Cob PAR Footprint

[Green_Skunk]

Is there a resource we can use to see the COB PAR footprint at differing heights? I'm partial to the Cree 3590's because of their size. I'm trying to find the right distance to place the cobs from each other so the edges overlap and essentially create an 'even' PAR reading or as close as possible.

(Yes I am aware that PAR is not everything but I am just starting to understand the spectrum which plants utilize for photosynthesis i.e. 440-680 cant think of the name)

 

[CobKits]

Is there a resource we can use to see the COB PAR footprint at differing heights? I'm partial to the Cree 3590's because of their size

LES size makes next to no difference in pattern. all cobs have pretty much the same pattern unless you use reflectors or lenses

 

[Green_Skunk]

LES size makes next to no difference in pattern. all cobs have pretty much the same pattern unless you use reflectors or lenses

Appreciate the response. Would you happen to have a chart for PAR on different COBS? Or know where I can find one?

 

[CobKits]

heres a chart with ppfd/W

 

[HazednConfused]

Ahhh, cxm22 reigning champ! Running 4 with a 240 54b meanwell.

 

[Green_Skunk]

Ahhh, cxm22 reigning champ! Running 4 with a 240 54b meanwell.

What size area?

 

[HazednConfused]

31"×16". More light than I need!

 

[Rocket Soul]

You can try this thread:
https://www.rollitup.org/t/lens-and-reflector-optics-for-cob.893660/

Parmaps for cxbs at 50 w, at 12 and 18 inches, refelctive walls and open space. This would be slightly older bins but you should be able to extrapolate using cobbys graphs.
For even coverage most people here seem to go for 1 per foot2. You can also try diffusers to even out hotspots. Hope it helps

 

[wietefras]

Is there a resource we can use to see the COB PAR footprint at differing heights?

You can find the disitribution pattern of the COB in the datasheet.

The footprint of what do you want though? Of all the light or only the part in the "beam angle"?

You could take the beam angle and calculate the size of the circle for each of the heights you wish to compare. For instance at 25cm (10") the circle of light for a 120 degree beam angle would be about 87cm (34") in diameter. At 50cm (20") it would be 20/10=2 times bigger etc.

But then the beam angle is only the cone where the light intensity is at least 50% of the maximum straight under the COB. There is still quite some light beyond that beam angle. IIRC something like 20%. So you wouldn't be incorporating that into the footprint. Also, the light is not of the same intensity over the whole circle.

A good rule of thumb for the height of the fixture using 120 beam angle COBs is to take the heart-to-heart distance of the COBs as the height. So when the COBs are 12" apart, you also hang the fixture 12" above the plants.

 

[Green_Skunk]

You can find the disitribution pattern of the COB in the datasheet.

The footprint of what do you want though? Of all the light or only the part in the "beam angle"?

You could take the beam angle and calculate the size of the circle for each of the heights you wish to compare. For instance at 25cm (10") the circle of light for a 120 degree beam angle would be about 87cm (34") in diameter. At 50cm (20") it would be 20/10=2 times bigger etc.

But then the beam angle is only the cone where the light intensity is at least 50% of the maximum straight under the COB. There is still quite some light beyond that beam angle. IIRC something like 20%. So you wouldn't be incorporating that into the footprint. Also, the light is not of the same intensity over the whole circle.

A good rule of thumb for the height of the fixture using 120 beam angle COBs is to take the heart-to-heart distance of the COBs as the height. So when the COBs are 12" apart, you also hang the fixture 12" above the plants.

Thanks for the response, Wietefras! That last portion was what I intended to work out by looking at the PAR footprint of different COBs and overlapping the edges where they are weakest to create a more evened light canopy. Would a "distribution pattern" give me what I'm looking for? This would just be one part of the equation to my COB build. Thanks for stopping in

And yes my goal is to get to 12" of the plants even if I have to use dimming.

 

[Green_Skunk]

You can try this thread:
https://www.rollitup.org/t/lens-and-reflector-optics-for-cob.893660/

Parmaps for cxbs at 50 w, at 12 and 18 inches, refelctive walls and open space. This would be slightly older bins but you should be able to extrapolate using cobbys graphs.
For even coverage most people here seem to go for 1 per foot2. You can also try diffusers to even out hotspots. Hope it helps

Wow what a great resource friend! Thank you!

 

[CobKits]

every setup is different based on cob power/optics/reflector.

in generl if you want even light at 12" off canopy your cobs need to be spaced at 12"

 

[wietefras]

Thanks for the response, Wietefras! That last portion was what I intended to work out by looking at the PAR footprint of different COBs and overlapping the edges where they are weakest to create a more evened light canopy. Would a "distribution pattern" give me what I'm looking for? This would just be one part of the equation to my COB build. Thanks for stopping in

And yes my goal is to get to 12" of the plants even if I have to use dimming.

You would need to use the distribution pattern in your calculations of the footprint. It's not that difficult, but not that easy either.

Just saying it's easier to go with the rule of thumb or to get a lux meter to check uniformity.

Dimming your COBs does not matter for the height. It's only the distribution of light which gets affected by the height really. Of course by going higher you will incur some more wall losses, but that's just a waste of light/electricity. It's only a few percent difference as well.

For the distribution of light it doesn't matter if your COBs are at 50% or 25%. The distribution stays the same.

You should pick your total PPF (total amount of light) to match the space. ie add the PPF for all the COBs up and divide by surface area to get a rough estimate of the PPFD (intensity). You will need to deduct some wall losses, but it's all just an estimate anyway and the plants do fine with a lot more or a lot less light anyway.