In my experience growing indoors with Chilledpuck LED builds is that the leaf temperature throughout my flowering canopy is on average -4.5f compared to the room's air temperature. Compared to when I used to grow with HID lighting, the leaf temperature would be from -0f to -2f at most. This doesn't sound like a significant difference however I grew several cycles with LEDs before deciding to try higher flowering temperatures to see if I could get the yields that I used to get under HID and in doing so I found the results that I was looking for when initially switching to LED: Improved quality AND quantity.
Initially, upon switching from HID growing to LED growing, I was using all of the same environmental parameters with the LEDs as I was with the HIDs except for having even more intense light at 1500ppfd average with the LEDs vs 1000ppfd average across the canopy before with the HIDs. To me, this meant I should have bigger and denser buds, a higher per plant yield, and faster overall growth rates. My results with using all of the same equipment in the same environment and same parameters were only slightly improved and overall, disappointing. However, after raising the temperature of each week of the grow cycle by +4f and properly calculating the leaf vpd using an IR thermometer, I found much-improved success in all areas.
I achieved my success by raising all growth stage room temperatures from 80f week 1 to 72 week 9 with the HIDs to 84 week 1 and 76f week 9 with the LEDs, for example. I believe that this "General Recommendation" grow environment parameters chart (
https://cch2o.com/general-recommendations/) was designed with HIDs in mind (-2f leaf differential temperature) as the leaf vpd comes in at 1.19kpa week 1 after calculating vpd in kpa using a leaf temperature of 78f and 60% RH. The chart finished with a week 9 leaf vpd at 72f (room temp) and 40% RH and a leaf vpd of 1.45kpa (-2f leaf temperature).
Today, I still follow this chart and find it to produce pristine results with the only change of increasing the weekly room temperature values in all stages and weeks of growth to +4f and adjusting the RH at each week to follow a vpd cycle that I have found works best for my plants in my system. For example, for week one of veg I run my LED grow room at 86F and 65% RH. By using this VPD calculator:
https://pulsegrow.com/pages/vpd-calculator, the leaf vpd can be found to equal 0.98kpa using a leaf differential temperature of -4f. I have found that once a plant has matured into the vegetative stage having at least 3 or 4 sets of side branches, that growth rates are best with a leaf vpd of about 1.0kpa. As the plants' life stages advance into flower I gradually increase the leaf vpd all the way to 1.45 at week 9 of flower.
In order to achieve the results that I am with your LEDs, I recommend using an IR thermometer to measure your leaf temperatures all over your canopy at mid-day (lights on) and find the average value. Then look at what your room temperature is averaging during that time and find the difference. Use these values in the VPD calculator that I shared with you to determine how you need to program your AC and Dehuey to achieve the VPD appropriate for your plants' stage of growth. I find that 0.70 kpa is best for clones and seedlings, 1.0 kpa is best for veg and 1.3 kpa is best for flower. I do not monitor the vpd at night as I find that to not be cost effective. I have not conducted any experiments but I predict that the improvement in results I would get by running an extremely oversized condensation dehuey or even a desiccant dehuey would not even be close to worth it. My rooms do not get above 50% RH at night at any stage of growth and that is all that I conern myself with regarding night vpd currently.
I hope this post can help growers using LEDs to get the most out of them. I have seen other LED growers post online that they have also found success using higher temperatures as the LEDs produce less IR radiation and offer less heat to the plants' leaves and this is best to be compensated for by increasing room temperatures. As previously mentioned my vegging plants grow like mad in my ebb n flow hydroton system with LEDs and a day room temperature of 86f and RH of 65%. Urbanremo on youtube and my IR thermometer both worked in conjuntion to solidify my decision to experiment with the increased room temperatures and I do not look back. Urbanremo, in a recent LED garden update of his in his flower room, stated that he finished his plants at 78f (presumed room temperature) and he has much less light on his plants than I did and my buds were not nearly the same size! Raise those temps and maintain proper vpd and I bet your results will improve!
Happy growing!
TLDR: I increased my room's temps +4f from what I would be using with HID to achieve the best results!
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