Changing distance to plants vs dimming

i tend to agree with greengenes as i run in a tent, but it also depends on situation. if they are tiny clones, dimming is fine. if they are really tall you will lose out on a lot of "penetration" (i hate that term as its so abused) by running too close

like as an example say you can get 700 ppfd to the top of canopy by either dimming or raising the lights and running it hotter:

dimming at say 6" distance: 700 ppfd at canopy, your light intensity will rapidly fall off 6-12" into the canopy as that is 2 and 3x the distance from light to top of canopy

raise light to 18" and crank it up: same 700 ppfd at the canopy, and much higher ppfd at 6 and 12" below canopy than the example above, as it is now only 1.33x and 1.66x the distance from light source to top of canopy at those respective depths. You can use the inverse square "rule" (which isnt super applicable in many applications but should give you at least a minimum intensity by pretending youre in an open non-reflective space

PLUS if in a tent or appropriately sized room youre getting all the reflected light off the walls penetrating lower canopy from different angles

Greengenes707 said:

And prefer full and raised to hit a lower PPFD. I simple get more growth faster, and is hardier.

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i personally think this keeps stretch down as well when a plant has overall uniform intense light top to bottom

CobKits said:

if they are really tall you will lose out on a lot of "penetration" (i hate that term as its so abused) by running too close

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How would that work? It's really the opposite. Not only have you lost 20% of the light to begin with, you also lose the light at shallow angles which can much easier slip between the leaves.

HPS growers put their light close to the plants (half the advised distance) to increase penetration. And that really does work.

I'll bet that if you have plants that struggle with too much light that it's better to lose some of that light. If you have healthy plants growing in a system that allows them to cope with that light (usually not the case in soil) it's better to give them all they can take.

guess we'll have to agree to disagree.

Thanks @CobKits ! good point.

It's not a matter of opinion though.

Although things also depend on the grower. If you are growing under HPS and you are getting 0.7g/W at best, your plants won't be able to deal with very high PPFD when you switch to COBs. HPS growers who are already in the 1g/W to 1.3g/W range have a much better optimized system and can go much higher in PPFD and still have benefit.

People keep throwing that chart around where the max PPFD is at 1500umol/s/m2. That's a leaf test though. They measured a leaf and checked how much light it could take for a very short term. It's not a test for the whole plant over a longer term. Poorly maintained plants won't even be able to cope with 700umol/s/m2.

For penetration, it also matters if you grow a few single plants with lots of room around. Or if you have a grow where the canopy is pretty much completely filling up the place. In the case of the latter, you won't get penetration from direct light. Direct light hits the canopy and basically that's it. You need the spread and shallow light from all the COBs around close to the canopy to get light to pass through. The little bit of diffuse light coming all the way from the walls isn't going to do much.

wietefras said:

For penetration, it also matters if you grow a few single plants with lots of room around. Or if you have a grow where the canopy is pretty much completely filling up the place. In the case of the latter, you won't get penetration from direct light. Direct light hits the canopy and basically that's it. You need the spread and shallow light from all the COBs around close to the canopy to get light to pass through. The little bit of diffuse light coming all the way from the walls isn't going to do much.

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From this I assuming it's better to focus lights directly over bud shots than leaves from other part of plants? As this method will be better not to have popcorn buds...
It seems no matter how much PPFD you have over complete plant, if you don't have light over buds, they'll get fluffy.

wietefras said:

It's not a matter of opinion though.

Although things also depend on the grower. If you are growing under HPS and you are getting 0.7g/W at best, your plants won't be able to deal with very high PPFD when you switch to COBs. HPS growers who are already in the 1g/W to 1.3g/W range have a much better optimized system and can go much higher in PPFD and still have benefit.

People keep throwing that chart around where the max PPFD is at 1500umol/s/m2. That's a leaf test though. They measured a leaf and checked how much light it could take for a very short term. It's not a test for the whole plant over a longer term. Poorly maintained plants won't even be able to cope with 700umol/s/m2.

For penetration, it also matters if you grow a few single plants with lots of room around. Or if you have a grow where the canopy is pretty much completely filling up the place. In the case of the latter, you won't get penetration from direct light. Direct light hits the canopy and basically that's it. You need the spread and shallow light from all the COBs around close to the canopy to get light to pass through. The little bit of diffuse light coming all the way from the walls isn't going to do much.

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Until you have a 3D topography map of every incident angle(including reflected) and every angle of leafs surface...you are as much of an opinion as anyone. You are thinking in a simple(not how reality works) flat plane. Canopies, as great a grower can be, are not flat, and nor are the plants that take on that light.

The notion that incident angles matter sounds very much like an opinion yes. The leaf either absorbs the photon or not. The few photons that bounce off will go to the next leaf.

Show me any research that certain angles work better than others?

Leaves are aimed at the strongest source of (blue) light. Which will be the nearest COB above it. The penetration will come from the COBs surrounding that COB. Which means that that light will be at shallower angles than the light coming from the COB overhead and it will be easier to slip under the leaf and penetrate deeper.

So you start with 20% more light at the canopy. From there it's extremely to simply check how much light penetrates the canopy. That's a lot more when the lights are 12" instead of when they are 24".

All you need is a quantum or lux meter really.

Stop assuming and read. I never said "certain angle work better than others"

I said you change them. And by doing so you do not get the same 3D interaction changes that a simple single perpendicular spot measurement can portray. Relfected, refracted, transmitted....simple flat plan measurement can not account for.

And also stop assuming that "raising" it mean by meters or feet. Reductio ad absurdum is not a good way to show a point.
Inches mater in the game of maintaining ppfd. But factors and variable change with every adjustment.

So again. Flat plane does not show the true photon density of an entire crop.
I and most others grow crops, not a few leaves on top a plant.

Incident angle, leaf orientation information and studies(yes there are better angles than others)...

- https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/treephys/23/18/10.1093/treephys/23.18.1255/2/23-18-1255.pdf?Expires=1497811385&Signature=Wx623pjpxhcI3p1XibM2BsG1LKqHJuo7CWDWGfxHccw3LJvsZ9bwYG74WG5kDnays2aEpcEKQVLo~yzqZ~2nJQ41VfWutxYvNO4dWCL4MphzVIWzoD9rZExBdnNDT68ItYynpHtgiOhngcVQXVxQBwccKJWQVlSt0R68sQc1ekd714uuZDnZK7~-2-irZ84IxWzlv3hC6Gi94Dp72olzEEmUgwu4RKCXdmUaPsBFX1mtmrLjiJamZWofThjGlHXrxBDEAj7xebG~0CR7yFttRp-GTg5-RMmQanYySZklzOEnCAk5w5lydbxb3B32xcR6DkkMQHIWq4Lo04oKo1SNbA__&Key-Pair-Id=APKAIUCZBIA4LVPAVW3Q

- https://www.jstor.org/stable/2444470?seq=1#page_scan_tab_contents

- http://onlinelibrary.wiley.com/doi/10.1046/j.1469-8137.2003.00765.x/full

- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3400442/

thanks for links, why you gotta drop those on sunny summer days

Greengenes707 said:

Stop assuming and read. I never said "certain angle work better than others"

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I read it and you are just stringing along a few terms to sound cool.

I said you change them. And by doing so you do not get the same 3D interaction changes that a simple single perpendicular spot measurement can portray. Relfected, refracted, transmitted....simple flat plan measurement can not account for.

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See? You really say nothing concrete with those words. I could say the exact same thing to the opposite. In fact I did, but with an actual explanation of how it works.

And also stop assuming that "raising" it mean by meters or feet.

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Stop assuming and READ! I said when you raise the lights from the optimum 12" to 24". Which is exactly what you do.

So again. Flat plane does not show the true photon density of an entire crop.

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It DOES. You measure it at one level and the light travels down from there. There really is no magical difference in how the light propagates down whether the fixture is at 12" or 24". The photons will be absorbed somewhere. Better on the plants below that plane than on the walls above them.

You are telling people to waste 20% of the light on some mumbo jumbo about 3D interaction. While everybody knows that photons on the plants is what grows them. You will have to come up with some hell of an explanation on how losing 20% of those photons (or adding 25% more photons initially, to compensate for that loss) is somehow going to be compensated for by "3D interaction".

Those links shows nothing of the sort. If anything, the opposite. Of course a single leave will have more chance of reflecting the photon when it hits at a shallow angle, but where does it go? To the next leaf. That's only helping in penetration. We're talking about a whole crop and penetration to lower parts of the plant.

What I'm saying is pretty much the same reason that Acacia crassicarpa has vertical leaves. Even though the leaves would work better individually when they were aimed directly at the light. Thanks for proving my point I guess.

KonopCh said:

From this I assuming it's better to focus lights directly over bud shots than leaves from other part of plants? As this method will be better not to have popcorn buds...
It seems no matter how much PPFD you have over complete plant, if you don't have light over buds, they'll get fluffy.

Click to expand...

Photosynthesis happens in the leaves. Not so much in the buds themselves. But yes if the lower leaves don't get light they don't produce anything to send to the buds nearby.

Also, the temperature lower in the grow will be lower. That drops photosynthesis levels as well, so another reason for less production there. The plants transports it's resources to where it's warmest. So that will be mostly to the parts which are most exposed to the light/heat as well.

wietefras said:

Photosynthesis happens in the leaves. Not so much in the buds themselves. But yes if the lower leaves don't get light they don't produce anything to send to the buds nearby.

Also, the temperature lower in the grow will be lower. That drops photosynthesis levels as well, so another reason for less production there. The plants transports it's resources to where it's warmest. So that will be mostly to the parts which are most exposed to the light/heat as well.

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So if you have auto strain with dominant central cola which is 40cm above rest of buds, better to put light on leaves 40cm under top of the plant... And central cola will still grow the best despite it hasn't much leaves.
Correct?

wietefras said:

I read it and you are just stringing along a few terms to sound cool.

See? You really say nothing concrete with those words. I could say the exact same thing to the opposite. In fact I did, but with an actual explanation of how it works.

Stop assuming and READ! I said when you raise the lights from the optimum 12" to 24". Which is exactly what you do.

It DOES. You measure it at one level and the light travels down from there. There really is no magical difference in how the light propagates down whether the fixture is at 12" or 24". The photons will be absorbed somewhere. Better on the plants below that plane than on the walls above them.

You are telling people to waste 20% of the light on some mumbo jumbo about 3D interaction. While everybody knows that photons on the plants is what grows them. You will have to come up with some hell of an explanation on how losing 20% of those photons (or adding 25% more photons initially, to compensate for that loss) is somehow going to be compensated for by "3D interaction".

Those links shows nothing of the sort. If anything, the opposite. Of course a single leave will have more chance of reflecting the photon when it hits at a shallow angle, but where does it go? To the next leaf. That's only helping in penetration. We're talking about a whole crop and penetration to lower parts of the plant.

What I'm saying is pretty much the same reason that Acacia crassicarpa has vertical leaves. Even though the leaves would work better individually when they were aimed directly at the light. Thanks for proving my point I guess.

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I'm not going to argue with you if you won't read and understand.(YA...you seem to consciously choose to not respond the quoted white paper studies)
I have presented the info(white papers) as well as my interpretation of that info. As well as my real world applications of the methods described.

I did not wake up one day and say...yes I love using full power nearly all through....I love paying the electric company.
I also never said to raise to a point of 20% loss...more assumptions on your part. I woke up and said...wow that is such better growth!.

You're a smart dude and most of your studied information is usually correct. This time it is not and you will not even begin to get over your unfounded stuck ways.

So again...I have presented the factual information that supports what I stated. I have also presented the real world results of such application. You have yet to show any real world or even a white paper to dispute what you are proposing(you are claiming that a flat plane measurement using a quantum meter can tell you all captured light...false) As well as the denial of more metabolic rate from the "wasted energy".

I'm done...I will read if you post actual studies if you ever present them, but am done showing you to the water. Drink or not. My plants or I really could care less.

Greengenes707 said:

I'm not going to argue with you if you won't read and understand.

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You said nothing that can be "understood". All you did was post some vague assumptions.

I posted matrix measurements from Malocan showing 20% loss of light on average by going from 12" to 24". So when you advise to hang the lights at 24" instead of 12" you are in fact telling people to waste 20% of their light. I have measured the same 20% loss in a grow tent which I use for small grows. So, that 20% is a fact.

In return you offer nothing that would compensate for that. Only some vague statements (or more like strings of terminology) about how something "might change":
"It is impossible to show and compare with out a 3D map showing and recording every bit of light that is received by the canopy from all angles."

That's like when someone in the car asks if we are going over the speed limit and you answer "Well we have to account for the angle of the throttle peddle, the wind resistance factor of the car, the rolling resistance of the tires, distance traveled while under acceleration, torque of the engine, octane level of the fuel in the tank, wind direction, wind speed and of course the airspeed velocity of an unladen swallow. We cannot account for all of these, but we must be speeding yes". With no explanation of how this conclusion must be true.

Then I simply look at the speedometer or my GPS and see that we are not speeding at all.

Or in this case, I use a light meter and from that it's immediately clear that both at canopy level as well as below the canopy the light levels drop off dramatically when the lights are at 24" instead of the optimum 12".

It's common knowledge that number of photons hitting the plants is king (way before spectrum and incident angles). So you will have a lot of work to do to overcome that. Saying that we cannot know the "3D interaction" and such does not make a convincing case that would win back that 20%.

The only situation where your assumption would work is if the plants were photo inhibited to begin with. Indeed losing 20% of the light would improve their situation. Or if you are looking at some massive grow where wall losses are relatively negligible.

BTW If people want their lights at 24" they should use optics. 24" would be the optimum height for a fixture with 90 degree optics. With optics you would lose "only" 15% of the light instead of 20% against bare COBs at 12".

KonopCh said:

So if you have auto strain with dominant central cola which is 40cm above rest of buds, better to put light on leaves 40cm under top of the plant... And central cola will still grow the best despite it hasn't much leaves.
Correct?

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You would run the risk of hurting the cola though. You tend to fry the top of the cola when you go too close. You'll get dried out leaves in the top and the upper part of the cola will turn dry, hard and tasteless.

But that's indeed what some HPS growers do. They lower the lights to half the advised distance and in doing so partially sacrifice the few tops sticking out higher above the field in return for a bigger crop lower down.

Personally I like the cola's more though since they are easier to manicure. I don't go closer to the plants than 8". I don't care so much about larf either. Just turn it into oil, edibles or hash.

wietefras said:

I posted matrix measurements from Malocan showing 20% loss of light on average by going from 12" to 24". So when you advise to hang the lights at 24" instead of 12" you are in fact telling people to waste 20% of their light. I have measured the same 20% loss in a grow tent which I use for small grows. So, that 20% is a fact.

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You have your plants at 18" and are getting 800µmols ppfd.
2 days later they are at 10" and getting 1100µmols ppfd
What do you do???
A) raise your lights to maintain 800µmols ppfd
B) Dim your lights to reach 800µmols ppfd

YOUR ANSWER: ???

I have done both.
I get more growth(lateral shoots, nodes, and tighter node spacing), faster growth(less time to fill an area with the same amount of nodes), And harinder growth(larger stems and more root development)

What are you results?

wietefras said:

In return you offer nothing that would compensate for that. Only some vague statements (or more like strings of terminology) about how something "might change":
"It is impossible to show and compare with out a 3D map showing and recording every bit of light that is received by the canopy from all angles."

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Do you really not understand what 3d is???
You have a plant that is not shaped flat and perpendicularly to the light. Some leaves are, some are not, many are in between.
Light comes from all angles and hits plant matter at all angles, and is not accounted for by a simple flat plane quantum map. BEcause the canopy and light patterns are 3d. Not sure why that is too much for you to grasp.

wietefras said:

That's like when someone in the car asks if we are going over the speed limit and you answer "Well we have to account for the angle of the throttle peddle, the wind resistance factor of the car, the rolling resistance of the tires, distance traveled while under acceleration, torque of the engine, octane level of the fuel in the tank, wind direction, wind speed and of course the airspeed velocity of an unladen swallow. We cannot account for all of these, but we must be speeding yes". With no explanation of how this conclusion must be true.

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That is so inaccurate that I can't believe you wrote it.
There are no different variables there like you are trying to portray with your car variables. All I have presented is the simple goal of getting photons to hit the plants and be used. That is it. You will not get beyond you flat plane to see that. But that is your conscious choice. The evidence and studies have been given to you to choose how you would like.

wietefras said:

It's common knowledge that number of photons hitting the plants is king (way before spectrum and incident angles). So you will have a lot of work to do to overcome that. Saying that we cannot know the "3D interaction" and such does not make a convincing case that would win back that 20%.

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Stop deflecting and open up your vocabulary.
3d interactions = photons hitting plants from more than 2d. 360*. You can not account for every photon interaction by simple flat plane spot measurements. Does that help expand your of vocabulary?

My experience measuring various light sources suggests there will be an exact height for a particular lamp in a particular space where the average PPFD is highest. Raising or lowering the lamp from that height will reduce the PPFD either way, either because the light is too concentrated in the center and outer readings suffer or because the light get's weaker in the center with no corresponding increase in outer readings.

This is usually 14-16 inches for the retail lamps I've sold, 90 degree optics and emitters running 45-75 watts. Running without reflectors puts the same lamps in the 10-12" area. Lamps with many smaller cobs/leds spaced out properly may get as close as 4-6". Large bulbs with reflectors may need 24" or more to hit the sweet spot.

It does make sense that the lamp should be kept in the sweet spot which means moving the lamp up as the plant grows. Dimming would be useful for keeping the lamp in the sweet spot when lower PPFD is desired.