Heat Output - COB vs LED

Discussion in 'LED and other Lighting' started by kbone123, May 17, 2018.


    kbone123 Member

    What are the typical temperatures you guys see in your tents above ambient and what lights do you use?

    I bought a cheap blurple LED from Amazon (Phlizon 900w) thinking that I'd be okay with it as long as I went in to it knowing full well that it was 200w of actual draw with less efficiency than better models.

    However, the heat output seems to be a bit high for what it is and I'd like to return it and look elsewhere.

    Currently, the unit heats up a 3'x3'x6' tent to ~82F when ambient room temp is ~75F with a 4" inline fan acting as exhaust on maximum. This of course also ends up heating up ambient in the process making my AC unit have to also work harder. A 6-8F increase over ambient seems to be higher than what LEDs should produce.

    I'm now looking more towards a DIY COB solution with Citizen Gen6 COBs and 120mm fanless heatsinks with a Meanwell 200W driver. However, I don't know if this will even solve my issue. Will this COB setup get my tent below 80F?

    HydoDan Well-Known Member

    Actually for cobs you want a higher leaf temperature... 82F is where I run...
    Send it back and build your cob setup.. Place a fan above the cobs blowing down..
    Your AC won't be needed..
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    Chef420 Well-Known Member

    I recently bought rapidled’s 3x3 vero 29 kit with the substrate. All I’ll say is amazing. Six smaller light sources instead of one big one.
    Here’s the kicker: better coverage, half the power of my former 600w hid, and a fraction of the heat. Basically it runs at ambient. And you can take excellent pictures, if it matters.

    coreywebster Well-Known Member

    It should be the same heat but you will get more light from the cob set up.

    What is the 4" inline fan your running?
    I ask because although I flower with cobs and Quantum boards I still use a 600w Metal halide in veg tent (unless its peak summer)
    I have a 5" ruck fan in a 4x4, but its a loft tent, so its super low profile at 5 foot at its highest. Point is that's a low volume tent and thus should heat up but my 5" ruck keeps it running high 70s and that's using a variable speed controller and only having it on number 2 of 5 speeds.
    I would of thought a proper 4" inline extraction fan should be able to pump enough air from a 3x3x6/7 to maintain proper temps using only 200w of lighting, even if you are recycling the air.

    To me the solution wouldn't be to swap 200w of this to 200w of that, it would be to make sure that fan is designed for the job its trying to do and to make sure that hot air is removed from the tent and then from the room the tent is in.
    Last edited: May 17, 2018
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    ANC Well-Known Member

    Fans don't cool, they can at best move some hot air around.
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    coreywebster Well-Known Member

    How is that relevant to the situation?

    kbone123 Member

    It is a Vivosun fan and scrubber combo that I rigged up to have a direct connection with each other to minimize stress on the fan. It literally goes scrubber -> fan -> exiting tent. No ducting or anything blocking or inhibiting flow rate in any way.

    I spent a fair amount of time and effort testing things in regards to air flow to maximize displacement. Short of rigging a ghetto heat tube to the light itself, I'm not sure I can reduce temps much more through just displacement of air.

    I am seeing a fair amount of arguments stating that ALL lights of any type will eventually put out their drawn power as heat regardless of light efficiency. ex. 200w draw = 200w END heat regardless of COB/LED/HID. COBs are just better at turning it into light first before the light then hits something and creates heat. Am I correct in this regard?

    My current plan is to try creating high heat and low heat portions to the tent using something like a poster board attached to the light. Everything above it will be the high heat portion which is where the exhaust is. At least then, if it gets to 82-85F, the plants should still be hopefully in the 77F range. Is this reasonable?
    Last edited: May 17, 2018
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    Nutria Well-Known Member

    You re right about heat, 1 watt = 3,41 BTU

    (HPS has far more far red than leds.)
    You need less watts to have the same light output.
    less watts = less heat

    kbone123 Member

    Thank you, but for once, I am someone not too concerned about light output or yield. This light will suffice for my needs. I am mainly concerned about heat output and most effectively handling it.

    There are of course many options like intaking cold air directly from AC, exhausting hot air out of the building, using a portable AC in the tent and displacing the hot air out (least efficient), etc. However, I am trying to find the most efficient way of dealing with it that hopefully doesn't result in either heating up my apartment, especially in the hotter portion of the year (making my AC work harder), or blowing a fan directly out of the window in the summer (imagine the scolding you'd get from parents if you ever did this while the AC was running).

    In reality, 82F doesn't seem like much. It is certainly out of the Goldilocks zone for cannabis cultivation, but not a deal breaker. I'm hoping that separating the hot and cold parts of the tent might allow that to fall just enough for it to be more reasonable for the plants.

    CobKits Well-Known Member Rollitup Advertiser

    low 80s is actually ideal for LEDs
    a mongo frog

    a mongo frog Well-Known Member

    Same as for HPS. Not sure where all this leaf temp via LED is coming from. Different lights different temps? Someone must of read a college study and linked it in a thread. Run 77-81 and make sure your water is not cold when one waters and your good. Who cares what light is being used.
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    kbone123 Member

    Oh really? That works then LOL.

    My guess is that a certain range of light, perhaps IR, might create a need for a certain leaf temperature over another. I don't know the sciences behind it all, I just try to pay attention. :dunce:

    I can definitely run 77-81 then.

    CobKits Well-Known Member Rollitup Advertiser

    its HPS's (or the suns) IR's effect on leaf temp
    ideal with hps is upper 70s to low 80s air temp
    ideal with LEDs is low to mid 80s air temp

    leaf temp same in both cases

    all light heats up leaves.
    IR more so than other spectrums
    LED has little to none

    ANC Well-Known Member

    I do try to keep them under 80 once flipped.
    Don't want to boil off those terpenes and esters.

    Randomblame Well-Known Member

    You should always get used air out of the room. A ducting hose to the window is best! In the winter you will need the heat, in the remaining time completely dispose it is the best you can do. Blowing hot air out of the window means intake of fresh air in the same time. So unless you run CO² it's the best way.

    with HPS you get leaf temps of ~27-28°C at 25°C ambient.(because of it IR radiation)
    With LED and 25°C ambient you get only 22°(warmwhite) or 20°(blue/red).
    To get the desired leaf temps of 27-28°C ambient temps needs to be 28-30°C on the LED side.
    It's a bit more difficult to keep your humidity where you need it with higher ambient temps. Air tends to dry out quicker and this leads to an higher VPD.
    The table below is very useful to find the right setting at different temperatures.

    VPD Chart, Temps vs. RLF.gif
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    KonopCh Well-Known Member

    55-60% RH is a bit too high in flower?
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    Randomblame Well-Known Member

    Nope! At night, <50% is good to aviod boitritis/bud rod but over the day there is no problem.
    I've 30°C and 65% humidity currently(end of week 8 ) and the girls pray all day long. 50-55% at night with dehumidifier!
    Now I start my finishing program for the last two weeks and reduce intensity by 20-30% to get ambient temps around 25°C and I start using the UVB tube the whole day. I don't want trich's that dry out too fast because of the heat so for that reason I use lower temps+more UVB when the girls starts ripening.
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    KonopCh Well-Known Member

    Interesting. I've never try more than 50% RH last 4 weeks in flower. I was rather cut all leaves to get RH down. Even with indica strains are you the same?
    Will try next time without that and see what happens.
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    Randomblame Well-Known Member

    Defoliation only where it is "necessary", so eg. to let the light fall deeper or fresh air can circulate better (lollipopping), but in total not more than 20-30%.
    I've seen many removing all the adult leaves too early(around day 30-40} and I'm sure that's too much goodness and reduce potential yield. Removing leaves means to me they lost all their main energy collectors and the smaller, lets call it bud-leaves, are the only source for energy and CO.
    At the end when the plant starts ripening its far less dangerous to remove more and more leaves. They will start dropping from below anyway.
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    kbone123 Member

    I'm having a little trouble understanding that chart. Is it telling me that if I ran 45C in the tent with 80% RH it would be okay? Seems :fire:, no?

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