No, I think many of the leaf temperature studies you find online used "high-priced" thermo-detectors and "expensive" infrared video equipment to measure cannabis leaf surface temps under various lighting and growing-environment temperature conditions (for their LED vs HID/HPS comparison).
You argue cheap measuring equipment: My answer; I think, a lot of the time, the "higher-expense" of the instrument or equipment, in general, only guarantees increased precision, rather than complete and infallible accuracy. I think measuring and laboratory equipment are only as good as the operator and the calibration standards used to "zero" the devices - "cheap" or "expensive".
I would also argue that the majority of growers, by-and-large, do not use this chart in their grows. Therefore it is irrelevant. Temp and humidity can vary significantly, day-to-day - in most amateur small-scale grows, medium-scale amateur grows and outdoor grows. Unless you have a "professionally" sealed grow room with multi-big-dollar environmental equipment, most growers cannot obtain this level of environmental control constantly (so is the chart important? - really? - to most growers here at the 420 website?).
I think indoor environmental engineers mostly use this chart for sizing, paring, and integrating A/C, air handling and dehumidification/humidification systems in professional grows. I do not know if the VPD is a very good management tool for all 420 crops - one size does not fit all.
First, it assumes an "idealized" rate of photosynthesis for max transpiration and nute flow. That is never the case in any type of grow. Plant-to-plant, leaf-leaf-to-leaf, all the time. In fact, if you examine the original research for your chart you will find there were many assumptions made regarding the "actual" rate of photosynthesis on a section of leaf and how those same assumptions changed regarding shaded or sunshade leaves. Their experiemental estimates were made based on "certain" plentiful assumptions. No plant is an idealized hybridized and constant "photosynthesis machine" where all things and plants are "equal".
Next, the chart assumes all 420 plant varieties, 420 species and 420 sub-species, react in the same way to one idealized set of environmental conditions. That is not the case either. Some like it hot and dry, some like it moist and cool (and any derivation in-between). Bad logic to assume all 420 like one "idealized" environmental regime for any particular stage of growth.
Last, I think in "real-life circumstances" you find a lot of variation in professional and amateur goals regarding their "grow". Techniques and methods vary widely. Plant stress is one of the most important cannabis growing techniques with many various methods of application.
For example, it is clear that certain stresses on 420 plants, at the correct time in their growth phase,
aid, rather detract from vigor, potency and yield. Why do we do all these physical LST and HST techniques if not? Environmental stresses are similarly important as plant "stressors". The whole "droughting" crowd understands this (
@Krissi1982 , et.al. - "team" not "crowd", sorry
@Krissi1982 ). Temperature and RH are just other forms of potential stressors 420 growers use to "condition" their crop. Stress the 420 and the 420 will seek to alleviate the stress, maybe in an interesting and valuable way (or as I say: "Spank them and they will response.").
In mean I like "vanilla ice cream" but there are other flavors more interesting - keeping the same "speculative" environmental condition crop-to-crop is like eating vanilla ice cream every day. I'm a "Rocky Road" fan. Some 420 varieties response well to a "rocky road" of growth with increased vigor, higher potency and better yield.
Therefore, environmental stress or "idealized norm" is neither good or bad, right or wrong, it is just an opinion rather than "imperial rasta ganja dogma". The above chart may be best applied in large-scale professional grows rather than as a "everyone do this" new-age "miracle-gro".
In addition, the above chart is "pretty cool" (in it's rainbow colors and hard-to-read enumerations), however, I do not know if it is more useful as an engineer's guide to proper environmental grow management or as a general reference for idealized transpiration and nutrient delivery under idealized environmental conditions based on questionable assumptions regarding maximum obtainable rates of photosynthesis. In "Engineer-speak".
The "ideal" case is not usually the "real" case - in any "case".
I think you should research online "cannabis leaf surface temperature studies" and check out the information there - don't mind-lock on a certain pretty chart that gets passed around the forum. Finally, do research and mark the assumptions used to create the "rainbow-420-
-chart" - it will make your head swim.
There are plenty of times "engineering logic" produced with poorly-made research assumptions has let us down and wilted our path-row of Earthly delights.
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