COB distance
- Thread starter Megalomando
- Start date
HydoDan
Well-Known Member
Without reflectors I run mine at 16" all the time.. veg and bloom.. move em down a couple inches.. see what happens..
I have seedlings 10" from a Citizen 1812 @ 54 watt.. no bleaching!
ttystikk
Well-Known Member
I find it's the per chip wattage that tends to be the main determinant of bleaching distance.
Mine don't bleach beyond 6", often less, but I'm running mine at 50W.
frica
Well-Known Member
Light stress causing leaves to yellow, it's a bit similar to a nitrogen deficiency but it's not as easy to pluck the leaves.
The flowers also turn a really nice looking white colour (Which is why we call it bleaching).
It's not something you want.
majins
Well-Known Member
Bleaching is when the color is burnt out of it so it goes all white.
Tacoing is when the leefs start to roll up. Like a taco.
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Iv never had bleaching under Cree 3070s at 60W. They have gotten as close as 5 inches
I dont really have much height in my setup tho since I put the tent on its side. 6.5 X 3.3 X 3.3
So I only have half a foot I can lift or drop the lights.
I try to aim for 12 inchs at the end of stretch.
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. Stronger exhausts/fans are need I guess.hey guy u all seem to know your shiz about these cobs ...I have purchased hlg 240h=c1750 driver db cree chip cxb3590 36v 6500k I also have a dimmer on 36 in linear frame...its just my first cob and I wanted to try out for mothers and to get cuped just slightly rooted babys goin ..iv heard 36 in from top for fresh rooted just transplanted in cups....when they start growing move down to 24 in.. keepem at 24-18 in during veg in big containers mothers how does this sound to you guys ?
HemiGrind
Well-Known Member
Sounds good 
. I have the same HLG driver powering my 3590 cxb's (3500K) and I used similar distances for vegging. HydoDan runs at 16" (above post). I ran at 22"-24" for VEG. idk about sprouts, I use flouro for my seedlings until 5th leaf set and topping, then move to tent with COB's at 24". You could probably do 24" on seedlings @ 60%-70% using dimmer and just increase the intensity to 100% at 5th leaf set.
. I have the same HLG driver powering my 3590 cxb's (3500K) and I used similar distances for vegging. HydoDan runs at 16" (above post). I ran at 22"-24" for VEG. idk about sprouts, I use flouro for my seedlings until 5th leaf set and topping, then move to tent with COB's at 24". You could probably do 24" on seedlings @ 60%-70% using dimmer and just increase the intensity to 100% at 5th leaf set.
KonopCh
Well-Known Member
Two questions for you LED guys...
Enviroment: 80x80cm tent
Light: 280W COBs, around 50% efficient, without reflectors
Distance to plants: unknown
So, if distance (as I read) is not important in tent with reflective materials, at what height should I place COBs?
One is saying 30cm, one is saying it doesn't matter in tent (as high as possible).
Photons are bouncing from walls and hits different parts of plant. Also photosinthesis is in leaves so you don't need to put COBs directly over buds. Seems logic to me.
But... my experiment says other story. If I keep distance more than 30cm, I get airy/larfy/leafy buds at bottom of branches. And that way I cannot cover all plant/buds with my COBs so I guess that is not optimal also. So I move COBs 30cm from colas instead of whole plant. So I wonder if photosinthesis is in leaves, why aren't buds hard from top to bottom?
Enviroment: 80x80cm tent
Light: 280W COBs, around 50% efficient, without reflectors
Distance to plants: unknown
So, if distance (as I read) is not important in tent with reflective materials, at what height should I place COBs?
One is saying 30cm, one is saying it doesn't matter in tent (as high as possible).
Photons are bouncing from walls and hits different parts of plant. Also photosinthesis is in leaves so you don't need to put COBs directly over buds. Seems logic to me.
But... my experiment says other story. If I keep distance more than 30cm, I get airy/larfy/leafy buds at bottom of branches. And that way I cannot cover all plant/buds with my COBs so I guess that is not optimal also. So I move COBs 30cm from colas instead of whole plant. So I wonder if photosinthesis is in leaves, why aren't buds hard from top to bottom?
wietefras
Well-Known Member
First of all the height is determined by the uniformity which you aim for. Usually professional growers aim for at least 80% of average light intensity in the darkest areas.
If you go too high you do lose light on the walls. I measured 20% less light after moving the lights up from 30cm to 60cm and 30% less light going from 30cm to 90cm. It's not the doom and gloom of "inverse square" which people toss around. Inverse square would mean you lose 75% of the light by doubling the height, which obviously doesn't happen. Still, you lose significant amounts of light by moving the lights up too high.
The actual losses will depend on reflectivity of your walls and beam angle of course, but also on the size of the grow. A big grow will have relatively less light on the walls.
Photosynthesis happens in the leaves, but it's product gets transported in the plants to where it's warmest. So that will be usually be the upper area of the plant.
KonopCh
Well-Known Member
This is measured in empty sealed tent?
So total lumens divided by 80% is what I must get in the darkest area? Only have LUX meter.
SouthCross
Well-Known Member
I've had the same experience.
I'm currently using four CLU48 driven at 50%. Estimated wattage is around 200. Having a plant run wild and grow past 130cm. Once it finished stretching, including being tied down. The tip top of the bud is 26cm from the light surface. No reflectors. 61cm x 122cm tent. No burning, no change of colors, no indication it's too much light.
Seeds were sprouted at 89cm. Seedlings were at 76cm. From there the light was raised to maintain the distance. Until one plant decided to grow 30cm higher then everything else in the space and forced me to Damn near raise the lights till they touched the top of the tent.
wietefras
Well-Known Member
Well you try to get as close to the real situation as possible, but it's not an exact science. The plants wont die if you get the light distribution a bit off. I've had taller tops as close as 10cm away from a COB and it was fine too.
The idea is to check for 80% of the average light intensity. You can do that with a lux meter (assuming you don't have different colored lights in the tent).
KonopCh
Well-Known Member
I know they'll not die.
I just want squeeze as much as possible with that setup and maybe go beyond 1,5 GPW.
Can you explain how to meassure average light intensity please? Divide tent floor (80x80cm) into 20cm squares (with some black paper to prevent reflectivity) and calculate average? Or when I fill SCROG net with plants, then I take meassurments every 20cm square?
Randomblame
Well-Known Member
Measure the brightest point in the center, then measure in one of the corners. Difference should be as low as possible. For a PAR map divide the whole area into equal squares, preferably 1ft². Then measure in the center of each square and note the value read out.
Do the same @12, 18 and 24" heights or what ever you want.
You can cover the surface with a green screen if you want but a lux meter could give out wrong readings because it weighted green light most. So it is not realy neccessary, you anyway convert lux to μMol what is not more as a good guess.
BTW,
There is a thread to convert lux readings in μMol/s here in the LED section, try the search engine. As far as I can remember a 3500k COB has a conversion factor of 0,01415, so 50.000lx x 0,01415=~707,5μMol/s
I'm using 0,015 for all of my COB's, because they are supplemented by some deepreds and I do it only to get an idea of my coverage.
If you don't need real #'s a cheap 10$ lux meter is enough.
Do the same @12, 18 and 24" heights or what ever you want.
You can cover the surface with a green screen if you want but a lux meter could give out wrong readings because it weighted green light most. So it is not realy neccessary, you anyway convert lux to μMol what is not more as a good guess.
BTW,
There is a thread to convert lux readings in μMol/s here in the LED section, try the search engine. As far as I can remember a 3500k COB has a conversion factor of 0,01415, so 50.000lx x 0,01415=~707,5μMol/s
I'm using 0,015 for all of my COB's, because they are supplemented by some deepreds and I do it only to get an idea of my coverage.
If you don't need real #'s a cheap 10$ lux meter is enough.
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wietefras
Well-Known Member
Yeah something like that. Or if the your fixture is symmetrical then measure only a part (like half or a quarter of the surface). Or even just a single line and sort of "guesstimate". It's not really that precise.
To estimate the PPFD, I divide the lux meter values by 70 .
Megalomando
Well-Known Member
I started the thread awhile back but still haven't found the answer yet. I am running 3 heatsinks, each has 4 CXB3590 I'm growing in a 4x4x7 enclosure with tips at least 1' away from any part of the plant. Even when keeping the power down to 150W per heatsink I am finding bleaching and browning leaves.
Under the canopy the leaves and buds are all green and these do not get direct light. Just the parts getting direct light have this problem. When following others using these cobs and drivers, no mention was made as to max power before leaf bleaching. I'm seeing this bleaching and yellow/brown leaf turning, even on the nuggets now everywhere there is direct light. Indirect light seems to keep them happier.continuously but nothing specific to go by.
Right now I have the drivers all turned to their least output (60W for four CHB3590 ) and I am seeing green growth but those touting the CXB3590 as the goto COB were not having this problem back then, or at least bringing it up.
So some help/suggestions please; has anyone else made a light with 4 CXB3590, driver HLG-185-C1400A. If you have had leaf yellowing and browning with these lights, what wattage gave you the best growth?
Thanks!
Meg
Under the canopy the leaves and buds are all green and these do not get direct light. Just the parts getting direct light have this problem. When following others using these cobs and drivers, no mention was made as to max power before leaf bleaching. I'm seeing this bleaching and yellow/brown leaf turning, even on the nuggets now everywhere there is direct light. Indirect light seems to keep them happier.continuously but nothing specific to go by.
Right now I have the drivers all turned to their least output (60W for four CHB3590 ) and I am seeing green growth but those touting the CXB3590 as the goto COB were not having this problem back then, or at least bringing it up.
So some help/suggestions please; has anyone else made a light with 4 CXB3590, driver HLG-185-C1400A. If you have had leaf yellowing and browning with these lights, what wattage gave you the best growth?
Thanks!
Meg
ttystikk
Well-Known Member
Ok so if I'm getting this right, your running a total of 12 chips over a 4x4' canopy?
I'd raise them up so you have 2' between light and leaves. This will help with heat, light distribution and should reduce bleaching and burning.
Can you post some pics of your setup? Often the issue can be easily spotted.
I'd raise them up so you have 2' between light and leaves. This will help with heat, light distribution and should reduce bleaching and burning.
Can you post some pics of your setup? Often the issue can be easily spotted.