Why we should be running Higher Temps for LED lights

[lefthandseeds]

Thanks for posting this @Mr.Sparkle. It totally makes sense and I’m glad to see there’s some nice thermal imaging data to back it up.

This is the resolution of the sentiment that LEDs make plants want more magnesium. They’re actually just cold.

[Seamonkey84]

I just set it to turn on at 89f or 65rh. That sounds right?
I just read that it should be up to 80F and 40-50% humidity during bloom, would the higher temp need the higher humidity I set?

[Shaggy450r]

No as you dont want that increased. Maintained. Just trying to find the sweet spot to allow the plants to be a bit warmer. Is how I took it.

[Tejas]

I read the article and the results were interesting. Their statement pertaining to LST and CO2,
“CO2 supplementation will also generally raise the optimal photosynthesis temperature, so the ideal LST for photosynthesis is dependent on environmental conditions as well as the type of plant.”
It would have been interesting to see how, from a FLIR perspective, supplemental CO2 actually how it increased photosynthesis temperature. My temperature is in the mid-70’s and I use sup CO2, I need to get my IR temp gun and check LST and go from there

[Seamonkey84]

Oh, so bring the rh setting down to 50-55%?

[Shaggy450r]

You veg or flower??

[Shaggy450r]

I’m wierd, if I change things ill monster drink it up and hang out till 3 4am after lights off and box cools to see what happens.

[Seamonkey84]

This is setting up in my bloom chamber, but they are Currently still in veg. I’m flipping the plants on Sunday and I’d rather just set it and forget it.

[Tejas]

This was a point made in the analysis:
“ Keep in mind that relative humidity affects how much evaporative cooling can cool the leaf, and that relative humidity is relative to the temperature. If you have 50% relative humidity in a 75 °F room and just heat the air up to 84 °F, the relative humidity will drop to 37%, and evaporative cooling will have a greater effect on leaf surface temperature.”

[Who]

I used a laser thermometer and checked my leds against my cmh’s and there isnt that much difference, less then 10 degrees.

[Mr.Sparkle]

@Gpaw

Is it safe to assume that the delta between leaf and ambient temperatures in veg are similar in flower?

My observations is its the same other than the shift plants do before lights out veg or flower where they start shutting down and the leaf temps bump up to room temps.

@Seamonkey84

Then what humidity should I set the fan to trigger at? If I’m venting for humidity, would that offset the desired temp too much and just chasing my tail?

Whatever humidity would put you in a nice VPD range when lights are on, its a balance of the two and for myself i found sometimes that me driving the RH lower would in turn drop my temp lower than i wanted so i ended up with settings that were more conservative in there leeway to allow bit higher temps and humidity

@Northern_Loki

Good point and interesting to think about. You could probably run the VPD formulas to estimate (or simulate) the transpiration differences … actually using the leaf temperatures in the formulas. The simplified versions consider leaf temps to be at the same temperature as the surroundings.

What’s cool, also, noting the leaf temps one could diagnose when the plant is getting too much light or is under stress as it sheds the excess energy as heat and/or as it shuts down the stomata.

Exactly some charts you can input or they display different Leaf temperatures such as this link i typically go to when looking at VPD https://www.dimluxlighting.com/knowledge/blog/vapor-pressure-deficit-the-ultimate-guide-to-vpd/

Also thats what led me to increasing my temperatures as a whole, i was running into the situation where the plants were shutting down and being droopy at less light levels than what ive had happy successful grows under, i drew a conclusion that at the colder temperatures i was running at the plants ability to shed any extra energy or at least cope and thrive with the increased light levels were diminished as that rate of transpiration limited how much light the plant could handle, all started down this path when i had removed some droopy sad plants and left them on the counter for a couple days, and due to me being busy with work when i came back they were the happiest they ever were just sitting on the counter under no light.

@ShiskaberrySavior

Excellent topic @Mr.Sparkle vpd is important as watering .

Indeed it is

@lefthandseeds

This is the resolution of the sentiment that LEDs make plants want more magnesium. They’re actually just cold.

Very well may be the case with the people that seem to need mag also consider calcium uptake is supposedly higher when the plant is exposed to high light intensity’s where it cant cool itself effectively.

Though my knowledge on the specifics of various functions of elements required in plant growth and how that relates to environmental factors is on the lesser knowledge side.

@Tejas

It would have been interesting to see how, from a FLIR perspective, supplemental CO2 actually how it increased photosynthesis temperature.

Would indeed be interesting.

@Who

I used a laser thermometer and checked my leds against my cmh’s and there isnt that much difference, less then 10 degrees

As noted in the article CMH’s run cooler leaf temps than say an HPS, though less than 10 degrees difference is still a decent amount all things considered.

[GnomeyByNature]

This is very interesting to me as well…

I am def further behind than many if not all of you in my experience and am looking forward to testing this out as well with my next build…

I still want to learn more about VPD and I guess my question is if what this is really about is staying in the higher temp range of the VPD charts where while you could be in a ideal VPD ratio but at a lower temp range it might actually not be ideal… it seems there is opportunity for a new chart to be made that possibly combines VPD, lumens/par, and CO2 as well…

I have a general hunch/theory that the more transpiration you can generate (maybe more so for veg) the better (as long as you have your air circulation and foliage separation in check to prevent bud rot). The reason I believe this is that with more transpiration this should be like a “well oiled machine” where inside the plant it is essentially more fluid. Theoretically nutrients/water are being taken up and delivered through out at a higher rate which I believe would lead to faster growth and repairs… this could tho also in turn lead to problems showing themselves faster/more dramatically as well… this is all theory and I really have nothing to back it up tho but I wouldn’t be surprised if there were studies out there showing some of this lol

@Chronickyle and thoughts from anyone else, I was thinking about some how using the heat from external drivers pumped back into a vent near the bottom of the grow space. Have that fan hooked up to temp for increase, maybe a another vent/fan from pure ambient to lower it. Put them on timers maybe for day/night but also thinking about how they may be incorporated with dehumidifying.

[nube]

Good stuff. In general, higher temps increase photosynthesis. However, keep in mind that there’s no one size fits all answer. The facts are different varieties want different temps and light intensities, and our job as growers is to do the best we can.

I’m sure there’s more research on specific cultivars of cannabis grown under LEDs, but here’s a good start on temps and photosynthesis and transpiration on several from different regions:

2011 Chandra et al Temperature response of photosynthesis in different drug and fiber varieties of Cannabis sativa.pdf (206.3 KB)

And works citing that paper:

https://scholar.google.com/scholar?cites=17663478981228347694&as_sdt=4005&sciodt=0,6&hl=en

[GramTorino]

Good thread.

Co2 supplemented or not, here’s a great techno read.

CO2 Enriched Hydroponic Growing | Manic Botanix

[nube]

Here’s another paper by Nelson & Bugbee that shows the difference in ambient to leaf temp is very little between various light sources: HPS, Sunlight, LED:

2015 Nelson Bugbee Analysis of environmental effects on leaf temperature under sunlight HPS and LED.pdf (2.0 MB)

Here’s the relevant quote,

Because LED fixtures emit much of their heat through convection rather than radiative cooling, they result in slightly cooler leaf temperatures than leaves in greenhouses and under HPS fixtures, but the effect of LED technology on leaf temperature is smaller than is often assumed.

[cdnBuddy]

Do these temperatures in flower have any effect on terpenes?

[nube]

Unfortunately there’s very little scientific data I can find on the subject as it relates to cannabis or the major terps other than boiling points, which are almost all very high - over 100C. But my intuition says probably not much at the temps we’re talking about with LED, and definitely not compared to the high leaf temps in greenhouses our outdoors in the late summer, or under normal temps in HPS grows (see FLIR shots in first post).

And think about all the famed skunk grown outdoors in the deep south and Appalachia. It was hot as hell for a large portion of flowering, even late flowering and during drying, but the finished buds were legendary.

In my experience, the biggest driver of terps are the genetics. Next is the quality of the grow, dry & cure. Last is probably the grow temps, as long as they’re under 95F or so with LED. I’ve grown a lot of indoor and outdoor bud that hit 100F in late flowering, especially in the desert, but came out juicy and stinky as hell. Not everyone has AC in their home or grow.

[valleymicro]

Quick comment. Did some testing and measuring of VPD. One thing that I noticed was higher temps causing lower humidity and increased VPD. Maybe it’s just my setup. I had to lower the temp to achieve a better humidity and VPD range. Leaf temp (77) was not far off from room temp (79-80). This is under Timber Grow Lights.

[Bostonbud]

Nube quotes Nelson bugby … believe him.
For anyone interested dr. Bugby of utah state has you tube videos about a variety of grow topics / lighting…etc. I consider his work to be a must see for any serious grower. He has the ability to make complicated topics easily understandable.

[Who]

his studies are awesome, I like how he beats a round the bush a bit so its not like the U of Utah is doing studies on cannabis so they dont loose there grant