COB users - What is your lux at canopy?

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logan9fingers

Well-Known Member
Hi,

I have a 350w diy cob unit and I am trying to figure out the optimal height to keep the light at. Its on a pully.

What wattage unit do you have and what is your lux at canopy level? How far is your light from the plants.

My light drops down to 30k lux around 6 inches from the light. At around 20 inch away lux is about 8k. The cobs I have are each giving out 7k lumens x 7 cobs @ 50 watt. I should be getting 49000 lux over one meter square. Which is equivalent to a 400w hps.

Im wondering do hps users experience the same kind of drop at distance from the bulb or if somehow the intensity is better despite emitting the same amount of light.
 
L

logan9fingers

Well-Known Member
I think i have an issue to be honest. Im only using a standard android light meter on my S6 but I am running 7 50w bridgelux vero 18s hanging from a board and at 2ft away from the light im reading a lux of around 30k. Im running them at the test spec of 34v @1.25 amps.

But the coverage isnt that great. This is only directly under the light. Which is 600 x 400mm. Off to the side of the light it drops off to between 7000 and 10000 lux.

My area is only 4ft by 3ft. The lights give out 7000 lumens per cob. I should be getting 45k lux over my whole floor space.

From what im reading i need 30k-75k lux for decent flowering. Im thinking that from reading others posts a 400w hps in an air cooled hood would provide much better coverage of my area.

Otherwise it may be an issue with cob spacing. Maybe I have them too far apart. Closer together perhaps will provide a stronger beam. Im loathe to unwire my wiring and redrill the board to try. They may be at miniscule different heights/angles because they are hung to board by chain. Idk.

Disappointed.
 
wietefras

wietefras

Well-Known Member
Optimal height is determined by uniformity. If you hang the light too low you get hot spots and dark areas. When you hang the light too high, you lose too much light on the walls. The trick which is usually applied is to make sure the uniformity is such that the darkest spots still get 80% of the light of the average over the whole area.

So say the average over the whole area is 20k lux, then the least you should see is 16k in the darker areas.

You should space the COBs uniformly over the area. There is no point in bundling them in the center. That just will create a bigger hotspot there and mean you need to increase the height even further.

BTW Those smartphone lux meters aren't very reliable. They also tend to be very sensitive to the incident angle of the light. Straight into the sensor is measured much more than under an angle.
 
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logan9fingers

Well-Known Member
I see what you are saying about the spread. I took this to be main appeal of using a cob set up. But even with the naked eye I can see the intensity is quite poor only a short distance away.

I am thinking for the amount that I spent, and the effort taken to build it, a better option for my space would have been a 315w cmh. The cooling required for the cobs that I have takes up around 15w.

Thats 365w of cob lighting that cant adequately cover my wardrobe. with the cost of the drivers, heatsinks, fixings, wire, solder and connectors coming to around 350.

I could have bought a phillips agro cmh, ballast, hood and bulb with hanging fixtures for about 250. Added a cooling fan and still saved 30w of power.

I think i still may buy one for flower.
 
sixstring2112

sixstring2112

Well-Known Member
logan9fingers said:
I think i have an issue to be honest. Im only using a standard android light meter on my S6 but I am running 7 50w bridgelux vero 18s hanging from a board and at 2ft away from the light im reading a lux of around 30k. Im running them at the test spec of 34v @1.25 amps.

But the coverage isnt that great. This is only directly under the light. Which is 600 x 400mm. Off to the side of the light it drops off to between 7000 and 10000 lux.

My area is only 4ft by 3ft. The lights give out 7000 lumens per cob. I should be getting 45k lux over my whole floor space.

From what im reading i need 30k-75k lux for decent flowering. Im thinking that from reading others posts a 400w hps in an air cooled hood would provide much better coverage of my area.

Otherwise it may be an issue with cob spacing. Maybe I have them too far apart. Closer together perhaps will provide a stronger beam. Im loathe to unwire my wiring and redrill the board to try. They may be at miniscule different heights/angles because they are hung to board by chain. Idk.

Disappointed.
Click to expand...

First off that phone is going to lie to you lol.but if your really seeing 30000lux @ 2 ft you are doing fantastic. This I just took from 2 feet directly under a 600w hps that was new on jan 3rd.it is also inside a cooltube that was cleaned the same day.but lux does not tell the whole story and i dont think a 400w hps will be any better than your veros at the currents you are using.
20170116_175919.jpg

This is from under a gavita @ 42 inches and the lamp is at least 6 months old and its also set at 800w,big difference but when i use my par meter the difference is much closer on both of these and my 50w cob setups.
20170116_180433.jpg
 
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logan9fingers

Well-Known Member
sixstring2112 said:
First off that phone is going to lie to you lol.but if your really seeing 30000lux @ 2 ft you are doing fantastic. This I just took from 2 feet directly under a 600w hps that was new on jan 3rd.it is also inside a cooltube that was cleaned the same day.but lux does not tell the whole story and i dont think a 400w hps will be any better than your veros at the currents you are using.
View attachment 3877804

This is from under a gavita @ 42 inches and the lamp is at least 6 months old and its also set at 800w,big difference but when i use my par meter the difference is much closer on both of these and my 50w cob setups.
View attachment 3877808
Click to expand...
This is great info dude thanks a lot. I will buy a proper light meter rather than a new light in that case. The comparison with intensity at distance with hps was exactly what I was looking for.

I am on week 2 of a run of autos. This is only my 2nd ever run first being with 200w of cfls so hoping for a major yield boost.

I will post the actual readings that I get with a light meter when it arrives for comparison. And try to hang a tad higher for a more widespread coverage in the meantime.
 
sixstring2112

sixstring2112

Well-Known Member
logan9fingers said:
This is great info dude thanks a lot. I will buy a proper light meter rather than a new light in that case. The comparison with intensity at distance with hps was exactly what I was looking for.

I am on week 2 of a run of autos. This is only my 2nd ever run first being with 200w of cfls so hoping for a major yield boost.

I will post the actual readings that I get with a light meter when it arrives for comparison. And try to hang a tad higher for a more widespread coverage in the meantime.
Click to expand...
I have the hydrofarms par meter and its very useful and was only about 140.00 i coulda easily bought an apogee for 5 bones but after much reading for what i needed this one is perfect, and within a few points of the best meters.
 
P

Plant Lobbyist

Well-Known Member
sixstring2112 said:
I have the hydrofarms par meter and its very useful and was only about 140.00 i coulda easily bought an apogee for 5 bones but after much reading for what i needed this one is perfect, and within a few points of the best meters.
Click to expand...

I use it more than the Li-cor.

The sensor is much larger on the Hydrofarm as well.

So long as it is within 50umol +/- it works fine for me.
 
BuddyColas

BuddyColas

Well-Known Member
logan9fingers said:
I think i have an issue to be honest. Im only using a standard android light meter on my S6 but I am running 7 50w bridgelux vero 18s hanging from a board and at 2ft away from the light im reading a lux of around 30k. Im running them at the test spec of 34v @1.25 amps.

But the coverage isnt that great. This is only directly under the light. Which is 600 x 400mm. Off to the side of the light it drops off to between 7000 and 10000 lux.

My area is only 4ft by 3ft. The lights give out 7000 lumens per cob. I should be getting 45k lux over my whole floor space.

From what im reading i need 30k-75k lux for decent flowering. Im thinking that from reading others posts a 400w hps in an air cooled hood would provide much better coverage of my area.

Otherwise it may be an issue with cob spacing. Maybe I have them too far apart. Closer together perhaps will provide a stronger beam. Im loathe to unwire my wiring and redrill the board to try. They may be at miniscule different heights/angles because they are hung to board by chain. Idk.

Disappointed.
Click to expand...
The distance between your cobs?

And if you're running 7 cobs at 42.5 watts each and trying to cover 12 square feet, then that is about 25 cobs watts per square foot. I don't think you're going to find happiness until you get to 30-35 cob watts a square foot. Just my experience.
 
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logan9fingers

Well-Known Member
BuddyColas said:
The distance between your cobs?

And if you're running 7 cobs at 42.5 watts each and trying to cover 12 square feet, then that is about 25 cobs watts per square foot. I don't think you're going to find happiness until you get to 30-35 cob watts a square foot. Just my experience.
Click to expand...
At the moment they are in 2 rows of 3 about 200mm apart. With one in the centre of the fixture.

Ive raised the light up now and am getting an even 15-20k accross the floor area. Still on my shitty android meter but its all I got till a new one arrives.

Obviously it is all dependant on the actual readings with a decent light meter but, using the readings for a new 600w hps above as a barometer, I cant be getting less than the equivalent 400w hps at a distance of 2 foot. Again thats if this phone is even in the same ball park as the light meter reading.

A 400w hps would be the maximum I would put in this space due to heat concerns so if I can match the light output im happy.
 
nevergoodenuf

nevergoodenuf

Well-Known Member
My friend runs all his SE and DE 1000w @ 200,000 lux, so I had mine calibrated with my light to that. I do wish I had 100k and 150k checked.
200klux to PPFD[897].jpg
 
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MissyGoddess

Well-Known Member
This is my cob light. I don't have a lux meter but I have a Par meter. I have my cobs spaced 16" apart and 16" from the plants. Par is between 600-700 at the canopy in a 3.5'x3.5' area. Cree CXB 2700k 90cri @ 1400mA.

CobLight.jpg
 
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