They make several that do just that. There is a flaw that most people don't take into account that leads to issues when someone unfamiliar with VPD tries to employ a chart like above. You need to take into account the leaf temperature or things CAN go wrong very quickly. But i still feel its a decent ballpark chart to go buy if you understand VPD
The kPa values above are a good set of parameters for different stages of growth but as i stated its not that simple. The type of lighting can have great effect on the actual VPD, lights such as quantum board LED's provide no IR or UV spectrum that will increase the leaf temp. While other like CMH, HPS and MH all provide different amounts and add in the intensity differences from wattage and hanging height etc. it can vary greatly changing the actual VPD. The key to using VPD is taking leaf temp into account. Leaf temp is generally a bit cooler than air temp, usually about 2-5F cooler
Here is an good article and a calculator that takes the guess work out for you:
https://www.questclimate.com/vapor-pressure-deficit-indoor-growing-part-3-different-stages-vpd/
You can copy and make your own calculator in excel.
For example if you take the chart above at 77F the min/max is 74/64% RH for Veg. Now lets add the leaf temps into the equation.
With a leaf temp of 5F cooler at 77F room temp the ideal RH range now becomes appox 60/50% RH. You can see how much this can impact your grow and would likely develop mold/fungus and transpiration issues if you just followed the chart above.
VPD is almost magical when you get it down in my opinion it eliminates so many problems and provides great growth rates. In my opinion the people who say its hogwash are the people who have been doing it wrong. DO YOURSELF THE FAVOR and follow the directions in the link i posted to make your own calculator.
In fact i will just post it. I did not make this nor take any credit for the info.... Just passing it along.
Enter the formula on the next line into spreadsheet cell A10 (copy and paste it).
=3.386*(EXP(17.863-9621/(A7+460))-((A6/100)*EXP(17.863-9621/(A5+460))))
You will type-in 3 values into 3 other cells:
- Cell A5: The air temperature (A5 in the formula)
- Cell A6: The air %RH (A6 in the formula)
- Cell A7: The leaf temperature (A7 in the formula)
Cell A10 will then give you the total VPD for that grow room condition.
Hope this helps some of you a bit
