Vpd. Leaf temp, 10° lower then room temps?

[Michigangrows2]

In 8x8 gorilla tent. veg stage. 6-7 weeks. 2. K6000 alibaba 660w quantum boards. 1256 led diodes each. 9 plants 15 gal. Pots. Promix hpcc. Leaf temps are 10 degrees lower then room temp. According to the calculators to be at .08 or above, humidity is super low at 70° 72° or even 80° it claims 35%@70, 40 to 45 up to 80° with my leaf temps. Pots are staying heavy for 5 days or more. Used to be every other day or 2 max. 6F4Mind u at 80 my leaves were all canoeing up and felt papery. Even at 75 they dont feel quite like a fresh wet leaf, rather dry like 2000 grit sand paper. Is 35%-40% gona be detrimental or should i be more concerned with actual vpd# over a low humidity number#. Or is there a point to which i need the leafs at certain temps..cause at 75° leafs at 65° Also have a room with 4 gavita 1700s and that room aswell leaf temps are 10-12° cooler. Ive read alot and most time is 5 to a couple degrees difference. Im brand new in any forum at all. So bare with my forum etiquette. I try to read my azz off and learn the most i can. Very first run pulled 8 1/2 lb trimmed and dried, off the 4 gavitas. Not the seasoned grower, but not too dense either lol. General hydro all 37 bottles ahahahah (the whole line). Also any pointers based on pix. im a acceptor or negative criticism well!! Knowledge is key! These wer transplanted from 2 gal bags 14 days ago. Main issue is vpd though! Do also have falling ph issues in the medium. Constantly like down in the the 4.7 4.9 on occasion ive dropped 50 gallons of 7.0 or higher water trying to break the buffer, usually to no avail. And thats hours and hours of drenching. I believe i was over feeding frequency upon run off tests and journal everyday ive found lots of stacking of ppm and with my run off numbers i can adjust per next feed/water. However even the plants at 5.5 5.6 5.7 do not like it either u can imagine how the 4.7s looked. I have been able to get them in the 6.0 or above but its a struggle, dolamite lime and all. I have however saved every one, not thrown one out yet and pulling down 3rd run in 7 days. Again sorry im all over the place. Ive never posted before, anywhere. If i got questions i read read read and ask my friends who all grow...but no 2 rooms are the same, or what comes along withem lol.

 

[Billy the Mountain]

Sorry man, I can't read that wall of text, I'll address the title though.

I don't think it's physically possible for leaf surface temp to be 10 degrees below ambient

3-5 degree difference is the most I've measured or read about

 

[Michigangrows2]

Leaves are very much cooler

Sorry man, I can't read that wall of text, I'll address the title though.

I don't think it's physically possible for leaf surface temp to be 10 degrees below ambient

3-5 degree difference is the most I've measured or read about

Sorry man, I can't read that wall of text, I'll address the title though.

I don't think it's physically possible for leaf surface temp to be 10 degrees below ambient

3-5 degree difference is the most I've measured or read about

Leaves are very cool to the touch, i mean they feel like there definitely alot cooler than the room itself. Maybe buy a second Infared therm.

 

[Michigangrows2]

Sorry man, I can't read that wall of text, I'll address the title though.

I don't think it's physically possible for leaf surface temp to be 10 degrees below ambient

3-5 degree difference is the most I've measured or read about

I took out the unnecessary! In 8x8 gorilla tent. veg stage. 6-7 weeks. 2. K6000 alibaba 660w quantum boards. 1256 led diodes each. 9 plants 15 gal. Pots. Promix hpcc. Leaf temps are 10 degrees lower then room temp. According to the calculators to be at .08 or above, humidity is super low at 70° 72° or even 80° it claims 35%@70, 40 to 45 up to 80° with my leaf temps. Pots are staying heavy for 5 days or more. Used to be every other day or 2 max. 6F4Mind u at 80 my leaves were all canoeing up and felt papery. Even at 75 they dont feel quite like a fresh wet leaf, rather dry like 2000 grit sand paper. Is 35%-40% gona be detrimental or should i be more concerned with actual vpd# over a low humidity number#. Or is there a point to which i need the leafs at certain temps..cause at 75° leafs at 65°

 

[CWF]

Not sure what units you're using for VPA, my vegging plants are younger/smaller and I'm keeping them around 1.0 - 1.2 kPa, which translates to around 60% RH. Leaves are around 4 degrees cooler than room air temp at canopy. (30 DLI LED)

 

[Michigangrows2]

Not sure what units you're using for VPA, my vegging plants are younger/smaller and I'm keeping them around 1.0 - 1.2 kPa, which translates to around 60% RH. Leaves are around 4 degrees cooler than room. (30 DLI LED)

Im using kpa but based on 10° leaf diff. I have read for hours on end and have seen people mention 10° cooler in scientific studies and a couple forums ect....

 

[Rurumo]

Low humidity will increase the rate of leaf transpiration resulting in lower leaf temps. Raise up your RH and temps and you'll see a huge difference.

 

[CWF]

You wrote .08 kPa, not 0.8 (twice), so that's what I commented on. I'll leave further discourse to the more experienced, but 0.9 kPa is pretty fine for veg IMO.

 

[MidnightSun72]

Sorry man, I can't read that wall of text, I'll address the title though.

I don't think it's physically possible for leaf surface temp to be 10 degrees below ambient

3-5 degree difference is the most I've measured or read about

It's possible if you have a lot of air blowing by the canopy causing the LST to drop. Floraflex had a post about this they had their LST at 72-74 despite the room being in the 80s. They said it stopped leaf burn on their MAC1 pheno.

 

[Billy the Mountain]

I took out the unnecessary! In 8x8 gorilla tent. veg stage. 6-7 weeks. 2. K6000 alibaba 660w quantum boards. 1256 led diodes each. 9 plants 15 gal. Pots. Promix hpcc. Leaf temps are 10 degrees lower then room temp. According to the calculators to be at .08 or above, humidity is super low at 70° 72° or even 80° it claims 35%@70, 40 to 45 up to 80° with my leaf temps. Pots are staying heavy for 5 days or more. Used to be every other day or 2 max. 6F4Mind u at 80 my leaves were all canoeing up and felt papery. Even at 75 they dont feel quite like a fresh wet leaf, rather dry like 2000 grit sand paper. Is 35%-40% gona be detrimental or should i be more concerned with actual vpd# over a low humidity number#. Or is there a point to which i need the leafs at certain temps..cause at 75° leafs at 65°

I doubt it
If that's what's you're measuring, you need to calibrate your thermometers.
There's no way a leaf can transpire fast enough to be 10 degrees below ambient

 

[MidnightSun72]

I doubt it
If that's what's you're measuring, you need to calibrate your thermometers.
There's no way a leaf can transpire fast enough to be 10 degrees below ambient

 

[McShnutz]

I'm still experimenting with this but in veg I stayed as close to 1 as possible. Now in flower at 1.6

I too have a few sporadic fan leafs that have a papery feel. Took some ppfd reading and it turned out, the right side of my tent was registering a DLI of 65. Way to high, and no C02 is being used for this grow. DLI of 40-50 seems to be doing the trick now.

 

[Billy the Mountain]

Im using kpa but based on 10° leaf diff. I have read for hours on end and have seen people mention 10° cooler in scientific studies and a couple forums ect....

Do you have a link? I'm always willing to learn something new.

Every article I've read, and every measurement I've done, LST is a few degrees below ambient under LED lights

Are you using the same thermometer for both measurements?

Growth will be very slow at 62f leaf temps

 

[Kassiopeija]

so this is what u get when u do the ice water trick
(...or false calibration)
and why HPS is better than LED heheheee

 

[Michigangrows2]

Do you have a link? I'm always willing to learn something new.

Every article I've read, and every measurement I've done, LST is a few degrees below ambient under LED lights

Are you using the same thermometer for both measurements?

Growth will be very slow at 62f leaf temps

They are indeed slow growing thats what brings me here. I figure a leaf temp of 62 is not great. I have the ac infinity set up with controller..the humidity matchs the dehu. So i assume its gota be very close. Also a few of the jar ones that show temp and humid there all within 3+/- or so. Also just thru in my gavita el2 controller with 2 temp probs (no humid) and they all match..only thing i have not been able to do i use a second temp gun. Leaves are very cool to the touch 62 or close seems correct. Ive even left the gun in different spots in the tent to let it get to room temp

 

[Star Dog]

I'm surprised they're using a crap thermometer that's below par.

General Laser Temperature IRT217 Infrared Thermometer 10 1 Home Draft Detection for sale online | eBay

Find many great new & used options and get the best deals for General Laser Temperature IRT217 Infrared Thermometer 10 1 Home Draft Detection at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I wouldn't put too much faith in cheap ir thermometers ime they're very inaccurate.
Here's a example

technically I'm dead.

 

[Michigangrows2]

so this is what u get when u do the ice water trick
(...or false calibration)
and why HPS is better than LED heheheee

Never grew with hps. Lots people close to me do. Good friend also just switched to gavita from hps. He is trying his best not to sell them to me and hang his hps back up. Lots of different issues with led. Im learning first hand with led so im just taking most faults with grain of salt..yet im a perfectionist and i know most all issues are user error.

 

[Michigangrows2]

I'm surprised they're using a crap thermometer that's below par.

General Laser Temperature IRT217 Infrared Thermometer 10 1 Home Draft Detection for sale online | eBay

Find many great new & used options and get the best deals for General Laser Temperature IRT217 Infrared Thermometer 10 1 Home Draft Detection at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I wouldn't put too much faith in cheap ir thermometers ime they're very inaccurate.
Here's a example
View attachment 5102934
technically I'm dead.

My guyyyy thats the same damn gun im using ....im a awesome mechanic/ do every damn thinger..i grabbed it from a buddy in a small garage clean out bundle..figured be nice for converter tests heating ect auto stuff..but once i spent last 3 weeks or so reading every thing i can on vpd i been using it l. Didnt wana break the 199 for harbor freight filr gun or whatever thermal imaging gun

 

[Billy the Mountain]

They are indeed slow growing thats what brings me here. I figure a leaf temp of 62 is not great. I have the ac infinity set up with controller..the humidity matchs the dehu. So i assume its gota be very close. Also a few of the jar ones that show temp and humid there all within 3+/- or so. Also just thru in my gavita el2 controller with 2 temp probs (no humid) and they all match..only thing i have not been able to do i use a second temp gun. Leaves are very cool to the touch 62 or close seems correct. Ive even left the gun in different spots in the tent to let it get to room temp

Use the same IR gun and take the temp of a piece of wood, a book, or whatever's handy that's been acclimated to the same environment (wait a few hours). Ideally near the leaves you'll be measuring.

Take the leaf temp and the temp of your "control"

The difference is your leaf temperature offset

 

[Star Dog]

My guyyyy thats the same damn gun im using ....im a awesome mechanic/ do every damn thinger..i grabbed it from a buddy in a small garage clean out bundle..figured be nice for converter tests heating ect auto stuff..but once i spent last 3 weeks or so reading every thing i can on vpd i been using it l. Didnt wana break the 199 for harbor freight filr gun or whatever thermal imaging gun

If you take your own temperature it'll give you an idea of it accuracy, it should be around 37c +/-