PAR vs PUR measurement of light, efficency
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Old 12-16-2008, 08:11 PM   #1
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PAR vs PUR measurement of light, efficency


This is a new thread to discuss the differences in terms of growth, asethetics and brands of various bulbs of using PAR and PUR measurements.

Some background is useful as these terms are not as familiar to many hobbyists:

Photosynthetically available radiation (PAR) is defined as the amount of radiant energy available within the approximate spectral range of 350 to 750 nm (Tyler 1966). Instruments commonly used in studies of photosynthesis are PAR meters; that is, they report 400J700 I,h) or total PAR. Photosynthetically usable radiation (PUR) is defined as
the fraction of photosynthetically available radiant
energy of such wavelengths that it can be absorbed by
the algal and plant pigments. Light is selectively absorbed
by most algae in the blue and red regions of the
spectrum, causing the transmitted light to be concentrated
in regions of the spectrum where algal pigment
systems are ineffective at trapping light for photosynthesis
(Sullivan et al. 1984). PUR is necessarily less than
PAR, and PUR will depend on both the pigment complement
of the microalgae and the spectral composition
of the available submersed radiant energy.

It has been suggested that we can calculate PUR through a light calculator and thus have a more precise method of measuring light than PAR. However, I have argued that without knowing the pigment complement of the plants in question, none of which are known............nor have been quantified near as I can tell, maybe I have not searched enough yet, you cannot say much about it. Research also supports this view.

PAR will always be equal to or higher than PUR.
I do not dispute that. PAR meters are also easy to measure with, the methods for measuring specific PUR wavelengths and intensities is not.
Modeling calulators can and do have issues, and need results to verify.

I'm asking and debating whether it can be measured and verified in the aquarium to the same argument made by PUR calculator proponents. There is not enough evidence to say that there is at this point.

You can speculate without support, but you cannot say much else.
What I am asking and looking for is some meat on the bone here, some real support that it makes a difference that aquarists can see, measure, quanatify, heck, anything other than "belief" and yes, I "feel good".

Here's an algal back ground paper that discusses what is involved and the methods to measure PUR in situ, a much higher bar than using a PAR meter. Given that most bulbs used already have a good amount of Red and blue anyway, this starts to get pretty insignificant and difficult to test and support any differences using PUR vs PAR for aquarium plants.

I remain unconvinced.

http://www.new.aslo.org/lo/toc/vol_31/issue_3/0557.pdf

Show me some quantum yeld differences, Relative growth rates differences between PAR and PUR with typical bulbs.

Something.

Are comparison of modesl is detailed here:
http://222.aslo.org/lo/toc/vol_44/issue_7/1599.pdf

While there was a difference between PAR and PUR models in biomass, look at the variation, it's quite a bit. Adding 300 species of plants and that would go even higher. There was good correlation with the PAR model and production, see the last Figure 9, also, look at table 1.

Add less light difference and general good PAR/PUR ratio to begin with with FL lights, we have less differences. I've supported my view, time to support yours. Show me something that suggest what is claimed with PUR really helping anyone with any aquatic plant using typical lighting used in the hobby vs PAR. You may use google, any resources available that you might have to show this.

Do not say personal junk here. Support the view and stick to the topic.

Regards,
Tom Barr
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Old 12-16-2008, 09:42 PM   #2
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Very interesting read, Tom. Admittedly, I'm out of my depth in much of it, but I still want to sit down tonight and try to wrap my mind around what you're saying. Which is what, exactly? That PAR varies for each plant species? I would definitely support that view through basic observation. Who hasn't noted changes in growth patterns when changing a bulb from one "color" to another?

Some older background reading from Aqua Botanic to get others involved in the discussion:
http://www.aquabotanic.com/lightcompare.htm
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Old 12-16-2008, 10:02 PM   #3
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What I take from it is that you can't measure a bulb/fixture's PUR out of context; especially without more research having been done regarding the actual light absorption of the photosynthetic pigments of the individual plants/corals in question.

And therefore since the research on PUR for FW plants seems lacking, PAR is currently a better measurement when evaluating light efficacy.

Is that an accurate summary of your argument, Tom?
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Old 12-16-2008, 10:10 PM   #4
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PUR is much more specific and calculated. But as Tom eluded to, we would have to analyze every single one of our plants' clorophyl to even begin to TRY to make sense of it. Doesnt seem worth it to me, PAR will work IMO.
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Old 12-16-2008, 10:14 PM   #5
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I better go start another pot of joe

Colombian anyone?

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Old 12-16-2008, 10:16 PM   #6
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I think for those who are REALLY into plants, they'd find PUR research fascinating and applicable; it would actually give some credence to those ongoing debates "are some bulbs really better for red plant growth than others..."
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Old 12-16-2008, 11:15 PM   #7
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Quote:
Originally Posted by bsmith782 View Post
PUR is much more specific and calculated. But as Tom eluded to, we would have to analyze every single one of our plants' clorophyl to even begin to TRY to make sense of it. Doesnt seem worth it to me, PAR will work IMO.
That's my argument.

I need to get something useful and significant out of it or else I have a tough time supporting it, as much as I like to and all etc..........but my desire for that vs what I can reason is not a reason for support.

PUR is great, but you need to show a difference in the quantum yields between two lights. I'll accept algae even, since there's only a few studies done on macrophytes.


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Old 12-16-2008, 11:29 PM   #8
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Originally Posted by lauraleellbp View Post
I think for those who are REALLY into plants, they'd find PUR research fascinating and applicable; it would actually give some credence to those ongoing debates "are some bulbs really better for red plant growth than others..."
I'm really into plants, but I do not buy there's a difference with 95% of the bulbs used by plant folks, PAR is plenty acceptable, far simpler to measure in the tank with these other variables.

Sure you can plug a bulb type into a calculator and get theoretical PUR from that. Then also use a PAR meter in situ. But that does not mean the real PUR is that value.............which is what was being argued. That's no slam dunk, not even close. Additionally, if it's about being able to chose the most efficacy of the bulb, well, if it's more efficient and "better" we should then see a significant different in the rates of growth from X bulb vs Y bulb.

If not and if there's a large % variation, there's no sense even making a model more complicated and obtuse. Why make things more difficult?
There has to be a good reason to do so.
And I have not seen one presented yet

I do not think you can say anything about the color of red plants and the PUR/PAR issue here. Plenty if not most plants that are red are shade plants, like all aquatic species. Color development is a large goal for some, but we see wide ranges of color and wide ranges of light and nutrients, CO2 etc. Hard to say that much there.

Let us keep it to the PUR PAR issue.

I need a good reason to support PUR vs PAR. I have not read any decent papers on aquatic plants that suggest much, nor algae.
I've read a few, near as I can tell, folks debating here and me have not read any.

The papers presented(3 so far) all made predictions and then verified them with measurements for their models. The results are not supportive for us as the light is not that different for the brands and models used. In the papers, they are very different, even there, there's not a large factor in the differences.

Given that, I'm having a tough time supporting such a model for use.
PAR has trade offs, I agree, but PUR has as many.

Most tend to go with PAR and if there is not agreement there, or in the cases of extremes, then you look farther and consider PUR, but that is supported with real PUR data/methods from the systems, not a theory calculator.

Regards,
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Old 12-16-2008, 11:47 PM   #9
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Quote:
Originally Posted by GulfCoastAquarian View Post
Very interesting read, Tom. Admittedly, I'm out of my depth in much of it, but I still want to sit down tonight and try to wrap my mind around what you're saying. Which is what, exactly? That PAR varies for each plant species? I would definitely support that view through basic observation. Who hasn't noted changes in growth patterns when changing a bulb from one "color" to another?

Some older background reading from Aqua Botanic to get others involved in the discussion:
http://www.aquabotanic.com/lightcompare.htm
And in Ivo's article, we see that virtually all the typical used bulbs are about 2:1 ratio for PAR:PUR, so using PAR is rather well correlated with PUR.

So why use PUR as long as the measures are the same?
I don't get it.

"The PUR ranking roughly repeats the trend observed with PAR efficiency ranking: the same high-efficiency bulbs in terms of PAR/Watt rank high in the PUR/Watt list. In other words, the two parameters correlate well. "

Which is why using a PAR meter is as effective. This was also supported in the research paper.

The argument Ivo was supporting was more for looking at Lumen and Lux vs PAR in Ivo's article. Looking at PUR involves the efficacy of Biological systems,this is no longer about Engineering. You need some statistical support that X bulb really can produce more growth rate than Y bulb.

Theory and models need reflected into real world biological data that supports the model. And that............is the crux of it. PAR seems to do that well and the meters are relative cheap and we can measure many things in situ and ask and answer many more questions using that.

The red/blue % is interesting and you'd suspect a large % of red and a small amount of Blue would yield the best PUR.

Regards,
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Old 12-17-2008, 01:52 AM   #10
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As usual, I am confused here. When I use a PAR meter I get a reading that drops as I move the sensor away from the bulb. So, how can a bulb have a unique PAR value, unless it is stated for a specific distance from a bare bulb (no reflector)? What am I missing here?
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Old 12-17-2008, 08:52 AM   #11
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who are we arguing against in this thread? it makes total sense to me that PAR is a more "economical" way of measuring light in our tanks vs. PUR....PUR just seems to over complicating something that really doesn't need to be.
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Old 12-17-2008, 09:14 AM   #12
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I will not argue about wheather PUR is better than PAR. If you don't want to use it, then don't.

But if you could buy a cheapo Lux-meter and with the calculator get the PAR (and PUR) measure with it, would it be useful?
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Old 12-17-2008, 01:58 PM   #13
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Quote:
Originally Posted by defdac View Post
But if you could buy a cheapo Lux-meter and with the calculator get the PAR (and PUR) measure with it, would it be useful?
defdac, seems like you got Tom really thinking.

your calculator will accomplish it. But as outlined in Ivo's paper, it all comes down to the quality of the provided spectrum. I know, philips or osram usually provide good spectra for their bulbs but most of the remaining manufacture of aqua plant bulbs don't. Proprietary information...

Said that, the PAR/PUR value still can be off quite a bit from reality with the calculation. On the other hand it will be a indication of the light quality.

A PAR meter will measure the usable light from my hobbist need more reliable and accurate than a LUX meter.

It for sure would be a interesting exercise to run all currently commonly used bulb through the calculator to get the base numbers documented and compare new "magic" bulbs against the database.
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Old 12-17-2008, 02:05 PM   #14
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Quote:
A PAR meter will measure the usable light from my hobbist need more reliable and accurate than a LUX meter.
And you really need to be that accuarate? 40 vs 41 or even 45 mmol?

You need accuracy when it comes to PAR, but not to the extent that PUR becomes interesting?

Seems you guys have really narrowed down what is interesting or not..
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Old 12-17-2008, 02:08 PM   #15
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(Just got my Apogee meter btw. I paid in total $155 for the UPS freight and $150 for the meter... )
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