Is this enough LED for now?

[aquanaut]

Hi all, it's been a long while since I've grown. Back then used to be setup with a 600w HPS in a 4x4 tent. Things have changed for me and now I'm limited to a 2x4 tent. Heat was a problem back then so I opted for LEDs following some guides on here.

I ended up with 3x Cree CXB3590 CD powered by HLG-240H-C2100B. Is this pretty close of a setup compared to my old setup of 600w HPS? If not, would 3x more of the same LED be the direction I should be going?

I ran the DIY led calculator jar and it says my PPFD based on canopy area is 638.16. Doing some searching on the forum it seems I want to be around 800~1000 PPFD... so maybe.. 1 or 2 more leds?

Thanks in advanced!

Pic of tent as of now

 

[aquanaut]

Gotcha.. for what it's worth I'm in a 2x4 tent now. 4 wide, 2' deep. So using your math, if I did half so.. around 4~5 leds sounds about right for a 2x4 tent. Back then I never passed using 600w hps and was happy with my results. Heat was a major issue for me with hte 600w hps.. so I could never adventure into the 1k realm.

 

[HideousPenguinBoy]

You got it. You are using that calculator right. At 2100mA it's 4 COBs for 844.63PPFD and 5 COBs for a 1057.35. And you'll need to get another driver and space them to avoid hot spots. (you seem to have all this under control already)

If you had infinite cash, running 12 COBs on a HLG-320H-C700 would net you the least heat. (due to efficiency less watts would go to heat) Moreso if you went to 72V.
Less cash, running 8 COBs on a HLG-320H-C1050.
And so on. This is just me giving more info than you need, just in case it could help. I run mine at 1050mA and I'm making a vent hood (reused plastic and wood scraps) to get the extra heat out of there, just because my place is hot. If you end up having heat issues, try that out to catch the heat off the heatsinks before it mixes in the tent temp.

 

[aquanaut]

Awesome! Thanks for the reply! You actually just opened my eyes to how I can achieve lower heat. Is there some sort of efficiency map vs current for the CXB3590 leds? Or.. How does one calculate the extra heat a given led would produce over the current range?

 

[HideousPenguinBoy]

Glad it helped! In the calculator it has the COBs' efficiency in one of the lines. You can just pop through them real quick to get the numbers. Cree COBs are pretty great when running at low amperage. Vero29Gen7 are more efficient than Cree at higher amperage (and cheaper), but... you want efficiency over all. You should also check out Quantum Boards and my fav, ChilLEDs. They are like COBs but spread over a whole board. I'm unsure of QBs numbers but I believe ChilLEDs are the highest efficiency boards out there with adjustable spectrums. Check them all out! ::excited nerd squee::

 

[aquanaut]

Ordered 3x more CXB3590s along with a pair of HLG 1400mA drivers. Planning on running 6x 3590 @ 1.4A and according to the calculator I should be around 900 ppfd.

I'm excited to try lowering my existing 3590s from 2.1 to 1.4A and watching my temps drop . What driver are people using to run 700mA? Same one I'm getting just dimmed?

And does anyone have any PPFD calculations for running my setup @ 700mA? With the 3x 3590s at 2.1A I hit 86F over the hot weekend and was hoping to lower that by goin to 1.4 or even 700mA... I know light is light and there _will_ be heat, but I'm trying to hit a good efficiency number vs heat generation.

 

[HideousPenguinBoy]

And does anyone have any PPFD calculations for running my setup @ 700mA? With the 3x 3590s at 2.1A I hit 86F over the hot weekend and was hoping to lower that by goin to 1.4 or even 700mA... I know light is light and there _will_ be heat, but I'm trying to hit a good efficiency number vs heat generation.

1050mA is a good medium between efficiency and number of COBs needed. If you got $$$ to spare and heat is your ONLY though, go for the 700mA. DL the COB calc and get to playing with it!

 

[CobKits]

Awesome! Thanks for the reply! You actually just opened my eyes to how I can achieve lower heat. Is there some sort of efficiency map vs current for the CXB3590 leds? Or.. How does one calculate the extra heat a given led would produce over the current range?

whatever the wattage you put in your tent must come out of your tent. doesnt matter if its 600W of HPS, 600W of cobs, or a 600W heater. 600W of cobs gives more usable light than either the hps or the heater tho

 

[CobKits]

And does anyone have any PPFD calculations for running my setup @ 700mA? With the 3x 3590s at 2.1A I hit 86F over the hot weekend and was hoping to lower that by goin to 1.4 or even 700mA... I know light is light and there _will_ be heat, but I'm trying to hit a good efficiency number vs heat generation.

you want your tent at 86 with LEDs tho

 

[aquanaut]

Excuse my old school way of doing things, but I've always been under the impression w/o CO2 you want to be below 82~80F or so. I'm all ears on any new information

 

[Randomblame]

Nope,
best PS at 30°C also without CO²...

 

[MasterpieceNutes]

whatever the wattage you put in your tent must come out of your tent. doesnt matter if its 600W of HPS, 600W of cobs, or a 600W heater. 600W of cobs gives more usable light than either the hps or the heater tho

Cobkits is right as usual. Kinda oversimplified though, So I'm gonna extrapolate on your wisdom a little cobby.

I like to imagine heat as a liquid.. It pours out of heat producing items at varying rates.. A 600 watt heater: like a fire hydrant. 600 watts of 2100ma LEDs: Heavy running faucet. 600 watts of leds running at 800ma: light running faucet. Now imagine your room/tent as a bowl with holes in it.. Your fan opens an even bigger hole.. If the heat 'liquid' overtakes the holes ability to get rid of it, then it starts to 'overfill' the bowl/ tent/ room.. Then we get heat stacking.. It will get hot in there!

If we had some completely sealed rooms, the 600watt heater room would stack heat the fastest and would plateau somewhere pretty hot. But then the other rooms would follow.

THEY would ALL get very hot and EVENTUALLY stabilize at relatively the same max temps.. Just at different speeds. 600watts of radiation dissipation at work. Heat is the FINAL breakdown of light.

@2100ma, your tent couldnt cope. Different story at 800ma, with same amount of wattage but 2.5x more cobs required..

The culprit is what format that wattage comes out of: What's most/least effective at turning our watts into light is the final factor. (Obviously the item with the highest lm/w rating is our target, but costs limit how far to push this).

I'm rambling for reasons not hard to guess, lol. Hope it helps tho'

 

[kushedy]

Interesting read. My curiosity was tweaked by Cobkits & Randomblame’ s comments about temps. I hate to do it but I gonna have to ask, can you dumb that down a bit for me?



I don’t really understand the graph that Randomblame posted & am also like Aquanaut of the old school way of doing things. I.e. flowering temps significantly below the temps suggested.



Not disputing in any way just want to get my head round why plants can take/thrive in higher temperatures under LED than they can under hps.



cheers

 

[aquanaut]

From the graph Randomblame posted, it seems to be measuring Photosynthesis (absorption?) over PPFD.. and the graph lines are the ambient temps?

So if I'm reading this right... I want to be between 77~86F for optimal photosynthesis.

Where is this graph sourced from? I'd like to read more if you have any more data to share. And someone mentioned that with LEDS you do want to be hotter.. why is that?

 

[CobKits]

From the graph Randomblame posted, it seems to be measuring Photosynthesis (absorption?) over PPFD.. and the graph lines are the ambient temps?

theres a lot going on there its a multi-variate analysis

basically more ppfd will give you more photosynthesis at any given temperature, and is diminishing returns (i.e you get less out of going from 1000 to 1500 as you would going from 500 to 1000)

BUT! dont underestimate the power of temperature.

500 ppfd@ 30C has the same net photosynthesis as 1500 ppfd at 20C or 40C.

now it pretty obvious why some guys can do better with an HPS vs LEDs if they are not paying attention to temperature

this leads into your next question. HPS lighting has a bunch of infrared energy which tends to raise leaf temps. so somebody using HPS in a room at 77F/25C will have a leaf temp thats closer to 86F/30C and have excellent results even if the PPFD is lower

say in the same room they swap out an LED, at lower wattage and dont pay attention to temperature. The lower wattage results in a lower ambient temperature, say 72F/22C. to exacerbate this, LED has little IR energy and leaf temp rise isnt so high. now even if the LED has more PAR its going to lag behind the canopy at proper temperature. with LEDs 80-90 seems to be the sweet spot (90 is a little high, but LED plants at 90 will still do a lot better than HPS plants at 90 where they stretch and foxtail which are undesirable.

 

[aquanaut]

Great explanation CobKits! Thanks!

 

[kushedy]

Thanks for the responses guys. I did a little research online & found an article about running LED grows warmer because of the lack of IR which matches what you've said heere. Makes sense. The suggestion was to run at 28C minimum!
So now during the summer the struggle is not going to be keeping the grow room temps down but instead, letting the grow room warm up but trying to keep the heat-sink temps down. I try to keep my cobs as cool as possible & manage to keep them pretty much cool to the touch (the surrounding heat-sink that is). In a room with temps 28-30C that is going to be tricky keeping an LED array cool. Bit of a balancing act.

 

[KonopCh]

@CobKits I have 29-30°C in my small (80x80cm) tent. Also high humidity around 60-70%. I've tried all options with fans (intake, exit air, clip fans) but the same story everyday. You have 3x3 tent as I see. How do you manage temp and humidity (especially with big plants - evaporation)?

 

[CobKits]

we have a cool climate, just coming into summer. when on 12/12 its at night and its pretty much 50 degrees out every night so i dont have issues. you might need AC or just a dehuey to drop humidity a bit. 30C isnt bad at all

 

[MasterpieceNutes]

@CobKits I have 29-30°C in my small (80x80cm) tent. Also high humidity around 60-70%. I've tried all options with fans (intake, exit air, clip fans) but the same story everyday. You have 3x3 tent as I see. How do you manage temp and humidity (especially with big plants - evaporation)?

Your temp/humidity is good. You will naturally get higher humidity with higher temps as plants ramp up metabolism and transpiration. Keep good airflow/ air exchange in your room and this is GOOD.

Tying this thread together: We're going after lighting solutions that run cool enough to keep our rooms temperature keeping ambient @ <88ish F. Without AC = Bonus. (I run a 10x12 room 2kw with ZERO AC).

Why <88: Larf, spinach, foxtailing..

Why <88. Plant metabolism is DRIVEN by temp. Light and CO2 are LIMITING factors. Plant metabolism maxes out at about 88, low 90's with supplemental co2. PAR 9.0+ is required to drive it too.

Why>70 Plant metabolism is driven by temp. Plants grown at 86 vs 70 will grow about 50% faster. Ramp up temp= ramp up cal-mag feed (transport nutes= fuel metabolism).


Why keep higher humiditys? Because thats where your plants need to be. Vapor pressure deficit chart ftw. Just keep good air circulation and you'll get no powdery mildew. Lollipop away lower branches to increase airflow.

http://www.just4growers.com/media/1315/vapor_pressure_deficit_relative_humidity_chart_small.jpg

YES. at 86f =mid70's humidity. I assure you, plants love it. Air exchanges + air circulation = win.

I shoot for 84. kind of a sweet spot with some elbow room. Definitely hitting top10 percentile of metabolism optimums. Frost hard nugs is the final win.