What are ideal temperatures going by vpd ?

Looking at vpd chart a humidity level of 60% is within good range at 23-24°c where 25°c and above is stressing the plant .

Is this correct

Keeping temps at 23-24 60% humidity throughout vegging is optimal ?

Usually I'm hitting about 28° ... Saying that my light intensity could be better adjusted to drop heat output

I'm fortunate enough that with the colder weather and lower temps in the house that it seems to be in the sweet spot vpd wise when the lights are on, though the temp is only 72f or so with nothing but constant ventilation, lower to mid 60%. I do keep a wet towel in the tent and flower room when the lights are on.

I tried running at a higher temp with a humidifier in the tent but no way would the one I got make any difference with the fan running. And if i shut the fan off until the humidity got up it never reached the 84F set point I ran in the summer.

So I've decided the vpd with light on is much more important than trying to keep the temp up in the mid 80fs. Especially since the house temps will drop into the lower 60fs at night soon.

Vpd involves considering three things: 1. Room/enviro temp; 2. Leaf temp; 3. Humidity. You’ll need to pick up an IR gun to read that accurately - with leds led temp is usually 3-4 degrees below room temp, depending on whether you have IR etc in the spec or not. But you can’t really guess the leaf temp with much confidence as a 1 degree difference in leaf temp has a big impact on vpd.

vpd also only comes into play when plants are photosynthesizing (ie when lights on), and you can dial in vpd at varying temps and humidities but changing one factor may require changing another to get the vpd back in line. There’s no real ‘ideal’ temp for vpd; there are just ideal combinations of temp/humidity/Leaf temp

Understanding vpd gives you great insight into your grow, but you need to understand it first - google and read a couple of articles, then use this: