What distance are you running your COB’s

I’m using a timber grow light 300w x6 cxb3590 prefab unit and was wondering what everyone’s preference is. After about a week I’m seeing the plants happiest with the light 24” from the canopy at full power. The website says they can be as close as 12”. I started off high at around 30” at first, and slowly adjusted to see what the plant could tolerate, but I was having to dim the fixture to about half power to avoid bleaching when I got to about 12”, I’m currently in week 6 of veg with a very happy Guava D female and just wanted to get some input from people that have some experience. I know this has been mentioned in other posts but there’s such a wide variance in recommended heights, from 12”-30” that I thought it wouldn’t hurt to ask what peoples individual preference is with a couple grows under their belt. I also have the reflectors mounted btw.

12’’ for me

And that’s at full power?

I have some 3590's, prefer to run them full and a little higher, works well for me typically 14-18" above canopy depending on the area I'm trying to cover off.

depends on cob spacing for the most part.

my rule of thumb is distance to canopy should be at least as much as the distance between cobs

if your cobs are 18" apart and you are 12" from canopy you will have areas of lower light intensity in between them

Thanks for the insight guys, I was reading an older thread about a guy running some100w Vero 29’s and he had to raise them about 36” at full power to keep his plants happy. Kinda glad I went with the cree since you can have them a little closer to the canopy. It was a hard choice between the two, but Dan was super helpful, and it really was the best customer service experience I’ve had in a LONG time.

Med68w said:

Thanks for the insight guys, I was reading an older thread about a guy running some100w Vero 29’s and he had to raise them about 36” at full power to keep his plants happy. Kinda glad I went with the cree since you can have them a little closer to the canopy.

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if you ran the crees at 100W which they are plenty capable of, they would be basically indistinguishable from the veros to your plants

Hi! Same config than you here.. I mean same Intensity (1400mA/50W per COB) but more chips and total Watts.
While the flower stage, 12"/14" with my ledil Angelina reflectors 90° and 10"/12" without optics.

Thanks, I’ve also noticed the plants are happier when my temp is around 82f. And after reading this article on leaf surface temperature, there’s yet another benefit to switching to led. Savings on cooling costs are going to be nice.
https://www.blackdogled.com/lst

I have my Timber vero's at 18 inches above the canopy at 100 percent.. plants are diggin it.. my first indoor grow so i am still reading and learning all i can.. Peace

CobKits said:

depends on cob spacing for the most part.

my rule of thumb is distance to canopy should be at least as much as the distance between cobs

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My rule of thumb is distance to canopy should be at most the distance between cobs or strips. With COBs you can lower the height to close to 2/3 the COB spread and with strips even half.

So with the COBs 12" apart, you can go as low as 8", or raise up to a maximum of 12". With strips 12" apart you can drop down to 6" even.

The distance to the canopy is only about uniformity of the light distribution. Go too high and you're wasting lights on the walls. Go too low and you create hot spots and dark spots.

If you are at the "correct height" for good light distribution and you still see it's too much light for the plants, then you're fixture is producing too much light and you should dim it. Of course you could raise it to waste light on the walls too, but that's just well ... a waste. Still in a pinch that works too.

BTW if you have only one COB/board/strip then usually the distance to canopy is the smallest of width or depth of the grow area. Ie a single COB in a 2x2 tent should be at most 2' above the plants. Again that's the upper limit, you better go a bit closer. In practice 18" works best.

im running citizen 200w about 13 inches above the canopy on full power. is it best to run cobs at full power during flower? so far the plant (amnesia cbd) seems to be flowering a slow compared to what im used too.

A $14 fleabay light meter I use. I shoot for 50k lux min at tops. Not scientific but works with white light. I have 4 zones of 4 cobs each zone. Shorter phenos I either lower the light or crank up that zone to reach the desired light intensity. I bend and tie etc. Some are 12" from the light. Some 16 or so. ymmv

For me it’s around 16-18” & that’s with one cob per square foot. I have a lux meter winging its way to me as we speak but from multiple grows of the same strain I get much healthier happier plants at 16-18”.

If I run with my LED’s any closer I will at some point in the grow start seeing issues.

I'm at about 13" right now with no issues. I'm running a 200w timber light one cob per square. ft.. I started dimmed at 50% for about 10 days and 20". Full power after that and gradually lowered over a week. Don't know if that was the perfect combo but it seems to be working now. I'm 28 days since breaking ground.

giantsfan24 said:

I'm at about 13" right now with no issues. I'm running a 200w timber light one cob per square. ft.. I started dimmed at 50% for about 10 days and 20". Full power after that and gradually lowered over a week. Don't know if that was the perfect combo but it seems to be working now. I'm 28 days since breaking ground.

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Humidity in veg 27% .....little low ?

Dave455 said:

Humidity in veg 27% .....little low ?

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Possibly but it hasn't hurt in the past.. It varies between 25% and 40%.

kushedy said:

For me it’s around 16-18” & that’s with one cob per square foot. I have a lux meter winging its way to me as we speak but from multiple grows of the same strain I get much healthier happier plants at 16-18”.

If I run with my LED’s any closer I will at some point in the grow start seeing issues.

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Have you tried dimming the COBs and then hanging them closer? 10" should really be fine with one cob per sqft. I run them at 8" even. Got my biggest yield that way.

You lose 1 to 2% of the light on the wall for every inch you go up. So instead you could just dim the lights by up to 20% and get the same amount of light on the plants while using 20% less electricity.

@wietefras
I did run 25w per cob some time ago with the cobs 12" above canopy. I kept the wattage & hanging height constant nearly all the way through flowering. My plants grew very well for the bulk of the grow but right towards the end I started seeing slight discolouration on some of the leaves so lifted the height of my cobs by about 10cm which seemed to keep my plants happy till harvest.

I have since in general been running with at least 16” at anything from 24-40w per cob with no issues. That said on my last grow I neglected my scrogging duties & ran out of space.

I ended up with my buds around 10” away from my cobs which they really didn’t like.

Even with my cobs dimmed down to 25w per cob I ended up with leaves slowly changing colour & going brown & crispy.


My personal take is the intensity is too much for the plants to keep up with so they start kicking out signs of deficiencies or lock out & then crisp up. If I manage my height better I don’t have this problem at all. I still pulled 1.5gpw so couldn't grumble to much but that’s my experience of hanging height anyway.

About a foot n a half. Minimum of a foot.