Hey Ice. If you do not mind me asking another question about lights and showing my noobishness with my ignorance, I would like to know why wattage is so important to yield. I mean why do you and so many others compare yield to how much wattage your lights draw? Wouldn't par footprint, spectrum, and canopy penetration be more important? Just curious.
I ordered another 350 xml this past week. I will get it early this week. When I was talking with Advanced on the phone, I told him that I had the lights at 20 inches over the canopy and I was only getting about a 2.5 - 3 foot squared foot print of direct light. He said I was not the first one to tell him that. LOL. Yes I know they use a par meter and a grid at given heights to figure out the footprint. But maybe they need to rethink what they are calling core. Anyway with the third light and they way that the lights will overlap on the margins I am hoping to get about 15 squared feet of core coverage and then we will see what happens on the margins.
I hope you do not mind this post. I did not mean to hijack.
Hey Bamalabrat!
I never mind LED questions
Well I think what you are asking is why people including myself list grams/watt??
Grams Per Watt is not really a measurement that means much, besides kind of bragging rights in a way, as well as a goal for most growers to achieve. I personally track grams per watt really just to get an idea of how my grow turned out, but really there is not quantifiable rhyme or reason to it, other than my personal goal for my grow area, and a number to try and beat next grow.
Before LED lights came into the market strong, a good HPS grower was typically hitting about 1 gram per watt (according to talk around the forums and others) but now that LED is out and slightly less wattage can be used (about 20% less is typical), now you are seeing growers hit slightly higher than 1 gram/watt, and more towards 1.4 grams/watt I seem commonly. Again, this doesn't really mean too much and I will explain why.
The reason why grams/watt is really just a bragging right, and not a solid piece of data could be explained like this. Say you have 2 growers, one in hydroponics with synthetic nutrients, the other with organic soil. In most cases the hydroponics plant will yield much higher than that soil organic plant and if you were using the grams/watt, the hydro grower would have a much higher gram/watt.
Now lets use the same example, 2 growers, one hydro with synthetics, the other with soil and organics, but this time the organic grower heavy yielding strain like blue dream, the hydroponic grower has a low yielding strain like cookies. Now you would see a more even gram/watt most likely between the 2 growers.
Now lets use one more example: 2 growers, 1 hydro synthetic, 1 organic soil. They each have the same environment, same genetics, but one scrogs their plant, and the other just grows it without the training. The scrogged plant most likely would yield higher than the one without training. Again there is a difference in gram/watt even though its the same growers, same environments.
I'm tired while writing this, so I hope it makes sense. But basically I wanted to show how gram/watt has so many variables that can effect it, really you can't use it to measure much beside use it as a guideline or goal. Now one could use it if lets say they have grown the same genetics the same process for a couple years under HPS lights, then they switch over to LED, but every single other thing is exactly the same as before, only the light changed. Now lets say that the next year or 2 the grower uses LED. quite possibly the difference in gram/watt for HID vs for LED would show a slightly better efficiency, therefore the grower since nothing else was changed, could say, yes I am using my electricity more efficiently than before. But for this kind of measurement to even have a slight bit of accuracy for judgement, every single variable would have to be the exact same, except for the change in lights...
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Now I'm not sure about the 2nd part of your question, but I think you may be referring to how some people say things like, "you should use at least 35W per SQ foot" or "50w/sq foot is ideal". This used to be somewhat accurate for HID lighting because HID lights didn't change much in technology over the last 30 years, and their output is fairly uniform, even and similar. So back before LED's, a lot of growers would refer to HID lighting by saying "50w per sq foot is good" and things similar to that and it could be deemed as decent guidance.
Now that LED has entered the picture, wattage per square foot is no longer a valid way to estimate lighting. The reason for this is LED's are very directional, usually the footprint contains a very hot/intense spot over the center 1'x1' area, and as the footprint widens, the intensity drops off very very quickly. Since LED usually does not have a uniform/even coverage, using watts/sq feet can't really show how the light would actually illuminate an area properly because different LED's spread the light differently depending on quality of chips, lenses, reflectors and other optics, led array density and other things. So the example I like to use is a flashlight, lets say a 5w flashlight. Now this flashlight has a zoom lens, and you can make it a floodlight, or a very intense single spotlight. If we were to shine it on a surface, quite obviously the spotlight would be very small footprint, but very intense, where as the floodlight setting would have a very large footprint, wiith very low intensity. Both cases though, are both from the same 5w flashlight. So if you wanted to measure a light source by wattage per sq feet, would it work in this case? nope!
You are right, the correct way that lighting should be measured is by using measurements of PAR or Fluency rate is the fancy word for it. This is how professional researchers, greenhouses and agriculture do it and cannabis is no different in the way light is measured. Now Measurements of PAR can be used in different ways.
First there is PPFD, which stands for Photosynthetic Photon Flux Density, and this measures how many photons (the quantity) are falling on a 3 meter square, every single second. The reason that PAR measurements (fluency rate) or PPFD is used by many professionals, is because it translates directly to how a plant uses photons and is directly related to the rate of photosynthesis. A plant is a photon counter basically, and it takes around 8 photons absorbed to destroy/break apart one molecule of CO2. So the more photons a plant is receiving the higher the rate of photosynthesis up to what is called the saturation point when the plant can't handle any more photons.
Now PAR measurements can be also taken in a way called PPF, or Photosynthetic Photon flux. This is typically measured in an ulbricht sphere or integrating sphere, which is a highly reflective sphere, a light is placed in, and it measures the total photon output in all directions of the light. This type of measurement doesn't have much application in LED since many things effect a LED and the way it outputs light, but is very useful for HPS and MH bulbs. What PPF is used for mainly is showing how many photons a bulb at a certain wattage puts out, vs another bulb at the same wattage, or photon efficiency. Since the bulbs are placed in a reflector of choice, and the reflector doesn't change the light output between bulbs, the PPF will show which light is providing more photons, which then can be reflected down to your plants (total photon output is PPF)
Now is using PPFD perfect? well yes and no. for judging plant lighting in the aspect of coverage, it is ideal, but there is a problem with PPFD and PAR readings. PAR stands for all the photons between UV and IR (violet to deep red) and sometimes even includes some UV and IR depending on the meter and who is measuring it. These are the photons that plants use for photosythesis. Now the problem is that each photon is given a counted number, but does not tell what color/wavelenght each photon is, it measures them all equally. Some photons will be absorbed better than others, for instance green is typically absorbed about 79% where as blue and red/orange is around 99% and deep red around 95%. So for other things that can effect plant growth like photomorphogeneis, PAR doesn't help at all. And this leads into the spectrum part of your question.
Plant lighting and the proper spectrum is not quite known by scientists and botany researchers as of yet. We have a good idea of what spectrum is ideal (the sun) but there are many conflicting research papers about how each species of plant uses these spectrum differently, and how they effect the plants growth. Since the Perfect spectrum is unknown and the area as a whole needs a lot more research, there really is no answer of what spectrum is better than another...and no way to measure it or quantify it. We do know certain things, like plants absorb more red and blue then green (slightly) and that when using red light, adding IR will help increase photosynthesis (Emerson effect) this is why you see a lot of LED lights with red, blue and white chips in them but this is also the reason that every LED company has a "proprietary spectrum" and they are all different.
The fact is, nobody really knows what is ideal. And there really isn't a way to measure it, unless we measured a specific strain/genetic phenotype with a lab and a largely controlled study, using machines to test the rate that the plants use the available CO2 in a sealed container. We would have to test each band of light/wavelength and then plot the results to get an idea but even this could change with different genetics, even if its the same plant species. Most complex land plants will be similar, but still act independently of each other if you get down to the details. So to answer your question, spectrum is not really a way to quantify a light better than another, because at this point, we only know so much about spectrums and how plants interact with them, so mostly is a educated guess choosing between spectrums.
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Canopy Penetration is another word that is tossed around a ton, without most people really understanding what it means, because it really isn't set with a single definition or measurement or solution. To one penetration might mean a super bright intense light has better penetration because its brigher. To another penetration might mean that the bottom leaves are getting enough light. Now does penetration always equal a brighter light...not exactly. Since there is no proper definition of penetration for plants, or a way to measure it, the way I consider looking at is as the "range of acceptable light" meaning that a certain light will illuminate a plant from the top, to the bottom, with the right range of intensity or PPFD (photon count). Or another way of saying it "is my entire plant getting the right light from top to bottom"
A plants needed light is called in the horticulture world DLI or daily light integral. This is the total amount of photons a plant needs during its daylight period. To simply explain it lets use our favorite plant cannabis. Its said in the reasearch I have done that cannabis needs a DLI of 22-65 Mol/Day/meter squared to grow properly. If we were to break this down to PPFD, this would mean in a 24 hour daylight cycle, a cannabis plant would need a PPFD of 255 micromoles/m2/s-1 to 751 micromoles/m2/s-1 with no dark period. Therefore if you are vegging plants, this tells you the PAR measurements needed to be at optimal light for optimal growth. Now if you wanted to know for flowering, in a 12/12 schedule, you would multiply those numbers by 2, since you are removing half of the days light (12 hours vs 24). This would mean that cannabis needs aat least 510micromoles/m2/s-1 up to 1500micromles/m2/s-1 for optimal light during flowering.
Now back to penetration and the acceptable range of light. Knowing now what PPFD you should need, you can determine the "range of acceptable light" or penetration in flowering should be between 510 micromoles and 1500micromoles. So by knowing this andd when you look at a lights PPFD chart over a 4x4 grid, by looking at the different readings between heights, you can see what the range of this light would be. For instance if you have a light that puts out 1500 umols at 24 inches, and only puts out 500umol at 36 inches, then you can see that the penetration for optimal growth would be about 1'. Now this penetration can be perfected by different things. You could achieve better penetration wiith lenses that focus the beams of light, to make more of a spotlight type beam, which lengthens the range of acceptable light, because light doesn't spread out as fast in a narrow beam. Another way to achieve better penetration is to use multiple lights, hung at a distance from each other. This reduces shadowing from a single overhead light, and allows light to enter the canopy at multiple angles, reducing shadowing and giving better penetration. Another way to increase penetration is simply adding reflective material to the grow area which reflects the light and increases the angles the light can penetrate the canopy. So again you see, there isn't one definition of penetration, and there are many ways to achieve better penetration. But when you see companies saying better penetration, do you think they really know what they mean? I don't
since its so loosely defined and without a way to measure.
Since light spreads out and loses intensity over distance (inverse square rule) a light that we use for growing plants usually has a very limited "range of acceptable light" where as our sun millions of miles away has nearly the same intensity on the ground as it would on top of a 20 story building. Quite obviously the sun has a huge "range of acceptable light" where as a grow light may only have about 1' to 3' of "range of acceptable light)
So now you have a PHd in plant lighting...LOL j/k... I hope you followed that ok since it is a pretty in depth explanation with a lot of terms that many are not familiar with. I also hope it helped explain plant lighting to you so you can understand it much better.
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As far as the advanced led panels.. thats awesome you are getting another. I really don't know why pretty much every LED company I have come across online stretches their coverage areas on their recommended grow area/footprint. I really don't understand why they do this, other than they actually don't understand plant lighting either. One could say that some plants like lettuce have a much lower DLI than cannabis, therefore, the light actually has a larger footprint for lettuce than it would for cannabis. So I guess they could justify it as for low light crops, but unfortunately they don't and most LED companies are clueless in terms of what I just typed above. Not saying this is the case with advanced, as they do provide a lot of solid data on their products, but I still don't know why they stretch the footprint, even having done the PPFD readings, they should know exactly what size the lights are good for. Every LED company I have come across does this, I don't know why.
The overlapping of the panels will actually expand the area, as you are getting light from both panels to raise the PPFD in between the lights to acceptable levels. I would guess that putting 2 xML 350s side by side, with about 1 1/2' to 2 feet in between would give a coverage area of about 3' x 7' or so maybe even 3' x 8'.
Well now that Chapter 1 of my book is done...LOL I will be quizzing you all tomorrow, and no cheat notes either! lol j/k everyone.
Hope this helps everyone understand lighting much clearer now