As
Freakshow68 noted, in late flowering is a must control humidity to avoid mold. As i dont use CO2 supplementation, i havent problems with it, as i can set humidity about 40% without mayor problems. But the highest humidity i would try in late flowering is 55%.
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Since knna posted the VPD info I've been monitoring my leaf temps, and instead of being 3 C lower, they are 3 C higher at the hottest point! This sends VPD to 1.76. The obvious conclusion: Is my 1000w too close? Would I get faster growth by backing the light off and increasing room temp?
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Have you measured it on the upper surface of the leaf? The right way is measuring it at the bottom surface, with the sensor well blocked from the light. Radiant heat from the light affect temp measurements strongly.
Anyway, its very usual having top canopy leaf temps near or over ambient temp, due to radiant heat and top leaves having the highest metabolism rate. Leaves from 2nd or third node (counting from top) gives less extreme figures and are more representative of the whole plant.
Link with info about devices to measure leave's temp (and other growing parameters, as soil water potential):
USU CROP PHYSIOLOGY LABORATORY: RESEARCH: INSTRUMENT EVALUATION AND NEW TECHINIQUES
In the pdf about infrared termocouple sensors, it states that accuracy of those sensors (with sensor's body temp corrected) is below 0.2ºC.
If taking more accurate measurements, the leave's temp is still some degrees over ambient, then, yes, raising the lamp would help.
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My ambient co2 is never below 1000 ppm, and usually its right around 1200, without co2 supplmentation. I'm not sure why it' so high, but obviously I'm in the "slight co2 enrichment" zone. But considering I'm trying to set up the 'ideal' environment (self-contained cab, air conditioning, heating, bottled co2, lots of light) I need to decide whether I should (a) vent the cabinet and just use the ambient, co2-rich air to control RH, or (b) seal the cabinet and use a dehumidifier and co2 supplementation, which would allow precise control over co2 levels via a C.A.P co2 controller.
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Do you live over a farm?
That ambient CO2 is very high. I wish i have the same
Maybe strong traffic ? (cars
).
I think is no sense supplementing CO2 with that ambient level. To have that rich CO2 air is a God gift for a grower! Just control the humidity in the late flowering to avoid mold. That way, your plants cant get clear benefit from the increased CO2, but they still grow awesome. Ensure there is enough water potential (not dry soil or whatever media you use) to avoid strong hidric stress. A bit of drough stress cost a bit of weight, but increase resin production.
When you outdoor air is dry, is very easy reducing humidity, you only need to increase exhausting flow.
Think that the VPD range provided is for optimize grow rate. Going out it dont kill your plants, only get a reduced grow rate. Only when VPD goes very outrange it creates problems (similar to an overfert or root damage).
knna