PPF to PPFD

Abiqua

Abiqua

Well-Known Member
I am right to assume when going from PPF to PPFD [my cab is less than a meter [.38 actually] ...That my ppfd actually will increase above my umol/s measurement/guess?

....when PPFD is given from a manufacturer with no height, isn't that important....i.e my reading will be vastly different when taken @ 12" [25cm's]?

I am just doing a guesstimation from my lux reading and then converting to umol/s [based on a constant just a little lower than the sun]

I am running 2x 3070 AB 3k's and 1x V29 3k @ 1050mA in a 3.5 sq ft cab....@ 18" i was able to get a reading of just under 25K lux...giving me [using 50 as a constant] roughly 500 umol/s....

My cab is probably more like .35 of a meter...so is that 500umols / .35 meters = 1420 ppfd? that seems way too high???

Someone correct my math, so I can advise others, without giving them this clusterfudge ^ :joint:
 
SupraSPL

SupraSPL

Well-Known Member
For starters, here is where the math puts it

CXA3070 3K @ 1.05A = 38W @ 46.7% = 17.7 PAR W X2 = 35.4 PAR W
Vero29 3K V1.2 @ 1.05A = 37.8W @ 41.8% = 15.8 PAR W

17.7 + 15.8 = 51.2 PAR W emitted (then you can subtract reflector/lens losses)

Both CXA3070 3K and Vero29 3K V1.2 are 4.66 umol/s/PAR W (thank you @alesh !)
so 51.2 PAR W * 4.66 umol/s/PAR W = 238.6 umol/s emitted

238.6 / .35 sq meters = 682 PPFD averaged
 
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Abiqua

Abiqua

Well-Known Member
SupraSPL said:
For starters, here is where the math puts it

CXA3070 3K @ 1.05A = 38W @ 46.7% = 17.7 PAR W X2 = 35.4 PAR W
Vero29 3K V1.2 @ 1.05A = 37.8W @ 41.8% = 15.8 PAR W

17.7 + 15.8 = 33.5 PAR W emitted (then you can subtract reflector/lens losses)

Both CXA3070 3K and Vero29 3K V1.2 are 4.66 umol/s/PAR W (thank you @alesh !)
so 33.5 PAR W * 4.66 umol/s/PAR W = 156.1 umol/s emitted

156 / .35 sq meters = 446 PPFD averaged
Click to expand...
Shouldn't it be 51.2 PAR W emitted? 17.7+17.7+15.8
 
SupraSPL

SupraSPL

Well-Known Member
So if you use the constant of the warm white fluoro, 75, you get 25000/75 = 333 PPFD. But who knows, that constant is a tricky thing to guess at and the accuracy of the luxmeter is abysmal LOL. Using the constant of the sun, 25000/50 = 500 PPFD

Yes good catch! Fixed. 682 is a very good place to be IMO.
 
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Abiqua

Abiqua

Well-Known Member
SupraSPL said:
So if you use the constant of the warm white fluor, 75, you get 25000/75 = 333 PPFD.

Yes good catch! Fixed
Click to expand...
Cool thank you Supra, that is all I needed....although I need to tune my PAR readings some more...I am running @10" or so above the canopy, so I should have a good amount higher than 3-400 ppfd, which is a relief!

EDIT
Actually I may need to drop down some if 680 is my number....10" may be too close :)
 
SupraSPL

SupraSPL

Well-Known Member
Are there highly reflective walls on all sides? The 682 number is before reflection losses. Even with highly reflective walls there will be significant losses 10-15%?, some of the photons bounce upwards, some go through many lateral bounces and ~10% will convert to heat on each bounce.

The resulting PPFD number would be averaged over the canopy, so if there are any tall colas they get higher intensity, the area directly below the emitters higher and the edges lower.
 
Abiqua

Abiqua

Well-Known Member
SupraSPL said:
But who knows, that constant is a tricky thing to guess at and the accuracy of the luxmeter is abysmal LOL.
Click to expand...
Agreed and I have been using an average like .015 or something weighted a little towards red...just to even it a bit, since the lux sensor [arduino & BFH1750 sensor] is definitely photometric sensitive, with peaks around 500 and 590.....there is clipping on the ends, what else is new? :)
[spectral response.png

SupraSPL said:
Are there highly reflective walls on all sides? The 682 number is before reflection losses. Even with highly reflective walls there will be significant losses 10-15%?, some of the photons bounce upwards, some go through many lateral bounces and ~10% will convert to heat on each bounce.

The resulting PPFD number would be averaged over the canopy, so if there are any tall colas they get higher intensity, the area directly below the emitters higher and the edges lower.
Click to expand...
Everything is covered in White satin semi gloss with 5% TiSO, going on 20 months old though......From what I read on the indagro pdf....a PPFD reading is the area based on a specific height.....any thoughts?

obviously that goes with what you are saying above,,,taller cola's, more intensity, higher ppfd...corners and slow growers less intensity, lower PPFD?
 
SupraSPL

SupraSPL

Well-Known Member
Right PPFD is basically a small reading the size of the sensor, extrapolated to 1 sq meter of canopy. So if the reading was 600 PPFD, that means if the entire sq meter was at the same intensity as the sensor, it would equal 600umol/s.

Intensity does change depending the height of the light, but ultimately the light should be set at the correct height to achieve even coverage of a particular canopy size. For example if you were using lenses and swapped out the 60 degree for 90 degree lenses, you could bring the light closer to achieve the same intensity. Therefore a different "correct" height for each situation resulting in the same PPFD.

The cool thing you can do with a lux meter, if you have a nice sized bud in the last few weeks of flowering, you can check the intensity around that bud and make a note of the lux. Then you can arrange your COBs to try and achieve that same intensity in as many parts of the canopy as possible.
 
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