(μmol/s)/(PPFD) with respect to Hang height
- Thread starter ChiefRunningPhist
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- hang height ppfd umols μmol/s
wietefras
Well-Known Member
No it does not. The point is not that inverse square law does not occur at all, but that when you reflect light back into the same space it does not spread out according to a "square law". You are then only left with reflection losses and inverse square is irrelevant for a grow room with reflective walls and/or overlapping light sources.
How far does light travel in a glass fiber cable? I'll give a clue, for miles. So where is inverse square law then? Maybe the light is constrained inside the glass fiber and cannot spread?
Green houses have lights hanging on the ceiling. Many meters above the plants. According to inverse square almost no light would reach the plants from that far. Yet somehow it works. Overlapping of the light sources makes the difference maybe?
wietefras
Well-Known Member
That link only contains utter nonsense.
ChiefRunningPhist
Well-Known Member
I'd semi agree with your perceived disregard for ISL if you're designing your light to need close-by reflective walls in order to achieve whatever PPFD you claim. But even then there's certain hang heights that work better than others... You're not eyeballing reflector edge angles (if you have). You know the beam angle of the chip you're using and the distance from the reflective wall, ect. So to say that ISL has no place in a light designed to be used near reflective walls is misleading. And not every light is desgined to use a nearby wall as a reflector.
The multiple point source statement is false. The fact stands that the light intensity at canopy will be inversely proportional to it's hang height. ISL most certainly plays a huge role in greenhouse lighting. As you say, there's not much of the initial intensity left when they hang that high... that's why they need so many. Also they are maintaining PPFD below canopy much better than if the lights were hung 24" away.
Fiber optics utilize NIR not visible and work on a bit of a different principle. ISL still applies inside a fiber cable though. Once something starts on a trajectory it can't be moved from it's trajectory magically. Something needs to act upon it. Light can't change its beam angle by itself, it can't disobey the ISL, putting barriers in the way and changing the trajectory of the light doesn't diminish the ISL, rather you're only manipulating the light, and based on the ISL. You wouldn't have to have a reflector built in such a way if the light didn't follow the ISL. The tent wouldn't act like a huge reflector if the light didn't exhibit the properties described by the ISL. It's always there.
Someone didn't decide to make a physics law one day and say that light has to obey it. No, they observed light, and based upon those observations they came up with the ISL. It's been proven, not because someone wanted it to be true, but because it is.
eatled
Active Member
Unless you have a relevant citation your "theory" does not hold weight.
You make an assumption there is an applicable reflective surface.
Does Inverse Square hold up if no reflective surface exists?
I did enjoy your comparison to fiber but that's a whole different set of laws and statistical probability. The surface properties (e.g. diffraction) in fiber do not exist in open air. You could use optics to create a collimated beam to nullify the inverse square law but that would not work well for the plants.
First you must calculate the energy of the photons that come directly from the point source(s) to the target points.
If it were possible to calculate reflection probabilities to each target point, taking scatter, absorption, transmittance, phase of the photon into consideration it still will not nullify Inverse Square Law of the direct photon paths. You sum the reflected photon energy with the direct energy. Both the direct and reflected waves must follow the Inverse Square Law, there are no exceptions.
ISL is a basic elementary law of physics and reflection is extremely complex. Reflected waves are measured not calculated (estimated) due to the complexity.
You need to understand a photon is an oscillating sub-atomic particle. It's not like a ball bouncing off a surface. It's reflecting off the energy of an atom not a flat surface.
What? I mean seriously. What is so different about a greenhouse light that it can defy an elemental law of physics? It somehow works because it does. Maybe you are missing the summation of the photon energy from of all the fixtures rather than the light directly above the target point. If the target point is receives photons from every light where the path is unimpeded. Greenhouse light is supplemental to solar and is not expected replace solar.
Really? Come on now. It's a simple table with Inverse Square calculations. Many here should find it quite handy when adjusting light height and intensity.
I checked a few of the calculations and they appeared to be correct. I do not understand why you would refer to ISL as utter nonsense.
It's not fair to the readers of your opinion without explaining how your theory is superior to that of Einstein, Planck, and Feynman.
I need more than faith than you are correct. Faith is believing what you know ain't so. Nobody deserves to be helped who don't try to work himself, and "faith without work" is a risky doctrine. I'm sorry I cannot take your theory on faith, you must include citations and a valid argument. Just because you say ISL is not applicable is not proof.
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wietefras
Well-Known Member
Are you seriously claiming that you need 100 times the amount of light when you hang them 2 meters high as opposed to 20cm?
They don't need "so many". You simply need say 800umol/s per square meter of grow area (or whatever you are going for). It does not matter if the lights are at 20cm or 2 meters.
Well you would see some more reflection losses if it's higher, but for a greenhouse those wall losses are negligible since the room is so huge. That's why they can hang them so high.
A greenhouse light plan is simply calculated to send enough light into the grow area. The height and number of light sources only determines the spread and therefore uniformity. That's all.
There is no one who applies inverse square calculations on fixtures.
ISL applies of course, it's just irrelevant when considering hanging height of a fixture in a grow room. Reflective wall losses and uniformity of light are the values actually affected by the height.
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wietefras
Well-Known Member
Yes and it's utterly useless. Especially the way you apply it with that penetration nonsense where you left out the top part.
You need 25600 or 32000umol/s/m2 at 5" to still get 400 or 500umol/s/m2 at 40". If ISL actually applied!
So you were comparing a 25600 to 32000umol/s/m2 stadium light to a 400 to 500umol/s/m2 flashlight and then conclude that the stadium light has a better spread of light. Wow really?
You'd need a 13 kilowatt light fixture over a 3x3' area to pull this off (if ISL actually applied the way you have convinced yourself it does).
It's just staggering how you can even believe that any of this works the way you claim it does.
I'm not saying anything to contradict anything they say. You are.
Light going into a room does not disappear until it's absorbed. You pretend it does.
You actually measured this yourself when you were using one of your other banned aliases before. You actually showed that ISL does not apply to hanging height of a fixture. Yet still you keep pretending it does
For anyone doubting actual science instead of bro science. Just try it yourself. Hang the fixture on the ceiling. Take an intensity measurement 20cm below the fixture and then 200cm below. Do you see only hundredth of the light intensity going from first to second measurement? Really?
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Moflow
Well-Known Member
I can't wait! Been too quiet for too long......
eatled
Active Member
I was not comparing any such thing.
All I am saying when light travels through open air, ISL applies. No matter what you say.
BTW umol/s/m² is a measure of irradiance on a 1 m² surface not the intensity of a lamp.
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eatled
Active Member
That's just silly talk.
I have not claimed how it works, I'm just saying it work in response to you say ISL does not apply to grow lights.
What I find staggering is how your mind still almost functions.
That is ridiculous. Do you even think before you type?
I think you mean an irradiance or illuminescence measurement. Do you have an intensity meter?
True. The problem is that the majority of reflected photons will not be absorbed by leaves.
Eat lead
ChiefRunningPhist
Well-Known Member
How do you calculate the hang height to achieve 800 μmol/s? Will the walls effect this target PPFD? Believe it or not, but that calculation, your HID spacing, hang height, HID fixture beam angle, ect for the target PPFD of 800 μmol/s, is literally based on and making use of what the ISL describes.
I honestly think you get it despite the times you contradict yourself, but tbh, imo, it just seems like you just don't want to call it the ISL. You'd rather call it a uniform spreading, or a distribution, or something of that nature. It's the same thing but scientifically referred to as the ISL. There's certain things you're missing.. Like if the point source isn't a 360° emmission ect, but you're pretty much understanding. I don't think I can explain any better than I already have. I know that I'm correct, and that these are the facts. I'd urge you to call your local university and ask for the physics department and explain your situation, they'll be able to thoroughly explain it in person so there's no ambiguity and sometimes hearing it from someone else will make a difference.
Because the room is so huge, those losses are actually more so, than what a smaller room would exhibit. You have less light reflecting back in to scew the primary trajectory into a secondary trajectory. Losses would be more.
Engineers do. Light consultants do, most will use a program, but what do you think the program does?
ChiefRunningPhist
Well-Known Member
It depends, I think you'll agree that if the emission were 360° instead of 45° that you'd need different hang heights to achieve the target PPFD. In order to calculate what distance you'd need you'd need to take into account beam angle eh? When you try to use an ISL modeled from a 360° emmission but the light/fixture isn't a 360° source then you're calculation will be off.
I'd have to look harder into the rayleigh range ect to have a more scientific/mathematical explanation because I'm still perplexed atm about the rayleigh range and lasers, but like I said your university is a much better source on the matter than I. I know what I know, but I also only went through undergrad, those other guys are the real brains..
wietefras
Well-Known Member
You multiply the the total number of m2 by 800umol/s and divide the light sources uniformly over the space. Height is not relevant for that.
Ehm I just said:
Height is only relevant for distribution. When you need to spread light over 10m2 you need more height then when you want one COB to cover 1sqft.
Again I'm not debating that inverse square law applies. The fact still is though. No one calculates ISL when they are calculating how many lights to hang or how to space them or how hight to hang them.
But I guess at this point you are just debating semantics.
I'm not. You simply don't understand what I'm saying or you are reading only fractions of it and not the whole thing.
They would be more in absolute sense, but still negligible. A bigger room has relatively less wall space relative to the floor space than a small tent.
wietefras
Well-Known Member
Yes you were. You just don't understand that you did.
Just use your calculator. When you get 500umol/s/m2 at 40" how many umol would that same light source give you at 5"? 32000K yes.
That's the only thing of all that you say which is true. The only thing that does say is that the light spread out though. That doesn't mean it disappears. That's where you are going wrong.
Exactly. You are finally getting the hang of it. If you had really understood what you that statement actually meant.
It means that if you spread 800umol/s over a 1m2 space you get 800 umol/s/m2 average light intensity. See how height is nowhere mentioned in that calculation?
Rocket Soul
Well-Known Member
I smell primo, exclusive asshattery...