What's the optimal temp and RH ranges when using LED

[Kola_Kreator]

That VPD garbage is a main reason for the flood of lower quality cannabis. 80 degrees and 70% humidity in flower will not yield high quality cannabis.

VPD is great for commercial greenhouses with Ag crops, etc

If you are growing in a room indoors the best temp/RH to strive for is Veg 77-80/50% Flower 72-75/35-40%

Cuttings or germination 88/high humidity

Some cultivars actually prefer RH above 65 for the entire grow. We only lower RH during flower to prevent mould and pest issues.

 

[Billy the Mountain]

You are raising an interesting point Billy. Most articles indicate that leaf temps are higher than ambient, like mine, but logic tells you the leaves are working more efficiently when the leaf temp is lower. Almost of primary importance when deciphering vpd. Food for thought.

I'm curious where you read that an LST above ambient is normal; I can assure you it's not.

There's only a few edge cases where the LST would be above ambient, and none of them are desirable.

• Way too bright, where the rate of evaporation simply can't keep up
• Very low humidity where the rate of transpiration decreaes
• Leaves covering other leaves, preventing evaporation

Bottom line is that a healthy plant in a reasonable environment will have an LST below ambient.

If your plants look good and your environment is sane, I'm 99% sure your results are due to measurement noise.

I encourage you to try the experiment I suggested, using only one measuring device.

** I just now checked some week old seedlings I started, the leaf temp is 72, other stuff (using same IR gun) in the tent is 75, thermometer says 76.

 

[Modern Selections]

Some cultivars actually prefer RH above 65 for the entire grow. We only lower RH during flower to prevent mould and pest issues.

Jungle strains may prefer that high of humidity but that's about it. Exactly, lower RH or risk mold and fungus.

 

[Kerowacked]

When it comes to LST, growers should follow these basic guidelines:

• Most cannabis plants’ LST should fall between 72 and 86 degrees – generally warmer than the ambient air.
• https://cannabisindustryjournal.com/feature_article/optimizing-your-led-spectrum-for-leaf-surface-temperature/amp/
• 
  There are others, but again i am not disagreeing with you.

 

[Billy the Mountain]

When it comes to LST, growers should follow these basic guidelines:

• Most cannabis plants’ LST should fall between 72 and 86 degrees – generally warmer than the ambient air.
• https://cannabisindustryjournal.com/feature_article/optimizing-your-led-spectrum-for-leaf-surface-temperature/amp/
• 
  There are others, but again i am not disagreeing with you.

Interesting; all the more reason to get growing info from non-cannabis sources.
LST seems to be a recent discovery for the cannabis sector.

There's plenty of info out there, but one example tidbit from Functional Ecology:

Stomata deserve special attention as they simultaneously regulate leaf budgets for water, CO2 and heat. The leaf surface temperature depends greatly on the opening level of stomata, suggesting an analogy between stomata and a thermostat. The level of stomatal opening directly and proportionally sets the stomatal conductance for water vapour. Higher conductance directly elevates rate of evapotranspiration, which in turn depresses leaf temperature (Campbell & Norman 1998). For example, modelling of the leaf energy budget shows that a 40-fold increase in stomatal conductance can cause leaf temperature to drop by 15 °C in large leaves under full sun (Campbell & Norman 1998).

 

[Kerowacked]

Here’s anotherbut i really think Billy has raised an interesting point about getting leaf temp below ambient for max production.

 

[Billy the Mountain]

Here’s anotherView attachment 5321656but i really think Billy has raised an interesting point about getting leaf temp below ambient for max production.

I just realized I overlooked an important point.
Everything I've stated is correct, but only applies to plants grown under LED lighting. (LST<ambient)

It just dawned on me that the info you posted is for HID lighting and makes sense
IR heats the leaves directly, LST > ambient

HID never crossed my mind, oops.