Led lights= More mg?

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Willie Nillly

Active Member
Just switched from hps to led when I found I couldn't find a ballast any more. Using Roots dry organics like always. Seems like I'm seeing a mg deficiency.I never experienced this with hps. Is it normal for this to happen? Any help is appreciated.
 
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Phytoplankton

Well-Known Member
There is some debate on whether LED lights cause an increase in the use of Ca and Mg. It probably wouldn't hurt to add a little extra Ca/Mg. The mechanisms are kinda complicated, LED's result in faster growth, because the light is more intense, it has also been found that, particularly when changing from HPS to LED, that the VDP changes because the plants are generally growing in a slightly cooler environment, as LED's don't generate as much heat, so transpiration is lower. Pictures would help.
 
Billy the Mountain

Billy the Mountain

Well-Known Member
amneziaHaze said:
well considering that for the same wattage you will get 2-3 times more flowers its normal to need more magnesium
Click to expand...
Agreed!
The oft-repeated fallacy that LEDs require more Mg is a classic example of correlation not being causation.
The significant difference is the dramatic increase in output which requires a corresponding increases in nutes.
There's nothing inherent in LEDs that make a plant require more Mg.
 
Week4@inCharge

Week4@inCharge

Well-Known Member
Willie Nillly said:
Just switched from hps to led when I found I couldn't find a ballast any more. Using Roots dry organics like always. Seems like I'm seeing a mg deficiency.I never experienced this with hps. Is it normal for this to happen? Any help is appreciated.
Click to expand...
yup, it's the census and plausible that LED's are not as full spectrum as they claim to be so you'll need to supplement with some cal mag. During the stretch look into supplementing with some water soluble calcium phosphate.
 
Billy the Mountain

Billy the Mountain

Well-Known Member
Week4@inCharge said:
yup, it's the census that LED's are not as full spectrum as they claim to be so you'll need to supplement with some cal mag. During the stretch look into supplementing with some water soluble calcium phosphate.
Click to expand...
(I assume census was a typo)

A consensus of whom says the LED spectrum is worse than advertised? It's certainly not from independent 3rd party reviewers.
You're suggesting that if LEDs had a more narrow spectrum, even more CalMg would be required?
Following that logic, HPS lamps should require substantially more CalMg since their spectrum is so poor.
 
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Roguedawg

Well-Known Member
Increasing total EC works better for me than increasing Mg by itself. If you think your having Mg problem giving Ca at same time is not good idea. In coco increasing total EC for first week after transplanting is all it takes, you can probably drop EC down after that.
 
Week4@inCharge

Week4@inCharge

Well-Known Member
Billy the Mountain said:
(I assume census was a typo)

A consensus of whom says the LED spectrum is worse than advertised? It's certainly not from independent 3rd party reviewers.
You're suggesting that if LEDs had a more narrow spectrum, even more CalMg would be required?
Following that logic, HPS lamps should require substantially more CalMg since their spectrum is so poor.
Click to expand...
Good point, I've never used HPS so maybe lucky I haven't? LEDs do put out the PAR big time, I sometimes wonder if I should dial it down a bit during flower.
 
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Lou66

Well-Known Member
Billy the Mountain said:
Agreed!
The oft-repeated fallacy that LEDs require more Mg is a classic example of correlation not being causation.
The significant difference is the dramatic increase in output which requires a corresponding increases in nutes.
There's nothing inherent in LEDs that make a plant require more Mg.
Click to expand...
That's wrong.

The yield per area is equal with led, you just use less energy to get to the finish line. So the same yield needs the same amount of fertilizer.

What is different is the lower transpiration under LEDs. They have little infra red light which heats up the leave. Hot leaves transpire more. Mg (and Ca) is passively taken up with water. With lower transpiration und LEDs less Mg is taken up. That leads to the symptoms.
The solution is to increase room temp. Increasing Mg in the fert works also but only up to a point. Increasing transpiration is better.
 
Week4@inCharge

Week4@inCharge

Well-Known Member
Lou66 said:
That's wrong.

The yield per area is equal with led, you just use less energy to get to the finish line. So the same yield needs the same amount of fertilizer.

What is different is the lower transpiration under LEDs. They have little infra red light which heats up the leave. Hot leaves transpire more. Mg (and Ca) is passively taken up with water. With lower transpiration und LEDs less Mg is taken up. That leads to the symptoms.
The solution is to increase room temp. Increasing Mg in the fert works also but only up to a point. Increasing transpiration is better.
Click to expand...
Lowering the humidity? Transpiration is controlling the environment aka VPD.
 
Billy the Mountain

Billy the Mountain

Well-Known Member
Lou66 said:
That's wrong.

The yield per area is equal with led, you just use less energy to get to the finish line. So the same yield needs the same amount of fertilizer.

What is different is the lower transpiration under LEDs. They have little infra red light which heats up the leave. Hot leaves transpire more. Mg (and Ca) is passively taken up with water. With lower transpiration und LEDs less Mg is taken up. That leads to the symptoms.
The solution is to increase room temp. Increasing Mg in the fert works also but only up to a point. Increasing transpiration is better.
Click to expand...
Your second point is a valid one, but I'd consider that more an environmental issue than a lighting issue. The ambient temps running under LEDs should be higher since the leaves aren't directly being cooked by IR.
 
W

Willie Nillly

Active Member
Phytoplankton said:
There is some debate on whether LED lights cause an increase in the use of Ca and Mg. It probably wouldn't hurt to add a little extra Ca/Mg. The mechanisms are kinda complicated, LED's result in faster growth, because the light is more intense, it has also been found that, particularly when changing from HPS to LED, that the VDP changes because the plants are generally growing in a slightly cooler environment, as LED's don't generate as much heat, so transpiration is lower. Pictures would help.
Click to expand...
Temps in the mid 70's. No tent.
 
amneziaHaze

amneziaHaze

Well-Known Member
Willie Nillly said:
With the 600 I'd have 6 3galpots average 3 oz each.
Click to expand...
half a kg? i get that with a 300W led and 20 days veg 4 plants

you can use a phone app that is free and you get the light spots good. if its an expensive mobile phone then there is a good chance it has a good light sensor. i know samsung s23 showed pars almost perfect
 
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