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LED watts per plant, or square foot?

Discussion in 'LED and other Lighting' started by WDIK, Feb 20, 2014.


    WDIK Active Member

    Trying to do more preliminary research. My 6 Bridgelux Vero 18s from Digikey just arrived, but it will be a while before I build my array. I have a 3 plant CFL auto grow going in the tent at the moment.

    I have read that it's not the number of plants, but the size of the grow space that is important. My tent is small, with a 2'x4' floor space, so 8 square feet. I have also read that 30-40 watts per foot should be about right.

    If I drive my 6 COBs at 40w each, that puts me right at the number for 30w per foot.

    Am I figuring correctly? Or does anyone have other suggestions? I'm only planning 2 plants for my next grow and am planning to scrog and maybe try hempy buckets.

    Any info is appreciated.


    ETA: It just seems crazy to me that I could get enough light from these "relatively" small COBs. :dunno:
    smokey the cat

    smokey the cat Well-Known Member

    These things are like tiny slivers of the sun - despite nearly damaging my retina with em numerous times, my brain actually struggles to understand how bright these tiny things are.

    I've got about 40-45W of Vero per square foot - and run em only 3' from cab floor. Still in early testing phase, but this definitely seems more than bright enough. As for 30W - dunno. Might be tempting to chuck another 2-4 v18 in there down the line.

    Interested in seeing what you find

    Mellodrama Well-Known Member

    I just read Bridgelux's .pdf. It appears that 40W could be met by driving them above their "typical" voltage/amperage described in Table 3. They're not saying you can't do that. On Page 4 they even give a predicted lifespan when run at TWICE the rated forward current. I'll assume you know what you're doing but wanted to point that out.

    WDIK Active Member

    I hadn't read that part I had only really looked at the tables. If I'm reading the section you are referring to correctly, I should be fine. Let me know if you believe I am missing something. Thanks.

    "Bridgelux projects that the Vero18 family of LED array products will deliver, on average, greater than 70% lumen maintenance after 50,000 hours of operation at two times the rated forward test current. This performance assumes constant current operation at up to 2 times the nominal test current (2X drive current as is indicated in Table 4) with case temperature maintained at or below 85°C. For use beyond these typical operating conditions please consult your Bridgelux sales represe ntative for further assistance."

    WDIK Active Member

    That brings up an important safety issue. Very dark sunglasses required to work with these things?

    PetFlora Well-Known Member

    If you have them inside reflectors you will minimize the problem, while helping penetration
    WDIK likes this.

    Mellodrama Well-Known Member

    WDIK, you bring up something I'd been thinking about for the last few days. People are different. SupraSPL has a way of looking at DIY LED. He's looking for maximum efficiency, which means driving the LED's softly and staying far away from electrical/thermal limits. If that means buying more parts to meet illumination goals, so be it. That philosophy appeals to me.

    Some people might say that's like buying a 500 HP Corvette, then driving it as if you were a Toyota Prius hyper-miler. Some people are gonna want to mash the throttle and get the most light that they can.

    To each his own. But if it were me, and I wanted to run them fairly hard, I'd at least stay on the safe side of the nominal voltage and current as recommended by the manufacturer. If you want to run them beyond those numbers, that's certainly your call. I just wanted to make sure you knew what you were doing. For the Veros, it looks like nominal is 1050 mAH and 29.5 V = 31 W.

    Look, I'm really new to this, so my advice could very easily be wrong. If it is, somebody will probably correct me, then we'll both learn something.

    I googled around re: the Vero's a little bit. One of the articles (second to last paragraph) wondered about Bridgelux indicating that the Vero's can be run way past nominal, but wasn't sure what to make of that.

    There are two things I want to point out about the Bridgelux quote you copy/pasted. Are you OK with a 30% degradation over time? More importantly, do you have the tools to check for Tj and increase cooling if it's above 85 deg. C? 'Cause all bets are off it goes above that...
    WDIK likes this.

    WDIK Active Member


    It's all good and I am very new to this also. I picked the 40w number as I don't believe that is pushing them too far over. I believe Smokey said he was running his Vero 18s at 50w. The 40w number is also in the middle of the variable wattage of the drivers I have ordered. I'm trying to stay "in the middle" for safety and longevity sake.

    The plan right now it to run active cooling over each COB.

    Please feel free to offer any more thoughts. i am learning quite a bit.

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