CXB3590 1500W

bggrass

Well-Known Member
photon flux [µmol/s] / area [m^2] = photon flux density [µmol/s/m^2]

photon flux = 1000 µmol/s
Area = 1 m^2
1000 / 1 = 1000 µmol/s/m^2
so for one square meter the photon flux = photon flux density!

ever heard about the inverse law of light?
distance is a main factor in this calculation


View attachment 3548424
from: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/isql.html

a distance change from 12 to 18 inch and your numbers are going down to 50%
View attachment 3548447
From: https://www.rollitup.org/t/how-to-plot-ppf-chart-with-quantum-sensors-for-led-light-comparison.881113/#post-11844361


Inverse-square law
https://en.wikipedia.org/wiki/Inverse-square_law

and the next big factor is the "Beam angle"
So @guod, based on your post would you say that the numbers that we get for PPFD are at the source of the light (at the cob surface)? For r do we use the distance (6", 12', 18'....) and do we need to convert the distance to meters? Based on the formula S / (4 pi r^2) = I, then " I " will be the PPFD at the given distance? @SupraSPL I hope I'm not sidetracking your thread. I just can't help myself, the conversation is too good.
 

alesh

Well-Known Member
Why yes, I have. Now, please show me the math I can use to quantify those effects!
Well you should be good with trigonometry.

guod is completely right that if we double the distance, intensity drops to 1/4. But my point is that, for growing purposes, we use reflective walls and/or overlapping sources which kinda negates this effect and we're back to average PPFD as PPF/area.
 

ttystikk

Well-Known Member
Well you should be good with trigonometry.

guod is completely right that if we double the distance, intensity drops to 1/4. But my point is that, for growing purposes, we use reflective walls and/or overlapping sources which kinda negates this effect and we're back to average PPFD as PPF/area.
I'm good with averages. LOL
 

bggrass

Well-Known Member
Well you should be good with trigonometry.

guod is completely right that if we double the distance, intensity drops to 1/4. But my point is that, for growing purposes, we use reflective walls and/or overlapping sources which kinda negates this effect and we're back to average PPFD as PPF/area.
It seems to me that overlapping and reflective walls will make up for not having spots with less light. As of the intesity, it will be different at different levels. We can go back to the the average PPFD but it will be a different number.
By the way, can you post the trigonometry formulas, let's look at them?
 

ttystikk

Well-Known Member
It seems to me that overlapping and reflective walls will make up for not having spots with less light. As of the intesity, it will be different at different levels. We can go back to the the average PPFD but it will be a different number.
By the way, can you post the trigonometry formulas, let's look at them?
Like anything else, reflective walls and overlapping lighting patterns can be accomplished relatively well or poorly. Done well, these effectively delay the onset of the consequences of the inverse square law for a distance roughly equivalent to the width (short side) of the panel or array. Again, this is based on observation and personal experience and I don't have much math to defend it.

What's more, there are well known penetration and even canopy saturation benefits to multiple light sources, making it more beneficial than an approach with few, relatively brighter light sources. The extreme case is one stationary light source and we all know what happens if you don't train your plants there, lol
 

SupraSPL

Well-Known Member
Thanks Supra, that makes sense.
Would you say that
PAR x umol/s = PPF ?
and do we generally use 9-10% loss from various factors (lenses, reflectors, walls)?
And do we use another function for distance from canopy? In other words, do PPF and PPFD change if the lights are at 6", 12", 18"....?
Yes that is correct PAR W * umol/s/PAR W (QER) = PPF

I think 10% is a reasonable estimate for lens/reflector losses from PPF to PPFD when using COBs. The spectrum king TEMPO test by Cree measured 6% loss from a glass lens.

Because LEDs emit their light in a cone pattern rather than a globe pattern, they behave much differently than the classic inverse square law describes, so beam angle has to be taken into account as guod mentioned. We can position the LEDs at the right height from the canopy so the majority of the light emitted reaches the canopy, spread as evenly as possible. Lateral light will get "redirected" to the canopy by the reflector. Some lateral light will end up hitting the wall and some portion of that light will reach the canopy. So I think it should be possible to keep total losses from PPF to PPFD around 10% and that is why I use that number.

So the distance from canopy will vary in every setup because it will change depending on your desired PPFD and many other factors such as: COB model, COB power, COB number, COB spacing, heatsink adjustability, canopy shape/depth, reflector angle, lens, etc. So there is no simple relationship between distance to canopy and PPFD that we can use to help DIYers, we have to focus on the desired PPFD first and design from there. If there are height restrictions, we can work with that parameter in mind though.
 

bggrass

Well-Known Member
Yes that is correct PAR W * umol/s/PAR W (QER) = PPF

I think 10% is a reasonable estimate for lens/reflector losses from PPF to PPFD when using COBs. The spectrum king TEMPO test by Cree measured 6% loss from a glass lens.

Because LEDs emit their light in a cone pattern rather than a globe pattern, they behave much differently than the classic inverse square law describes, so beam angle has to be taken into account as guod mentioned. We can position the LEDs at the right height from the canopy so the majority of the light emitted reaches the canopy, spread as evenly as possible. Lateral light will get "redirected" to the canopy by the reflector. Some lateral light will end up hitting the wall and some portion of that light will reach the canopy. So I think it should be possible to keep total losses from PPF to PPFD around 10% and that is why I use that number.

So the distance from canopy will vary in every setup because it will change depending on your desired PPFD and many other factors such as: COB model, COB power, COB number, COB spacing, heatsink adjustability, canopy shape/depth, reflector angle, lens, etc. So there is no simple relationship between distance to canopy and PPFD that we can use to help DIYers, we have to focus on the desired PPFD first and design from there. If there are height restrictions, we can work with that parameter in mind though.
Thanks Supra. I was thinking I can add a box for user input for distance from canopy and then use the ppfd we get initially run it through the formula @guod posted and get the ppfd at canopy based on the distance.

I could be wrong though.... that's why I'm asking

Or should I run the par values through that formula....

I can add a box for distance between cobs as well....
 
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SupraSPL

Well-Known Member
It could be done but it would be very complex and probably questionable accuracy. Once you have COB spacing, power and PPF figured, it would require that we adjust the inverse square law for each particular beam angle, how much light was hitting the wall, how close are the walls and how reflective are they, are there walkways on certain sides of the canopy, where is each COB in relation to the wall. All those variables would really start to come into play if we increased the distance to canopy beyond the "sweet spot" for that particular lamp. So the ideal distance to canopy is not very adjustable once the lamp is built. Rather than changing distance to canopy, you could dim the lamp down or boost it and the PPFD would change, but the height would not need to change.

So if you want to increase the distance to canopy you could use narrower lens/reflector angle. If your design has the COBs packed closer to together, increasing distance to canopy will help improve uniformity and coverage, and that would require a narrower lens angle to keep the light off the walls as much as possible. If you are designing for a larger vertical height I would recommend lenses over reflectors. This would also allow for fewer COBs run at higher power. This results in a less efficient use of floor space but maybe an easier space to work in.

If you want to decrease the distance to canopy, you would have to spread the COBs wider to improve uniformity and use a wider lens/reflector angle. For short distances to canopy reflectors may be a better option than lenses. If you are running short plants and short distance to canopy this may open the possibility for a shelf system to make better use of floor space, especially doable in veg. This design would perform best with more COBs, smaller COBs and/or running them softer. This approach can improve the space efficiency and electrical efficiency of a grow, but can result in an larger more complex fixture like my "heatsink armada".
 
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bggrass

Well-Known Member
It could be done but it would be very complex and probably questionable accuracy. Once you have COB spacing, power and PPF figured, it would require that we adjust the inverse square law for each particular beam angle, how much light was hitting the wall, how close are the walls and how reflective are they, are there walkways on certain sides of the canopy, where is each COB in relation to the wall. All those variables would really start to come into play if we increased the distance to canopy beyond the "sweet spot" for that particular lamp. So the ideal distance to canopy is not very adjustable once the lamp is built. Rather than changing distance to canopy, you could dim the lamp down or boost it and the PPFD would change, but the height would not need to change.

So if you want to increase the distance to canopy you could use narrower lens/reflector angle. If your design has the COBs packed closer to together, increasing distance to canopy will help improve uniformity and coverage, and that would require a narrower lens angle to keep the light off the walls as much as possible. If you are designing for a larger vertical height I would recommend lenses over reflectors. This would also allow for fewer COBs run at higher power. This results in a less efficient use of floor space but maybe an easier space to work in.

If you want to decrease the distance to canopy, you would have to spread the COBs wider to improve uniformity and use a wider lens/reflector angle. For short distances to canopy reflectors may be a better option than lenses. If you are running short plants and short distance to canopy this may open the possibility for a shelf system to make better use of floor space, especially doable in veg. This design would perform best with more COBs, smaller COBs and/or running them softer. This approach can improve the space efficiency and electrical efficiency of a grow, but can result in an larger more complex fixture like my "heatsink armada".
This was a very good insight Supra, thanks. I'm gonna sit on that info for sometime and think about it. Thanks
 

Megalomando

Well-Known Member
If it were me I would put 4 50W COBs on a 3.5" X 40" and run an 80mm fan in the center. That will spread them out, use the heatsink efficiently and use the fan power efficiently. Having 2 heatsinks rather than 1 will also give you more adjustability for your canopy. That is just one way to do it there are so many configurations
View attachment 3545253
I've decided to use a 5.886 x 36" heatsink http://www.heatsinkusa.com/5-886/ with the 4 COBs running at 50W each and spaced 8" apart with 2" spacing on each end. I'm wondering if this should be sufficient for passive cooling? I have 120MM fans if need be but would prefer to keep it simple and not make a shroud & wiring for the fans if I don't need to.

Another question is how closely do the drivers need to be mounted from the COBs? I noticed on page 1 of this thread, they were separate from the panels. I had been thinking of using spacers to elevate them 2" above the heatsink if this heatsink runs passive but placing them outside the tent would allow me some extra elevation of the panels, though not much.

Thanks!
 

bassman999

Well-Known Member
I've decided to use a 5.886 x 36" heatsink http://www.heatsinkusa.com/5-886/ with the 4 COBs running at 50W each and spaced 8" apart with 2" spacing on each end. I'm wondering if this should be sufficient for passive cooling? I have 120MM fans if need be but would prefer to keep it simple and not make a shroud & wiring for the fans if I don't need to.

Another question is how closely do the drivers need to be mounted from the COBs? I noticed on page 1 of this thread, they were separate from the panels. I had been thinking of using spacers to elevate them 2" above the heatsink if this heatsink runs passive but placing them outside the tent would allow me some extra elevation of the panels, though not much.

Thanks!
Hopefully someone else will reply, but for now I am.
That heat-sink should be more than adequate for 200W.
Distance from cobs to driver isnt important as long as you run higher AWG wire depending on length or wire.
You can wire cobs with 18AWG, then run 16 or 14AWG wire to the driver(s) for example by simply connecting them with Wago connectors.
 

SupraSPL

Well-Known Member
I've decided to use a 5.886 x 36" heatsink http://www.heatsinkusa.com/5-886/ with the 4 COBs running at 50W each and spaced 8" apart with 2" spacing on each end. I'm wondering if this should be sufficient for passive cooling? I have 120MM fans if need be but would prefer to keep it simple and not make a shroud & wiring for the fans if I don't need to.

Another question is how closely do the drivers need to be mounted from the COBs? I noticed on page 1 of this thread, they were separate from the panels. I had been thinking of using spacers to elevate them 2" above the heatsink if this heatsink runs passive but placing them outside the tent would allow me some extra elevation of the panels, though not much.

Thanks!
That amount of surface area is sufficient for passive cooling, however that design was not intended for driver on board because it will block the convection and create a very hot spot under the driver. In reality, the heatsink will benefit hugely if it is being hit by some airflow from the circulation fan. I have CXA3590s on identical 5.88" passive in the veg space, one gets hit directly by the fan and the heatsink is 90F, the one next to it does not get hit and it is 108F. 108F is OK for passive cooling but it demonstrates the difference.
 

Positivity

Well-Known Member
I've decided to use a 5.886 x 36" heatsink http://www.heatsinkusa.com/5-886/ with the 4 COBs running at 50W each and spaced 8" apart with 2" spacing on each end. I'm wondering if this should be sufficient for passive cooling? I have 120MM fans if need be but would prefer to keep it simple and not make a shroud & wiring for the fans if I don't need to.

Another question is how closely do the drivers need to be mounted from the COBs? I noticed on page 1 of this thread, they were separate from the panels. I had been thinking of using spacers to elevate them 2" above the heatsink if this heatsink runs passive but placing them outside the tent would allow me some extra elevation of the panels, though not much.

Thanks!

I made a remote driver setup recently. I just put a plug on the driver end and one on the cob end. Extension wire with appropriate ends to connect the light and driver together. Haven't had any problems...better than putting a driver on a hot heatsink.

easy push in plugs...stranded wire is more pliable which is nice but it needs to be tinned for a good fit in the plug

http://www.amazon.com/Wago-LUMI-NUTS-Connector-Luminaire-Disconnect/dp/B003JUVGLK/ref=sr_1_fkmr0_2?ie=UTF8&qid=1448312167&sr=8-2-fkmr0&keywords=wago+luminaire+plug

18awg lamp wire...

http://www.amazon.com/Coleman-Cable-094008957-Repair-25-Foot/dp/B00271HB8E/ref=sr_1_4?ie=UTF8&qid=1448312487&sr=8-4&keywords=18awg+lamp+cord
 

Megalomando

Well-Known Member
Good info there for me. I'm not familiar with the driver technology for COBs and if it was DC, distance from the COB and gauge of wire would be critical. So it's either pulsed DC or AC that you can remote it. That's good to know. I'll remote them and save me some grief. Thanks!
 
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bggrass

Well-Known Member
So I was playing with the inverse square law formula and it doesn't really seem to be working for the distances we need. For examle, let's just forget that we are talking about leds and just think of it as numbers, if your input strenght S = 1600 and you enter 6" for "r", converting "r" to meters we multiply by 0.0254, so here what happens

I = S / (4 * pi * r^2)

I = 1600 / (4 * pi * (6 * 0.0254)^2) = 5517

I get a bigger number than the input. This happens when I enter small decimals for distance. It seems to work straightforward with distance being 1+ meters. I'm sure there's an explanation....
 

ttystikk

Well-Known Member
So I was playing with the inverse square law formula and it doesn't really seem to be working for the distances we need. For examle, let's just forget that we are talking about leds and just think of it as numbers, if your input strenght S = 1600 and you enter 6" for "r", converting "r" to meters we multiply by 0.0254, so here what happens

I = S / (4 * pi * r^2)

I = 1600 / (4 * pi * (6 * 0.0254)^2) = 5517

I get a bigger number than the input. This happens when I enter small decimals for distance. It seems to work straightforward with distance being 1+ meters. I'm sure there's an explanation....
Did you account for the effect of lenses?
 
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