LED and room temp

H

HashBucket

Well-Known Member
I live in an area that is almost entirely dedicated, in a business sense, to growing cannabis. A huge majority of my neighbors do just that: indoors and outdoors.
Mine is indoors, and I consider the outdoor growers to be the 'canary in the mine.' As long as the authorities allow them to operate, I'm prolly ok.
ANYway, I'm sitting in a local beer bar/hamburger joint hefting a cold quart and there were three guys sitting at a table behind me talking. One of them recently purchased 10 Gavita pro 1700e LED units. He is about 10 days into a flower run, after a two week veg under HPS.
I perked up and started actively eavesdropping.

One of them was trying to convince the another one that if he uses LED he must keep his room warmer than usual. For optimal weight he needed to keep the room at 75 to 85 degrees Fahrenheit.

I have two of the exact units in one of my rooms with 24 plants under them. They are mixed in with the DE Gavitas. I am doing a side by side comparison and test to see if I want to switch the whole room (or do both).

I admit to a lack of knowledge about LED, which is why I'm testing. But, I've never heard that higher heat thing with LED. I was always under the impression that the plant starts shutting down at 80, why would the type of light make a difference?
I know there's people here that know more than me about this subject here ... so chime in. Should I turn the heat up?
 
H

HashBucket

Well-Known Member
Isawthelight said:
I imagine the temperature/LED talk had something to to with Vapor Pressure Deficit.
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Wow.
That chart is some kind of confusing.
Too technical for my little pea brain.

I subscribe to the KISS methods, and this is way too scientific for me.

Also, the chart makes NO sense. I have to keep RH above 62% but less than 47% ... depending on whether VDP is 0.8 or 1.1. But, what IS VDP, and is it the same as VPD?
 
wietefras

wietefras

Well-Known Member
What 1212ham said. HPS radiates heat onto the plants. You can feel the heat coming off those bulbs. With led not so much. Leds mostly give you convection heat. ie heat that rises up from the coolers. It rises away from the plants towards the exhaust fan and it's gone.

That's actually why I have my exhaust taking air out from the bottom of the grow. That way the heat from the leds gets dragged through the plants. It gives a much more uniform temperature through the plants too. Otherwise it will be 80F on top of the canopy and then well below 70F below the canopy. The lower temp under canopy decreases photosynthesis there and I feel it makes for more larfy buds lower down.
 
2

2com

Well-Known Member
wietefras said:
What 1212ham said. HPS radiates heat onto the plants. You can feel the heat coming off those bulbs. With led not so much. Leds mostly give you convection heat. ie heat that rises up from the coolers. It rises away from the plants towards the exhaust fan and it's gone.

That's actually why I have my exhaust taking air out from the bottom of the grow. That way the heat from the leds gets dragged through the plants. It gives a much more uniform temperature through the plants too. Otherwise it will be 80F on top of the canopy and then well below 70F below the canopy. The lower temp under canopy decreases photosynthesis there and I feel it makes for more larfy buds lower down.
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Rocket Soul said:
One trick for maintaining RH and higher temps with a vented grow is to inverse; extract from the bottom and intract on top. Its very cost effective as nothing new is needed
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I've never heard of that. Interesting idea. It is a bit of a fuck around though, not possible mid cycle.
Thanks for the idea though.
 
Gond00s

Gond00s

Well-Known Member
indianajones said:
Hey @HashBucket I've used LEDs at temperatures between 74-78°F and still hit 2+ grams per watt. I think it all depends on variety, some plants just like it hot, some do fine in the mid 70s.
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all depends my plants just like upper 80's and they are loving the extra heat their transpiring more I think atleast their wanting 4 gallons a plant a day
 
sandman83

sandman83

Well-Known Member
Airwalker16 said:
Why would this be impossible at any point? Just flip your fans the other way.
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erm personally, I would have to clear the girls out of the way and it is a jungle, then I'd need a ladder and to disconnect the fans. I think I'll probably go down to a single HPS in the middle and LEDs on the sides, the room I'm using is larger than I need.
 
Airwalker16

Airwalker16

Well-Known Member
sandman83 said:
erm personally, I would have to clear the girls out of the way and it is a jungle, then I'd need a ladder and to disconnect the fans. I think I'll probably go down to a single HPS in the middle and LEDs on the sides, the room I'm using is larger than I need.
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Why aren't your fans mounted outside your tent/room?
 
sandman83

sandman83

Well-Known Member
Airwalker16 said:
Why aren't your fans mounted outside your tent/room?
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probably a good point, was just the easiest design to get ventilation setup at the time once growth got explosive. I have plans to redesign but the girls will need to be harvested first. I only recently got the tents still learning, just vegging in them and probably use one to dry while the rest finish.
 
Airwalker16

Airwalker16

Well-Known Member
sandman83 said:
probably a good point, was just the easiest design to get ventilation setup at the time once growth got explosive. I have plans to redesign but the girls will need to be harvested first. I only recently got the tents still learning, just vegging in them and probably use one to dry while the rest finish.
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Tents dry perfectly. As long as you're hanging whole branches with just large fan leaves taken off.
 
rustyshaclkferd

rustyshaclkferd

Well-Known Member
Higher heat means more transpiration more transpiration(as long as its healthy breathing) translates directly to more water/feed taken up by the plant... add Co2 and high vpds to increase increase percentage of stomata open and you have a even stronger correlarion by default to yield


It has its draw backs, keeping neutral or close to neutral night/day temp differentuals and RH in check becomes harder as moisture content of warm air quickly becomes a RH spike as temps drop... mo money mo problems
 
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