12by12 led panel - one can increase lateral branching and bud sites and also can keep plant short - 3-5 feet - we are talking about side lighting

 

[Wastei]

Light color has a direct impact on plant shape ("morphology") and, to a lesser extent, yield.

Blue heavy lights have been used in veg because blue light tends to produce plants that are short, compact, and have a lot of foliage. Some blue light is needed in flower but blue light also reduces yield.

Red heavy lights are used in flower because red light tends to promote cell expansion.

If you're using a typical "white" LED, you have no control over the spectrum but it is something you may want to consider when purchasing a grow light. If your grow is in a confined space and/or you grow sativas, which tend to grow taller, a light with more blue in the spectrum will help keep plants from growing too tall.

On the other hand, a red heavy light will get taller plants and will give you a greater yield but those plants will tend to have a larger internodal space.

Yield is primarily a function of light quantity. Cannabis loves light//cannabis requires a lot of light and, assuming that the other aspects of your grow are well done, you plants should thrive up to the light saturation point which is 800-1000µmols.

Internodal length has to do with genetics more than anything else. Light intensity control stretch more than the spectrum.

Yield is primarily a function of environmental factors, and light quantity is just one of those factors. If you don't have all the other environmental factors met, the plant can't do anything productive with the excess light.

 

[Delps8]

Internodal length has to do with genetics more than anything else. Light intensity control stretch more than the spectrum.

Yield is primarily a function of environmental factors, and light quantity is just one of those factors. If you don't have all the other environmental factors met, the plant can't do anything productive with the excess light.

No question - environmental factors and genetics are the big drivers — those are "givens".

Re. your assertion about "control stretch". "control" - I don't believe that we can "control" stretch or, for that matter, that we can "control" much of anything when it comes to dealing with living things, thus my use of words such as "tend to".

Light intensity will influence stretch, no question. We've all seen picture of gangly seedlings, right? In fact, I managed to kill a couple of sets of seedlings by, among other things, not providing enough light. They grew tall…until they died.

Research shows that reduced light levels tend to increase internodal space, to produce tall plants, and to result in plants that have lower yield and quality (ratio of flower to inflorescence). So, yes, you can make a plant grow taller by reducing light levels and, for your trouble, you will tend to get lower yield and reduced quality. No surprise - lower light levels will result in lower photosynthesis but, if you want a tall plant, keep turning down the light and see how things turn out

To that point, I've seen growers state that their intent of reducing light levels to get their plants to stretch. I wouldn't do that to a plant because the penalty of giving a plant reduced levels of light is demonstrable, repeatable, and significant.

Re. your assertion that "Light intensity control [sic] stretch more than spectrum." To paraphrase Dr. Bruce Bugbee, light color ("quality") impacts plant morphology while light quantity impacts yield. You can find lots of research that confirms his statement. In contrast, I haven't found any research that would support your assertion "Light intensity control [sic] stretch more than the spectrum."

In fact, I have voted with my wallet - I use a veg light for veg and a flower light for flower. Though there is no such thing as "an experiment of one", my plants have had the growth characteristics that I expected after reading the peer reviewed research (and the good Doctor B) - they have been compact with dimunitive internodal space and dense inflorescence in veg and yet, with one exception, they have to grow extremely tall with significant inflorescence when I swap out the veg light in favor of the flower light. Yield has been over 900gm/m2 in a few cases, despite thrips infestations for a few of those.

 

[Wastei]

No question - environmental factors and genetics are the big drivers — those are "givens".

Re. your assertion about "control stretch". "control" - I don't believe that we can "control" stretch or, for that matter, that we can "control" much of anything when it comes to dealing with living things, thus my use of words such as "tend to".

Light intensity will influence stretch, no question. We've all seen picture of gangly seedlings, right? In fact, I managed to kill a couple of sets of seedlings by, among other things, not providing enough light. They grew tall…until they died.

Research shows that reduced light levels tend to increase internodal space, to produce tall plants, and to result in plants that have lower yield and quality (ratio of flower to inflorescence). So, yes, you can make a plant grow taller by reducing light levels and, for your trouble, you will tend to get lower yield and reduced quality. No surprise - lower light levels will result in lower photosynthesis but, if you want a tall plant, keep turning down the light and see how things turn out

To that point, I've seen growers state that their intent of reducing light levels to get their plants to stretch. I wouldn't do that to a plant because the penalty of giving a plant reduced levels of light is demonstrable, repeatable, and significant.

Re. your assertion that "Light intensity control [sic] stretch more than spectrum." To paraphrase Dr. Bruce Bugbee, light color ("quality") impacts plant morphology while light quantity impacts yield. You can find lots of research that confirms his statement. In contrast, I haven't found any research that would support your assertion "Light intensity control [sic] stretch more than the spectrum."

In fact, I have voted with my wallet - I use a veg light for veg and a flower light for flower. Though there is no such thing as "an experiment of one", my plants have had the growth characteristics that I expected after reading the peer reviewed research (and the good Doctor B) - they have been compact with dimunitive internodal space and dense inflorescence in veg and yet, with one exception, they have to grow extremely tall with significant inflorescence when I swap out the veg light in favor of the flower light. Yield has been over 900gm/m2 in a few cases, despite thrips infestations for a few of those.

You're very contradicting in your reasoning, but that's ok. Why do think plants growing outdoors grow taller with bigger coverage? They have a complete spectrum if anything?

Reason is the DLI(daily light integral) isn't sufficient otherwise they would grow stouter like indoor grown plants because of the higher light intensity. Saying spectrum do more than cumulative PAR's for regulating stretch is laughable at best. All the best of luck to you in your endeavors!

 

[Delps8]

You're very contradicting in your reasoning, but that's ok.

My apologies if I've mixed anything up - I tend to write quickly. I'm not clear on what I've said that's contradictory. Your point re environment and genetics is absolutely spot on. My assertion re morphology being a function of light color and yield being a function of light quantity is what "the literature" states. If you have data or can cite research that differs, please cite your sources.

Why do think plants growing outdoors grow taller with bigger coverage? They have a complete spectrum if anything?

I'm not clear on the question. As I stated in my previous reply, plants that aren't receiving much light will grow significantly taller than a plant that is receiving more light (granted those are not well defined terms) and that a comes at a price - lower yield and lower quality. Research on that topic is easy to find.

Reason is the DLI(daily light integral) isn't sufficient otherwise they would grow stouter like indoor grown plants because of the higher light intensity.

Ah, got it. A rhetorical question and one that uses terms that aren't defined and are vague.

"Why do you think that plants grow taller (outdoors) with bigger coverage (yield?) ?" That's a very example of the traditional definition of "begging the question". It's also nothing that I've suggested so that's a twofer — you're begging the question using a straw man.

I think you're asserting that cannabis grows better outdoors than indoors. Over the long term, I don't think that's correct, and I think there are a lot of reason why that's not the case. Having said that, if you've got data on it, great. If not, it really flies in the face of a lot of things we know about agriculture but I won't argue those points, I'll allow you to prove you point (whatever is actually is) rather than trying to disprove something the definition of which is unclear. "Nailing jelly to a tree" and all that.

Saying spectrum do more than cumulative PAR's for regulating stretch is laughable at best.

"cumulative PAR's" - DLI?

"regulating stretch" - I don't use words like "regulate" but I suspect that English is not your first language so I'll go with the gist of what you're writing rather than the specifics.

I'm not arguing that spectrum has a greater influence than DLI. I've described how different factors influence plant morphology, plant yield, crop quality, etc.

I didn't compare the impact of the two and I haven't used the word "regulate" nor any language that could be reasonably construed to imply that as being my meaning. If you think that's what I'm writing, it's not because of what I've written but perhaps a combination of English as a second language and/or reading comprehension and/or some other factors.

All the best of luck to you in your endeavors!

And to you, as well!

 

[safeman]

No question - environmental factors and genetics are the big drivers — those are "givens".

Re. your assertion about "control stretch". "control" - I don't believe that we can "control" stretch or, for that matter, that we can "control" much of anything when it comes to dealing with living things, thus my use of words such as "tend to".

Light intensity will influence stretch, no question. We've all seen picture of gangly seedlings, right? In fact, I managed to kill a couple of sets of seedlings by, among other things, not providing enough light. They grew tall…until they died.

Research shows that reduced light levels tend to increase internodal space, to produce tall plants, and to result in plants that have lower yield and quality (ratio of flower to inflorescence). So, yes, you can make a plant grow taller by reducing light levels and, for your trouble, you will tend to get lower yield and reduced quality. No surprise - lower light levels will result in lower photosynthesis but, if you want a tall plant, keep turning down the light and see how things turn out

To that point, I've seen growers state that their intent of reducing light levels to get their plants to stretch. I wouldn't do that to a plant because the penalty of giving a plant reduced levels of light is demonstrable, repeatable, and significant.

Re. your assertion that "Light intensity control [sic] stretch more than spectrum." To paraphrase Dr. Bruce Bugbee, light color ("quality") impacts plant morphology while light quantity impacts yield. You can find lots of research that confirms his statement. In contrast, I haven't found any research that would support your assertion "Light intensity control [sic] stretch more than the spectrum."

In fact, I have voted with my wallet - I use a veg light for veg and a flower light for flower. Though there is no such thing as "an experiment of one", my plants have had the growth characteristics that I expected after reading the peer reviewed research (and the good Doctor B) - they have been compact with dimunitive internodal space and dense inflorescence in veg and yet, with one exception, they have to grow extremely tall with significant inflorescence when I swap out the veg light in favor of the flower light. Yield has been over 900gm/m2 in a few cases, despite thrips infestations for a few of those.

side lighting can be used to control height BUT increases lateral branching and bud sites

 

[Sativa1970]

I experimented with the same LED light setup using side by side comparison with 8 hydroponic clones. Genetics and light intensity were identical for every plant. Blue light 6500K promotes dense vegetative growth because it replicates the summer spectrum. Cutting the light time to 12/12 under 6500k will reduce the stretch. After the stretch, when you have two full length pistols per bud sight, you can switch the spectrum to the 2000K-3000K range. The red end replicates the natural fall spectrum of light and promotes bud growth.

Using the same 9 light configuration, I found keeping one contradictory light had the best effects. eight 6500K and one 2700K during veg gave the most lateral branching with close nodes. Flowering under eight 2700K and one 6500K gave the highest yield.

Is switching spectrum necessary? No. Blue gives more bud sights and red gives bigger buds. The worst case would be having to support a tall, top heavy plant with many small buds on light deprived lower nodes. My yield had a range of 15% comparing controlled mixed spectrum to just 2700K start to finish. There was just a 10% range when I swapped one odd light into each schedule. Heavy/pure red was lowest, heavy/pure blue was middle and heavy blue veg with heavy red flower was the highest yield.

 

[Delps8]

I experimented with the same LED light setup using side by side comparison with 8 hydroponic clones. Genetics and light intensity were identical for every plant. Blue light 6500K promotes dense vegetative growth because it replicates the summer spectrum. Cutting the light time to 12/12 under 6500k will reduce the stretch. After the stretch, when you have two full length pistols per bud sight, you can switch the spectrum to the 2000K-3000K range. The red end replicates the natural fall spectrum of light and promotes bud growth.

Using the same 9 light configuration, I found keeping one contradictory light had the best effects. eight 6500K and one 2700K during veg gave the most lateral branching with close nodes. Flowering under eight 2700K and one 6500K gave the highest yield.

Is switching spectrum necessary? No. Blue gives more bud sights and red gives bigger buds. The worst case would be having to support a tall, top heavy plant with many small buds on light deprived lower nodes. My yield had a range of 15% comparing controlled mixed spectrum to just 2700K start to finish. There was just a 10% range when I swapped one odd light into each schedule. Heavy/pure red was lowest, heavy/pure blue was middle and heavy blue veg with heavy red flower was the highest yield.

Good info and hats off to you for going down the rabbit hole!

"8 hydroponic clones." - that's the ticket. Any experimentation that doesn't use clones is invalid.

The results you've seen are right in line with what researchers have demonstrated and with how cannabis growers have been growing their (indoor) crops for decades — blue in veg, red in flower.

"light deprived lower nodes" - I believe that bud development is a function of light falling on the plant not a function of the amount of light falling on the bud site. One author, who is just plain coco for cannabis, states that it does not make a difference. I'm in that camp because, while flower sites can photosynthesize, that capability is greatly reduced compared to the photosynthetic output of a leaf receiving the same amount of light. To that end, I would argue that leaf tucking is another example of something that a grower does that is of, at best, zero value to the plant and, though the impact might be small, does reduce yield when all is said and done.

A factor that is significant is what I refer to as "the blue photon penalty". Bugbee has produced a paper that discusses the reduction in yield in cannabis when the crop is exposed to different levels of blue light in flower. As the percentage of blue light increased from 4% to 20%, crop yield was reduced. At 20%, yield was down something like 10%. I can't find the paper at the moment but will be happy to post if…

[time passes]
Gotta love Google - here's the paper that describes reduced yields as the % of blue increased:
"Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids"


Other papers that might be of interest:
"The E!ect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L"
"Light matters: Effect of light spectra on cannabinoid profile and plant development of medical cannabis"

Per an earlier posting, I've voted with my wallet. Like earlier generations of growers, I use a veg light and a flower light. If you check my grow journals, the impact of the blue light is especially noticeable.

The last item I'll post is the text of the transcript, with very little cleanup, from a Bugbee video (bright lad that I am, I captured the text but didn't capture the title…) and I think it's "Cannabis Grow Lighting Myths and FAQs with Dr. Bruce Bugbee" but all of his videos are worth watching.

From the video:

"
I'm Bruce Bugbee, president of Apogee Instruments and also professor of Crop Physiology at Utah State University. In this video today, we're going to talk about the basics of lighting as it applies to cannabis.
This is profoundly misunderstood. The database is filled with a lot of myths that we have studied over the past year. And so we're calling this Cannabis.
This first part of the series is just focused on lighting, which is one of the key parameters. Apogee has spent decades refining instruments to quantify light, the types of light, the intensities of light. Those, in my experience, those instruments are underutilized to help refine the cultivation of cannabis. And part of it is just because people don't know how to interpret the data and how to make the measurements.
As a company, Apogee instruments motto is “we help people make measurements.” And part of that is our ongoing education to help people interpret the data that they get, make sure the measurements are high quality, and that's what this video is about. With a focus on cannabis.
We're not focused on all the other crops like lettuce that's grown under electric lights. Just cannabis.
Utah State University is one of the few agricultural universities that now has a license to study hemp at the University. And when I say cannabis, I mean both hemp and marijuana. Our license isn't for marijuana. It's only for hemp. But the studies apply to both types of cannabis. So,I’m going to talk about cannabis in this video. So, it’s pretty hard to underemphasize the importance of light when you’re growing a crop. And this next slide, which I've used many times in many talks, really focuses on that.
Here's the nine cardinal parameters. If you were to take a university class, you would be reviewing each of these parameters. Four of the parameters are in the foliar environment temperature, humidity, air velocity or wind, and carbon dioxide. Four in the root zone environment we have temperature down there, amount of water, nutrients, and oxygen. We teach whole classes on each one of these parameters, and we may do a series on cannabis on each one of these parameters.
But today we're going to focus on the one that is absolutely critical, and that's light.
And we put this right at the top… let's see if this… see if we can get this back… and then let's go to pen tool… there. There we go. Light… and let's see if we can get that yellow to emphasize the light. Light is coming in from all directions on this plant and it drives the optimum levels of everything else. If you turn the light up, you have to give the plants more water because it drives the flux of water through the plant… I should have drawn this in yellow or in blue for water flux in the plants. You turn the light up, you need more nutrients, you need more oxygen in the root zone. It drives everything.
So often we get questions from people saying “My light must be too high. My plants are turning yellow or purple or some color.” What it really is an imbalance between the amount of light and the optimum levels of all these things. It's like a racecar. Cannabis is a race car that can go incredibly fast. If everything is optimum, you can give cannabis exceptionally high levels of light. And I'm going to go into how we measure that and quantify it. If all of these other parameters are also optimum.
If you give it more light and you don't have the right nutrient balance, or the right water, or you don't have elevated CO₂, you're going to have problems with the plant. But it's not fundamentally caused by the light. It's caused by inadequate levels of the other parameters.
Be like a racecar. I'm saying you got a giant engine, you're out at the Utah Bonneville Salt Flats, you're going 700 miles an hour, and the tires blow on the car. And you say ah dang it the engine was too big. No the engine wasn't too big! You didn't have the right tires for that big of an engine. That's the analogy of how important it is to get the lighting right.
So let's start with how we even measure light. So many people say how much light do I need? And they'll say oh keep your plants about 30 centimeters, about a foot, away from the lights.
Let me show you how bad that is as a measurement of light. And in order to do this, we have set up here in the Apogee studio two lights of different wattages. And I'm going to do a demonstration now to show you how important that is. So I’ve got to step over here and plug the light in. Wheel this in… now here's two lights. Let's get them right in the screen. Two different wattages of lights. They’re both LEDs. I could turn them toward the screen, it'd be incredibly good. Now we've set this up so we can measure… if I can do this… right there. We can measure the intensity of the light from these. Here's the number right here. We’ll get into what this means in just a second. But it's 27 µmols of photons right now. That's the light from the studio. If I put this over here… 7 µmols. Now the is plenty of light for humans to work in. A well-lit office has 7 µmols. That is way too low to grow cannabis. You can tell these are a little brighter.
What if we said it's µmols here, how bright is it over here? Oh it might be 50 µmols over here. Let's take a look. We're going to go under this light. Now let's see if we can do this. Can you see the screen? I think you can. I'm going to hold this right here about a foot away. You see the number we're getting? 300 µmols. A well-lit office is 7 to 10 µmols? And this is 300 µmols? And it looks a little brighter, but it doesn't look 20 or 30 times as bright. It's much, much brighter. That's a foot away.
What if that was our measure for cannabis, and we say here's another light let's go a foot away? Now we put it under this light. Look at this. I got to get it centered. 3000 µmols. Depends on exactly how far away, but we're approaching 3000 µmols. If I go a hair closer there it is, 3000 µmols under this light. And we go under this light. Same distance. We're down around 300 µmols. That is almost an order of magnitude more photons under one light than the other, and the only difference is the input wattage. This is a low input wattage. This is a high input wattage. It's not color of light, it’s input wattage.
So I hope you can see that just saying put your plants some distance away from the lights is a very inadequate way to precisely grow cannabis. You've got to have a meter. Our eyes are one of the worst meters for plants. Our pupils contract to reduce the amount of light getting to our retina in bright light. So we're a terrible light meter in terms of intuitive estimating of light. We really need an instrument to measure it. So this is a demo of the fact that you can't do that.
Now remember that number. Let's take 300 µmols, and how much cannabis could we grow with that? Now I'm going to stop here and take these out of the way so we can interpret the data… Now we're back with a white screen that we can take a look at what we just measured. So, first of all, let’s draw what we call a light response curve for plants in general, and then we'll draw a light response curve for cannabis. So as students in my classes know over the years I draw a lot of XY plots to take an input variable here and look at response. So what we're going to put over here is Pn. This stands for net photosynthesis. And over here we're going to put PPFD. Photosynthetic Photon Flux Density. That's what we just measured with that Apogee meter. This graph starts at zero here, and zero here. If this was Introduction to Plant Science and we asked this question, everyone would say well of course light, or photon flux, drives photosynthesis. So that curve is going to look like that. And if this was Plant Science 101, we would count that as a correct answer. But if it's a more advanced class, we know that the higher the light this doesn't keep going up forever.
Plants can't keep using all those photons. So a more correct answer looks like this. And we can even erase this top incorrect answer and go back to this. There's a more correct answer because it levels off at high light. Now notice I didn't put any tick marks on here yet because we just measured 300 µmols and almost 3000 µmols out of that other light. But there's one more thing that makes this curve even more accurate, and I'll put that in blue. If you take a plant and put it in the dark, it gradually respires and dies. You can't keep it in the dark for weeks or months.
So this line doesn't go through zero right there. In the dark, we get a negative number. The plant is shrinking. It's dying. And we turn on the lights, and it goes like this. So there's some point right here where there's just enough light to keep the plant alive. This, by the way, is called the light compensation point when there's enough light to get it to zero.
Now let's put some tick marks on this axis. Photosynthesis… oh let's make this go to 60 up here. Now the units for this are µmols per m² of leaf per second of time. This is how fast it's fixing carbon and dry weight. Now let's put some tick marks on this. If we go up to here, what's full sunlight? If we went outside in the summer at noon what would we get for high light? We would get 2000. That's an important reference point, 2000. These units are µmols of photons per m² per second. And this over here could be just yield of the plants, but these are the units that we’re measuring to get the light. Now if that's 2000, 1000 is right here, and 500 is right here. On… the way I drew this graph… Wow.
We have to have 400 µmols just to get above zero. Now this only happens in a dense crop. But let me see if I can erase this… erase these lines… and I'm going to draw two lines on here… let's go back to green… We're going to fill this back in. Here's our green. There's 500. Now let's go to blue. If we did these measurements for lettuce. Lettuce is a widely grown crop. Very widely studied. It is also a low light plant. Lettuce grows fine in much lower light than cannabis. So if we draw a curve for lettuce, first of all it starts here. It goes up, and at about 500 µmols lettuce is done. And it might even go down out here with really high light. This is lettuce. There.
Now what if we put cannabis on here? Cannabis is life in the fast lane. It takes a lot of light. You can grow cannabis much faster. We're going to put cannabis in red. First of all, it doesn't really have a low gear. It has a high respiration rate. Cannabis looks something like this. Look at this curve! Look at that curve! Wow! This is cannabis. It keeps going up until µmols.
So cannabis is a very high light crop. You can give it a lot of light, but you've got to have all the other inputs optimized. For sure you need elevated CO₂ for cannabis. And ample water. It's usually automated watering. It's a balanced nutrient solution. That's a topic of a whole other talk. But our data don't indicate cannabis needs unusual nutrients, but it needs a balanced nutrients. And not too much. Usually there's toxicities from too much nutrients. And if you have this high light, and the water is going through the plant that fast, you have to be careful not to have too much nutrients. But the point is, look at cannabis. Corn is like this, too. Corn is a very high light field crop. So now we get a meter to measure this. And if the leaves are green, we're using the photons efficiently, and we have high photosynthetic rates. Let's take a look on this now. A closer look at this unit down here. This is generally a widely used unit, but it's not universal. And let's take a look at this. And I can do that on the next screen. Now let's go back to green.
Multiple acronyms are used to measure light. And the most common one is PAR, and the P always stands for Photosynthetically Active Radiation. Let's go to a slightly smaller… line size… That's a pretty fat line. All right. Now we've got a PAR. This is a generic term for all photosynthetically active radiation. But it could mean watts per meter squared, and that's confusing. So a more rigorous term is PPFD. That stands for Photosynthetic Photon Flux Density. And this always means that number from the previous one, moles of photons. And you think of photons as like tiny little marbles falling out of the sky to fill a box. They can be colored marbles, but they're all marbles. We're measuring this flux of photons coming into the plant. Per meter squared per unit area of a surface area per unit time, and we always use per second. That's the unit for PPFD.
Now this is a big number. A mole. And so it's really a µmol. Ten to the minus six moles per second. And this number ranges, we just showed that in the other slide, zero up to 2000 µmols. It's a huge range. Remember those lights we measured? One was 300 µmols. One was over 3000 µmols because it was a high wattage light, and we're real close to it. These are the keys. Now we'll come back to this later but PPFD is the number that we’re after here for light.
Now let's go to another screen. We're going to take our same screen here. And we had PPFD. Zero. Let's go all the way to 2000. This is very bright light. We rarely get this high of light under electric lights, but we could. And over here we're just going to put yield. Not photosynthesis anymore because photosynthesis leads to yield. How much light is necessary?
What's really key about this is not the instantaneous light. We're going to put our graph on here again. Something like this. The exact shape varies with different cultivars, but it doesn't vary very much. It turns out it's not exactly the PPFD, it is the DLI. Daily Light Integral. So as this implies an integral, it means we add up all of the photons. This is per second, and every second we accumulate them. What if this was rainfall? PPFD would tell us the rate. How fast is it raining per second? But usually what we want to know is how much did it rain yesterday? The total amount of rain. And that's the daily light integral called DLI.
Let me show you how to convert. Once you see this you'll know it forever. Let's put 1000 in here. We're going to convert from PPFD to DLI. 1000 µmols per m² per second. Now we want to know per day. Well there's 3600 seconds per hour. So this is 3.6. Now notice this is 1000, and that's 3000, and when you multiply these together the thousands cancel. And this is 3.6 moles. Now no micro anymore because we just multiplied two big numbers together. 3.6 moles per m². Now this is per hour. We're still not there. That's per hour.
For cannabis, when it's in the flowering stage, we would typically give it 12 hours per day. Multiply these two together 3.6 and 12. I know this because I've done it so many times. That comes out to be 43.2 moles per m² per day. And that number right there this is so important we'll put it in red… is the DLI. If you had 1000 µmols per second continuously for 12 hours, you get 43 a day. This is high light, but cannabis responds to this. In our studies, we can push them even higher than this. We've never gone to µmols, but we've gone close to it. We've gone to 1800 µmols up to where we've gotten this number close to 60.
Outside in the summer under full sunlight on sunny days DLI can get to 60 moles per m² per day. That's an incredible DLI. Cannabis grows outside in full sunlight, and it loves it. It responds to it. So you can run the DLI up extremely high. Now how low can you go? Well here would be 500 µmols. And you see the point here. There's some diminishing returns. The line still goes up, but it's curving over. So 2000 µmols doesn't give us twice the yield of 1000 µmols, but it's still higher. So we keep raising this… here would be 500 µmols right here. But the point is, you’ve got to know this input to have reproducible studies, and to get it you need to measure it.
Let's take a second to review some of the instruments that Apogee uses. All of them are a little sensor. Here the quantum sensor is blue. That's the one we used a minute ago to measure these. This one plugs right in to a laptop. Here's a USB cable, and you can plug right in. You’ve got to remember to take the cap off of these. The optics here are really rugged, but we still ship them with the cap to keep them perfect. Plug this right into a laptop just like I did, and you'll see the numbers on the screen. If you want something more portable, here is a handheld meter with a separate sensor. These also come with the sensor right in it. That's another option. And one of the options that's big and catching on fast is Bluetooth. This is a Bluetooth module. It’s like a data logger. It measures and stores the data, and then you just transmit this data right to your cell phone. So this is a powerful option and there's plenty of graphics associated with this for measuring the light. All of them go to this sensor. If you jump up another level, this gold cube is a spectroradiometer, which gives you all the ratios of colors. But these other instruments are down in a few hundred dollars. This instrument is over two thousand dollars. It's much more sophisticated, but this is what researchers use to get everything exactly right in all of these.
So we get questions all the time on issues relating to light. And I just addressed one of them daily light integral (DLI). We can push daily light integral easily to 30, to 40, to 50. And the yield keeps going up if everything's optimal.
Let's… in terms of how much light it tolerates, this is true even for young seedlings. We once took… one of our research projects right now is to push the rooting of cuttings of cannabis with very high light. This just sounds amazing. But for years and years we keep plants in really low light with cuttings because they didn't have any roots. We're finding if we can keep them watered we can even push a cutting with very high light levels. And certainly a young plant. You can push them hard with high light. Again as long as the other inputs are not limiting growth.
What about darkness? Let's go to another screen. Another topic. We'll put this one in blue. Now we're going to do hours per day. It's a different graph. Hours. Here's noon. Here's midnight. And here's midnight. And of course here's PPFD. We have no evidence that suddenly turning on the light shocks the plants.
They can get out of bed and go right to work. They don't need to ramp up slowly. But let's say we turn on the lights at 600 AM. We run them high until 1000 PM. If we ran… this would be 16 hours of light.
Now if we're in flowering phase… let's go back to red… if we're in flowering phase we might run them from AM to 8 PM like this. And this is a 12-hour photo period.
So there's really just two photo periods for cannabis. A 16, and even an 18 hour, photo period for veg. And in fact some of our data indicates this could even be 24 hours per veg. Just get the plants growing with a high DLI. And then when we want them to flower, we switch to 12.
Now here's the question. So this is all fine. What about right here? This number right here is darkness. How dark does it have to be for cannabis at night? This is something we're actively studying right now in my laboratory at the University. There are some literature reports that indicate that cannabis is exquisitely sensitive to trace amounts of light pollution. Just a little bit of light will cause problems with cannabis.
We have a wealth of literature on poinsettias. They're one of our most sensitive crops to light pollution. Without excellent darkness, those top leaves of cannabis don't turn red. They're called Brax. They don't turn red.
Is cannabis more sensitive than poinsettias? We don't know yet, but we know it needs to be very dark. We call this reagent grade darkness, and it's like somebody sleeping. Some people are bothered by a tiny light sleep and other people it doesn’t matter. But we think cannabis is quite sensitive to this.
For this reason, Apogee has made an extended range quantum sensor that’s calibrated to rigorously measure light pollution. Now remember we were doing µmols per m² per second and were getting numbers in the hundreds? This particular sensor can measure 0.01 µmols per meter m² per second. It's a unique meter that can detect trace amounts of light. And it helps you determine whether it's absolutely dark. It's an extended range sensor. It even picks up the photons from security cameras, which there's possibilities for those to affect cannabis. That's a topic for another video. So extended range quantum sensor for light pollution studies.
This is getting down around full moonlight, and we know that full moonlight doesn't affect cannabis or any other plants. But it might not take much more of that to be a big deal.
Let's talk about cultivars, differences. Many people say geez this happened in one, and something else happened in another. We have an emerging number of different cultivars for cannabis. As you probably know if you're watching this video, I won't write them up here, they're all cannabis sativa. And underneath that we have indica and sativa. So it's cannabis sativa sativa. Our studies at the University indicate there's definitely differences in those. Leaf width. Leaf size. But in terms of response to all these parameters I'm talking about, there's not a significant difference between the types.
You can push both types of cannabis with high light. They both love high light. They both evolved out in the field. The differences can be in yield. They can be in photo period sensitivity. Some cultivars of cannabis we think can take 13 hours of light over here. Some might be able to take 14. But in terms of pushing them with high light, they're all similar.
Let's think about some of the other cultivars. One of them… some of the other questions we get… one of them is what about light quality and the synthesis of what we call cannabinoid compounds. That's THC, CBD, CBN, CBG, all the different cannabinoid combos. Then in another class of compounds there's terpenes. What about light quality? And it could be a whole other talk, and I have given other talks on this. They’re in other videos on the Apogee website. So if you're interested in this, look for other videos on this.
Here's the take home message. We don't have evidence that changing the colors of light makes a significant difference on cannabinoid synthesis. Let me say that again this is an amazing statement. Light quality does not have a huge effect on the ratios of cannabinoids. This is in spite of many people claiming it does. Our data in general don't support that there's big effects. I didn't say there was none. We just don't see big effects. We're still actively studying that, and stay tuned because we're looking at all kinds of different ratios.
Now let me conclude on one part of light that is enormously important. And we're going to go to a new screen. Last slide… I don't like to draw those… I’m going to draw the axes in blue. This is 400 to 700 nm. And this is the wavelength of light. If you're going to get a degree, an honorary degree, in cannabis science you got to memorize these two numbers... We use lambda to express this. And the unit here is nanometers. So this is colors of light. This is what you would use this spectroradiometer to measure.
So I think most people know, but let's review this. Right here if we do 500 and 600 nm. This area right here, 400 to 500 nm, is blue. It looks blue to the human eye, and we call that range blue. Now we go to 500 to 600 nm, and that range is green. And now we go to 600 to 700 nm, and that range is red. For many of you this is review, but it's important to have the basics. Alright, photosynthetic radiation stops right here. Our historic and classic definition of this is 400 to 700 nm. Period. If there's a photon at 701 nm, we don't count it. If it's at 399 nm, we don't count it.
Is that right? Really? The big chop? No, they don't chop off like that. We've known that for years. This is just a useful approximation of photosynthetic radiation. But, now that we have LEDs that we can fine-tune all these wavelengths, we are reexamining what we have used for half a century. And there's two specific wavelengths that are huge. I think I'm still on red. Right here… no let's go to red… right here this is far-red… if I can get that up here… FR. Rar-red. Now we're going to look at far-red. And that is out here to 750 nm. Right here. Our eyes have trouble seeing this. It's just like a dull glow of a red burner on a stove or electric burner. You couldn't read a book by this. But it has powerful effects on plants, and it adds 750 nm.
Our data indicate that these photons cause photosynthesis. They certainly cause changes in plant shape. We can make plants branch more. We usually make them taller with more far-red. But these photons are critical. Because of that… well before I get to that… let's talk about the other end down here.
Blue. These photons, especially 350-300 nm. This of course is all ultraviolet. Our eyes don't see this. Historically electric lights we try to get rid of this. We try to get rid of this. They're not useful for human lighting, but they have powerful effects on plants. Especially this region at 350 nm right here of UV.
Our data indicate these photons cause photosynthesis as well. So I think we're going to see an emerging change in the definition of photosynthetic radiation maybe from 350 to 750 nm. We'll see. Multiple laboratories are studying this. Because of this, Apogee has come out with what we call an extended range quantum sensor. And that is a sensor that measures everything from 350 nm way out here. It picks up… here’s security cameras, they have a big peak out here that's centered around 830 nm. That extended range picks up all these photons. And for some kinds of lights these photons are critical. You want to know what they are. Even though the classic quantum sensor doesn't include them, the Apogee extended range quantum sensor does include them.
So UV photons have the potential to reduce disease in plants. They have the potential to trigger cannabinoid synthesis in plants. So we're putting a lot of energy into studying the potential use of UV photons in plants. Again stay tuned.
And one more thing, we get a lot of questions about optimum ratios of colors for both growth and photosynthesis and for cannabinoids.
And let me fall back on the one principle here that has guided us, and that's the percent blue photons. And let's do this in a different screen… here's my marker… for years, before we had LEDs, people said you want to do metal halide for veg before they became reproductive. And you would typically be giving oh maybe even an 18 hour photo period during that time. During veg. Then the prevailing wisdom was the switch to high pressure sodium during the reproductive phase. And that's flowering.
Now many people said oh god that's all a myth… Not exactly. Metal halide has 30% blue photons… this is having trouble… 30% blue. The higher the blue photons the more compact the plant. So metal halide was very effective at making nice compact plants.
High pressure sodium, on the other hand, only has about 4% blue photons. Sunlight has about 30% blue. They switch to high pressure sodium because it's a much more efficient light, and you can get bright intensity. But it had low blue. But the blue didn't matter so much during flowering because the flowers kept the plants short. So there was a reason to go with a high blue light during veg and then a very efficient light during flowering.
And we've seen that in cannabis. It's a ratio of blue photons for plant height and then the efficiency of the light after that. So what we like to see are very efficient lights. The ratios of colors are less critical. We do like to see lights with enough green photons so you can diagnose plant disorders. Those green photons usually come from white LEDs. It's important to look for microscopic insects. Subtle disorders. You’ve got to be able to see the plants to do that. But after that, it’s just the efficiency of the light.
If you search for design light consortium on the internet, the acronym is DLC. That is an independent company that has now been listing many lights from many manufacturers and their test results from independent test laboratories for the efficiency of the light. The unit for light efficiency… and not a lot of room… is… put this over here… is µmols of photons out per Joule of electricity in. The really efficient lights, LEDs, are now getting up to 2.5 µmols per Joule and even higher than that. They're incredibly efficient. Ten years ago, we were half of that efficiency for lights. But it's critical to get an efficient light and a broad spectrum light so you got enough colors to see the plants. Thanks for listening."

 

[Sativa1970]

Bugbee was one of the two prophesiers that sent me down that rabbits hole. Unfortunately my brain and google won't remind what the other prophesier name is. Three weeks from now it will randomly come to me. That lecture was on how equatorial plants all bloom at the same time around the world considering there is no real change in day length. The light spectrum dose shift with equatorial seasons.

There is no accurate spectral analysis for standard home LEDs. My theory as to why mixing the light helped was that it rounded out the spectrum. If you are trying to make a high efficiency home light at a given Kelvin, any light outside that lights target frequency is wasted power. Plants use all spectrums, at all times, but the percentage of each spectrum needed varies. Summer daylight is predominantly 6500K and fall is predominantly 2700K but the full spectrum is there year round. It's just to what percentage is outside the predominant Kelvin.

The low Jmol photons from those LEDs disperse and degrade exponentially over just a vary short distance. Any leaves attached to lower nodes will not receive as much light energy. Without that energy the bud sight will not develop to the same potential. I believe I ran those lights at 6 inches and there was a noticeable production drop on buds at 12 inches from the light. I may have those exact distances wrong because it was a few years ago. Lowering the stretch means closer top nodes. Closer nodes means more bud sights in that optimal light zone.

 

[Mayne]

SideLighting, and DIFFUSION makes the big difference outside. Not to mention use of larger pots, which allow for large plants because larger BASE WIDTH. TREES like to grow roots horizontal to stabilize itself. Bigger trunk thickness, bigger base, Bigger branching, MORE branching,because the plant knows it can support itself.

Outside, every angle is hit with light, indoors, most often, its just the tops.

Light diffusion, is also a factor, thru clouds and haze, breaks the light spectrum almost evenly by the time it hits your plant, where as LED, they are like lasers.

As far as stretch, its either doable thru Temp change at night, ( cold causes stretch, ) or could be from red spectrum use.

 

[Sativa1970]

SideLighting, and DIFFUSION makes the big difference outside. Not to mention use of larger pots, which allow for large plants because larger BASE WIDTH. TREES like to grow roots horizontal to stabilize itself. Bigger trunk thickness, bigger base, Bigger branching, MORE branching,because the plant knows it can support itself.

Outside, every angle is hit with light, indoors, most often, its just the tops.

Light diffusion, is also a factor, thru clouds and haze, breaks the light spectrum almost evenly by the time it hits your plant, where as LED, they are like lasers.

As far as stretch, its either doable thru Temp change at night, ( cold causes stretch, ) or could be from red spectrum use.

Side lighting is effective if you can get enough photons to the plant. I use 300wats on top light and 300 wats side light per plant. The weak LEDs (no offense intended) from OP or florescent with an effective range of 6 inches to 1 foot is not really worth the cost and time spent adjusting it. Too far away and it has little effect. Too close and you burn the plant.

Passing light through a defuser or filter will not change the spectrum, just the amount of light energy reaching the plant. Red and blue filters stop all but that color and white just stops green. The reason why indoor growers only focus on the top without diffusers is for two reasons. Focus the energy on cola production and even high quality lights have difficulty comparing to the sun. If you could get all 45wats of an LED light to hit only a 1 foot square, 1 foot away from the cob, without bouncing off any reflectors, you would be close to the suns energy on a sunny day. Turn on a grow light outside on a sunny day. See how close you have to get before you erase the fixtures shadow from the sun. Now try it with an LED in a clip light.

Red spectrum, lacking blue promotes elongated growth. The blue spectrum, lacking red keeps it in check by promoting slow stocky growth. When you flip to 12/12 and the plant already wants to stretch give it dominantly blue to reduce elongation. After the stretch go dominantly red to promote bud elongation. It's the lack of red or blue, not the use of, that causes the effect.

 

[safeman]

I experimented with the same LED light setup using side by side comparison with 8 hydroponic clones. Genetics and light intensity were identical for every plant. Blue light 6500K promotes dense vegetative growth because it replicates the summer spectrum. Cutting the light time to 12/12 under 6500k will reduce the stretch. After the stretch, when you have two full length pistols per bud sight, you can switch the spectrum to the 2000K-3000K range. The red end replicates the natural fall spectrum of light and promotes bud growth.

Using the same 9 light configuration, I found keeping one contradictory light had the best effects. eight 6500K and one 2700K during veg gave the most lateral branching with close nodes. Flowering under eight 2700K and one 6500K gave the highest yield.

Is switching spectrum necessary? No. Blue gives more bud sights and red gives bigger buds. The worst case would be having to support a tall, top heavy plant with many small buds on light deprived lower nodes. My yield had a range of 15% comparing controlled mixed spectrum to just 2700K start to finish. There was just a 10% range when I swapped one odd light into each schedule. Heavy/pure red was lowest, heavy/pure blue was middle and heavy blue veg with heavy red flower was the highest yield.

Thanks for the very good information - seems like not many growers do this -sidelighting.. Now check this out- have seen florecent lighting put /lay on top of growing container -saying that this will increase yields ???

 

[bluter]

basic kelvin for flower is 2700 - 3500. basic kelvin for veg is 3500 - 4500. led light specific.

outside of either end is extreme on a led grow light. some mfgrs add in ir which is in the extreme red and which most plants use very little of.

 

[Mayne]

Side lighting is effective if you can get enough photons to the plant. I use 300wats on top light and 300 wats side light per plant. The weak LEDs (no offense intended) from OP or florescent with an effective range of 6 inches to 1 foot is not really worth the cost and time spent adjusting it. Too far away and it has little effect. Too close and you burn the plant.

Passing light through a defuser or filter will not change the spectrum, just the amount of light energy reaching the plant. Red and blue filters stop all but that color and white just stops green. The reason why indoor growers only focus on the top without diffusers is for two reasons. Focus the energy on cola production and even high quality lights have difficulty comparing to the sun. If you could get all 45wats of an LED light to hit only a 1 foot square, 1 foot away from the cob, without bouncing off any reflectors, you would be close to the suns energy on a sunny day. Turn on a grow light outside on a sunny day. See how close you have to get before you erase the fixtures shadow from the sun. Now try it with an LED in a clip light.

Red spectrum, lacking blue promotes elongated growth. The blue spectrum, lacking red keeps it in check by promoting slow stocky growth. When you flip to 12/12 and the plant already wants to stretch give it dominantly blue to reduce elongation. After the stretch go dominantly red to promote bud elongation. It's the lack of red or blue, not the use of, that causes the effect.

hummmm,

 

[Sativa1970]

Thanks for the very good information - seems like not many growers do this -sidelighting.. Now check this out- have seen florecent lighting put /lay on top of growing container -saying that this will increase yields ???

Any part of the plant that is green contains chlorophyll. All chlorophyll is capable of converting light into simple sugars, but only at the rate they can gas exchange through the cell walls. Stems are minimally porous but leaves are cemeterial and equally porous on all sides. So in theory, you can light any/all sides of a leaf. Up lighting will help compensate for any leaves being shaded from above. The effectiveness of doing this is first based on the light used. Minimal lighting will have minimal effect. An 18" florescent bulb under a 6 foot tall plant won't do much. Same light under a 2' plant could help. An actual grow light would be the best results but is it worth the electricity and resources vs placing that light over another plant. The other issue with underlighting is the gas exchange. O2 is lighter than air so it will accumulate under leaves blocking CO2. You must have good air flowing through the plant to promote the efficient gas exchange.

So if you have the resources and the desire or need to optimize one plant, yes it can work.

 

[Mayne]

First off, Sativa, Im not arguing with you. This is nothing more then grower banter.

from my findings, you can literally hit a plant with 2000 par LED light without burn if its diffused, and of course cooled. You would absolutely see droop if DLI is maximized, 60+ DLI, which as Dr. Bugsy said, the plant can take from seedling to harvest. Polycarbonate, does infact change spectrum DIRECTION, in a mixed fashion, same as a white wall is better then a reflective surface. even as Dr. Buggy said, PHOTON FOCUS, can be detrimental to the plants, much as literally 95% of LED lights do exact. They are FOCUSED or Direct, like lasers, like i said in my post above. Just like alot of LEDs are short of Green waves, with an addition of a polycabonate diffuser, the green waves are meshed. a Polycarbonate also allows reds to be meshed better, and reduces the UV to almost zero, which again, is beneficial to plants.

I personally find that indoor growers, do things for reason to reduce a plant that is meant to be 10 ft tall, to a plant that is 10% of that, lol. and for evident reason.

The addition of Blue waves, keeps the plant miniature in veg. Reducing the blue, would produce a taller, more rebus plant in the long run. I think after the first 3 weeks, blue should be reduced from the spectrum. and the last 3 weeks should be increased, and decrease Reds, till chop. The increase in Blues, will make for a harder, denser nugs. I personally, would enjoy elongation prior to flip. Open those sights up. Of course you need the room to accomidate, lol. Which again, in turn, helps with light penetration.

Also, UV should be givin in Clumps, and not continuous. I think a big mess up in the LED industry, is the addition of UV, but a stand a lone UV, giving in intervals, is much much much more beneficial.