PAR measurement thread

[Rahz]

If the goal isn't to get a reading from a spot measurement then PPF is the right measurement, and umol/j to see how efficient the emitters are. Percentage of lumens to LER is also a good way to look at efficiency.

PPF is the best we have at the moment, but not perfect since it doesn't bias red or blue. The recent test I did seem to indicate there's not a lot of difference once a bias is applied, but it was enough to change the order when the results were already close.

Spot measurements are useful when comparing two sources with the same radiation profile, but they don't truly represent PPF or PPFD. They measure the PPFD in a .75x.75" area or whatever size the sensor it. They are useful relative to one another.

The best way to test two lights with dissimilar optics will be to create par footprint charts and find the average which would represent PPFD and a rough PPF could be extropolated. A tighter grid with more measurements will produce a better result. Taking known PPF figures and comparing them with the test data can indicate how well the method is working, but there's reflective losses to consider, etc.

 

[Shugglet]

Zero but of all other aspects of the environment are the same then the last thing to consider is how to optimize light for your given area.

PPF is not effected by environment... PPFD is....

That wasnt retorhical though. If ppfd is significantly impacted by environment it is certainly not the best benchmark to compare lights. Correct?

 

[MeGaKiLlErMaN]

If the goal isn't to get a reading from a spot measurement then PPF is the right measurement, and umol/j to see how efficient the emitters are. Percentage of lumens to LER is also a good way to look at efficiency.

PPF is the best we have at the moment, but not perfect since it doesn't bias red or blue. The recent test I did seem to indicate there's not a lot of difference once a bias is applied, but it was enough to change the order when the results were already close.

Spot measurements are useful when comparing two sources with the same radiation profile, but they don't truly represent PPF or PPFD. They measure the PPFD in a .75x.75" area or whatever size the sensor it. They are useful relative to one another.

The best way to test two lights with dissimilar optics will be to create par footprint charts and find the average which would represent PPFD and a rough PPF could be extrapolated. A tighter grid with more measurements will produce a better result. Taking known PPF figures and comparing them with the test data can indicate how well the method is working, but there's reflective losses to consider, etc.

Thank you! This is what Im trying to say, multiple emitters doesnt seem to pan out correctly compared to a single hot spot when you look at the PAR compared to the PPFD, I have taken my own measurements had have seen this first hand.

PPF is not effected by environment... PPFD is....

That wasnt retorhical though. If ppfd is significantly impacted by environment it is certainly not the best benchmark to compare lights. Correct?

I have no idea what environment is adjusting the amount of light per area you are receiving... Is it foggy in your room? Thats the only thing that would change the light hitting the plants environmentally speaking.

 

[Shugglet]

Thank you! This is what Im trying to say, multiple emitters doesnt seem to pan out correctly compared to a single hot spot when you look at the PAR compared to the PPFD, I have taken my own measurements had have seen this first hand.




I have no idea what environment is adjusting the amount of light per area you are receiving... Is it foggy in your room? Thats the only thing that would change the light hitting the plants environmentally speaking.

I would think walls and reflectors could potentially have a significant impact of ppfd. No? We are talking mircomoles of energy here....

How much of an impact can changing reflectors have on a ppfd reading?

 

[MeGaKiLlErMaN]

I would think walls and reflectors could potentially have a significant impact of ppfd. No? We are talking mircomoles of energy here....

How much of an impact can changing reflectors have on a ppfd reading?

It would change moderately, but not my too much from what Ive seen. at 6in with no reflector I get the same output as I do at 12" with one... I have my PPFD nuumbers on my signature.

 

[Shugglet]

PPF isolates one variable, the light.

PPFD introduces many variables into the mix... it's really that simple.

 

[Shugglet]

It would change moderately, but not my too much from what Ive seen. at 6in with no reflector I get the same output as I do at 12" with one... I have my PPFD nuumbers on my signature.

You're top post in your sig is flawed... about the blurple light... fyi.

And the 6in results are not there...

 

[MeGaKiLlErMaN]

You're top post in your sig is flawed... about the blurple light... fyi.

Do you have any proof of this? Because I have said before until I SEE it Im keeping it there... Ive seen the Kinds results, Osram and a few Mars ones... all were not up to par whit hps in my experience.

 

[MeGaKiLlErMaN]

PPF isolates one variable, the light.

PPFD introduces many variables into the mix... it's really that simple.

No it doesnt add more variables... it gives a better answer... Being a more accurate representation of how much light gets to plant height... As @Rahz states.

 

[Shugglet]

No it doesnt add more variables... it gives a better answer... Being a more accurate representation of how much light gets to plant height... As @Rahz states.

So height from the plant effecs ppfd but not ppf. That's an added variable my friend...

 

[MeGaKiLlErMaN]

So height from the plant effecs ppfd but not ppf. That's an added variable my friend...

I stated that they would have to be the same... But thats the case with measuring PPF anyways...

 

[Shugglet]

Do you have any proof of this? Because I have said before until I SEE it Im keeping it there... Ive seen the Kinds results, Osram and a few Mars ones... all were not up to par whit hps in my experience.

20.1 / 650 is not less than .5 closer to .87g/w

 

[wietefras]

It already matters what you think are reflective walls. Popular choices like diamond pattern and white plastic tend to reflect rather poorly.

So it only gives a "better answer" for your specific test environment.

:edit: Either way the proposed measurements give nothing in the way of a standardized reflective setup. It's just a dark room again where lights with a wide beam angle are at a huge disadvantage compared to tighter beam angles.

A laser would be perfect according to these tests.

 

[MeGaKiLlErMaN]

20.1 / 650 is not less than .5 closer to .87g/w

There were two lights....

 

[Shugglet]

I stated that they would have to be the same... But thats the case with measuring PPF anyways...

That is not the case with ppf because it doesn't even account for it...

 

[MeGaKiLlErMaN]

That is not the case with ppf because it doesn't even account for it...

Then thats an issue right there... I have my info from measuring my own. Its really not a hard thing to follow. Its just not standard.

 

[MeGaKiLlErMaN]

This is an example of how you would use the PPF to get an expected PPFD value
;
Lamp PPF Output:1,100 μMol/S
Grow Area:4’ x 4’ = 16 sq-ft = 1.49 M2
Grow Losses off Canopy:20% = 80% used
Light Actually Used = 1,100 x .8 = 880 μMole/s
SampleAveragePPFD
Formula: 880μMole/S÷1.499 M2= 591μMole/M2-S

 

[Shugglet]

There were two lights....

Ahhh I see. They don't look like the same light though. I stand corrected on tbh at point lol.

 

[Shugglet]

This is an example of how you would use the PPF to get an expected PPFD value
;
Lamp PPF Output:1,100 μMol/S
Grow Area:4’ x 4’ = 16 sq-ft = 1.49 M2
Grow Losses off Canopy:20% = 80% used
Light Actually Used = 1,100 x .8 = 880 μMole/s
SampleAveragePPFD
Formula: 880μMole/S÷1.499 M2= 591μMole/M2-S

So how is getting an estimate using actual data better than using the actual data it's based on? You seem to be using ppf without even realizing it.

 

[MeGaKiLlErMaN]

So how is getting an estimate using actual data better than using the actual data it's based on? You seem to be using ppf without even realizing it.

No you misunderstand... This was an example on how to estimate PPFD by taking the PPF and doing math. Im suggesting that you take many PPF reading and find the actual PPFD. Mainly because its hard to compare 16 sources of light to one. So PPFD is the better option because I cant really work this backwards. If I take the math provided and work it backwards...

I would land around 1798.8 PPF with 850W.. since I know my actual amount of light that I am getting around 1200PPFD...

But thats deceiving since a Gavita states that they put out 2000 μmol/sec PPF but only get around 620 PPFD.