Lighting COB Watts- per plant or per square foot?

[VitaMan]

Should I light according to square feet, distance from canopy, or by number of plants?

I have a unit with 5 cobs, which draws between 66W and 339W depending on whether you run one, four, or five lights. They each have active cooling, so I think it's fair to say a little over 60W per COB.

The manufacturer says it is a good fit for a 4x4' tent with 4 plants, so when it is fully lit it would be similar to 500W HID.

I have 3 smaller plants in a 2x2' under one COB, and I wonder if I am under-lighting them and should run four COB instead.

I am a bit trigger shy because I made the mistake of growing a single plant in the same space with all five COB for a while, which stunted it. It's all I've got so I don't want to take an uneducated risk.

-don't know if this matters, but 2 are in early bloom and all three get OverGrow a few times per week. The tent never gets very hot...in fact I would like to boost that.

Edit Sept 20: I am tagging @BigSm0
As a manufacturer of high quality lights, you probably have the most expertise to answer this question!

 

[918AutoGrower]

I’d go by the usable square footage....not just the overall square footage of the tent (unless you plan on having a plant canopy that will cover the entire tent from corner to corner.

What kind of COBs are they? If they are full-spectrum white LED and are a good quality (such as the Cree CXB 3590), then 32-35 watts per square foot will get the job done. If they are blurple lights, you’ll need upwards to 45 watts per square foot.

Hope that helps!




Current Autoflower Grow

https://r.tapatalk.com/shareLink?sh...ads/New-3x-C4-Auto-Grow.1503982/&share_type=t

 

[VitaMan]

Here's some specs:

• Input: 85-277V, 50-60Hz
• Power consumption: 326W±3%
• Ingress protection: IP43/40
• Ventilation: Active cooling
• Working temperature: 35 – 45℃
• Ambient temperature: -20℃ – 50℃
• Optical data: Beam angle: 90 degree
• Color ratio: Custom spectrum PPFD (μmol·m-2·s- 1)
• Height above the Plant PPFD(μmol·m-2·s- 1)
• 30cm 750
• 50cm 550
• 70cm 326

 

[CoviklaFlaire]

I think 55w per plant is enough..

 

[918AutoGrower]

Well, they aren’t Cree lights. Do you know what kind they are or who the manufacturer is? What made you choose this light? Just curious.


Current Autoflower Grow

https://r.tapatalk.com/shareLink?sh...ads/New-3x-C4-Auto-Grow.1503982/&share_type=t

 

[VitaMan]

Well, they aren’t Cree lights. Do you know what kind they are or who the manufacturer is? What made you choose this light? Just curious.

Below are the main factors

• I had blurple LED from the same manufacturer a few years ago and they were really good.
  
• They have a verifiable 9 light COB (600 watt) that was compared side by side to a 1000 watt HID and did just as well, but one of the COB plants went on to win a cup. (I saw the actual cup)
  
• Full spectrum- they are almost white with a pinkish hue
• They supply the large industrial farms
  
• I drove to the manufacturers city to meet them (cheaper, faster, and way more interesting than shipping) and one of the staff mistakenly quoted me a price on a smaller unit so they had to honor it. Even with gas and time I paid the same as I would if shipping just 2 of our AFN members' (excellent) lights.

 

[VitaMan]

I lit 4 COBs a few days ago. The plants are thriving, so signs of stress of light burn just yet.

 

[Banjacked]

Be aware that "burn" from LED lighting is NOT the same as "burn" from traditional HID, it can sneak up much slower and will show as more like bleaching on buds rather than crispy leaves, unless a leaf actually touches the LED when the effect is instant

 

[Deville]

My Mars COB is only 105W, in tent 2x'2',it can still work well, I think its light efficiency is very high

 

[VitaMan]

About 12 days of 4x COB (aprox 240W actual) and no signs whatsoever of burn or bleaching, no fox-tailing.

I think it may be partly strain, but I am guessing that mostly it is up to timing- once they are in full bloom, the extra watts are beneficial, but in early growth too much can stunt them.