Par meter and ppfd questions

linky

linky

Well-Known Member
Hey all, I just received my par meter I ordered from rapidled.. this one here

http://www.rapidled.com/apogee-sq-120-quantum-sensor/

I have it hooked to my meter and set to dc millivolt.

I tested with a 4 cob vero 29 fixture I have here over some plants vegging running at ~75 watts per cob.. I get a reading of about 130 about 12" below the light and 180 at 10" (big drop from just 2 inches, sheesh)

I multiply that by 5 and get 650, if I were to take measurements from all over the canopy area and find that average would that be my ppfd then? So if I got 650 everywhere I took a measurement from my ppfd would be 650? Is this correct?

thanks!
 
OLD MOTHER SATIVA

OLD MOTHER SATIVA

Well-Known Member
i asked that ages ago..it took forever to get even one answer that was not over the tech top..

the answer[and i know somebody will say its wrong] is:

YES...................[ as long as you are measuring it over one sq meter]

so don't sweat it..its how everything grows that counts..

disclaimer:[not a techy]

ps..MMMMM..Apo...geee
 
wietefras

wietefras

Well-Known Member
PPFD is a single measurement. Usually you take measurements all over the canopy (or grow surface) and average those out to get an "average PPFD" over the whole. To check uniformity, you usually want the darkest spots in to get at least 80% of that average. If it's less than that you need to raise the lights further, but that would mean incurring more wall losess. So it's always a compromise.

When you raise the distance by 2" the light gets distributed over an area that's 44% bigger (unless the light is confined by reflective walls). So the difference you see is almost exactly in line with the inverse square law. It should drop to 125umol/s/m2 even.

@OLD MOTHER SATIVA ,There is no need to measure it over a square meter. PPFD is defined as the light intensity you get if you distribute a certain amount of photons per second (PPF) over a square meter. It's just the definition of PPFD.
 
pirg420

pirg420

Well-Known Member
Im in the process of making some updated par maps for our lineup of lights and for ppfd id like to use numbers from the par meter instead of theoretical ppfd numbers.

If i were to take a par measurement at the center of each square foot (9 readings from a 3x3, 16 readings from a 4x4 etc) and average out the numbers, would this suffice?

Any help is appreciated, thanks
 
BuddyColas

BuddyColas

Well-Known Member
linky said:
Hey all, I just received my par meter I ordered from rapidled.. this one here

http://www.rapidled.com/apogee-sq-120-quantum-sensor/

I have it hooked to my meter and set to dc millivolt.

I tested with a 4 cob vero 29 fixture I have here over some plants vegging running at ~75 watts per cob.. I get a reading of about 130 about 12" below the light and 180 at 10" (big drop from just 2 inches, sheesh)

I multiply that by 5 and get 650, if I were to take measurements from all over the canopy area and find that average would that be my ppfd then? So if I got 650 everywhere I took a measurement from my ppfd would be 650? Is this correct?

thanks!
Click to expand...
In one of the Apogee videos they freely admit some of the red photons are not going to be counted with the shape of the response curve for the 120. Just curious if Apogee has any correction factors for warm cobs. If you are running 3000K 80 or 90CRI your 650 reading could be significantly higher.
 
REALSTYLES

REALSTYLES

Well-Known Member
BuddyColas said:
In one of the Apogee videos they freely admit some of the red photons are not going to be counted with the shape of the response curve for the 120. Just curious if Apogee has any correction factors for warm cobs. If you are running 3000K 80 or 90CRI your 650 reading could be significantly higher.
Click to expand...
Yes they do @SupraSPL has them I've got to look on my computer to find them.
 
linky

linky

Well-Known Member
BuddyColas said:
In one of the Apogee videos they freely admit some of the red photons are not going to be counted with the shape of the response curve for the 120. Just curious if Apogee has any correction factors for warm cobs. If you are running 3000K 80 or 90CRI your 650 reading could be significantly higher.
Click to expand...
Interesting, I am almost done with another led I am building, would be nice to get some somewhat accurate numbers of it.
 
pirg420

pirg420

Well-Known Member
pirg420 said:
Im in the process of making some updated par maps for our lineup of lights and for ppfd id like to use numbers from the par meter instead of theoretical ppfd numbers.

If i were to take a par measurement at the center of each square foot (9 readings from a 3x3, 16 readings from a 4x4 etc) and average out the numbers, would this suffice?

Any help is appreciated, thanks
Click to expand...

Anyone have any insight on this?
 
linky

linky

Well-Known Member
BuddyColas said:
This is a great video. You might like it.
Click to expand...
Great video, now I wish I would have gotten the sq 500 sensor though instead of the 120. How much of the led's we are using (cobs) go into the "deep red" as he explained it, the 650 to 700nm?
 
linky

linky

Well-Known Member
CobKits said:
all of them, and its significant outside of any cobs other than 70cri 5000k and up
Click to expand...
So the my apogee 120 sensor is kinda useless then I guess haha. Blah, I should of done some more research before buying it I suppose.
 
BuddyColas

BuddyColas

Well-Known Member
linky said:
Great video, now I wish I would have gotten the sq 500 sensor though instead of the 120. How much of the led's we are using (cobs) go into the "deep red" as he explained it, the 650 to 700nm?
Click to expand...
I think they have a correction factor. Like instead of using 5 as the multiplier it would be greater...6ish? I think a call or email to Apogee might get the multiplier you seek. And if you get it for say 3000/80 and 3000/90, please share.

Your meter is not useless. It will still help you build and position your lights for the most even photon coverage you can get. And you know the reality is your real PAR reading is higher. If you have a friend with a Licor or the Sq 500, you can put them side-by-side and take a reading and generate your own COB multiplier.
 
linky

linky

Well-Known Member
BuddyColas said:
I think they have a correction factor. Like instead of using 5 as the multiplier it would be greater...6ish? I think a call or email to Apogee might get the multiplier you seek. And if you get it for say 3000/80 and 3000/90, please share.

Your meter is not useless. It will still help you build and position your lights for the most even photon coverage you can get. And you know the reality is your real PAR reading is higher. If you have a friend with a Licor or the Sq 500, you can put them side-by-side and take a reading and generate your own COB multiplier.
Click to expand...

Email sent to Apogee, I will see what they say.
 
pirg420

pirg420

Well-Known Member
CobKits said:
some people might be into that but with all the reflectors in your design, many would rather see a real par map with demonstration of coverage and uniformity
Click to expand...
Yes i just want to add a PPFD number to our par map, so it will show the individual readings as well as the average. thanks for the help guys
 
CobKits

CobKits

Well-Known Member
linky said:
So the my apogee 120 sensor is kinda useless then I guess haha. Blah, I should of done some more research before buying it I suppose.
Click to expand...
even your buddy growmau5 uses a $30 light meter to balance out his garden

plant response will tell you a lot more than a deadly accurate meter about what your plants like, but you can go to the best part of your garden, with any meter, and take a reading, in order to replicate that throughout the garden. its all relative (assuming same spectrum/light type throughout garden)
 
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