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Growing Under LEDs at Temps Above 80F

Fixer

Active member
I've just eliminated the HPS lights from my grow room and am trying to determine if I should heat the space. A fellow grower who is all LED tells me I should crank the temp up to 80F plus. Anyone have any direct experience? Thanks
 

Fixer

Active member
Thanks! I've had a number of successful harvests under the LEDs while I had the HPS lights running in the room and the high temps weren't necessary. My friend claims that the LEDs don't throw IR light so the high temp is necessary to achieve the correct VPD. IDK!
 

Koondense

Well-known member
Veteran
Your friend is right, higher temps for led growing are ok. 28-30°C is a good environment for plants under leds, keep an eye on the humidity.



Cheers
 

Fixer

Active member
Your friend is right, higher temps for led growing are ok. 28-30°C is a good environment for plants under leds, keep an eye on the humidity.



Cheers


Thanks! Are the higher temps necessary? I just got into the season where my AC isn't running 24/7. I was hoping the room would heat itself with just the LEDs.
 

SuperBadGrower

Active member
The range mentioned by Koondense is exactly where you will see peak performance. Light intensity, temperature and photosynthesis are very entangled, if it's 70 F and the plants see 1000 PPFD, that's a bigger problem than if they see 600 PPFD
 

Fixer

Active member
The range mentioned by Koondense is exactly where you will see peak performance. Light intensity, temperature and photosynthesis are very entangled, if it's 70 F and the plants see 1000 PPFD, that's a bigger problem than if they see 600 PPFD


I've been keeping the room at 75F. I'm considering bringing it up to 81F. Do you think it's worth the extra energy to heat vit?
 

exploziv

pure dynamite
Administrator
Veteran
picture.php


From: https://fhs-bio-wiki.pbworks.com/w/page/12145771/Factors effecting the rate of photosynthesis
You can also fiind this graph on various other sites, just search for "photosynthesis over temperature".
 

f-e

Well-known member
Mentor
Veteran
The graph looks off. I have seen another where the peak is 28c which aligns with my own findings.

I can't grow below 77f I'm just wasting my time.

The temps for led's debate circles around transpiration. Air movement is another answer and lower RH. Without making adjustments (or even with them) Calcium is a common problem. The use of calmag type things is another answer. A calcium nitrate additive being ideal as leds promote N usage. You can also use Nitric acid for it's 30% availability and ability to unlock Calcium from hard water supplies by forming Calcium Nitrate. I'm at the edge of my knowledge here but believe the Calcium gets carried to the root because it's attached to the N. The N is taken leaving the Ca in place for an exchange. I say again, I'm reaching.

You could add N with urea but then the N is taken and something undesirable left at the root. The calcium nitrate (calnit) route seems ideal for LEDs

Edit: Most calmag things list the Ca as an oxide equivalent but the N quota on the bottle tells you calnit was used to some extent.
 

SuperBadGrower

Active member
Here some actual research on the weed plant;


from: Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions


To study the photosynthetic response of C. sativa under
different PPFD and temperature levels, leaves of twenty
vegetatively propagated, four month old plants from a
single mother plant of high yielding Mexican variety
were exposed to a range of PPFD (0, 500, 1000, 1500 and
2000 ?mol m-2s-1) and temperature conditions (20, 25, 30,
35 and 40 oC) under controlled humidity (55 ± 5 %) and
CO2 (350 ± 5 ?mol mol-1) concentration to determine
suitable environmental conditions for it’s optimum
photosynthetic assimilation. Thereafter, leaves were
acclimated under optimum light and temperature
conditions and exposed to different CO2 concentrations
(250, 350, 450, 550, 650 and 750 ?mol mol-1) to study the
effect of CO2 on photosynthetic and water vapour
characteristics of this species.

The rate of photosynthesis (PN) and water use efficiency (WUE) of Cannabis sativa increased with photosynthetic photon flux densities (PPFD) at the lower temperatures (20–25 °C). At 30 °C, PN and WUE increased only up to 1500 ?mol m?2s?1 PPFD and decreased at higher light levels. The maximum rate of photosynthesis (PN max) was observed at 30 °C and under 1500 ?mol m?2s?1 PPFD. The rate of transpiration (E) responded positively to increased PPFD and temperature up to the highest levels tested (2000 ?mol m?2s?1 and 40 °C).
 
Last edited:

f-e

Well-known member
Mentor
Veteran
The paper suggests 30c and 95,000 lux. Mid day sun stuff, no more. That seems reasonable.

The paper has a couple of issues. One is the 350ppm of co2 when we know over 400 is normal and favours higher metabolic rates. Thus using 350 was unfair to the greater result. Also, 55% RH offers no adjustment for vpd. Again being suited to 25c. So two factors work to keep the 30c result down, yet the 30c result at full light wins in this competition.
 

mojave green

rockin in the free world
Veteran
Good info boys. I grow with HID but the temp parameters should be similar as long as the light is similar in intensity. Of course, one should not discount VPD. Anywho, I’m cranking my temp up a bit based on what I’m reading.
 

Koondense

Well-known member
Veteran
Please keep in mind the fact most leds are wavelength limited to around 700nm,some go to 760nm. Meaning there is very low IR radiant heat so the ambient temps need to compensate for the lack of IR which is abundant in sunlight and most hid lights.


Cheers
 

mojave green

rockin in the free world
Veteran
Please keep in mind the fact most leds are wavelength limited to around 700nm,some go to 760nm. Meaning there is very low IR radiant heat so the ambient temps need to compensate for the lack of IR which is abundant in sunlight and most hid lights.


Cheers
Watts are watts in regards to heat radiated by light fixtures. The heat comes from the bulb and the ballast with HID. The heat from LED’s is largely from the drivers, with LED’s themselves adding the rest. Still, if you run 500W HID, or 500W LED, heat output remains same. Good discussion.
 

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