Episode 151: Light, Spectrum, and Plant Signals — A Practical Guide with Dr. David Hawley part 1

Welcome to the Cannabis Cultivation and Science Podcast. I'm your host Tad Hussey of Kiss Organics. This is the podcast where we discuss the cutting edge of growing from a science based perspective and and drawn top experts from around the industry to share their wisdom and knowledge. Some quick updates before starting the podcast it's been a little while since my last podcast due to our hosting the first Cannabis Cultivation and Science conference in September at Collective Elevation in Bozeman, Montana. There were some amazing growers, researchers and experts I got to connect and personally network with and for our first conference I felt like it went as well as it possibly could have and I'm excited to plan for the potential of hosting it again next year. We have not officially confirmed for 2026, but the unofficial dates would be the last weekend in August of 2026. If you want to mark your calendar and plan ahead, some other news is we've added a bunch of new IPM solutions on our website. We are official distributors of Bioworks now, meaning we can sell epashield, Sufoil, X Root Shield Principle, their new Bavaria product, Cease, Millstop and everything else they offer. I have direct access to their pathology and science team and can put facilities directly in touch if it's helpful. In addition, we also carry Actinovate, Azegard, Grandevo, pyganic, regalia, sanidate, PFR 97 and much more. Our pricing is lower than Arbico and we can do custom quotes. On the commercial side, we have also added heavy metal testing on our website through a partnership with Cannabis Chem lab. For only $99 a test. They are an ISO accredited laboratory and can test soil, fertilizer, water and plant material for common heavy metals. This is the most affordable testing option for heavy metals so you can make sure you're in the best position to pass in some of the tighter regulatory states. Now onto this week's podcast. I'm very excited to share my conversation with Dr. David Hawley. In his role as Fluence's principal scientist, Dr. Hawley steers the company's Global Cannabis Crop Sciences program encompassing photobiological research, data, data analytics and cultivation consultation. Fluence's research has identified specific and diverse lighting strategies that consider crop yield, morphology, quality and economics that maximize commercial growers objectives, whatever their crops and production objectives may be. David is a passionate advocate for scientific integrity in the horticulture industry and brings his passion to the design and execution of Fluence's studies as several of which are published in peer reviewed journals. These studies form the foundation of Fluence's products and drive Fluence's mission to service the global horticulture industry with objective evidence based lighting solutions and education on what to avoid. Now onto the show. Hey, Dr. Holley, thanks for coming on the show.

Hey, dad, thanks for having me.

Yeah, absolutely. I've been wanting to have you on for a while now. I met you a number of years back at Photo X and a lot of people may not be familiar with what Foto X is. Do you want to touch briefly on that and tell them a little bit about yourself too?

Yeah, absolutely. So My name is Dr. Dave Hawley and I am the principal scientist at Fluence, which is a horticultural lighting company. I joined fluence in 2018 and I came from the world of academic environmental science. I was working at the University of Guelph developing lighting solutions for growing plants in space and then started working on cannabis and plant secondary metabolism and joined Fluence with the shared sort of vision and the shared values of helping the world grow smarter. That's our tagline and we stand by it and we aim to achieve that simply by doing objective scientific research and then making products based on what that research tells us. So Photox is kind of a celebration of that. It's candidly, it's not so different from from a lot of academic science conferences, but we really try to have Photox be this summit of horticulture science that bridges between academic and industry applications. So exposing people to the bleeding edge while also translating some of the more academic bleeding edge stuff to commercial application.

Yeah, it's a lot of what I also try to do with my podcast, this idea of simplifying and having a broader reach for science so people can see what's being done out there and getting it out to them so we could make better decisions in our gardens. So I, yeah, I had a great time and I remember when I was there the first time, I learned a ton of things. And we also talked about you showed a bunch of peppers from your growth chambers and how different lights affected the morphology of those peppers. How they grew was substantially different based on the spectrum. And I want to talk about spectrum, but I'm getting ahead of myself. Let's just start off right off the bat with some real basic lighting concepts or things that science has sort of proven over the years around lighting. I kind of want to start with lighting intensity. Sure. So there's this idea that was expressed at Photo X, you know, more recently this year, that essentially 1% more light equals 1% more yield. Now, I realize this is a very broad Generalization, it's going to change based off of cultivar environment. You know, there's a lot of variables that go into that. But can you talk a little bit more about that, just as a general statement?

Yeah, totally. So this idea that 1% more light translates to 1% more yield holds true in most plant species. And people really started talking about this in like recent years when Leo Marcellus from Wagner University published this and started talking about it a lot in the context of tomato. He's not the first person to come up with this, but he's the first person to kind of bring it to light, at least in the common kind of vernacular of modern horticulture, using LED systems and so on, which really have changed the way people talk about lighting. Honestly, it's just it's such a fundamentally different technology from high intensity discharge lamps or incandescent that came before that. But as it pertains to cannabis and the way that we've been talking about it at fluence, it's interesting because cannabis can take an awful lot of light. And this 1% more light is 1% more yield thing is true up until a point of photosynthetic saturation. And that ceiling is different based on your species. So like with, with tomato or cucumber, that ceiling might be around 300 micromoles per meter square per second. With strawberry, that ceiling might be around like 600 micromoles. With cannabis, that ceiling is more like 2100 micromoles, for example. So it's like an order of magnitude more light than you could put on other species. And it is important, like you mentioned, that there's cultivar dependence and interaction with other climate factors and so on. And that's very true. So in the case of cannabis, for instance, when we had this result, we saw it across three different spectra and three different cultivars. But if you were to look at the individual data for like one spectrum and one cultivar, that trend that we're talking about might not be accurate. You know, it might be like, well, I didn't really get 1% more yield for 1% more light. You lied to me. It's like, well, no, I didn't. If you look at this other cultivar, you'll saw that you actually got 150% more yield for 1% more light. And on this cultivar it's exactly 1% more light is 1% more yield, and so on and so on and so on. So when we make these sort of generalized statements, like 1% more lead is 1% more yield we're talking about kind of like a meta analysis that is pooling a lot of data from a lot of lighting scenarios and a lot of different genetics to say, okay, on average, this is the response that we talk about. And then that response can be attenuated based on whether there are other limiting things in the environment. For instance, if you're driving plants really, really hard, that means they're going to transpire a lot. Right. It's kind of like plants sweating. They're moving a lot of water up through the roots, through the vascular tissue and at the leaves to cool themselves down. But all of that water goes into the air. And if you're not managing that humidity load, then the plant slows down and then it doesn't matter how much light you add, if the plant can't transpire, it can't cool itself down, it won't photosynthesize efficiently and you won't put on that yield and you won't get that one to one return we're talking about. So a simple statement with a lot of complicated stuff behind it.

Yeah. And I remember Dr. Bugbee presented, I want to say 2019 was my first year at Photox. And in his talk he talked about how cannabis is a highlight plant similar to corn. Basically the more light you threw at it, the more yields went up, provided all other environmental conditions were optimized. However, there was also research at the time from Dr. Allison justice that she did in her facility, essentially showing that there is an intersection between yield and PPFD PAR levels where, yes, we may get an increase, but that increase slows down potentially, or the, the cost to produce that elect the electricity to get that yield increase made it not worthwhile from a commercial perspective. Has that research changed? Because I remember at the time we kind of were landing around a thousand PPFD, I think maybe 1200. Where are we at now with that in terms of what the research is showing you?

Yeah, so I'm not familiar with Allison's research specifically on that, but I think I understand the spirit of what's behind that, which is that again, I hate to be long winded, but there are a lot of complicated things that affect whether or not it's economically optimal for you to add light to your situation or not. And I'm just going to start there because that's the relatively easy kind of thing to pick on for context. Right. There are growers in Ontario where they're paying 3 cents a kilowatt hour for electricity. For them, energy is basically free. And so if they just keep putting more and more energy onto that crop. That's all profit, you know, and I'm exaggerating a little bit, but like, they're not paying for that energy and they're just dumping it into the crop and that's great for them. Conversely, there are growers in New Jersey and in California and in parts of Western Europe where energy prices are up to 38 cents kilowatt hour. Right. Like, that's really, really high. And so you need to make a very careful decision and do an economic analysis to say, you know, for the value that I get from my harvested product, whether that's a tomato, whether that's a bud or B bud or C bud, in the case of cannabis or, or any other crop, am I making enough revenue to justify the added expense for me to spend more money on electricity, put more light on this crop and, and, you know, everything else that goes with that. Right. If I'm pushing the crop harder and I'm growing bigger plants, that's going to affect my labor, it's going to affect my H Vac, it's going to affect cycle time. So it's not as simple as just saying everybody just pour more light, put more light on their crop all the time and then make more money. It's like, yeah, you will, but you'll also have more costs in a lot of cases. It's a very case by case thing to assess whether or not more light is always best. But in general, if I had to generalize, I would say at least in North America, the market value of cannabis is so high that for almost everyone, it makes more sense to put more light on the crop and get more yield.

Yeah. As I think about, it's the analogy I've used in the past. Talking about this is sort of like it's like driving a, a sports car really fast down the road. Like you, yes, you can go faster and faster, but everything has to be dialed in. You know, if you're not providing sufficient CO2, then you're not going to get the photosynthetic effects that you want from the light and you're wasting energy, you know, so it all does play together. And you're also more likely to see a dramatic change in, in the plant if you screw up, if you're running really, really high par levels. So I just think like, yeah, if everything's dialed in, then yeah, we could go with higher levels. But what, what do you think is a good range for the average grower? Keeping in mind that our listeners may be Anything from a home grower with three plants to, you know, someone with 3,000 or 30,000 plants in a facility. And to add to that question, what's the minimum amount of light for a flower, for a flower cycle that you think someone could get away with?

Yeah, I'll start there by saying I don't know and I don't want to give bad advice. So I'm just going to say I don't know what the minimum is. What I would say is in terms of a general range, you know, around a thousand micromole, like you said, that's a great place to play. In general, we see a lot of commercial growers hovering around 1200 these days. We see more and more growers creeping towards 1500 micromoles. And then we have some growers and this is, this is kind of like the extreme outliers, but we have some growers that are doing up to 1800 micromoles of top light and they're exploring sub canopy lighting or under canopy lighting options or inter canopy lighting options, which I don't want to go down that tangent right now because I suspect we'll get to light distribution later in the conversation. But that's a really cool strategy for them and it makes sense for them. But for the average grower, I would say between a thousand and fifteen hundred is a good place to play. We're finding that most people are succeeding, having good healthy plants without too much drama, if you know what I mean. Like, not random, like why is, why am I having foxtailing or revegging or some sort of weird morphology? Generally in that range, people are okay as long as they have basic environmental management stuff going on. They can control their temperature and humidity. And of course they are supplementing with CO2.

Since you brought up foxtailing and revegging, how does light impact those particular effects? Or this idea of newer white pistols on, on a bud or flowering. Flowering cycle? Because as I, as I understood it, I thought reveging specifically was tied entirely 100 to photoperiod. Is that not accurate or are there other things around there to.

From a literal standpoint, there are other ways to induce revegging, but from a practical standpoint, it is, it is primarily due to photoperiod. You're not wrong about that at all. Things like foxtailing or any number of other sort of funky morphological things that you can get are largely down to light intensity, you know, and, and the exact mechanism we don't know again, and I, I, it pains me to say that because as you have, as you've heard from me before, I really like to get in the weeds and talk about all the kind of biochemical stuff going on. But we don't know with foxtailing. What we've seen is that for folks that want to go with a higher light intensity, the instances of those sort of morphological outliers are lower when they're doing a more distributed light. And so by that I mean, if they, if they want to play at 1500 micromoles total, but maybe they're having some morphological issues when that's all top light. Then if they take, you know, 300 micromoles of that or 500 micromoles of that and put it as inter canopy or sub canopy instead of all at the top, not only are they getting greater bud uniformity throughout the canopy and elevated bud grade, but they're also not running into a lot of those morphological issues they were having before.

Yeah, I've always thought of light over, let's just say 1200 PPFD as being a stressor. But I think as I'm saying this, that's probably not the best terminology. Maybe it's more of a trigger that just allows for less plant stress in general as this thing's going so hard in terms of the amount of photosynthesis that's occurring due to the amount of light, it seems like to me, um, it's, it's much more open to stresses and other environmental triggers that can cause, you know, pretty significant morphological changes or other issues than I, I would normally see if I'd been running at say a thousand or 900 bpfd.

Uh, yeah, no, that's true. Um, but another way to look at that, right. Is I'm going to use an analogy of like how active a given human being is, right? Say you are somebody like me and you live a sort of like very average lifestyle where like you spend a lot of time sitting at a computer, you're walking around a lab, you exercise a moderate amount, but like it's a pretty kind of like middle of the road lifestyle, right? The difference between me and like an Olympic athlete, right, where they are training to be a sprinter or a high jumper or something like that. It's like they are performing physically at a much greater intensity and they can physically achieve much more than plant scientist Dave can, you know what I mean? But chances are they're a lot more likely to tear their ACL or roll their ankle or pull a muscle or something like that because they are operating at a really high intensity physically Conversely. Right. If someone has a totally stagnant life and they're living in a bubble and they do nothing, they're delicate in a different way. You know what I mean? So everyone ends up acclimating to their environment, whether it's a human, whether it's a plant, whether it's an athlete, whether it's somebody who doesn't do anything at all. And something like, you know, bringing you back to plants, if you're pushing them hard with highlight, you are getting plants that are like the Olympians. Right. They're performing really, really well. But to your point, yeah, they're probably a little less robust when a stressor comes along and you know, it's like, I don't want to go on too big a tangent here, but we get a lot of feedback about, you know, living soils versus like a salt media kind of thing. And people say, well, you know, salt, salt is better for these reasons or living media is better for these reasons. And what we tend to say is like, you know, for commercial horticulture, we are pushing the plants hard. Excuse me, we're pushing the plants hard. It is like driving a race car. And we don't want to introduce variables that could be stressors favorably for the plants in certain circumstances, but in these circumstances, that's like a hyper controlled, really intense thing. We don't want to introduce any stressors that we don't really understand really well and know how they interact with, with light and everything else that we know we're putting in. That makes sense.

Yeah. I mean, you're bringing up a broader issue with living soils in general, in science, just in the fact that there's so much variability. I mean, it's an issue across all soil science, I think, in general, but specifically in terms of cannabis research, most researchers don't want to do research in living soils because of the variability of those soils. It's sort of, it makes any replicability or conclusions that you might draw from it very challenging. So I understand why researchers want to do research with mineral salts in rockwool or cocoa, just a very inert substrate, because you can control and turn every single dial and keep everything the same across replicants. So I, I totally get that. Yeah.

Well, not to mention, you know, the liability that it carries with it if you're a company, like you're a technology provider, if you're a company that says, hey, use my substrate because it's going to do amazing things for your routing or it's going to do amazing things for your yield if you're providing living soils, and you really can't control exactly what's in that substrate every single time. And you're giving it to customers with an assurance that it's going to do something good for their crop. Well, what do you, what do you do when six months later you got a bunch of customers that come back to you and say, hey, this isn't performing like the last batch. What gives? You know, it's not that we're not interested in that kind of technology and living soils and stuff. And you know, on a personal level, I actually believe in a more kind of like holistic system, including living soils, but that's not something that commercially I'm going to bring to a customer because I can't speak to it. I can't give them an assurance that it's going to be the same again and again and again.

Yeah, I think that because the. Because. And this gets a little. A little complicated. But as. As someone who works specifically on that side of the industry, what I do find is we are able to replicate things fairly consistency if we stay within certain agronomic principles in terms of fertility. Because, yes, there are going to be differences in the, on the biological side. That biology is constantly in flux. It's. It's changing. It's not homogenous. Soils are. And in soils, I'm including living soils, which are technically soilless media are profoundly diverse and complicated and fascinating. And throughout all of those interactions, those microbial plant media interactions that are happening, what we're seeing from a very, very macro view is actually fairly consistent. I think the plant really does control and balance those things. Now, can you screw it up? Absolutely. And it does happen. But as a general rule, I find it easier. Easier for a lot of. At least in commercial facilities, more affordable because you're not constantly buying new media. And then also easier in a lot of ways because of the labor associated with it and the. Yeah, just the overall process. But that being said, it was interesting because I was at Photox and I was talking to, I think. I think almost everyone there was growing in mineral salts. Uh, a lot of the growers, at least I didn't talk to any, you know, specifically organic folks. Uh, but we're dealing with a lot of the same challenges. We had a lot of the same questions. Uh, it was a very collaborative conversation, even though we take different approaches on the, you know, on the fertility or media side.

So, yeah, just to jump in there, I'm. I'm really glad you made that clarification because it probably wasn't a good analogy for me to make in terms of speaking to, like, substrates, for instance. Um, I'm not an expert in that, but from what you're describing, it sounds like there actually, there is quite a bit more opportunity there than I had previously appreciated. And so, you know, probably too big a conversation for us to dive into right now, but would love to learn more about that from you and I'll. I'll probably just follow up with you after.

Yeah, yeah. The research just shows that a lot of the microbes that we're seeing in the soil are very similar, I guess, across the board. And we have pretty high levels of them. I mean, if. If the problem was that severe, you. Every organic farm. Because there's a lot of organic horticulture agriculture being done. Sorry, on scale right now. And we're not seeing massive crop failures due to these, you know, small differences versus what's being grown in, you know, greenhouses and, you know, under glass and using mineral salts. So I think there's more to it. But it is an interesting conversation and I. I do hope that someday there could be more science around living soils. At the same time, I also recognize that, like, I don't know how much I could derive from that science. Like, that's why I find the science that's done with. That's currently being done with mineral salts probably more interesting because it is just one less variable that we're controlling for. But anyway, let's get. We could go down a big rabbit hole there. Let's get back to lighting, where you definitely are an expert, where I know.

Where I'm talking about what I'm talking about at least a little.

One of the things that I heard at Photo X this year that I wanted to highlight around light intensity before we move on to other lighting topics was that, and correct me if I'm wrong, light intensity increases did not cause any changes in THC or total cannabinoids. Now, on that note, can you say if. Can you say if the research showed anything around terpenes or other secondary metabolite production?

Yeah. So I have to caveat this by saying that all of the research that I presented at Photox, and then I'll talk about here, I always say at commercially relevant intensities. And by that I mean the research that we've done from about, let's say a thousand micromoles up to 2,500 micromoles is the highest we've ever gone. And within that range. Yeah, we don't really see a big difference in thca cbga, cbda, and all the other cannabinoids that we're quantifying. And in the case where we're working with cultivars that can produce cannabivarins, we're not seeing a huge swing in cannabivarin concentrations either. As for terpenes, you know, it's. The short answer is that we're not seeing clear trends. The longer answer is that we are seeing that as a matter of spectrum and intensity, we can manipulate certain terpene ratios. Um, normally when I present this, I have. I have graphics to kind of support what I'm about to say. But what I'll say here is that in the world of terpenes, right, you can group them in different families. There are mono terpenes that are based on 10 carbon chains. There's sesquiterpenes that are 15 carbon chains. There's triterpenes and tetraterpenes and so on that just have increasingly longer carbon tails, or not carbon tails, but carbon chains. And then within monoterpenes, there are things that are more like, cyclic structured and things that are more linear structured. And the biochemical pathways that lead to these two branches, we can manipulate partitioning of these two pathways. Excuse me. So we have seen instances where by manipulating white and red and far red, we can change the ratios we get of cyclic versus linear monoterpenes. And we've manipulated ratios of monoterpenes and sesquiterpenes and things like that. And as someone whose PhD was in plant biochemistry, this is really exciting to me because I think, oh, okay, maybe there's a certain enzyme in this pathway that we're changing the activity of, or maybe there's a thing. And the mevalonate or non mevalonate pathway that we're manipulating. Because, you know, whether you get monoterpenes or sesquiterpenes or triterpenes or tetraterpenes, the precursors that make those compounds are called isoprenes. And whether you make your isoprenes in the plastids, like the chloroplast, or whether you make those isoprenes in the cytosol, which just kind of the. The goop that all your cell organelles float around in, whether you're making those ice breedings in the plastins of the cytosol, determines or influences anyway, what types of terpenes you're going to end up with. And so I think, oh, wow, okay. That's actually really complicated. Then there are a lot of regulatory Things that could be going on that change that partitioning. So when we see that light does play a role in this, it's inspiring. It inspires me to do more research and want to pursue it further. And I think a lot of people at the end of the day are really, really interested in diverse chemistry. You know, whether it's for a medicinal application or whether it's a psychoactive application or even just you, you prefer one flavor or another. You know, it's cool to see that we can manipulate this stuff with light and, and I, I eagerly await for there to be greater market demand for things like that, because right now we see things like that and we want to do more research on it. But research costs money and analyzing a bunch of individual terpenes and other compounds costs a lot of money. And right now no one is making lighting purchase decisions based on what can be done with terpene manipulation, which is a real shame. But if, if Fluence can't sell more lights because of something we discovered about terpenes, I therefore can't invest more money into that kind of research. You know what I mean?

Yeah, no, that makes sense. And it's a pretty broad research topic to try and tackle like that. That sounds like years or decades worth of work to really dial in. But what, what I'm hearing is the takeaway so far for just to catch growers up and correct me if I'm wrong here, but. But essentially 1% more light is going to equal 1% more more yield. Light intensity does not really change THC or total cannabinoids within commercial application ranges, normal ranges that we would grow this plant and then we may. Light does impact terpenes, but we don't know exactly how that occurs and how to manipulate it to our advantage yet. Especially as I think about this with the vast diversity of genetics that we have within cannabis already.

Yeah, exactly. Well said. And much more concisely said than me, so thank you.

Well, I just, I just want to hit the highlights for folks because this is a pretty complex topic. On, on that note, my, my thought immediately goes to the dilution effect. This idea that a plant has certain genetic potential. And we see this in other crops where as you grow more biomass, as you increase yield, I would assume that that THC would be more broadly spread across that biomass at a certain threshold. So like the plant has the capability to produce genetically at its potential only so much THC overall. And so as we spread that over larger leaf surface, more bud sites, my overall THC levels could go down but maybe that total cannabinoid content of that entire plant would stay the same. Do you want to kind of jump in on that?

Yeah, I would jump in simply to echo what you just said. You know, a simple analogy is if you put a teaspoon of sugar in a water balloon and then you fill up that water balloon, that sugar is very diluted. Right. Similarly, if you have a plant cell and it's got some THC in it, and you just sort of dilute that THC in a bigger cell, or you have like this total quantity of THC that the plant as a whole can produce, and you dilute it across a very big plant. Yeah, it'll be. It'll be less potent.

Yeah. And I don't know that we like. Because I know you've brought up the term, like, within a commercially applicable range. I think that there's a possibility that we haven't really hit that with cannabis in terms of THC and cannabinoids, because I do see people growing very large plants with the same genetics and still having high THC levels. But I. But this, that doesn't change the fact that this concept doesn't exist already and is a factor that people should be considering as they grow plants. So I just want to throw out that caveat, actually.

Tech, can I jump in on that? Because one thing that I'm really interested in is the research that's coming out of places like Van University. Van University, excuse me. And they have research showing that, you know, certain wavelengths of light, like blue, like uv, like far red at lower intensities, can significantly manipulate chemical profiles. That what we're seeing is that at higher light intensities, it really doesn't seem to do anything. And so I think about that, and I think, okay, well, there's. There's a lot of potential if you're a grower that wants to kind of take like a low and slow approach, kind of like, you know, if you're. If you're smoking some meat, you know, low and slow is the way to go. I think, oh, maybe you can do the same thing with cannabis. You know, play more like 4 to 500 micromoles and really dial in a chemical profile, whether that's with cannabinoids or terpenes, by using a really kind of specialized lighting recipe. Right. And I, I don't have an answer for this right now. I'm literally just thinking aloud. This is something I'm really interested in, and I want to do more research on. I think I would encourage people to look into this research. But again, it doesn't seem to hold true at these really high light intensities that most growers want for maximizing their yield.

All right, you brought up spectrum. Let's just dive into spectrum.

All right.

Why not? So can you, can you start off by let's. Let's. So, so spectrum's a range. Let's just start at the bottom of that range. Let's start in the UV blue area and talk a little bit about what it does, what the research shows, and maybe what's dispel some of the myths around the claims that we're seeing happening on these different wavelengths or spectrums.

Sure. And I'll keep this high level because I have a bad habit of getting really in the weeds about spectrum. But if you want me to dive deeper on something, please don't hesitate to ask. So starting with, as you say, the shortwave light, we're talking about UVB and then UVA and then blue.

Right.

In that order. They go from shortest to longest. Go ahead.

Let me pause you. Can we clump UV as one spectrum or should do we need to talk about UVA and UVB as specifically different spectrums?

These are distinctly different spectrums.

Okay.

Yeah.

In terms of, in terms of plant effect, I guess is the context.

Yeah, plant effect and the energy that these photons carry, and therefore also the health risks that these photons have. So maybe actually I should start with even higher energy photons or shorter wavelengths, and that's uvc. UVC light is a really amazing tool for certain applications in horticulture. It's, it's around 254 nanometers at least. That's the UVC that's most commonly deployed. And this is very dangerous light in the sense that it's a really. It has enough energy to break biochemical bonds, and that can give you a sunburn. It can hurt your eyes, like damage your eyes permanently, and it can give you cancer. Right. So for a lot of reasons, you don't want to be exposed to uvc. Having said that, all of these negative effects that it has on your biological cells, it has those same effects on things like fungal spores and bacteria and other pathogens that you might not necessarily want on your plants. So you can strategically apply UVC to do like a surface sterilization of your crop. And this is, this is broadly used in broader horticulture for like sterilizing strawberries, for instance, in a container. So really great technology, but obviously something you have to be very responsible with. And also you need to be mindful of the fact that you can't see it when, when it's on. It's not in the visible range of spectrum. So you might be exposed to UVC and have no idea, but then be very unwell after. So moving on from uvc, you then have uvb, which is less dangerous than uvc, but still dangerous. It's not something that you want to be exposed to. And again, it's another wavelength of light. You know, usually when we're talking about UVB, we're talking about maybe 285nm up to about 310nm. It's still dangerous. You're still not gonna see it. But it interacts with plants a little bit differently. It interacts with certain cryptochromes which are photoreceptors in plants. It also interacts with something called UVR8, which is a specialized UV receptor implants. And it can in certain cases induce something called systemic acquired response, which is kind of like boosting the plant's immune system. It gives it a chronic stress where the plant just says, hey, I need to live a hardier lifestyle and be more robust to the environment. So that's really cool. Again, the research is, I would say relatively sparse on UVB applications. And there are reasons for that. I mean, it is kind of dangerous. You don't want students doing it. The lighting technology is also not great. You know, it's not something that you necessarily want to use LEDs for just yet because you can probably do better with fluorescent tubes. And it's, you know, the lights all have kind of like a short lifespan. And for all these reasons, like there's a lack of research around UVB and there's opportunity for a lot more, which is exciting. Suffice to say we'll just move on to uva. And UVA is nice because this is kind of like when, when you go to a 90s party and there's like a black light and everything glows, right? That's uva. It's not terribly dangerous. Like you still wouldn't want to hang out in high intensity UVA for a long time or like shine it straight into your eyes and think that's a good idea. But as far as like plant interactions go, it's going to be received by again, cryptochromes. And I know I mentioned those already. Cryptochromes are pretty broad family of photoreceptors. Like there's Cry 1, Cry 2, Cry 3, Cry 4. And they absorb different wavelengths of light, but also they absorb differently at different light intensities. The thing about UVA is that, as far as I'm aware, a lot of the things that it does to plants, it can also be achieved with blue light, which for a lot of reasons, you would just go with blue then. Blue is cheaper, it's a lot safer. It's going to have a much longer lifespan. So I'll just segue right into blue and say blue is a great tool for things like inducing compaction. Right. The plants perceive blue as like, oh, I'm in sunlight, it's high noon. Good photons are getting to me. I don't need to stretch to get into better light. So actually they'll become a little bit more compact.

When you say more compact, I, I assume you're talking about internode spacing.

Yes, sir.

Does it also impact leaf morphology?

Yep, yep. So with blue light, you will, generally speaking, have thicker leaves. You will produce more callous on the leaves, which is like, kind of like the waxy. I'm sorry, callus isn't the right word. Cuticle is the world like the, the waxy film that's on surface of leaves to protect themselves from various environmental stresses. And in general, you'll also have more pigmentation in the leaves, so richer chlorophyll content versus if you just have like a, a white or a red light.

Now let me, let me back up a little bit because I have some notes here that I took. The notes that I took from Photo X said that. And correct me on this too. Three and a half hours of ubb, decreased THC levels. Is that in the research that was presented? And I'm not sure if it was by you or someone else. Do you know what I'm talking about there?

I don't know specifically what you're talking about, but I can generalize around the research that we have done on UVB as well as the research on UVB that I'm aware of from Dr. Bruce Bubby at Utah State as well as Dr. Yubin Zhang at the University of Guelph.

Yeah. What, so what are the effects of UV generalized in terms of yield, cannabinoid content and terpene production?

Yeah. So in general, according to all of the kind of like modern UVB research on cannabis, basically any amount of UVB is bad. And the more UVB that you apply, whether you apply it through a higher intensity or flux density, whether you apply an equal intensity but for a longer duration, the more UVB you apply, the worse it is for the plants. So yield goes down, potency goes down. The plants look very, very stressed out. We see the leaves canoeing, if you know what I mean. They kind of roll up and then they'll also curl in on themselves. It, you know, not to anthropomorphize, but it seems like they're really trying to just get away from the photons and protect themselves. So for the time being, we don't see any commercially beneficial application of uvb. That's not to say that we don't think there could be one, but the research that we've all done, and by we, I mean fluence, I mean Dr. Bugbe, Dr. Zhang. We've all taken the approach of applying UVB during flower development in hopes that it's going to do something good for cannabinoid biosynthesis. I think that there's opportunity maybe for UVB applied earlier in development, late prop or early veg with this idea that again, maybe if we kind of chronically harden the plants to uvb, maybe that will give some kind of downstream benefit, but we don't know yet.

Are there any claims being made in the market right now around UV that are. Because it sounds like, from what I'm understanding, UV light is not very efficient. Like it takes a lot more electricity to produce it versus these other spectrums. And it's potentially dangerous for humans and it doesn't seem to increase cannabinoid production. Are there any claims right now out there that you're aware of around UV that people should be cautious of?

Maybe, yeah. Again, I think that you've, you've nailed the risks and kind of the negatives of uvb, but the claims are out there that UVB will enhance secondary metabolism. And again, it's one of those things that we, we simply haven't seen it. So the companies that have done research on this or are familiar with research are, are less likely to make these claims, I think. I've also heard a claim that UV photons help draw par photons or photons in the range of photosynthetically active radiation. The claim is that UV can help somehow draw those photons deeper into the canopy and therefore you have more light penetration, which theoretically means more overall photosynthesis, which theoretically means more overall yield. That claim strikes me as particularly odd simply because photons don't interact with each other that way. And UV also, as a shortwave photon, bumps into a lot of things and is reflected from things. It certainly does not penetrate deep into a canopy. So I think it's a claim that. That sounds sort of exciting, but in reality is not something that growers should be taking too seriously.

I, I think there was another claim that I heard around UV and insect protection or insect deterrence. I don't remember exactly what it was, but I, and I believe there was some effect on insects from uv, but. But it was not replicated in commercial applications. It was just one study that was done. So I think there was some caution around that. Suzanne was talking to me about it and I don't want to misspeak, but I think there was something around there too you brought up. And I didn't even have this on the list of topics, but I think it's interesting you brought up light penetration because I've heard people say my light penetrates further into the canopy than light B or competitor light. How, how does that work? Because I, that, that got me into a conversation on this concept of the inverse square law, which I think is really interesting. I know you and I touched on it off air. How does that apply to horticulture and these conversations?

Yeah, so light penetration. I'm also very interested in this fluence. We used to say that white light worked so well for cannabis because of light penetration as opposed to something that's a more predominantly pink or a blurpal type like red, blue light. And we had said, well, for a couple reasons, you're penetrating deeper. You're not having all of your photons immediately absorbed by superficial leaves. And those green photons that will get absorbed by leaves but then retransmitted as longer photons, those will be more photosynthetically productive deeper in the canopy. These are all cool sounding nuggets of information that are actually somewhat supported in the academic literature. And there's really, really like cool papers that show light measurements at different depths in canopy and even within a given leaf. They'll say, you know, for a given leaf with certain light qualities, all of the photosynthesis is occurring on like the first couple layers of cells. Whereas with a more light white. Pardon me, with a more white light, you're getting deeper penetration and driving more photosynthesis deeper in the leaf. And again like that's, that is factually true in isolation, a single leaf will photosynthesize deeper in its leaf with a more white light. At least that's, that's what the science tells us. Now in practice, what we are finding is that, you know, we could be talking right now about cannabis or tomato or cucumber, uh, really any crop where you have like a really dense leafy canopy where it's it's really shaded as you go down through that canopy. What we're finding is that white actually isn't penetrating all that much better than something that's like 80% red and otherwise white. Right. And I call that spectrum out specifically because that type of spectral mix that looks pink to the eye but is roughly 80% red and the rest is just background white that penetrates pretty well too. And having something that looks white to our eyes, it's not really benefiting the crop in that way, unfortunately.

So I have a very low level understanding of how this all works, and I think it's really interesting because the way I understand this. So let me back up the inverse square law, I'm just going to state it, mathematical concept, that intensity is inversely proportional to the square of the distance. What does that mean? That's not very useful for the average grower. Essentially, in close distances from that light, as you move further away, these photons are going out. And as I understand, they're essentially spreading out. So they're hitting less leaves directly right below the light. And as you move further away from the light, it's going to drop off more dramatically. So the dish, like the example in, in the article I'm looking at here, it's like moving from 1 meter to 2 meters away, you're going to lose 75% of your light. But if you're way far away, 4 to 10 meters, that light intensity may only change by 5%. And obviously, so as we bring our lights closer to our canopy, we're going to have, and I see this with my light meter, we're going to have greater drop off as we move away. Because in my head, what I'm picturing is all these photons are shooting out of the lights. They're hitting off of all of these different things, whether it be the wall, the leaf, all these things, and then shooting around until they're being absorbed by the plant. How, how does this all really apply horticulturally? Like, how do we maximize this? Because I assume if I have a tight canopy and that that light is hitting that canopy, there really isn't potential for penetration. Like when I stick my light meter down below there, the photons just can't get through there. And so they have to be reflected off of something or they have to hit a leaf that's already maximized its photosynthetic potential and it's really just, I assume then just bouncing off at that point, it's not being absorbed. How, how, how wrong am I involved this in the way I'M describing it, you're not.

And, and Tad, you're very humble. I think you got to give yourself more credit because you have the, you have it right on pretty much all these things. So the way that I kind of think about the inverse square law and try to make sense of it is like if I go outside and I'm standing on the road and I think, oh yeah, it's basically this bright outside and I'm feeling this much radiant light and radiant heat from the sun, I don't think it's going to change a whole lot if I go up on the roof instead. Right. I've, I've technically gotten slightly closer to the sun, but my perception at that point is not good enough that I'm going to know the difference between how the sun feels and looks from my roof versus the road. Right. Because we're so, so far away from that light source that that is a trivial distance that I've changed from the road to the top of the roof to go kind of the opposite. And put this in horticulture terms, I'm going to give the example of people that are growing in multi tier applications, because in multi tier, people tend to have the plants much closer to lights versus if they're doing like a single tier kind of high base solution. So this is something that people do need to be aware of if they're doing plants that they know they want to grow in. Let's just say a thousand micromoles of light, right? It's like, well, okay, what do you mean by that? Do you mean a thousand micromoles when they're at their full height, or do you mean a thousand micromoles the whole time during their development or something in between? And sometimes people get not, not upset, but a little confused why they're not having the crop perform as expected. And it's, it's because you know, their, their plant spacing relative to that light isn't quite right. And really if, if they say, for instance, I want to have a thousand micromoles on the crop the whole time. Even my, when my plants are 10 inches tall versus 36 inches tall, it's like, okay, you can achieve that, but you're going to need to manipulate your light intensity throughout the plant development so that at top of canopy you are hitting that 1000 micromoles per meter squared per second. Conversely, if you have your light configured such that it's really intense down here when the plant is young and short, and then you let that plant grow up to the point where it's only a few inches away from the light. You gotta be really careful that you don't just end up cooking your plants, because the light density is going to be much, much greater close to the light like that.

Yeah, when I measure light intensity, I'm sure you're doing it much more carefully. But as a grower going around with a par meter or even a photon, you know, device, something that measures light, I kind of just quickly throw my light into different places or my meter, different places under the light to get kind of a rough average that I calculate in my head and say, okay, that's. Here's my highest bud, here's my lowest bud. My canopy's fairly even. What am I getting at the edge? What am I getting directly in the middle? And I make sure that that is approximately around whatever my target par levels are. Is that a good approach or is there a better way I should be doing that? Because we think we're talking about this like a thousand ppfd is evenly hitting our canopy. And as you know, that's just not the case. There's going to be spots that are 600, 700. There's going to be spots that might be 1200. What's the best way to average that or figure it out?

I think what you described makes a lot of sense. And then how particular you want to be with the light measurement and light mapping depends on the scale of the facility. So, for instance, if you have a large room and you have a lot of lights above the plant, particularly if those lights have. Have some optics that help light spread, you can expect a pretty good uniformity across the top of that canopy, right? And you can work with your lighting provider to develop a light design specifically using their light models. So, like in the case of fluence, right, we have Raptor, and we have Spider, and we have Viper and so on. And depending on the grower's objectives, right, we can manipulate the light design and the number of lights that they use, and even the platform of light they use to manipulate uniformity. Some growers say, I need to have a uniformity of 80% or better at any cost. And we'll say, okay, well, you can go a couple ways, right? You can increase the number of lights over the canopy so that you have, like, a lot of overlap between the lights, and you do get a really great homogenous light environment across the space. Other growers say, yeah, that's really not so important. You can reduce the number of lights. You can probably use a slightly different platform. Thinking about like Viper vs. Raptor in the case of fluence. Um, but for somebody that maybe has a smaller space. Right. Smaller spaces are always, always harder to make more uniform. And I'm not just talking about lighting. It's, it's harder with, with, with climate and nutrition and everything else. So I think the best thing that you can do is for a small space, manage reflections. Right. I mean, I, I realize this maybe isn't entirely what you're asking, but still, I, I would sell, sell someone. Go ahead.

Well, let me add on to my question then, because the other, the other thing I have is like these photons that are not hitting my plane. So as, as we move the, the light further away from the plant, there's less photons hitting the leaf directly below the light. All right? That's why my PPFD goes from, and let's just say 600 to a thousand, depending on how far away the light is from the canopy. Now my question is, because you brought up reflectivity. That, that was. My next question was like, and those photons are not losing energy per se, they're just not being directed as precisely straight down as I understand. They're like going off and hitting other things and reflecting and coming back. How much light loss am I really getting from a energy perspective? You know, times electricity I have to produce. If I have my lights five feet up using like a high bay greenhouse light versus these bar lights, am I really losing the light if it's just like bouncing around in a, in a given room with white walls and other plants or, or what? Cause. Cause the photons aren't losing energy, right? They're just cruising around till they hit something.

Yeah. So again, I hate to say it, but it's another complicated answer. Energy can't be lost, right? It can only be converted. So if a photon doesn't make it to a plant immediately, then it will go to the wall. And depending on the paint you use and the material of the wall and so on, you'll have, you know, a coefficient of utilization that describes how efficiently all your photons are getting to the plant and you know, becoming more plant. Basically, you can have a coefficient of utilization that corresponds to materials and colors as well. If you have nice smooth reflective walls that are painted white and have like a glossy paint and so on, then you can expect that that energy will make it to the plant eventually, but you will lose something along the way. Like some energy will be transformed to heat when it hits the wall. And then even when those photons get to the plant, it's not like 100% of that photon energy is converted to plant biomass. Right. That energy can either go into photochemistry, which is what you want, or it can fluoresce. In other words, it can cause a biochemical kind of interaction with the plant, such that the photon is re emitted as a slightly longer wavelength, or it can just produce waste heat and you can end up warming up the plant. So again, I know it's a little bit of a technical answer, but the short answer is that if you have a good reflective environment and you have the plants and the lights situated in such a way where you know you've, you've made some effort to capture as many photons as you can, it's, it's not that wasteful. At the end of the day, you're not losing a lot of energy to waste heat and things like that. But I mean, there's. That's good. So many caveats.

Yeah, yeah, that was. It's just something I've wondered about because I've. I always want to be efficient with my light and electrical use. So that's good to hear. That at least is getting there eventually or mostly reflecting? We've covered a lot of ground today and there's still so much more to unpack. Rather than rush through it, we're splitting this conversation into two parts. Join me in part two two where we'll dive even deeper into photobiology, spectrum and all things lighting. That was Dr. David Hawley from Fluence Lighting and you are listening to the Cannabis Cultivation and Science Podcast. Don't forget to check out the podcast page at www.kisorganics.com. just click on the Learn tab. Then podcast. And just a friendly reminder, we do have a Patreon channel with a free 7 day trial and tiers as low as $5 a month. We do book club, special cultivation tips and tricks, monthly video hangouts to connect and share your grow and even give out seed packs and other gifts at certain tier levels. Your support of Patreon or sourcing your products through Kiss Organics is what supports the podcast and I really appreciate it. Thanks for listening.