Estimating Lumens to PPF (or Lux to PPFD) for CXBs for a given color temp

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flat9

Active Member
Hi all. Forgive me if this is somewhere among vast amount of information on this site, but could someone please let me know how to get the PPF given the lumens for a given Cree color temperature? It's easy to look up the luminous flux from Cree's datasheets, and to get to Lux given the beam angle and distance from the canopy, but I'm stuck on the multiplier used to convert Lux to PPFD.

This site is a pretty nice calculator to get to Lux:

http://led.bannerengineering.com/plan-your-project/lux-lumen-calculator/

What I'm stuck at is the conversion factor used from here. What factor should I be using?
 
BuddyColas

BuddyColas

Well-Known Member
flat9 said:
Apogee lists some conversion factors for various bulbs (Cree not listed obviously as this site looks a bit old).

http://www.apogeeinstruments.com/conversion-ppf-to-lux/

I'm aware I can get ballpark estimates given instruments listed but it'd be nice to be on the money....
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If you want to be "on the money", you are going to have to drop some serious bucks and get a reputable PAR meter, OR you can use a LUX meter and this formula: LUX reading/1000 * 15 = PPFD. (The 15 conversion factor is an average for 3K, 3.5K and 4K cobs).
 
F

flat9

Active Member
Okay that's roughly what I was going with. Where did you get that factor by the way? If you're using someone's at home PAR readings as a baseline, unfortunately most of the cheaper meters have very shitty response curves that heavily attenuate the lower and upper range of the photosynthetically active spectrum.

It'd be nice to get access to quality one though and test this out. I'm surprised Cree doesn't do this already to be honest. Seems like they're missing out on marketing to a potentially huge number of people.
 
BuddyColas

BuddyColas

Well-Known Member
flat9 said:
Okay that's roughly what I was going with. Where did you get that factor by the way? If you're using someone's at home PAR readings as a baseline, unfortunately most of the cheaper meters have very shitty response curves that heavily attenuate the lower and upper range of the photosynthetically active spectrum.

It'd be nice to get access to quality one though and test this out. I'm surprised Cree doesn't do this already to be honest. Seems like they're missing out on marketing to a potentially huge number of people.
Click to expand...
I did access that conversion factor from this site...I just can not find it right now...but I will get it. Every time I think of buying a reputable PAR meter, like the new one from Apogee at $500, I think of all the cool cobs, sinks etc. that I could buy...then my LUX meter looks good again! So my LUX meter gives me a "ball park" PPFD reading and is excellent for adjusting and experimenting with cob spacing, bar spacing, wall reflectivity and checking the uniformity of the photons I'm laying down with my cob bars.

Also, we, that is cob growers, are a tiny part of Cree's business. So Cree is into lumens and lighting up people. Of course we are into lighting up ganga and using PAR! Just saying.
 
F

flat9

Active Member
Fair enough and thanks for the info. If you do find that convert I'd love to use it. I'm a hobbyist grower now (though ran about 80 sq ft before before). I probably gonna set up a little 2' x 4' space and was considering 2 of mau5's kits at Cutter but I'm wondering if 400w is overkill for that space and also how to properly space everything out....
 
Rahz

Rahz

Well-Known Member
Courtesy of SupraSPL

CREE CX series:
2700K 80 CRi = 321 (CREE verified LER)
3000K 80 CRi = 325 (CREE verified LER)
3500K 80 CRi = 324 estimated
4000K 70 CRi = 323 (Mr Flux calculated)
5000K 70 CRi = 324 (Mr Flux calculated)

Vero Version 2:
3000K 80 CRi = 323 (Alesh calculated)
3500K 80 CRi = 322 estimated
4000K 80 CRi = 324 (Alesh calculated)
5000K 70 CRi = 334.4 ( Alesh calculated)
 
alesh

alesh

Well-Known Member
Rahz said:
Courtesy of SupraSPL

CREE CX series:
2700K 80 CRi = 321 (CREE verified LER)
3000K 80 CRi = 325 (CREE verified LER)
3500K 80 CRi = 324 estimated
4000K 70 CRi = 323 (Mr Flux calculated)
5000K 70 CRi = 324 (Mr Flux calculated)

Vero Version 2:
3000K 80 CRi = 323 (Alesh calculated)
3500K 80 CRi = 322 estimated
4000K 80 CRi = 324 (Alesh calculated)
5000K 70 CRi = 334.4 ( Alesh calculated)
Click to expand...
And here's the rest in order to be calculate photon flux.
http://rollitup.org/t/cob-efficiency-spreadsheets.865238/page-3#post-11540587
 
BuddyColas

BuddyColas

Well-Known Member
flat9 said:
Fair enough and thanks for the info. If you do find that convert I'd love to use it. I'm a hobbyist grower now (though ran about 80 sq ft before before). I probably gonna set up a little 2' x 4' space and was considering 2 of mau5's kits at Cutter but I'm wondering if 400w is overkill for that space and also how to properly space everything out....
Click to expand...
I use 8 Vero 29 cobs in a 2x4 cabinet at around 288w at the wall. Makes for 700ish at the canopy. Those Cutter kits look great. I think 400 is to much and 200w not enough...but making 2 bars out of their kit and dimming would be the ticket for a 2x4. Seems very few were using the pin fin heat sinks a year ago. If I was building now I'd sure look at the Cutter kit. On the good side, once they start shipping I'll get to see how others build and grow with them.
 
BuddyColas

BuddyColas

Well-Known Member
flat9 said:
Okay that's roughly what I was going with. Where did you get that factor by the way? If you're using someone's at home PAR readings as a baseline, unfortunately most of the cheaper meters have very shitty response curves that heavily attenuate the lower and upper range of the photosynthetically active spectrum.

It'd be nice to get access to quality one though and test this out. I'm surprised Cree doesn't do this already to be honest. Seems like they're missing out on marketing to a potentially huge number of people.
Click to expand...
https://www.rollitup.org/t/cree-cxa-3000k-80cri-spectrum-analysis.832666/page-2
Check out post 39 from Mr. Flux
Pretty much the same as: LUX reading/1000 * 15 = PPFD
And, if you follow the math out on the posts from alesh and Rahz, you will have the exact efficiency and output of your cobs!
 
F

flat9

Active Member
Yeah okay so that's what I was going with for 3500k. Should be close enough..... still would love to have a nice quantum meter. :)
 
BuddyColas

BuddyColas

Well-Known Member
flat9 said:
Yeah okay so that's what I was going with for 3500k. Should be close enough..... still would love to have a nice quantum meter. :)
Click to expand...
OK, one more post and I’ll quit beating a dead horse.


Remember the LER numbers in post 8 above. Those are a very handy reference.


Bookmark the thread referenced by alesh in above post: http://rollitup.org/t/cob-efficiency-spreadsheets.865238/page-3#post-11540587 That is a gold mine of information, and in post 45 is the umols per joule of many popular cobs, AND (wait there’s one more).


In post 162 is an explanation by GG that really helped me. My inner cob finally lite up and I understood what they were talking about.


"You can think of lm/w as a test grade...and LER being the perfect score. divide the 2 and you have a % or grade.

lm/w ÷ LER = Efficiency

Efficiency(%) x disspated watts = PARwatt output

PARwatts x conversion factor = µmol output"



I went with 3500K also and built for 15 PAR watts a square foot and 1 emitter a square foot…and, after 2 grows now, I wouldn’t’ change anything. The cob bars so outperform my old HPS…it’s not even a contest.


I wish you well on your build.
 
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