LED PAR math

Greengenes707

Greengenes707

Well-Known Member
DoctorDelta9 said:
Ok...so again please correct me if I'm wrong
Total umol = 2016.73
25 ft2 = approx 2.322m2
2016.73 / 2.322 = 868.531
So I am within the sweet spot for both PAR an umol
Sweeeet
:clap:
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Ya buddy!!...suck on that gavita!

DoctorDelta9 said:
OK last stupid question!
How do you guys type the sign for micro ??
Typing umol instead of correct denotation makes me feel like a dummy...
Click to expand...
On a MAC it's...
hold alt/option button and M
 
heckler73

heckler73

Well-Known Member
I'm not sure if this is a problem, but depending what one normalizes to, it will affect the relation.
If one is normalizing to peaks, then using Photosynthetic response and the Spectral Power of a CXB3590, one sees:
CXB3590-PSR.jpg
If one is just comparing to PAR, then it is a box from 400-700nm...not exactly realistic. It may be handy as a first approximation, but considering LED's abilities to be tuned, it would make more sense for the sake of accuracy to use a proper response spectrum as the normal function, in which case the CXB is 75.6% in the PAR domain.

I suppose it comes down to what metric one is interested in and why. PAR had its time in the sun...We have finer tools at our disposal now. Why not specifically look at PS I & II response functions? How about using their relative spectra as a foundation of measure?
That way--with an appropriate reference database--one could say XYZ Light can grow Roses at Q% efficiency, Ganja at 110%, Finshaggy's SanPedro Tomato Cactus 0%, etc...
 
alesh

alesh

Well-Known Member
heckler73 said:
I'm not sure if this is a problem, but depending what one normalizes to, it will affect the relation.
If one is normalizing to peaks, then using Photosynthetic response and the Spectral Power of a CXB3590, one sees:
View attachment 3405605
If one is just comparing to PAR, then it is a box from 400-700nm...not exactly realistic. It may be handy as a first approximation, but considering LED's abilities to be tuned, it would make more sense for the sake of accuracy to use a proper response spectrum as the normal function, in which case the CXB is 75.6% in the PAR domain.

I suppose it comes down to what metric one is interested in and why. PAR had its time in the sun...We have finer tools at our disposal now. Why not specifically look at PS I & II response functions? How about using their relative spectra as a foundation of measure?
That way--with an appropriate reference database--one could say XYZ Light can grow Roses at Q% efficiency, Ganja at 110%, Finshaggy's SanPedro Tomato Cactus 0%, etc...
Click to expand...
That spectral response comes from Mr. McCree. It's average of several species. It had been done by using narrow-band monochromatic light and plants had no time for adaptation. It's a known fact that plants adapt on light they're getting. It's also a fact that plant respond differently to wider spectrum. Because of this I don't think that using spectral response as a normal function would be any more accurate.
 
C

churchhaze

Well-Known Member
I agree. I don't think it would add much in terms of accuracy over the u(λ-400) - u(λ-700) or unit step function gated in general.

Those action response spectra are more fuzzy and controversial, not to mention way more complicated.
 
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heckler73

heckler73

Well-Known Member
alesh said:
That spectral response comes from Mr. McCree. It's average of several species. It had been done by using narrow-band monochromatic light and plants had no time for adaptation. It's a known fact that plants adapt on light they're getting. It's also a fact that plant respond differently to wider spectrum. Because of this I don't think that using spectral response as a normal function would be any more accurate.
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Actually, I think that spectrum comes from Inada, but I could be wrong. (ahhh yes...Inada's work supported McCree's results).
McCree Inada.JPG
In any event, your contention is it would be equal to, or less accurate than using a PAR rectangle?
No...that is incorrect just on base principles, which McCree argued about in his papers.
By its very nature PAR assumes ignorance, but we know at least an average response function of 33-55 species to within 5% (with the greatest variance in the UV and deeper blue spectra...which is logical considering chemistry and energy bonds). Are you going to argue that cannabis is more akin to a rectangle versus the smooth, undulating distribution of McCree & Inada? The empirical evidence is not leaning in your favour.

I also find it difficult to reconcile your acknowledgement of plant response to "wider spectrum" while you then cut your legs and arms off at 400 and 700nm. Your follow-up conclusion based on such premises constitutes a non sequitur.

Don't misconstrue my intent. I am not saying PAR is garbage, I'm saying it is a loose metric for approximating quality of light. To that end, it should not be given that much weight. Otherwise, the BH1750 looks good with its PAR response of ~53%. But it sure lacks on the boundaries, eh?
CXB3590-PSR-BH1750.jpg

If only there was a way to boost or supplement those frequencies on the bounds...if only...

Cookie Crumbs.jpg

 
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churchhaze

Well-Known Member
"Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis."

The point we're trying to make is that PAR is a range, not a response. It describes a range of wavelengths, not weighted for a spectral response. Whether certain wavelengths should be weighted more than others is not the point. It's just as easy to be mislead by a lamp with a high response value because it's 660nm emitters only. In terms of describing the photosynthetically active range of radiation, it's most widely accepted to truncate. Even then, we have enough issues deciding where to truncate from. Bottom line is it would be too hard to describe a lamp with 1 number. PAR only tells you how much power or umol/s falls within a certain range, and nothing more.

Edit:

look in the Units section of PAR in wikipedia:

"The conversion between energy-based PAR and photon-based PAR depends on the spectrum of the light source (see Photosynthetic efficiency). The following table shows the conversion factors from watts for black-body spectra that are truncated to the range 400–700 nm. It also shows the luminous efficacy for these light sources and the fraction of a real black-body radiator that is emitted as PAR."
 
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churchhaze

Well-Known Member
It would be nice to know the LER and umol/J of radiation between 380nn-750nm for non photosynthetic reasons, but it would have to called something else, like PAR|380-750nm| to distinguish it from the more widely accepted 400-700nm.
 
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churchhaze

Well-Known Member
Let me try to make an analogy... probably not very good...

If you have 100 people, 90 employed and 10 unemployed, if 5 of them are only 50% good at what they do, is the unemployment rate 7.5% or 10%?

"the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis."

They might not be as good at the job (although I'm still waiting to see pink make a comeback), but they're still within the range of candidates that can be used in the process.

Edit: Man, what a terrible analogy!!!
 
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alesh

alesh

Well-Known Member
heckler73 said:
Actually, I think that spectrum comes from Inada, but I could be wrong. (ahhh yes...Inada's work supported McCree's results).
View attachment 3405722
In any event, your contention is it would be equal to, or less accurate than using a PAR rectangle?
No...that is incorrect just on base principles, which McCree argued about in his papers.
By its very nature PAR assumes ignorance, but we know at least an average response function of 33-55 species to within 5% (with the greatest variance in the UV and deeper blue spectra...which is logical considering chemistry and energy bonds). Are you going to argue that cannabis is more akin to a rectangle versus the smooth, undulating distribution of McCree & Inada? The empirical evidence is not leaning in your favour.

I also find it difficult to reconcile your acknowledgement of plant response to "wider spectrum" while you then cut your legs and arms off at 400 and 700nm. Your follow-up conclusion based on such premises constitutes a non sequitur.

Don't misconstrue my intent. I am not saying PAR is garbage, I'm saying it is a loose metric for approximating quality of light. To that end, it should not be given that much weight. Otherwise, the BH1750 looks good with its PAR response of ~53%. But it sure lacks on the boundaries, eh?
View attachment 3405721

If only there was a way to boost or supplement those frequencies on the bounds...if only...

View attachment 3405720

Click to expand...
I shouldn't have made that statement. You're right that if we weigh the PAR output by this spectral it will probably be more accurate. My point was, how much? I have 2 issues with this approach.
1) Adaptation. We don't know how that spectral response changes when plants have time to adapt for the light they're getting. I'm quite sure that I've read something where they measured much higher concentration of pigments utilizing green-yellow region in plants grown under a HPS. I know it's vague statement but I can't find it now.
2) That spectral response was done by using narrow band lighting (5 or 10nm). It just can't reveal plants' response if perhaps there are processes that require more than one wvl at the time.

That said, I'm pretty sure that what you're proposing would be more accurate than just PAR. However, calculated PAR is solid. There's almost no room for error. On the other hand, that can't be said about the spectral response and I believe that the issues I stated are reasonable.

And also I didn't cut anything. All I did was providing values for a range which some consider PAR. You can use whichever you like or none:)
 
Positivity

Positivity

Well-Known Member
What is all this info about? How to measure quantities of light?

Is the plant so picky?

Trying to quantify perfection?

Sorry, not trying to be rude but i see a lot of this as completely unneccessary for growing ganja. Speaking of which....where is the ganja lately.

Slight edit...i do appreciate alesh helping everyone that is interested in this stuff.
 
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AquariusPanta

AquariusPanta

Well-Known Member
churchhaze said:
Let me try to make an analogy... probably not very good...

If you have 100 people, 90 employed and 10 unemployed, if 5 of them are only 50% good at what they do, is the unemployment rate 7.5% or 10%?

"the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis."

They might not be as good at the job (although I'm still waiting to see pink make a comeback), but they're still within the range of candidates that can be used in the process.

Edit: Man, what a terrible analogy!!!
Click to expand...
What in the fuq is this, mane?!

:lol:
 
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