Light intensity vs VPD

K

Kreatiff

Member
Hey guys, have a trouble here:wall:
I have 20plants (5 WEEKS OF VEG) inside a 4 m2 place.
TEMP INSIDE: 17-20 C, HUMIDITY 60-65%
The lights are 25+ inches (~60cm) from the top of the plants.
in places, where light is directly above the plant, leafes are yellowish, like they have N deficiency
From the other side, plants ,that are further from light are dark green color.
it's obvious ,that plants suffers from too much light :idea:,cause they are from same mother, and i gave em same nutrients .btw lights are quantum boards on lm301h samsungs leds.
bongsmilieWhat are my thoughts:
As i was growing in identical room with same enviroment and same seeds last summer, i was not noticed any signs of overlight, furthermore, distance between lights and plants was 2 times closer then now .So... I am thinking, can it be because of VPD is not enought for that amount of light? According to VPD calculator, they are not in optimal range now. Has anyone noticed slower growing /and /or leaf color changes because of cold temps? (i don't mean more purple color on the end of flower, thanks)
I'll be happy for your advices, thxxxxxx:weed:
 
DanKiller

DanKiller

Well-Known Member
What is up with everyone growing in 15-20c ? Are you drying or growing ?
Raise temps somehow to 25-30c
Rh should always be low if you are in low temps.
Rule of thumb, high temp - high humidity, low temp - low humidity.
No such thing as too much light just like you noticed in your other grow with the light twice as close.
No doubt your VPD is totally out of range.
 
compassionateExotic

compassionateExotic

Well-Known Member
pulsegrow.com

The Ultimate Vapor Pressure Deficit (VPD) Guide

"Why devote an entire guide to VPD?" you might ask. The answer is that the vapor pressure deficit (VPD) is extremely important for growing plants. VPD helps you identify the correct range of temperature and humidity to aim for in your grow space. With VPD you can achieve the best results while...
pulsegrow.com pulsegrow.com
pulsegrow.com

VPD Charts in Fahrenheit and Celsius With Leaf Temperature

We made some easy-to-use VPD charts for both Celsius and Fahrenheit, for clone, veg, and flower stages. Hope you find them useful. For more information about VPD, and to make your own custom charts, check out our VPD Guide. VPD Charts for Fahrenheit VPD Chart for Clones in Fahrenheit -2F...
pulsegrow.com pulsegrow.com
 
K

Kola_Kreator

Well-Known Member
DanKiller said:
What is up with everyone growing in 15-20c ? Are you drying or growing ?
Raise temps somehow to 25-30c
Rh should always be low if you are in low temps.
Rule of thumb, high temp - high humidity, low temp - low humidity.
No such thing as too much light just like you noticed in your other grow with the light twice as close.
No doubt your VPD is totally out of range.
Click to expand...
Until you make the effort to educate yourself on VPD you probably should stop trying to give advise on the subject.
 
1

1212ham

Well-Known Member
DanKiller said:
What is up with everyone growing in 15-20c ? Are you drying or growing ?
Raise temps somehow to 25-30c
Rh should always be low if you are in low temps.
Rule of thumb, high temp - high humidity, low temp - low humidity.
No such thing as too much light just like you noticed in your other grow with the light twice as close.
No doubt your VPD is totally out of range.
Click to expand...
No such thing as too much light? :roll:
 
Last edited:
amneziaHaze

amneziaHaze

Well-Known Member
You didnt write the most important whats yoir wattage or ppfd at the tops.for leds up to 400w i would say thats a safe distance i dont have experience with more powerfull.

Then did you try to change places with the plants too see if the new one will yellow as well.

What nutrients are you using and what medium are you planting water soil coco....

Are all plants same clones or do you have different plants that like different amounts of food maybe its just overfeed your temp and humidity are normal nothing deadly in them
Allso maybe you are calculating vpd with room temperature and not leaf temperature they can be compleatly different
 
Ezleaves

Ezleaves

Member
HydoDan said:
I guess I'll have to do some investigation and comparison.. This chart was recommended to me by other members here..
Click to expand...
It’s a good chart and does the math, I guess I meant that it more so conflicts suggestions rather than charts. I’m using it but damn it’s so humid in the tent because of it.
 
Billy the Mountain

Billy the Mountain

Well-Known Member
HydoDan said:
I guess I'll have to do some investigation and comparison.. This chart was recommended to me by other members here..
Click to expand...
What makes that particular chart a little odd is that it uses a air temp of 32C, but a leaf temp of 24C; that's not realistic.
In a vigorous-growing, healthy plant, that's actively transpiring, leaf surface temps will be 2-3C lower than ambient.
I don't think there's any circumstance that you'll find a LST that's 8C below ambient.
That huge offset artificially skews the resulting VPD value.
 
HydoDan

HydoDan

Well-Known Member
Thanks for the clarifacation.. It was operator error on my part, I forgot to click the plus located to the right of the temps.. Looks better now.. Thank you!!
1707076993545.png
 
K

Kreatiff

Member
hey brozzas!
i made temps up, RH down, so the VPD right now is 0.9-1.2 (in this range), and...
all the siptoms are gone!plants looks healthy, dark green color on leafs.
i got the lesson - VPD IS SUPER IMPORTANT THING!
 
jimihendrix1

jimihendrix1

Well-Known Member
Heres a thought.

The SUN, is 2100umol.

In Nature, the CO2 level is. 421ppm. The highest its been, since humans have walked the earth.

In 1850. CO2 level, was about 180PPM. And the Sun, was still 2100umol.

Weed grows perfectly well, in these conditions.

Why, when indoors, 2100umol, will fry most if not all plants, even with high CO2 levels-1200ppm.

My theory is.

While seemingly Low, Outside. There is so much never-ending exchange, that even though low, its enough to supply the plants with a never ending, fresh supply of both Oxygen, and CO2.
And while the green parts of plants can get oxygen from Photosynthesis, from the plants release of oxygen/Transpiration, the ROOTS, rely on the oxygen, available, in the Atmosphere. Inside, the Co2 levels vs Oxygen levels, can get way out of whack.

The atmosphere in nature, is about 21% Oxygen, and .04% CO2. When growing, the further one deviates from the norms of what the plants evolved with, in nature, the les optimum, the outcome.

Most people that supplement CO2, never even think about supplying fresh AIR, along with it. Greenhouses, or places that have intake/exhaust fans, is the way to go. One can saturate the space, exactly as it is Outside.
 
N

nxsov180db

Well-Known Member
jimihendrix1 said:
Heres a thought.

The SUN, is 2100umol.

In Nature, the CO2 level is. 421ppm. The highest its been, since humans have walked the earth.

In 1850. CO2 level, was about 180PPM. And the Sun, was still 2100umol.

Weed grows perfectly well, in these conditions.

Why, when indoors, 2100umol, will fry most if not all plants, even with high CO2 levels-1200ppm.

My theory is.

While seemingly Low, Outside. There is so much never-ending exchange, that even though low, its enough to supply the plants with a never ending, fresh supply of both Oxygen, and CO2.
And while the green parts of plants can get oxygen from Photosynthesis, from the plants release of oxygen/Transpiration, the ROOTS, rely on the oxygen, available, in the Atmosphere. Inside, the Co2 levels vs Oxygen levels, can get way out of whack.

The atmosphere in nature, is about 21% Oxygen, and .04% CO2. When growing, the further one deviates from the norms of what the plants evolved with, in nature, the les optimum, the outcome.

Most people that supplement CO2, never even think about supplying fresh AIR, along with it. Greenhouses, or places that have intake/exhaust fans, is the way to go. One can saturate the space, exactly as it is Outside.
Click to expand...
That theory doesn't pan out really, if it did people would grow indoors in wind tunnels for air exchange lol. The sun is 2000umol sure, but that's the most, high noon at the equator... The actual DLI of the day would be more like what were doing indoors with 1000umol.
 
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