I measured leaf temperatures on 2 different strains, identical conditions/media/etc, and found one plant near ambient temperature & it’s neighbor was 5 degrees hotter & way out of VPD… 
Raises all sorts of new questions 
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That’s a big difference! Are they on different irrigation schedules? was the cooler one just watered?
I just got one of these meters and have only started to play w/ it, haven’t seen a difference like that across the canopy yet though.
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What are you using to measure? Temp sensor guns broadcast and receive data in a wide field. The temp displayed is often an average of the reported temps in a given area. If your measuring against somewhere with reflection of heat then it will report higher temps.
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This is true, can you adjust for emissivity? mines also on the cheaper end, so it has a narrow distance range for measurements. so maybe one leaf is out of that range?
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Usually can’t adjust them that I’m aware of. I would suggest maybe putting a flat black or grey peice of paper behind the plants to reduce the reflection of heat
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Overall my experience with temp guns is to expect around +/- 5 degrees for a cheaper gun. The top end ones are more accurate but generally not worth it unless you REALLY need a close to exact temp. Even then contact probes would be a better solution
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Maybe it’s a hot spot under your light or maybe a spot that doesn’t get hit as much with the fan?
What kind of light do you use?
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Sun 
in this case
IR non contact thermometer but taking lots of different readings…. Not great but close enough
No - totally identical feed & water
What this suggests to me is the high temp plant has more salt in the leaves and that some strains are just not well suited to hot outdoor growing…. Maybe?
Fwiw the cooler plant is pomelo punch & the hot one is jokerz…
Just observation not science
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Intriguing none the less!
Thank you for sharing.
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It may have to do with the stomata opening and closing.
That is typically how plants will cool themselves.
Some of the water drawn up through the roots exits the plant through pores – or stomata—in its leaves, hence the sweating.As this ”sweat” evaporates, heat is removed from the air, providing a cooling effect . However, if there isn’t enough water available or if relative humidity gets too high, the stomata close.
Other things can effect the stomata too.
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Calcium uptake and distribution at the whole-plant level is influenced by water flow.
So yes, if the stomata are closed there is minimum water flow, therefore limited uptake and distribution of Calcium is to be expected.
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