# Can someone tell me the TRUE reason for hard purple stems?

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#### Alwispy

I can imagine an xy graph with power on one axis and distance on the other. I wonder what the plot would look like. Would it be linear?
I think That would be practically super useful to at least have a general baseline. Thanks for volunteering to do this for everyone Bigblonde !

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#### HerbGardner

I can imagine an xy graph with power on one axis and distance on the other. I wonder what the plot would look like. Would it be linear?
In this case light behaves like a wave so it follows the inverse square law, and for our purposes exists in two dimensions (amount of canopy covered).

In other words, light is intense when close to the plant but rapidly (logarithmically) loses intensity with distance.

LEDs more or less have a linear efficiency of ~800 lumens per watt. Double the wattage and you get twice the lumens. This means we're only dealing with one dimension.

The plot you ponder would be linear if one of the axes were logarithmic, i.e. instead of 1,2,3,4 it goes 3.5, 10, 35, 100. Otherwise it would look similar to the above.

#### N1ghtL1ght

Staff
Supporter
I can't access that, what does it show?

#### N1ghtL1ght

Staff
Supporter
In this case light behaves like a wave so it follows the inverse square law, and for our purposes exists in two dimensions (amount of canopy covered).
View attachment 1346855

In other words, light is intense when close to the plant but rapidly (logarithmically) loses intensity with distance.

View attachment 1346845 LEDs more or less have a linear efficiency of ~800 lumens per watt. Double the wattage and you get twice the lumens. This means we're only dealing with one dimension.

The plot you ponder would be linear if one of the axes were logarithmic, i.e. instead of 1,2,3,4 it goes 3.5, 10, 35, 100. Otherwise it would look similar to the above.
If you have a free-hanging HID bulb without reflector then the flux-depreciation would be approximately be like this, yes. (That's why it states "point source"). This formulae also neglects any back reflection, and thus, is only applicable for either black walls or an open scenario.

For LEDs, the fixture's beam angle decides how "concentrated" the photons will flow so there is less decline of the fluxstrength with distance as in comparison to a point source, which is just a 360° beam angle.
This has some serious implications for their PPFD plots - which will show way higher under a 90° or even 60° beam angle (at the same distance measured) as in comparison to the normal 120° which alot whitelight diodes have without extra reflectors or lenses. But it doesn't mean a change in beam angle creates more light particles inside a growroom (this is the wrong association usually made by some folks prior to buying a fixture). There are some pros & cons vs concentration of the beam angle, so various techniques to manufacture a lamp have all a right justification depending on the setup used. But one shouldn't compare a PPFD plot of a 120° fixture vs one of a 90° fixture, as that would just lead to a false impression that the 90° is more efficient (when it may be quite the opposite).

In an ideal situation this formulae can be used to calculate the factor of the depreciation with distance of the irradiance/fluxstrength for any fixture (including a point source), if the beamangle is known:
1/(sin(beamangle/4)^2)

It returns these values for some of the standard angles used:
360°=1 (in this case the factor doesn't change the standard (I = 1/r^2) "inverse square law" formulation)
180°=2
140°=~3.04
120°=4
90=~6.83
60°=14.93

This formulae can be either derived via a 2 or a 3-dimensional calculation, as written here:

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#### Drgreenthumbs1

Hi guys, so this is my second grow with the same strain. On the last grow and this grow I’ve had purple streaking on my main branches, and solid purple on secondary branches that connect to main. The stems are so hard I can’t even crush them with my fingers to super crop. I had a pretty good mag deficiency earlier on and still see a few leaves here and there that show mag def, but overall most leaves are lush green. How can I fix this hard purple stem issue. Last grow wasn’t this bad.
Purple streaks in main stalk is almost always magnesium deficiency

#### BigBlonde

In this case light behaves like a wave so it follows the inverse square law, and for our purposes exists in two dimensions (amount of canopy covered).
Light exists in three dimensions when we move the light (or the plants) up or down. Vertical adjustments add the third dimension.

#### Ph 007

Light exists in three dimensions when we move the light (or the plants) up or down. Vertical adjustments add the third dimension.
Smoke enough weed you can get to the third dimension,
Or smoke weed drink beer you get their quicker

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#### Alwispy

I can't access that, what does it show?
Nuttin , I tried to delete

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#### Alwispy

Err alrighty then…. Is there an English translation that is practical for use ?

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#### Jay87

Iv had the exact issue that is being spoken about. For me I was under feeding. This is a complete new run for me with leds. Plus new nutrients tailor made to my water. I have never started on 1.6 ec but that was where I was going wrong. I’ll load some pictures as you can see how they got better. But my lights were very high. So could I have maybe had them lower? I kept them that far away as I was new to them, plus I was having issues with the purple stems and stunted growth.

#### Novaracer69

I wonder if it's just the instant max par for the day immediately straight out the gate and outside there's a smooth ramp up. And same with sunset I am thinking out loud but I did just finish a bowl so there's that

#### RootsRuler

I wonder if it's just the instant max par for the day immediately straight out the gate and outside there's a smooth ramp up. And same with sunset I am thinking out loud but I did just finish a bowl so there's that
Nope. Dr. Bugbee squashed that bro science.

I thought the same thing. I mentioned it to some of the sales reps at California Lightworks and they put it into their lights but Bugbee says their is no difference. I'm not sure if CL's engineers just did it as a common sense thing or if they actually looked into its effects but I'm going with the scientist on this one.

#### Novaracer69

Nope. Dr. Bugbee squashed that bro science.

I thought the same thing. I mentioned it to some of the sales reps at California Lightworks and they put it into their lights but Bugbee says their is no difference. I'm not sure if CL's engineers just did it as a common sense thing or if they actually looked into its effects but I'm going with the scientist on this one.
I think he's just scratching the surface. He admitted that this science is just really getting started. It might be alot more to it but it is happening. My back to back with clones says that we're missing something. That's not measurably right now.
Remember mr bugbee only speaks on what he has data on. And facts are we need more data no driven by students but people in the field IMHO

#### RootsRuler

I think he's just scratching the surface. He admitted that this science is just really getting started. It might be alot more to it but it is happening. My back to back with clones says that we're missing something. That's not measurably right now.
Remember mr bugbee only speaks on what he has data on. And facts are we need more data no driven by students but people in the field IMHO
I can live with that.

I've always been of the mindset that we are trying to mimic what nature provides but in a more controllable way. Sunrise and sunset happen in nature so plants must have adapted that in some way that benefits them.....or not. That is the question. When I mentioned it to CL they must've thought the same thing although I think part of their thinking was that they would be the first ones out of the gate with it if it proved to improve yields which would be a huge marketing boon for them. It's been over a decade that I had first mentioned this to them. I haven't seen any legal facilities employing sunrise/sunset and they would have much more to gain than you or I if this in fact had a positive effect which is what leads me to believe that it doesn't really affect growth rates.

#### Dirtbag

Supporter
I can live with that.

I've always been of the mindset that we are trying to mimic what nature provides but in a more controllable way. Sunrise and sunset happen in nature so plants must have adapted that in some way that benefits them.....or not. That is the question. When I mentioned it to CL they must've thought the same thing although I think part of their thinking was that they would be the first ones out of the gate with it if it proved to improve yields which would be a huge marketing boon for them. It's been over a decade that I had first mentioned this to them. I haven't seen any legal facilities employing sunrise/sunset and they would have much more to gain than you or I if this in fact had a positive effect which is what leads me to believe that it doesn't really affect growth rarates.
I can't remember where I saw it but I think some places have found a benefit to using a lot of far red before lights go out and after lights come on for a short period of time to mimic the spectrum at sunrise/sunset.
But I don't remember what the benefit is... I dont think maximum intensity is in any way negative if the chloroplasts are developed enough to tolerate the photon density. DLI regulates yield potential if all other variables are tuned in, I think it would only hurt yields to lower the ppfd much at all before and after lights go off or on. Lowering light at the start and end of the day would require a huge spike middle of the day to maintain the same DLI.
That being said, I'd be curious to know if anyone has experimented with starting the day with low levels and ramping up to such a degree that you are far exceeding the max ppfd for a short time during peak photosynthetic activity mid day, then tapering off as the plant nears bedtime. Like running a vented room up to 15-1600 at the canopy for an hour or two mid day, down to 750 or so for the start and end of the day.

#### PipeCarver

Supporter
I can't remember where I saw it but I think some places have found a benefit to using a lot of far red before lights go out and after lights come on for a short period of time to mimic the spectrum at sunrise/sunset.
But I don't remember what the benefit is... I dont think maximum intensity is in any way negative if the chloroplasts are developed enough to tolerate the photon density. DLI regulates yield potential if all other variables are tuned in, I think it would only hurt yields to lower the ppfd much at all before and after lights go off or on. Lowering light at the start and end of the day would require a huge spike middle of the day to maintain the same DLI.
That being said, I'd be curious to know if anyone has experimented with starting the day with low levels and ramping up to such a degree that you are far exceeding the max ppfd for a short time during peak photosynthetic activity mid day, then tapering off as the plant nears bedtime. Like running a vented room up to 15-1600 at the canopy for an hour or two mid day, down to 750 or so for the start and end of the day.
Not sure how far red these led's are but I have them 10 min before lights out to 10 min after lights out and same in the morning before lights on. I just shut 2 off I'm seeing it as too bright...now 3 weeks into flower...2 Pic is just before flip....and this today at 3 weeks

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#### RootsRuler

I can't remember where I saw it but I think some places have found a benefit to using a lot of far red before lights go out and after lights come on for a short period of time to mimic the spectrum at sunrise/sunset.
But I don't remember what the benefit is... I dont think maximum intensity is in any way negative if the chloroplasts are developed enough to tolerate the photon density. DLI regulates yield potential if all other variables are tuned in, I think it would only hurt yields to lower the ppfd much at all before and after lights go off or on. Lowering light at the start and end of the day would require a huge spike middle of the day to maintain the same DLI.
That being said, I'd be curious to know if anyone has experimented with starting the day with low levels and ramping up to such a degree that you are far exceeding the max ppfd for a short time during peak photosynthetic activity mid day, then tapering off as the plant nears bedtime. Like running a vented room up to 15-1600 at the canopy for an hour or two mid day, down to 750 or so for the start and end of the day.
OK but how would far red help you in veg? Sunrise/Sunset happens from day one of an outdoor plants life. I can see your point about far reds in flower but in veg I wonder what other benefit the plant has accommodated to?

As far as ppfd, sunrise period usually only lasts around an hour until full sun. Granted, position is different being that it is rising so I'm not sure if the light vector has a part to play in it but light energy from the sun is omnidirectional so it's hard to say if that is a factor or not. Your issue with DLI would be minimized if you went from zero to full in the first hour and full to zero the last hour. Maybe sunrise/sunset would be better suited to a 14/10 light schedule in flower so that you give them an hour to be exposed to full light energy and an hour to wind down and get them ready to go to sleep and they'll still get their 12?

#### Dirtbag

Supporter
OK but how would far red help you in veg? Sunrise/Sunset happens from day one of an outdoor plants life. I can see your point about far reds in flower but in veg I wonder what other benefit the plant has accommodated to?

As far as ppfd, sunrise period usually only lasts around an hour until full sun. Granted, position is different being that it is rising so I'm not sure if the light vector has a part to play in it but light energy from the sun is omnidirectional so it's hard to say if that is a factor or not. Your issue with DLI would be minimized if you went from zero to full in the first hour and full to zero the last hour. Maybe sunrise/sunset would be better suited to a 14/10 light schedule in flower so that you give them an hour to be exposed to full light energy and an hour to wind down and get them ready to go to sleep and they'll still get their 12?
I never said anything about using far red light near on/off in flower only, you must have misread something there.

As for the rest, I'm not sure, but I don't think that's exactly true about the sun being full after the first hour or so. Peak UV only lasts for a few hours early afternoon outdoors, since the sun is directly overhead and the light is traveling directly perpendicular through the atmosphere. Lower in the sky the sun's photons have a lot more atmosphere to pass through which filters out the UV rays.

#### RootsRuler

I never said anything about using far red light near on/off in flower only, you must have misread something there.

As for the rest, I'm not sure, but I don't think that's exactly true about the sun being full after the first hour or so. Peak UV only lasts for a few hours early afternoon outdoors, since the sun is directly overhead and the light is traveling directly perpendicular through the atmosphere. Lower in the sky the sun's photons have a lot more atmosphere to pass through which filters out the UV rays.

While your statement has merit I meant moreso that the sun is now fully exposed over the horizon. That's why I added that light vector may play a role which equates to what you said about light passing through the atmosphere.

#### plumsmooth

There are multiple reasons you can see solid purple stems, genetics are not one of them.
extreme root bound, severe under watering, untreated bug issues, and lack of calcium in their life.
Purple stems means you are torturing your plants. Stop abusing/stressing your plants.
want zero purple stems? try Nectar for the Gods Herc Harvest combined with their Olympus Up.
Calcium is NEVER implicated in Purple Stems?