Bleaching issue? LED

Have2

Have2

Well-Known Member
I do have a small issue... Everything is fine under the 1k hps double ended but under the LED... Weird.

I did a PAR test, I have an average of 834 ppfd. at the canopy. I found out that with ambient co2, a maximum of 1000ppfd is fine but, with co2, you can reach 1500 ppfd with no issue... So I run co2 at 1500ppm just to make sure they got plenty of co2.

However, I got some weird stuff, I would think of a nutrient deficiency but when I look at the plants under the hps, they are fine (~42-46" from canopy). I have some yellowing at the tip, etc. Could think of nutes burning, P, Calcium but... again, everything's fine under the HPS in the same system (rdwc)

I remember reading about a nutrient that was more required when growing under leds but I can't remember exactly which one (or if it's true).

What is your PPFD? Can we really pass the 700-800-900-1000 µmol mark?
I will raise the led a bit but I'm curious as to wth I can't go higher than this.. Or maybe it's because in veg, so the 18 hours vs 12 hours duration, they got too much light (DLI)

Thanks for any help!
 

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Shape Shifter

Shape Shifter

Well-Known Member
Various stages of light burn can look like some common deficiencies. One way to know if you have light burn for sure is to find a leaf that is burned where it was exposed to light and the rest of the plant is green because it was shaded. Do you have that?
 
Moflow

Moflow

Well-Known Member
Have2 said:
they got too much light (DLI
Click to expand...
You didn't mention what readings you were getting under the 1000W DE HPS or is the 834 ppfd average reading for both the led and hps?
What led light are you using?

I run around 800 - 1000 over 12hrs in flowering.
I start them flowering at around 600 and let them stretch into the higher umols.
300 - 400 umols over ~ 18 hours for vegging.
Some strains can handle higher light levels than others.
Extra Cal mag is sometimes required when growing under led light.
 
Have2

Have2

Well-Known Member
Shape Shifter said:
Various stages of light burn can look like some common deficiencies. One way to know if you have light burn for sure is to find a leaf that is burned where it was exposed to light and the rest of the plant is green because it was shaded. Do you have that?
Click to expand...
I'll take a look in few minutes but I think once you step down a bit from the light, it's greener.

I'll look under leaves right under those.

Replying shortly! :)
 
Have2

Have2

Well-Known Member
Moflow said:
You didn't mention what readings you were getting under the 1000W DE HPS or is the 834 ppfd average reading for both the led and hps?
What led light are you using?

I run around 800 - 1000 over 12hrs in flowering.
I start them flowering at around 600 and let them stretch into the higher umols.
300 - 400 umols over ~ 18 hours for vegging.
Some strains can handle higher light levels than others.
Extra Cal mag is sometimes required when growing under led light.
Click to expand...
The 834 is for led only. Has for the insanely masterful hps, I have a 645, average... Lol

Are you scrogging? I'm wondering since you're talking about letting them stretch into higher umols.

THANKS, for the calmag when going with leds.
 
Have2

Have2

Well-Known Member
Moflow said:
You didn't mention what readings you were getting under the 1000W DE HPS or is the 834 ppfd average reading for both the led and hps?
What led light are you using?

I run around 800 - 1000 over 12hrs in flowering.
I start them flowering at around 600 and let them stretch into the higher umols.
300 - 400 umols over ~ 18 hours for vegging.
Some strains can handle higher light levels than others.
Extra Cal mag is sometimes required when growing under led light.
Click to expand...
Forgot to ask, are you using co2?
 
Shape Shifter

Shape Shifter

Well-Known Member
ppfd is not uniform throughout the tent. There are hot spots and luke warm spots. One issue that is not being discussed is phototoxicity is wavelength specific. At least it is with humans. Probably plants too? So ppfd may not be a great measurement for this potential problem.
 
Moflow

Moflow

Well-Known Member
Have2 said:
Forgot to ask, are you using co2?
Click to expand...
No, I'm not using co2. I've a friend who uses co2 though and I think he goes up to around 1200 - 1500 ppfd
I don't scrog but my plants are usually clones and I train them to be of similar height.
20200726_181608.jpg
 
Have2

Have2

Well-Known Member
Shape Shifter said:
Various stages of light burn can look like some common deficiencies. One way to know if you have light burn for sure is to find a leaf that is burned where it was exposed to light and the rest of the plant is green because it was shaded. Do you have that?
Click to expand...
I toss leaves a bit and yeah, seems a bit due to light stress.... leaves are better slightly under the top canopy. I'm really wondering if it has to do with the DLI instead of specific wavelenght. I'll know in few days when switching to flowering. :)
 
Shape Shifter

Shape Shifter

Well-Known Member
I've had it where just a small part of the light exposed leaf was burnt white and the rest of the shaded part was perfectly green. That was obvious light burn. Various stages of light burn can look like deficiencies and too much light can create too much photosynthesis which can cause a nute deficiency. You can get a combo nute deficiency and light burn. The plants don't need max light in veg. So I take it easy in veg after burning some plants.
 
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