Pulse VPD Chart: Leaf or Ambient Temp?

[Cerebral Goo]

Are the target numbers on the standard Pulse charts the ambient tent temp or the leaf temp? It looks as though it would be ambient temp? My tent is 83* with 56% RH and the leaf temp is 78-80 in the second week of flower

Thanks!

 

[Tom Bombadil]

Looks like leaf surface temp

Avoid this common mistake when comparing LEDs to HPS – Thrive Agritech

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[tronN00dles]

Check out vpdchart.com.

That one allows you to enter both leaf and air temp.

 

[Cerebral Goo]

Looks like leaf surface temp

Avoid this common mistake when comparing LEDs to HPS – Thrive Agritech

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Thanks Tom! Also, how is the Double Grape? Have the DG, Strawberry Nuggets x Skywalker, Strawberry Nuggets x Forum Stomper, and Forum Stomper going on my first venture. May have to add an xtra carbon filter as my house is starting to smell like a tire fire!

 

[Cerebral Goo]

Check out vpdchart.com.

That one allows you to enter both leaf and air temp.

Thanks as well Tron. That calculator is pretty much what I was looking for. All the calculators I've seen will give you the kPa for the ambient temp and leaf temp, but they do not tell you which one (tent temp or leaf temp), or the combination of both, is the better target value. None of the websites I have found about VPD tell you which one to go by either. Maybe I'm missing something when reading...

 

[Bruce Campbell]

Technically, you could make a chart with either leaf or room temperature on the Y (left vertical) axis - so it's a good question.

Here's a chart where they actually label the axis as "Room Temp."

For the Pulse charts, I worked through the math (here) and compared to their example charts (here). Pretty sure they're using room temp on the vertical axis.

(For RH = 0%, Tair = 102F, Tleaf = 100F - I get 6.49 kPa, which corresponds to 102F / 0% RH on their chart.)

Thanks as well Tron. That calculator is pretty much what I was looking for. All the calculators I've seen will give you the kPa for the ambient temp and leaf temp, but they do not tell you which one (tent temp or leaf temp), or the combination of both, is the better target value. None of the websites I have found about VPD tell you which one to go by either. Maybe I'm missing something when reading...

To clarify, there is only one VPD in the tent and only one target value (for each growth stage). The VPD (vapor pressure differential) is the difference in air SVP (saturation vapor pressure at the room temp and room RH) and the leaf SVP (saturation vapor pressure at the leaf temp and RH = 100% inside the leaf). The question is really: which temp (air or leaf) is whoever made the chart listing on the chart axis when they report VPD values in their chart.

And, you're right - most articles / calculators don't take the time to clarify. In general, I would assume room temp, but you can always work the math yourself to confirm.

 

[Cerebral Goo]

Technically, you could make a chart with either leaf or room temperature on the Y (left vertical) axis - so it's a good question.

Here's a chart where they actually label the axis as "Room Temp."

For the Pulse charts, I worked through the math (here) and compared to their example charts (here). Pretty sure they're using room temp on the vertical axis.

(For RH = 0%, Tair = 102F, Tleaf = 100F - I get 6.49 kPa, which corresponds to 102F / 0% RH on their chart.)



To clarify, there is only one VPD in the tent and only one target value (for each growth stage). The VPD (vapor pressure differential) is the difference in air SVP (saturation vapor pressure at the room temp and room RH) and the leaf SVP (saturation vapor pressure at the leaf temp and RH = 100% inside the leaf). The question is really: which temp (air or leaf) is whoever made the chart listing on the chart axis when they report VPD values in their chart.

And, you're right - most articles / calculators don't take the time to clarify. In general, I would assume room temp, but you can always work the math yourself to confirm.

Thanks KDawg! Very good explanation. I did the math as well and assumed it was room temp with the numbers, but wasn't 100%. Seems like every time I have looked up the subject I had just burned one...so second guess myself. I greatly appreciate the info!!!

 

[CannabisMingus]

This may be helpful as well. HTH

 

[Cerebral Goo]

This may be helpful as well. HTH

Thanks mwilliams! I based my temp/humidity off of that chart and the Pulse chart, but as KDawg stated, most charts and calculators don't differentiate room or leaf temp on the axis. Being new and with all the bad info out there, I'm constantly second guessing everything. Seem to be right in the sweet spot for the moment, but controlling the humidity in the southeast is a pain.
Thank you once again for the reply!!!

 

[Delps8]

Are the target numbers on the standard Pulse charts the ambient tent temp or the leaf temp? It looks as though it would be ambient temp? My tent is 83* with 56% RH and the leaf temp is 78-80 in the second week of flower

Thanks!

I’m using a PulseOne and their docs specify leaf surface temp. The pulse actually uses the offset between ambient and LST to do the calculations.
It’s in the FAQ’s on their site.