Lumens, Lux, and Adding It all Up
- Thread starter ceestyle
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ceestyle
Well-Known Member
I emailed RIU, but he no likey me apparently.
ceestyle
Well-Known Member
So this gets complicated. Here is a good link explaining some of the differences between rating systems.
PAR Watts is a good way of measuring how much radiative energy is being produced in the relevant wavelengths per plant. You can figure it by taking the raw bulb spectrum and weighting it by the PAR plot I linked above.
The problem with this is that the response from a plant from a high vs. low energy photon (for example, blue vs. red) is often the same. The reason this is so is because a fixed energy input is required for a particular chemical process to occur, and all excess energy is wasted, converted into heat, luminescence, or other modes of energy.
An analogy would be me vs. fdd or browndirtwarrior stepping up to that thing at the carnival where you hit the target with the hammer, and it runs up the pole toward the bell. Say the bell is low enough that I can hit it. Then it doesn't matter if fdd or bdw can hit the target harder - we all make the bell ding - and the fact that they hit it harder might make the bell ring louder or the thing come harder back down the pole. All that matters in the end is that the bell dinged. I am red light, and the other two are, say, blue light.
The reason that this skews PAR watts is that watts is a unit based on energy. So, if we look at the PAR based on quantum efficiency (% absorbed/used photons vs. photons striking the plant), the white line here, and find that I'm 680nm (red), the others are 440nm (blue), but that we have the same quantum efficiency, what does that mean? It means that we induce the same average number of chemical reactions per photon, or dings per swing in our analogy. When you calculate PAR Watts, however, it tells a different story.
Since light's energy is inversely proportional to wavelength, the blue light has more energy. To be precise, it is in our case 680/440=1.54 x as much energy as the red light.
This means that when computing PAR Watts, the blue photon counts 1.5x as much as the red one, despite the fact that they induce the same reaction. By looking at the PAR plot, however, you can see that most red light is roughly 2x as efficient, so this is partially compensated for.
These differences, however, have led others to compute the meaningful radiation in terms of PFF - photosynthetic photon flux - the number of photons that are meaningful. This eliminates the aforementioned efficiency complications.
Anyway, it's complicated, but PAR Watts are not an altogether bad way to measure the amount of meaningful light. I'll convert those spectra to PAR Watts if I get around to it ... or blazed enough.
PAR Watts is a good way of measuring how much radiative energy is being produced in the relevant wavelengths per plant. You can figure it by taking the raw bulb spectrum and weighting it by the PAR plot I linked above.
The problem with this is that the response from a plant from a high vs. low energy photon (for example, blue vs. red) is often the same. The reason this is so is because a fixed energy input is required for a particular chemical process to occur, and all excess energy is wasted, converted into heat, luminescence, or other modes of energy.
An analogy would be me vs. fdd or browndirtwarrior stepping up to that thing at the carnival where you hit the target with the hammer, and it runs up the pole toward the bell. Say the bell is low enough that I can hit it. Then it doesn't matter if fdd or bdw can hit the target harder - we all make the bell ding - and the fact that they hit it harder might make the bell ring louder or the thing come harder back down the pole. All that matters in the end is that the bell dinged. I am red light, and the other two are, say, blue light.
The reason that this skews PAR watts is that watts is a unit based on energy. So, if we look at the PAR based on quantum efficiency (% absorbed/used photons vs. photons striking the plant), the white line here, and find that I'm 680nm (red), the others are 440nm (blue), but that we have the same quantum efficiency, what does that mean? It means that we induce the same average number of chemical reactions per photon, or dings per swing in our analogy. When you calculate PAR Watts, however, it tells a different story.
Since light's energy is inversely proportional to wavelength, the blue light has more energy. To be precise, it is in our case 680/440=1.54 x as much energy as the red light.
This means that when computing PAR Watts, the blue photon counts 1.5x as much as the red one, despite the fact that they induce the same reaction. By looking at the PAR plot, however, you can see that most red light is roughly 2x as efficient, so this is partially compensated for.
These differences, however, have led others to compute the meaningful radiation in terms of PFF - photosynthetic photon flux - the number of photons that are meaningful. This eliminates the aforementioned efficiency complications.
Anyway, it's complicated, but PAR Watts are not an altogether bad way to measure the amount of meaningful light. I'll convert those spectra to PAR Watts if I get around to it ... or blazed enough.
ceestyle
Well-Known Member
PUR is interesting. It's PAR, further weighted for what a specific plant, e.g. cannabis, can use. It will therefore not vary much from PAR, which is more generic.PUR, man, PUR. That's what is missing from the equation.
The one really useful thing PUR can account for, however, is that some plants max out in certain energies. So even if green has 10% efficiency, a plant can only use so much of it per unit area and then it doesn't give a crap. Otherwise, you could just load up on a billion green lights and still grow great pot.
Until PUR spectra are available for cannabis, it's not practically useful. In addition, this method of rating lights was introduced back in 78 in one research paper. If I had a dollar for every scientist in my field who wanted to reformulate their own definition for the problem they're addressing - complete with their own fancy acronym that they'd like to see catch on - I"d have a secretary typing this for me.
For the most part, I'm finding that it's used by the government for development of LEDs (as reported by the commercial vendor below), but being championed by the company that makes PURple bulbs. Besides that, there really isn't much information on it at all. No wiki = no cookie.
I think that with the basics and common sense - don't try to overcome spectral limitations with raw power - PAR's about as good as PUR.
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Seamaiden
Well-Known Member
I like it sticky best of all.IT'S A STICKY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Thanks whoever made it sticky!
ceestyle
Well-Known Member
who doesn't, and thank seamaiden and RIU for that.I like it sticky best of all.
Single White Pistol
Well-Known Member
What's the least amount of light you need to veg a plant?
homegrownboy
Well-Known Member
Why the least?
ceestyle
Well-Known Member
It depends on a number of things, most importantly what kind of results you expect. While you could keep a plant alive with a 60W incandescent, why would you?
This question cannot be answered meaningfully without more information - how big, what kind of growth you want ... why you would only grow one plant? I would assume when someone says 'the least' they are concerned about spending a few bucks on light. I cannot really identify with that being my primary concern, as opposed to, say, rate and quality of plant growth.
ceestyle
Well-Known Member
i think that's the same question, really.
You can grow a 2" plant under a 13W CFL just fine, but what kind of growth does that support when it gets to be 6", 12", or 18" ? Not much.
When I was a kid I grew a stringy plant under an incandescent. Would I do it again? Hell no.
You can grow a 2" plant under a 13W CFL just fine, but what kind of growth does that support when it gets to be 6", 12", or 18" ? Not much.
When I was a kid I grew a stringy plant under an incandescent. Would I do it again? Hell no.
Seamaiden
Well-Known Member
Ok, so let's complicate things a little more, from an outdoor grower's perspective. Surely sunlight has different qualities, as such, these qualities should be able to be quantified, scientifically. Is this an erroneous assumption?
What I am having a difficult task of determining is how important sunlight at time of day is to the plant's ability to photosynthesize. I am limited in that I can only grow on a southwestern-facing area, where square footage that is exposed to sunlight is becoming an issue. It gets direct sunlight, but later in the day.
If you like I will post pix to help illustrate what I mean, but essentially I've got some areas that are only getting direct sunlight at about 38.4*N-lat. (I think I've got that right) from anywhere between 2:15--7:30pm (guessing on the last number), and for the upper tier from 3:30pm--7:30pm. Is that going to be sufficient sunlight of sufficient quality? This is what I have been unable to ascertain with any precision.
I have just separated the plants based on perceived phenotype, in other words, what I perceive to be an Indica or Sativa dominant strain, or a dominant combination of the two. Completely arbitrary, other than based upon what I've read and seen now that I think about it, but, there ya go. I figure if there are differences in their needs based on that phenotype or preferential expression, maybe it will help me best meet them.
Maybe I'm looking in the wrong way (asking the wrong question), yes?
What I am having a difficult task of determining is how important sunlight at time of day is to the plant's ability to photosynthesize. I am limited in that I can only grow on a southwestern-facing area, where square footage that is exposed to sunlight is becoming an issue. It gets direct sunlight, but later in the day.
If you like I will post pix to help illustrate what I mean, but essentially I've got some areas that are only getting direct sunlight at about 38.4*N-lat. (I think I've got that right) from anywhere between 2:15--7:30pm (guessing on the last number), and for the upper tier from 3:30pm--7:30pm. Is that going to be sufficient sunlight of sufficient quality? This is what I have been unable to ascertain with any precision.
I have just separated the plants based on perceived phenotype, in other words, what I perceive to be an Indica or Sativa dominant strain, or a dominant combination of the two. Completely arbitrary, other than based upon what I've read and seen now that I think about it, but, there ya go. I figure if there are differences in their needs based on that phenotype or preferential expression, maybe it will help me best meet them.
Maybe I'm looking in the wrong way (asking the wrong question), yes?
homegrownboy
Well-Known Member
If that's the only light it's going to get then no...you need at least 12 hours of sunlight a day for proper growth...put the plant inside and grow under floruro's or cfl's for the time it's not getting any sunlight. I utilize the sun everyday i can...but i'm lucky and have the sun shining on my porch from 8:30am till about 6-7pm, and then the remainder of the time i stick them under my flouro's. The reccomended is a schedule of 18 on, 6 off, i myself now am doing a schedule of 16/8.
Seamaiden
Well-Known Member
Hm.. I've read in a couple of books and on this site that the minimum for direct sunlight, outdoors, is between 5-7 hours. Not 12.
Either way, I can't keep up the electricity on extra lighting, so that won't be happening. If I have to move the plants down below or reconstruct the shelving they're on, that's what I'll do. The light they're getting from 2:30pm on has been enough to give them some pretty good growth. It's the upper level that has me concerned (but also gives me floor space). I will be culling soon because I'm finally seeing some definite pre-flowers, some of which are inmistakable. If I end up having to cut out enough plants, then floor-space won't be a problem.
My question really has more to do with the quality of light during that time of day, as the more information I can tease out, the better I can adapt conditions for the plants I'm growing, and vice versa.
Either way, I can't keep up the electricity on extra lighting, so that won't be happening. If I have to move the plants down below or reconstruct the shelving they're on, that's what I'll do. The light they're getting from 2:30pm on has been enough to give them some pretty good growth. It's the upper level that has me concerned (but also gives me floor space). I will be culling soon because I'm finally seeing some definite pre-flowers, some of which are inmistakable. If I end up having to cut out enough plants, then floor-space won't be a problem.
My question really has more to do with the quality of light during that time of day, as the more information I can tease out, the better I can adapt conditions for the plants I'm growing, and vice versa.
homegrownboy
Well-Known Member
Quality?...ok...it's the sun, isn't it the same all day? I would think that the coolest time with full sunlight would be best, as heat will stress your plants and stunt them, and it only gets hotter throughout the day, so by 4-5pm it's the hottest time...at least where i am it is like that in the summer time.
Seamaiden
Well-Known Member
Yeah, that's exactly what I'm reading that most growers agree on, morning (eastern) light is better if it has to be cut up, so to speak. But, I can't do that, or almost all the neighbors would see what I have.
I don't think the sunlight's quality is the same throughout the day, though. You hit on one point that's coming up for consideration as things heat up, too. I've got to strike a balance between giving them the light they need, and protecting them from getting overheated (which, I've read, is one of the stressors that can lead to hermaphrodism in female plants, but no one's ever complained about their male going female).
Now, where I used to live, by 3-4pm you were getting the hottest part of the day (further south than I am now). Here, the days are noticeably longer, and at 5pm the sun is still pretty high (sometimes, so am I). On one hand I'm fairly certain it's good quality light (sufficient brightness, etcetera), on the other I am concerned that during this vegetative phase it may peter out too quickly before my garden is ready to flower. Btw, I've just begun the sexing of them, haven't been able to find pre-flowers before and now I am. If ONLY I could take pix through my jeweler's loupe.
Anyway! While the plants are growing I think about this shit and let it worry me.
I don't think the sunlight's quality is the same throughout the day, though. You hit on one point that's coming up for consideration as things heat up, too. I've got to strike a balance between giving them the light they need, and protecting them from getting overheated (which, I've read, is one of the stressors that can lead to hermaphrodism in female plants, but no one's ever complained about their male going female).
Now, where I used to live, by 3-4pm you were getting the hottest part of the day (further south than I am now). Here, the days are noticeably longer, and at 5pm the sun is still pretty high (sometimes, so am I). On one hand I'm fairly certain it's good quality light (sufficient brightness, etcetera), on the other I am concerned that during this vegetative phase it may peter out too quickly before my garden is ready to flower. Btw, I've just begun the sexing of them, haven't been able to find pre-flowers before and now I am. If ONLY I could take pix through my jeweler's loupe.
Anyway! While the plants are growing I think about this shit and let it worry me.
ceestyle
Well-Known Member
I think there are two major questions entangled in one another here. One of them I can answer, and one I can only speculate on.
1. What is the difference - if any - between receiving constant, weaker light, and the same total amount of light through some time-dependent intensity that depends on where the sun is in the sky?
From a photosynthetic perspective, this shouldn't matter. The flux of photons is so relatively sparse that at intensities we observe in nature, the plant's energy conversion machinery should not be overloaded. I've had to do the exact calculation for solar cell work, and there is very very little chance that two photons hit the exact same spot, so they don't physically interfere. If you jacked up the intensity, you would run into the problem that the supporting pathways for the carbon cycle simply could not keep up the rate of light conversion - assuming you had enough CO2 present to keep it running. As we have generally observed, however, along with the important wavelengths for photosynthesis, we also get IR, so before this happens we would get the leaf burning that we sometimes observe. If it weren't for these limitations, we could give a plant its day's worth of light in a minute! That sure make a light mover VERY efficient!
So assuming you have an intensity vs. time situation that looks like the attached plot, you can figure out the total energy you are giving your plants as being proportional to the area under each one of those curves.This again assumes that you're not spiking the energy so much that the plant can't digest what you're giving it. Given even total energy input, the plant has done the same amount of work to convert the light energy.
This is essentially the same principle light movers operate on: same total energy over a different amount of time. The short burst avoids the heating problems of the IR.
2. What affect do the differences in light distribution have on the plant?
This I can only speculate about. The fact that you're seeing preflowers doesn't surprise me. I've got outdoor right now that is in full-on flower. This alone defies the notion that if plants receive more than 12 hours of light - any light - that they will remain vegetative.
I would imagine that the response is a result of the decrease in total light that it has received, assuming it came from indoors. What makes sense is that the plant adapts to whatever environment it is in to grow vegetatively, and as the sun wanes - from whatever its maximum is - the plant responds by flowering. This would also explain why it is strain-dependent, as different varieties have evolved to thrive in completely different local environments.
I'll think more about this, but I think this is a case where - unless we have a botanist that knows what he/she is talking about - the experience of outdoor growers trumps for predicting how a plant will respond in terms of if it decides to flower or not.
Hope that helps.
cc
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Seamaiden
Well-Known Member
That is one hell of a serious answer there, cee. You are helping me get to the meat of what I'm trying to formulate in my head. I only have a very rudimentary light meter, and any/all sunlight pegs it high. I've also been wondering how greenhouse conditions would affect this plant, presuming it absolutely requires a barest minimum of five hours direct sunlight. Wouldn't it mimic shade? If so, how deep the shade (again, presuming this is a standard type of greenhouse of the type where other flowering plants can be grown)?
Look in my gallery, you'll see the current growing conditions. Been out there since seedling stage, but my husband just built me a rolling shelf unit that effectively doubles my usable floor space. Been utilizing LST as well. I also started a thread on the sexing process, did this after separating plants based on physical expression (phenotype?) in terms of growth habit and leaf structure. This will allow for some serious culling.
If I could easily take my own measurements, I've surely got the time. I just don't have the equipment (unless the camera has features I could use, Canon Rebel series DSLR). I do have fun turning the lens backwards for super macro close-ups.
Thanks for this, cee, this is very rep-worthy stuff.
Look in my gallery, you'll see the current growing conditions. Been out there since seedling stage, but my husband just built me a rolling shelf unit that effectively doubles my usable floor space. Been utilizing LST as well. I also started a thread on the sexing process, did this after separating plants based on physical expression (phenotype?) in terms of growth habit and leaf structure. This will allow for some serious culling.
If I could easily take my own measurements, I've surely got the time. I just don't have the equipment (unless the camera has features I could use, Canon Rebel series DSLR). I do have fun turning the lens backwards for super macro close-ups.
Thanks for this, cee, this is very rep-worthy stuff.
Ganjaglutin
New Member
I've Gotta A Pretty Simple Question.
Is There A Maximum Level Or PEAK Of Light A Single Plant Can Photosynthesize Or Use?
Is There A Maximum Level Or PEAK Of Light A Single Plant Can Photosynthesize Or Use?