# PAR vs PUR measurement of light, efficency



## GulfCoastAquarian (Jul 30, 2002)

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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## lauraleellbp (Feb 3, 2008)

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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## bsmith (Jan 8, 2007)

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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## Green Leaf Aquariums (Feb 26, 2007)

I better go start another pot of joe 

Colombian anyone?

-O


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## lauraleellbp (Feb 3, 2008)

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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## plantbrain (Dec 15, 2003)

bsmith782 said:


> 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.


Regards, 
Tom Barr


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## plantbrain (Dec 15, 2003)

lauraleellbp said:


> 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:icon_eek:

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, 
Tom Barr


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## plantbrain (Dec 15, 2003)

GulfCoastAquarian said:


> 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 PARUR, 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, 
Tom Barr


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## Hoppy (Dec 24, 2005)

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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## youareafever (Mar 18, 2008)

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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## defdac (Dec 28, 2003)

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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## Jens (Apr 21, 2006)

defdac said:


> 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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## defdac (Dec 28, 2003)

> 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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## defdac (Dec 28, 2003)

(Just got my Apogee meter btw. I paid in total $155 for the UPS freight and $150 for the meter... )


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## Jens (Apr 21, 2006)

defdac said:


> $155 for the UPS freight


Ouch. I would have been fine with Lux in this case


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## plantbrain (Dec 15, 2003)

Hoppy said:


> 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?


You are right, it has to be at the the specific same distance(and location along the tube, the PAR and PUR vary along the length's on a FL bulbs, measure it and see), I believe that was done when making such bulb to bulb PAR and PUR comparisons in theory. 

You can add or delete the reflector to see and also see how the reflector influences distribution at the surface, at the mid level and at the sediment in an aquarium. Water filters some of the PUR perhaps vs the PAR and changes thing, but I do not think there is much of that occuring in 60 cm or less, the typical aquarium depths. Maybe there is, but I'll assume there's not for now.

Regards, 
Tom Barr


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## plantbrain (Dec 15, 2003)

defdac said:


> (Just got my Apogee meter btw. I paid in total $155 for the UPS freight and $150 for the meter... )


WTH?

Dang!
Ouch!
I should have bought an extra and shipped it to you. 
Did they tell you this prior?

Oh man...........

Regards, 
Tom Barr


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## plantbrain (Dec 15, 2003)

defdac said:


> 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?


Perhaps,

But at 80$ or so for the cheapy one, I may as well get something better that does not need the conversion. Spend a little more to save on dealing with that.
The Apogee was about 2x the cost, but you get what you pay for. Now you could take that and measure and compoare the meter with the Lux meter and see how wel, the conversion works.

That's what I'd do. If there's little difference, say a R^2 of .9 or higher with 5-6 different bulbs etc and 10-20 measures, then okay.

You could say there's not much difference.

I do not think you will have an R^2 of 1 by any means, but with an field of correlation of around 10% the actual, you still have some play.

All this error adds up in the real world and you do not get this difference that you might with a simple theory model, but that's the old trade off there.
Sometimes you do get lucky and one think or a few predicts most of the error and correlation.

Maybe that will be the case here.
Maybe not.

I guess a friend does have a cheapo lux meter I could borrow.

Then compare this, with the LiCOR sphere and the 2 apogees.

Many different Cheapo lux meters are around though, each one would need to be measured against the apogee


Regards, 
Tom Barr


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## plantbrain (Dec 15, 2003)

defdac said:


> 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..


How profound it is? The idea was put forth about PUR calculations being helpful when you are trying to maximize efficiacyfor lighting aquariums. Not just "interesting or not".

Can we find answer that it makes a difference under real conditions?
You provided a model for PUR calculations for each bulb type based on the vendor claims(Let's assume those are correct) as a method to better chose a bulb vs PAR. 

Well, both PAr and PUR would depend on *where *the measure is taken really. You do not get that with PUR, it's theory only. They do not give the outputs at different points along the bulb end points do they? But we can measure PAR up and down the FL tube.
You will soon be able to measure this and see. Then ask is the PUR going to be the same up and down this same bulb also or is it the same ratio over the entire length?

I'm not so sure.

And at lower light, to the point where you want "the less is better approach", it might become very important, 5 micromol might make a difference right?

That is what you are arguing for with the PUR comparisions with bulbs?
Small difference make big changes under the right circumstances?

Say we have 35 micromol of PAR and 40 micromols of PAR.
This is about 15% more light. A fair amount. If we have 250 micromols, and another with 255, the difference is much much smaller relatively.
This was the point about chosing PUR ratings to begin with. Correct?
So those small changes make a larger difference when you are using less light.

I think most agree with that.
The other issue is that the PAR meter is measuring real data in the tnk, PUR is not. PAr errors are reduced and the accuracy s increased not just for the entire tank etc, but any specific spot in the tank can be measured.
PUR assumes the entire tank is fairly well uniform and the PUR and PAR is the same intensity along the entire length, but real world measurements do not show that for PAR.

Since what your goal is more focused on the lower ranges, smaller changes will have more impact it would seem. Maybe not. 

We also have the issue of spread of light and distance.
Does the PAR/PUR relationship change there? I suspect it very well might.

You get more even distribution when the bulb is placed higher, but you sacrifice intensity(less PAR/PUR). So what is the optimal distance?
How do reflectors influence the PAR/PUR relationship? This can improve growth by striking more area of the leaf, thus you could have less PAR and more growth.

Example would be a HQI above a plant say 20 cm away from the tip, and an equal PAR or PUR for that matter using 4 T5 bulbs spaced 6 cm apart. Same PUR, but...........you will get more growth from the T5's in that case.

You can have hot spots in other words depending on the distance away from the light.

I'll admit I am enamoured with PUR, however, I am also looking at the trade offs to get there. I think weighing the trade offs is important in coming to some conclusion about what is best to answer a specific question or obtain a goal etc. 

What is the question being asked here?
What is the best bulb choice for a planted tank?
Right?

If you consider distribution alone(along the length of bulb itself, at the surface of the tank, at 10cm, at the sediment etc) and the height, spread and reflector issue, man...............I'm having hard time saying much about what will give you the most already. What is optimal? 

Think about how the distribution changes as you raise the light up, or how might the distance between bulbs and the number will influence things.You can measure this with a PAR meter, you cannot say much about PUR though.

You can infer from a calculator, but not much else and I'm not clear on how those parameters and the plant's themselves will change PUR.

I'd like to know etc, but I do not see a simple method using a claculator.

There's not much difference significantly between a few micromol of PAR and PUR, but if there's a small difference between PUR of one bulb vs another, then it really does not matter much anyway. Most of the differences will get lost in the other parameters and errors.

How do we tease those issues apart?
A calculator will help some. But I wonder if it's everything made out to be.

Using the PAR meter you can measure relative changes in situ where you do see large massive differences in aquariums. PUR gives you a model and is subjected to many issues, like PAR model, but using a PAR meter gives the actual measured valves at a particularly real world place. 

Using the trade offs of the PAR meter with the model of the PUR can help resolve some of the issues, but it does not eliminate it entirely.
I buy that.

This gets around a lot of the issues like reflectors, water depth, distribution, differences at various height in the aquarium, sediment etc, bulb types etc.

This makes comparison of units and light the same for folks. I do not think we have enough info to say that and how much a difference PUR differences between bulbs really make as we have few easy methods to measure it in the tank itself. There is no such issue with PAR meters and thus makes a good method to use for comparing light overall. 

Otherwise we can go back to not measuring things and just estimating them based on models. I use these same "models" to estimate EI dosing. But folks poo pooed me for suggesting not testing the real individual tank etc.
However, I did that first, then went back and applied the model and it was validated.

I'm a strong supportor of using each method, models and real in situ data at answering things an looking at various other things I or other folks did not consider. But then when we do, then we can consider the trade offs and what is important. We also need some method to validate it- the PUR/PAR(The PAR meter will certainly help to some degree).

I'd like to see that here.



Regards, 
Tom Barr


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## defdac (Dec 28, 2003)

> Ouch!
> I should have bought an extra and shipped it to you.
> Did they tell you this prior?


No worries. They specified $90 at Apogee and then the Swedish "moms" (value added tax) came into play, but also some kind of extra expidition cost I have no clue where it came from. The hobby is cheap considering all plants I sell and I almost never buy any equipment for the tank so it was time for a new aquarium toy.



> But at 80$ or so for the cheapy one, I may as well get something better that does not need the conversion.


Yeah, I guess. But it's anyway kindof cool if someone with limited means or limited access to equipment could spend a little less and use the internet to find out a relatively close PAR-approximation and then decide to go all the way to spend a little more money on the real deal.

But when you have a close approximation to PAR and can compare that to other tanks you can perhaps set the lighting par aside and concentrate on aquascaping instead.

I know my PAR-meter will give me much more insight very fast, and then it will start to collect dust if I don't sell it. The difference is I will put some effort in making a calculator where you can insert a Lux-value and the spectral distribution and get a PAR-approximation. The real PAR-meter will help to see if that is possible and how close we can come and how much difference there will be.

I can also use my Project Star spectrometer to show that even if the CCD in digital cameras are not that great in capturing all frequencies it's close and I will show it doesn't matter much for the PAR/PUR measure.



> Well, both PAr and PUR would depend on where the measure is taken really. You do not get that with PUR, it's theory only. They do not give the outputs at different points along the bulb end points do they?


Oh ok. Here is where I myself make a very strong distinction between the actual PAR reading inside the tank and a measure to compare bulbs. More specifically which bulbs have most blue and red and how much electricity the bulb needs to produce it. This will vary a bit depending upon ballasts but that is really not of interests since you only want to know what the bulb is capable of inside a controlled environment (intrating sphere inside a lab). Exactly the same as the lumens-measure for the bulb. 

My current calculator then tries to expand this a bit and use these values to get a calculated average value for the bottom of the tank. Not so much to get a real deal in life super accurate value that can be proven by a real PAR-meter (althogh I hope I will be able to refine it quite a bit with my new PAR-meter). 

You mostly get a very refined way of comparing and computing light in tanks that is lightyears from watts per gallon.


> Say we have 35 micromol of PAR and 40 micromols of PAR.
> This is about 15% more light. A fair amount. If we have 250 micromols, and another with 255, the difference is much much smaller relatively.
> This was the point about chosing PUR ratings to begin with. Correct?
> So those small changes make a larger difference when you are using less light.


Agreed. Good example.



> There's not much difference significantly between a few micromol of PAR and PUR, but if there's a small difference between PUR of one bulb vs another, then it really does not matter much anyway. Most of the differences will get lost in the other parameters and errors.


It's a bigger difference than that, but the point is totally correct. The light will vary extremely much depending on where you will measure it in a planted tank but the thing with PUR-efficiency (not a PUR-reading) is to be able select the bulb that gives you the best possible start.

I did a quick measure beneath a Deltec Midday 6000K bulb and god at most 500 mmols. Did the same thing with an older Aquarelle bulb and got 800 mmols. That was a much bigger difference than I expected and quite frankly a bit troublesome because the maths says the PAR output of a bulb of the same wattage will not have that huge difference. Something that will be fun looking into.



> This gets around a lot of the issues like reflectors, water depth, distribution, differences at various height in the aquarium, sediment etc, bulb types etc.
> 
> This makes comparison of units and light the same for folks. I do not think we have enough info to say that and how much a difference PUR differences between bulbs really make as we have few easy methods to measure it in the tank itself. There is no such issue with PAR meters and thus makes a good method to use for comparing light overall.
> 
> ...


This sums it up pretty well what I will be doing. I have a generalized model and will see with the PAR-meter if it holds. It will be generalized and not depending upon exactly where in the tank but I hope I will be able to take into account alot of parameters like reflectors and spread etc.


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## aquanut415 (Jan 21, 2006)

wow you two. whats the point?? all this data and supporting evidence is practically useless unless hobbyists can apply it to our tanks. 

so what should people be taking home from all of this that we didn't already know?
plants need light, yes.... but we already knew that... plants also don't care what a quantum meter says about the PAR available to it. plants also grow under a wide variety of conditions, wattages, K ratings... but what does it really matter?

so long as the plants are growing, does it really matter who is more correct here? is it even applicable?


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## defdac (Dec 28, 2003)

aquanut, I hope I don't sound too harsh if I say you have totally missed the point of this entire thread. This is not a game of who is wrong or right, but to dwelve into lighting and find a generalized model that is easy to use by everyone to overcome the problems with the watts per gallon-measure that is really limiting folks in their light composition of their tanks.

If your light is fine and you grow healty plants and can focus on everything but light this thread is not for you.

If you have a nagging feeling you don't entirely know how to quantify your light and that your lighting amount not is entirely up to par to what other hobbyists use - or want to save some bucks. This is the thread for you.


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## aquanut415 (Jan 21, 2006)

defdac said:


> If you have a nagging feeling you don't entirely know how to quantify your light and that it might be up to par to what other hobbyists use - or want to save some bucks. This is the thread for you.


is this really what this is about?? cause it doesn't look like it to me. seems to me this thread is about pointing out facts that really can't be applied.

so how has all this info helped you? what changes do you plan to make? or what changes did you make to your setup once you learned all of the things you have pointed out? it seems entirely irrelevant.

the part that seems applicaable we already knew. plants need light, however they are not too particular about the specifics.


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## defdac (Dec 28, 2003)

> seems to me this thread is about pointing out facts that really can't be applied.


Ok, that's not it 



> so how has all this info helped you?


To be able to quantify how much light I have compared to others. This have made me look into better reflectors, better bulbs etc. To understand lighting better. To see that watts per litres or watts per gallon can be very misleading.



> it seems entirely irrelevant.


Yes to you who have found the ultimate lighting truth it's probably just a bunch of computations you can't see the value of.



> plants need light, however they are not too particular about the specifics


They are very picky if they don't have enough. Where I come from people use about 10 times less light than most folks here. Especially those newcomers that are new to the hobby.


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## aquanut415 (Jan 21, 2006)

defdac said:


> Ok, that's not it
> 
> 
> To be able to quantify how much light I have compared to others. This have made me look into better reflectors, better bulbs etc. To understand lighting better. To see that watts per litres or watts per gallon can be very misleading.
> ...



come on now... if you were just interested in learning what levels work, why would any of this be necessary? you said you already know people who keep planted tanks at lower wattages, or PAR or PUR levels or whatever. so what were you really trying to answer? it seems to me you already knew what you wanted to know.

and i do not think PAR measurements are worth much, other than as a way to compare the PAR output of different lamps/ballasts, thats it. i have no intention of changing my lights based on PAR measurements. PAR is just a number some people are going to be clinging to for some time, hoping they are going to cure all the problems with thier tanks because they are within the recommended PAR range. :icon_roll


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## plantbrain (Dec 15, 2003)

So John has been PM his observations, I've assumed them to be accurate(he's not going to lie to me is he? haha).

From that conversation, I think I had an old test method that will work very well to resolve the PUR/PAR model issue.

Note, this is not directly measuring PUR, rather, using dry weight and O2 as a method to infer PUR vs PAR. Often times it can be pretty messy and louse things up, cost too much etc and not really answer the biological question.

So here's the test, one I did on a 55 Gallon tank back, who knows, 15-20 years ago now, but I did not do dry weights, just look at the plants etc and judge from there.

+++++++++++++++++++++

A simple method to see is to use the 55 gallon tank into 2ft sections and have a hole filled plate between the 1/2's and place different bulbs on each 1/2. Then measure dry weight differences with the same Species of plant over time. Ideally a bank of 2-4 bulbs 24" long on each side, the plate serves to diffuse the same nutrients and CO2, water quality etc and to block over spray of light into the treatment. 

PAR can be made the same(this is important to make PAR independent and PUR the dependent variable here!!!) with raising or lowering the light distance between 2 bulb types with different PUR ratings. If you have the same PAR, but different PUR, and you get significantly different growth rates, then you have something meaty to chew on and say about PUR.

Cool eh?

That will answer the biological question.
Dry weights can be done for any species you pick, or you can tag a node and then measure new growth and take stem length increase and dry weight. 
You cannot use O2 however in that case, since it diffuses throughout the tank.

But........... you can measure the O2 from only the high PUR vs the lower PUR bulbs with the other treatment "off" however to get at that, not as easy and it's not "perfect" but it should say a bit more about the differences and see if that agrees with the dry weights.

If so, then you have good correlation for that method using O2 as the parameter. The system has fairly independent CO2 and nutrients, and PAR.
So you can see what PUR does over time to a number of plant species.

Pretty simple test a hoibbyist could do if they chose.
A scale, a tank, a light fixture pair and a DO meter. Not much else really. 
Ideally, you'd do 4-5 replicates at least so you'd need 4-5 x 55 gallon tanks.

But.............a hobbyists could do it and not need to measure PUR directly.
We can measure quatum yeild (sort of a PUR measure of sorts) directly for terrestrial plants, but the LiCOR 6400 is about 40K$ and they'd not take kindly to me putting it below the water. I have an adaptation using a small micro chamber using a CO2, PAR probe and O2 probe that can clamp on to the submersed leaf and compare a similar quantum yield. But I have not tried it out just yet.

Be kind of cool though. Then you could easily compare PAR and PUR influences bulb to bulb in any point you chose.

Another impact of PUR s PAR that came up with my discussion with John was the Blue light effect on photosynthesis.

The blue spike can and will increase O2 and relative to a red light alone.
So in terms of PUR, a blue + red vs a red alone bulb should have a higher PUR.
At least in terrestrail plants.......FW water plants have non functional stomata in most, many cases(this has not been looked at that in depth with the entire 300 species we keep, certainly most have never been studied as aquatic submersed plants).

What about a % of each light type at the same PAR?
Well, we should see a match point with optimal growth and % of each type.

I think there's somethin g to be said for PUR, but answering the question and finding a simple cheaper easy method is nice also:thumbsup:

As far as PAR, and using the meters, they are good for comparing light, better than Lux, as Ivo pointed out as well as most botantical references and measures, and when we are looking at light, it's a cheap easy method to use.

No one "clings to it" however, it's just the best we got for now till we answer the other unresolved questions farther down the line of questioning. It's not "ultimate truth", it is just one step closer to it is all.

Folks have used watts/gal, watts/meter, various math based models, but most researchers use PAR for comparing light, in some cases they need to see about PUR, but not that much with aritifical lighting except very rarely.
PAR is clearly a better unit and measure than Watt/gal. Why bother if I can use that watt/gal and still do pretty good?

This is not really much of a reason. 
You could say that why should anyone ever bother to test anything with that approach(NO3, PO4, Fe, KH, etc, plenty of folks don't also), I have with suggesting EI, but I still like to test and measure things also to answer basic questions and to confirm.

Using a PAR meter at least gets closer to having a more standard measure for comparing things for aquarist. Much like using KNO3 salts for NO3 and K+ additions. It's not the end all, but it can help keep the variation down as best we can. Certainly better than other options available. Researchers have the same issues, they rationalize and use PAR as well.

Perhaps later we will find a better way to add PUR to this method. Perhaps they(or myself) will make a PUR meter for the field we can use and make some predictions and conclusions to make the model better so we can use it for better predictive use.

But that is why Defdac is debating this, to get closer to the predictive nature of a model for light.

I have that same goal. Also, I think defdac and I have debated things for about 10 years or more now(we getting old!), we are well aware of the other and know this is not a personal thing, it's comes across much more heated than folks might read into here. In person, it's more of a conversation and a who dunnit type of mystery. I think a lot is lost on line there. Folks think I'm a crotchy old man, but if you met me, then you know otherwise, I'm just old

Still, being aggressive about a theory, model, advice, support, observations etc, not the person is what we are doing. Sometimes it comes out like we might be, but it's compartmentalized more than some might think.

I'm interested in the question itself, and how to best answer it with the resources I have available.

I think the 55 Gallon test tank described above does that pretty well and offers a simple non destructive method to measure and test also.

Then you can look at that question about PAR vs PUR and how much effect PUR really has relative to PAR.

Regards, 
Tom Barr


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## lauraleellbp (Feb 3, 2008)

I think our hobby is still behind the SW hobby in our overall depth of understanding the difference lighting makes to aquatic plants. Quite a bit of this is going over my head, but I'm still finding it completely fascinating! I appreciate the discussion and research you guys are putting into this. 

A question I have regarding measuring PUR in a planted tank application- are there other things in a tank that can absorb light and impact "actual" PUR readings other than the plants?


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## defdac (Dec 28, 2003)

> if you were just interested in learning what levels work, why would any of this be necessary?


Because "levels" would need to have an actual measure with a unit. 



> you said you already know people who keep planted tanks at lower wattages, or PAR or PUR levels or whatever. so what were you really trying to answer?


I guess I'm trying to find a measure that is easy to apply and understand for most folks. 1 watt/litres in a small tank can be equal to 0,5 watt/litres in a big tank, so the watt per litres or watts per gallon is somewhat fail. Things get even more complicated with different kind of reflectors and different kind of bulbs.

After I've measured my two different bulbs and found almost a factor 2 in difference just in PAR I'm even more convinced theres a lot to be won if one wants to get smart with bulb selection.

Do you want a tank that takes half the amount of electricity and grow the same amount of plants?

What you are saying is essentially "No, leave me alone, I don't want to change something that works, I don't know how much light I have and I am offended by you trying to find out free ways of quantifying light for hobbyists".


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## defdac (Dec 28, 2003)

> PAR can be made the same(this is important to make PAR independent and PUR the dependent variable here!!!) with raising or lowering the light distance between 2 bulb types with different PUR ratings. If you have the same PAR, but different PUR, and you get significantly different growth rates, then you have something meaty to chew on and say about PUR.





> But........... you can measure the O2 from only the high PUR vs the lower PUR bulbs with the other treatment "off" however to get at that, not as easy and it's not "perfect" but it should say a bit more about the differences and see if that agrees with the dry weights.


This is getting interesting. I really didn't was thinking of looking into correlating a PUR-measure against actual biological action although that ofcourse is the ultimate proof of concept.

I was more thinking that if I can correlate my model in my calculator and see it gives good prediction of PAR-levels on the bottom of a clean tank that would suffice to give a real comparison measure between hobbyists tanks.

-"I'm having trouble with plant x and I see we use EI with the same levels. Which light levels do you have?"
-"The calculator says I have around 100 mmol on the bottom"
-"Ok, I have only 10, perhaps will look into optimizing my reflectors/bulbs/wattages"

If I can predict the PAR-level on the bottom of a tank with my calculator and measure
about the same levels with my Apogee-meter that seems good enough.

Also going from PAR to PUR is quite easy math and logical very sound. I mean, are those photosynthetic action spectrums just made by up or are they usable?

I also want to make a strong point that even if you compare rather radicaly different spectrums measured completely different, the actual numbers will not change much.
Comparing a hobbyists spectral distribution, for example http://saurama.aqua-web.org/pages/06_sp_PhilipsAquarelle.htm with the spectrum from Philips will not change the numbers radically. If the spectral distribution shifts a bit due to age the numbers will also not change much if at all. The numbers are much more robust than you might first think and that is because we're talking area under the spectral distributions here. And not even that - the relative area distribution over two halves of the 400-700nm range. Don't be fooled by the fancy math and units here.

So, subtle changes of spectral distribution will not nearly give as much impact as the intensity loss because of age. That's a huge player for some phosphor mixes (GroLux comes to mind).


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## jjp2 (May 24, 2008)

Just to briefly summarize the PM conversation Tom and I had..

I have a 135 with 4 80W T5HO bulbs. I have 2 geissmann middays (6000K) and 2 geissmann aquablue (11000k). I choose these bulbs based on their spectum and intensity (PAR). This information is provide by geissmann. I use pressurized CO2 and dose ferts daily. When I use only one type of bulb in the same location, I notice a significant difference in the pearling rate and time at which the pearling starts between the bulbs. I have swords, red swords, crypts, anubias, anacharis, Limnophila aromatica, and some others. 

In my PM, I was saying that pearling can be used as a measure of growth, but Tom pointed out that growth needs to be measured over the day as plants will stop growing during the day. He did agree that pearling is a sign of accelerated growth, but that total growth may be similar over the course of the full day. 

In my tank, the Aquablue bulbs cause my plants to pearl earlier and at a high rate. I related this to PUR, since the midday has a broader spectrum and relative intensity. Tom pointed out this could be due to the amount blue light allowing the plants to utilize more CO2.

I also don't have measurement tools and don't want to pull plants from my tank to weigh, so my point is based on observations over weeks. If observations are taken over a long enough time period and charted, fluxuations in CO2, Ferts, etc would not be a factor in identifying trends. This is what most of us have done in science class during our school days to identify trends and validate hypothesis.

I rearranged my bulbs to satisify my own curiousity based on what I saw. I had expected the midday to pearl sooner and more due to spectrum and intensity but found with my tank this wasn't true. The overall result is what I wanted, but the individual results were suprising.


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## defdac (Dec 28, 2003)

> In my tank, the Aquablue bulbs cause my plants to pearl earlier and at a high rate. I related this to PUR, since the midday has a broader spectrum and relative intensity. Tom pointed out this could be due to the amount blue light allowing the plants to utilize more CO2.


PUR is calculated from a photosynthis action spectrum, which in turn is measured by measuring the rate of oxygen production on every frequency between 400-700nm.

If a lamp triggers heavier pearling compared to another lamp with the same wattage, it has higher PUR-efficiency.

Thus if you want heavy pearling and heavy photosynthesis you should pick a bulb with high PUR-efficiency.

I have seen the same thing when comparing GroLux with Aquarelle. No pearling with GroLux and when the bulb is changed to an equally old but not yet fully warm bulb and thusly not maximum intensity = heavier pearling.



> I had expected the midday to pearl sooner and more due to spectrum and intensity but found with my tank this wasn't true


Exactly. A bulb with high Lux (like the Midday) doesn't equal high amount of usable radiation. It equals high PAR, but not high PUR.


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## Craigthor (Sep 9, 2007)

Orlando said:


> I better go start another pot of joe
> 
> Colombian anyone?
> 
> -O


Fench Roast for me straight up :eek5:


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## plantbrain (Dec 15, 2003)

defdac said:


> This is getting interesting. I really didn't was thinking of looking into correlating a PUR-measure against actual biological action although that ofcourse is the ultimate proof of concept.


Yes, I figured that might "wet your whistle".:thumbsup:
A good question and good answerable method to get at it helps and then we can get a better understanding.

From there, we can improve it further.



> I was more thinking that if I can correlate my model in my calculator and see it gives good prediction of PAR-levels on the bottom of a clean tank that would suffice to give a real comparison measure between hobbyists tanks.


I think you can and might want to do both. This would give good support from any criticism. I guess I'm saying it's part of the plan, but doing both will give you much more power.



> -"I'm having trouble with plant x and I see we use EI with the same levels. Which light levels do you have?"
> -"The calculator says I have around 100 mmol on the bottom"
> -"Ok, I have only 10, perhaps will look into optimizing my reflectors/bulbs/wattages"


I think it's a bit tough to go with a predicted light value, if you have real PAR meter readings, and you know which bulb you had as well, then........you can really start to say more with that + the PUR, and if you have the biological data for support for PUR and PAR, then you could really be pretty confident about it.

I'd say there's a decent correlative relationship between PAR and PUR, but those other issues can come into play and while from a purly energy issue, it's significant, we need to have some way to say something about the plant differences, so we have to test them.



> If I can predict the PAR-level on the bottom of a tank with my calculator and measure
> about the same levels with my Apogee-meter that seems good enough.


I'd say so and buy that based on the data. Now you have a good measure in the tank and decent conversion range. Other than doing the above suggestion I had, this would be the next's best thing I would figure and was what you had in mind I think all along. It's easier than doing the test I suggest, but that would say a lot more than this also, so it would be worth it.



> Also going from PAR to PUR is quite easy math and logical very sound. I mean, are those photosynthetic action spectrums just made by up or are they usable?


Well, it depends on which PA spectrums and how the plant has and can adapt to. Then it also depends the angle of refraction, strike, diffusion with the water(rippling water vs still surfaces etc), shading from other plants, many things go into this that are unaccounted for.

The thing is when you take PUR into the real world and assume it will behave entirely the same as PAR, that's not a real safe assumption.

Maybe it is, I really do not see that it is and remain pretty uncertain.
Then the other question is it really any more predictive...........and useful vs PAR?

That's another issue. If so, then PAR or PUR would not matter much either way, since you just convert between them, most of those bulbs are about 1/2 the PUR vs PAR with few exceptions.




> I also want to make a strong point that even if you compare rather radicaly different spectrums measured completely different, the actual numbers will not change much.
> Comparing a hobbyists spectral distribution, for example http://saurama.aqua-web.org/pages/06_sp_PhilipsAquarelle.htm with the spectrum from Philips will not change the numbers radically. If the spectral distribution shifts a bit due to age the numbers will also not change much if at all. The numbers are much more robust than you might first think and that is because we're talking area under the spectral distributions here. And not even that - the relative area distribution over two halves of the 400-700nm range. Don't be fooled by the fancy math and units here.
> 
> So, subtle changes of spectral distribution will not nearly give as much impact as the intensity loss because of age. That's a huge player for some phosphor mixes (GroLux comes to mind).


I buy this part of the argument.
I've seen it in tanks and in other data.

What I have to wonder is that such data will really give you any better advange vs using a PAR meter in individual tanks? I think the PAr meter is much more useful overall to seeing about if there's enough light and if you are interested in the PUR, run it through the Calculator.

That will be an estimation still, but about as best you can do without doing the test I suggest.

But is it significant?
I'm not sure. I tend to think it's not in most cases.

You might find a few where there's the potential.\

Step back and ask the broader question:
So what are we going to get out of all this?
Are we really going to find the bare min of light watt using a certain bulb type and eek out a 5% faster rate of growth? Is that meaningful to us and will a lot of folks see that difference?

10% perhaps etc(See Bowes, Haller et al and under radically different light ranges than anything we see, even there there was not a large change), but not these smaller ranges. And that assumes everything else going on in the tank is good etc so you can make some use of the added little bit more PUR light.

PAR meters give us a good way to compare things based on what most now use. While some might use Gro lux, I do not know anyone that does here.
Most use those bulbs that fall in that 2:1 range for PARUR.

You can use the PUR data to pick the best bulb you like, then use the PAR to adjust the light to meet the needs of the plants also in the tank/s. That's a decent way to go about it also.


Regards, 
Tom Barr


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## defdac (Dec 28, 2003)

> I think it's a bit tough to go with a predicted light value, if you have real PAR meter readings, and you know which bulb you had as well, then........you can really start to say more with that + the PUR, and if you have the biological data for support for PUR and PAR, then you could really be pretty confident about it.





> Then it also depends the angle of refraction, strike, diffusion with the water(rippling water vs still surfaces etc), shading from other plants, many things go into this that are unaccounted for.


You're very correct here but if you think about it, do we really need to know exactly how much PAR (or PUR) is striking a part of a plant or even individual leaves?

For me it's much more important to know how much my hood is spitting out and reflecting down the tank, thus the *potential* of the light we decide to go for with a specific type of tank. What you then do with this "light potential" regarding trimming plants, using floating plants, and cleaning the tank glass, having the surface sparkling clean, cleaning reflectors and glass tops etc is up to you - you can be certain you have the same potential regarding light as Amano, Olive Knott etc.

This potential is much easier to make a model for and it will tell you much more than only the number of watts compared to the volume of the tank.

I my model you account for so many more things: How much potential active photons (and even usable photons) will be spread out over the top area of the tank and a specific tank area considering watts, attenuation, spectral composition, lumens efficiency, PAR-efficiency and PUR-efficiency.

To actually have a real quantifiable growth difference between PAR and PUR would be good and it would be nice if you could actually measure the 12% difference in PUR-efficiency between for example 965 and Aquarelle. Or the 16% difference between Floura and Aquarelle. It would be interesting. Useful? *shrug*. 

Then you ask the important question:


> So what are we going to get out of all this?
> Are we really going to find the bare min of light watt using a certain bulb type and eek out a 5% faster rate of growth? Is that meaningful to us and will a lot of folks see that difference?


It depends very much on how you go about things. Are you the type of person that use brute force and just buy the top of the line super duper light hood and be done with it, or are you a person of limited means and want to upgrade a little more sensible not wasting initial costs nor long time costs? 

Do you want to spend some time trying to figure out a reasonable light level or do you want to slowly add more and more until you hit the sweet spot?

There are alot of different approaches and I think we should be humble to what approaches folks like. No scenario is more "right or wrong" than the other, just different flavours.

The biggest problem for new folks in this hobby is getting a feel for what is "high light" or "low light". USA have a *completely* different view on what is "high light" than we in Sweden for example. And even among all hobbyists in all countries this notion varies a great deal. 

A calculator trying to make a somewhat realistic model will even out this alot - You can get an instant feel for how much light Amano, Oliver Knott etc drive in tanks where they manage the really picky weeds completely algae free. It's less what an experienced aquascaper generally think, but much more than an average community tank in Sweden for example.

I think we will go more towards thinking of "high light" as a light level where you can drive any plant, and what I have seen so far it's less than the general notion of "high light" in international forums.


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## lauraleellbp (Feb 3, 2008)

Out of curiousity, what are typical lighting levels in a Swedish tank? 

And are you referring to "typical community" nonplanted, or planted tanks?

B/c I'd say most "typical community" (nonplanted) tanks in the USA run less than 1wpg of T8 flourescent... it's when you get into planted tanks that people start getting upgraded fixtures.

I'm curious what light fixtures are popular for Swedish planted tanks versus here in the US.


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## plantbrain (Dec 15, 2003)

defdac said:


> You're very correct here but if you think about it, do we really need to know exactly how much PAR (or PUR) is striking a part of a plant or even individual leaves?


Depends............on what question we are asking. If it's about a foreground plant, then yes. They do not bolt for the surface(So most leaves around that area might be similar, or how pilied up on eachother will Gloss get before the lower leaves start to yellow?). If we are looking at a stem plant as it grows to the surface through time, then yes. If we want to measure the total light of a particular area, then yes.

You mentioned that you wanted to maximize the light bulbs efficiency.
In order to do that, you need to maxmize the plant"s exposure.
To measure that, you need to measure what that plant is being exposed too.

You need to know what the plant is exposed to.
That's why a PAR meter is good.
It answers that part. It does not answer what the PUR is reaching that plant.
From there, you can take the PUR data you have and 1/2. But with first using the PAR reading.

I do not think you are going to get much differences here, just the scale(2x higher reading for PAR in most cases).

1. How much PAR/PUR do you need or desire to chose a bulb vs another?
2. What about aesthetic choices for your eye?

Seems no#2 is more relevant and important given most of the bulb types are fairly close as it is.



> For me it's much more important to know how much my hood is spitting out and reflecting down the tank, thus the *potential* of the light we decide to go for with a specific type of tank. What you then do with this "light potential" regarding trimming plants, using floating plants, and cleaning the tank glass, having the surface sparkling clean, cleaning reflectors and glass tops etc is up to you - you can be certain you have the same potential regarding light as Amano, Olive Knott etc.


Or you can use the same bulb types and a PAR meter.
Let me ask you this, how do you know how high that lighting fixture is in Amano's, or Oliver's tank might be?

What if they gave micromols of PAR?
If you know the brand of the bulb, and had the PAR...........you really do not need any other infomation. Reflectors, ballast etc...............

That's why using a simple PAR meter resolves many such issues.



> This potential is much easier to make a model for and it will tell you much more than only the number of watts compared to the volume of the tank.


See example above, the PAR meter does it already, for any tank, anywhere.
That was the point of using them.

PUR is more about getting the most light that is biologically available to the plant from one bulb vs another.

These are not the same questions, goals or issues.



> I my model you account for so many more things: How much potential active photons (and even usable photons) will be spread out over the top area of the tank and a specific tank area considering watts, attenuation, spectral composition, lumens efficiency, PAR-efficiency and PUR-efficiency.
> 
> To actually have a real quantifiable growth difference between PAR and PUR would be good and it would be nice if you could actually measure the 12% difference in PUR-efficiency between for example 965 and Aquarelle. Or the 16% difference between Floura and Aquarelle. It would be interesting. Useful? *shrug*.


Yes, I think this is potentially important in chosing a higher PUR bulb vs another. But for the tank's themselves, we already know what the brand we bought is..............we need to see what our tank is being exposed to and the PAR meter is the tool to do that(or the one we have that's easy and cheaper).

Seems that the model could be pretty simple then.



> Then you ask the important question:
> It depends very much on how you go about things. Are you the type of person that use brute force and just buy the top of the line super duper light hood and be done with it, or are you a person of limited means and want to upgrade a little more sensible not wasting initial costs nor long time costs?


Some are, I do not suggest this however, never have. People will do what they will. I can deal with that type and adjust things accordingly for them and their goals, or focus more on the lower light, limited budgetted groups.
You have to address all the groups of folks and their goals, not just one.



> Do you want to spend some time trying to figure out a reasonable light level or do you want to slowly add more and more until you hit the sweet spot?


Well, you can do this pretty easily with the dimmable/programmable ballast, multi bulb systems or with hoods you can raise up/down etc.

Then you can change things with one system to suit many goals:thumbsup:
You can swap out bulbs and find ones that you like, whether the criteria be PUR or you just like the look of that bulb. Rather than arguing one approach in the goals, seems that a general understanding and looking at how to get many goals addressed is a better approach. I agree, the high light is a waste in 95% of the cases. 

I would approach, and usually do, from a higher light level and then reduce slowly to hit the sweet spot. But that spot will change as things in the tank change.

Sort of like dosing barely enough to avoid strong limitations.
It starts to become a knife edge there with light, cO2 or nutrients..........
Which is why I tend to look at this with more wiggle room in mind and not the bare minmium light(or nutrients or CO2 etc). 



> There are alot of different approaches and I think we should be humble to what approaches folks like. No scenario is more "right or wrong" than the other, just different flavours.


I'd say this: they have different _trade offs._
Not flavours:thumbsup:
Then the question becomes what is the best set of trade offs for folks's specific goal with their aquariums. Say I want min in/output, the idea of a sustainable ecosystem, I'd likely chose the non CO2 planted tank, no water changes, not high light, no CO2, balanced fish loads, minimal ferts, feeding etc etc.

Your goal is specific with respect to light. I'm asking what real utility is it to know a few % more PUR on one bulb vs another when we need some wiggle room and be above the bare min light level for plants?

Why push things so low you have a larger risk?
If efficiency and minimal goals are the real criteria, why not go non CO2?
You trade off the faster rates of growth, but you gain more wiggle room and use far less.

But ah............you still want faster rates of growth:thumbsup:
And to do that, adding more light does that(along with more CO2/nutrients).
You can slow the rates of growth down pretty good using PAR readings alone, so you still have a decent rate of growth, but one that's easily manageable.
These are the typical set ups I suggest for folks seeing a nice ADA tank etc to pick. Others go with the non CO2. Most buy the dang high light though:icon_roll

Still, the older and wiser, the "more tired" if you will, often try the non CO2 and are happy and surprised. Few newer folks seem to try non CO2 starting out. 



> The biggest problem for new folks in this hobby is getting a feel for what is "high light" or "low light". USA have a *completely* different view on what is "high light" than we in Sweden for example. And even among all hobbyists in all countries this notion varies a great deal.


Yes, most of the market here is Reef driven.
PAR meters will help and not so much the new folks, rather, the folks that help them. They have a baseline to compare the lights in the aquariums.



> A calculator trying to make a somewhat realistic model will even out this alot - You can get an instant feel for how much light Amano, Oliver Knott etc drive in tanks where they manage the really picky weeds completely algae free. It's less what an experienced aquascaper generally think, but much more than an average community tank in Sweden for example.


I think there's a lot more to Amano, Oliver etc and algae free, and the work involved than mere light. I have the bulbs and have the PAR readings from a number of ADA tanks. That's enough to make a conclusion and also a suggestion to folks starting out etc. PUR or a calculator is not even needed if that is the goal.

The question has been answered.

But....if you want to ask a different question with different bulb types, then you might suggest using a PUR, but are the bulbs really that different as far as PUR vs the color look to our eyes? I think most folks will chose based on asethetics rather than PUR.



> I think we will go more towards thinking of "high light" as a light level where you can drive any plant, and what I have seen so far it's less than the general notion of "high light" in international forums.


I agree. I get around on forums internationally for good reason. I've been a "nag" for many years about using less light. I think that was one of the few things George Booth, Steve Dixon and myself all agreed upon many years ago.

I've actually done this also, where someone will claim that you cannot grow plant X and plant Y and at a certain light combo/watt/gal etc, now we have PAR to compare and that makes things much easier and also makes some of the old notions we had really make a lot more sense.

The ADA fixtures where very low relative to the Watt used.
So many thought/assumed that they where really high wattages, they are really pretty low minmal light, but they look nice.

No calculator would have predicted that.

Regards, 
Tom Barr


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## jjp2 (May 24, 2008)

Throwing out a different thought, but it seems to be in line .... 

Could it be that algae absorbs light differently than plants and if the spectrums could be identified it may be possulbe to reduce them in bulbs so to reduce algae growth?

Could it be that plants prefer certain spectrums and increasing those alone without increasing the wattage or brightness make a big difference?

Has a spectral analysis on the ADA bulbs? Maybe they have found this and thats why their bulbs have a lower PAR but give such good growth and their tanks seem to have reduced algae.

Just some thoughts...


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## aquanut415 (Jan 21, 2006)

great post tom. i think you pretty much summed up everything ive been thinking in regards to this debate in one excellent post. dare i say possibly the best one ive read of yours in a while? :icon_eek:

especially agree with you about how knowing these values might effect our choosing of various lights. are we going to choose lights based on PAR or PUR values? or how it makes our tanks look? 

looking for a magic number to solve all the problems has never worked in the past, and isn't gonna happen in the future. you point out excellently that the parameters that do work in the tank change, so looking for one measurement of light that is gonna grow everything for everyone isn't really likely to occur.


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## defdac (Dec 28, 2003)

> Out of curiousity, what are typical lighting levels in a Swedish tank?


Normally the lighting that comes with finished aquarium sets, like Jewel, Aqua-El and so on. 


> I'd say most "typical community" (nonplanted) tanks in the USA run less than 1wpg of T8 flourescent...


That sounds about right and what most folks have here too. Often without reflectors and black hood. Reflectors alone on these kind of tanks often makes a *huge* difference.


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## defdac (Dec 28, 2003)

> 1. How much PAR/PUR do you need or desire to chose a bulb vs another?
> 2. What about aesthetic choices for your eye?


If you can't grow the plant you want to in the first place that answer is not as obvious as you want to make it. Also aquarists here in Sweden actually want’s the bizarre color of GroLux to emphasize the reds in fish.



> Let me ask you this, how do you know how high that lighting fixture is in Amano's, or Oliver's tank might be?


That is one of the points of the calculator.

You put in the data you have and it spits out how much theoretical max PAR it has on the bottom.



> If you know the brand of the bulb, and had the PAR...........you really do not need any other infomation. Reflectors, ballast etc...............


Yes and that data is easy to both get and make educated guesses about.



> That's why using a simple PAR meter resolves many such issues.


No, not at all. You will then know how much PAR you have in one or several spots in the tank and you don’t know at all how to reproduce it at home.

I want to to be able to compare setups for free and with educated guesses that give me a lot more than watt/gallon.



> But for the tank's themselves, we already know what the brand we bought is..............we need to see what our tank is being exposed to and the PAR meter is the tool to do that(or the one we have that's easy and cheaper).


No I want to predict how much PAR I will get with any setup in any tank. I don’t want to buy something and afterwards see how high or low PAR I got.



> Well, you can do this pretty easily with the dimmable/programmable ballast, multi bulb systems or with hoods you can raise up/down etc.


The calculator that makes prediction of how much light to buy is for those with little means. A dimmable T5 hood with a light computer is one of the most expensive things you can get in this hobby. That is not for everyone.



> I think there's a lot more to Amano, Oliver etc and algae free, and the work involved than mere light. I


You have totally missed my point then. I want to be able to analyze experts setup, mimic it and feel certain it will not be the light that limit my aquascaping endeavours. If I can’t grow the same plants they grow with their light levels I know it’s not the light I have to look into.

That is one big factor to rule out in favour for nailing the CO2, which is all that is left after EI.



> But....if you want to ask a different question with different bulb types, then you might suggest using a PUR, but are the bulbs really that different as far as PUR vs the color look to our eyes? I think most folks will chose based on asethetics rather than PUR.


This have nothing to do with aesthetics since you can calculate your light levels from whatever bulb you like.

That is a nice feature – you can drive more wattage to be able to select a dimmer bulb that is more aesthetically pleasing.

Or you can go the environmently friendly route.

But I will set PUR aside as I have done through this whole conversation because PAR seems more accepted in this crowd and you will get PUR for free if you want to. It’s up to each and everyone to see if they are useful.



> The ADA fixtures where very low relative to the Watt used.
> So many thought/assumed that they where really high wattages, they are really pretty low minmal light, but they look nice.
> 
> No calculator would have predicted that.


Mine have or at least will be able to 8) The spread of those ADA-MH fixtures are extreme. If you have them just a bit over the tank you will enlighten the room around the tank more than the tank itself.


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## defdac (Dec 28, 2003)

> Could it be that algae absorbs light differently than plants and if the spectrums could be identified it may be possulbe to reduce them in bulbs so to reduce algae growth?
> 
> Could it be that plants prefer certain spectrums and increasing those alone without increasing the wattage or brightness make a big difference?


No they work basically the same. Algae have accessory pigments as plants. Both use chlorophyll a and b. They need less light than plants so you will not be able to outcompete algae by fiddeling around with the light.


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## defdac (Dec 28, 2003)

> looking for a magic number to solve all the problems has never worked in the past


I don't do magic numbers.. If you think any of this is magic, this is not the thread for you.


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## aquanut415 (Jan 21, 2006)

thats exactly what you ARE doing. the fact you don't know it makes the rest of your arguments that much less interesting.

i also don't think taking specific pieces of data from various studies is a very compelling way to make an argument.


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## defdac (Dec 28, 2003)

No I don't do magic numbers, unless you think PAR is magic.


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## lauraleellbp (Feb 3, 2008)

> 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
> ...





plantbrain said:


> 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.





> 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,





plantbrain said:


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





plantbrain said:


> So here's the test, one I did on a 55 Gallon tank back, who knows, 15-20 years ago now, but I did not do dry weights, just look at the plants etc and judge from there.
> 
> +++++++++++++++++++++
> 
> ...


I think I'm missing something somewhere, and primarly what I'm struggling with is an application issue. Application in relation to plant pigments, since PUR as I understand the definition seems pretty tied to plant pigmentation. 

I'm struggling to figure out how PUR readings could be "standardized" in such a way that it would be a useful measurement for people growing plants when there is such a variety in plant pigmentation.

It seems to me like the results of the experiement that Tom suggested above could yield dramatically different results depending on the pigmentation of the plants selected for the study (for example, red plants vs green plants).

Can PUR be measured/calculated any other way than by applying a mathematical model that begins with PAR?

Or am I missing something?


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## defdac (Dec 28, 2003)

> It seems to me like the results of the experiement that Tom suggested above could yield dramatically different results depending on the pigmentation of the plants selected for the study (for example, red plants vs green plants).


Yes that is probably correct, but I don't know. So I agree it would be very interesting to do such a study with some different pigmented plants.



> Can PUR be measured/calculated any other way than by applying a mathematical model that begins with PAR?


The "mathematical model" is the photosynthetic action spectrum and that have been derived by measuring oxygen production from alot of plants for each frequency between 400 and 700 nm. It's an average for alot of plants.

So even if you get different action spectrums from different pigmented plants my *guess* here is that it will not be radically different so the PUR-efficiency measure for a bulb would change much. But it's an educated guess - mostly based upon all plants have chlorophyll a and b and they are the main light harvesters which are sensitive for blue and red.

So a calculated PUR-efficiency for a bulb will be an average for alot of plants. That's not bad either.


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## lauraleellbp (Feb 3, 2008)

defdac said:


> So a calculated PUR-efficiency for a bulb will be an average for alot of plants. That's not bad either.


But no one's done that research yet that we know of, correct?

Most of the research done so far has been on SW algaes?


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## defdac (Dec 28, 2003)

Don't exactly know what type of research you are meaning, but there are many measured action spectrums out there:
http://www.google.se/search?hl=en&q=photosynthetic+action+spectrum+-phytoplankton+-algae

The one I use is done for Elodea, but I also have one for Zooxantheallae in my calculator. They are a bit different but yields about the same segmentation of PUR-efficiencies in bulbs (the bulbs that are efficient for growing plants are also efficienct growing corals).
(The beta calculator is here: http://82.183.138.227/GTKTest/GTKTest.html )


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## defdac (Dec 28, 2003)

This is an interesting thing with the Apogee flux meter:








It seems less exact than my calculations and any spectral distribution from a bulb manufacterer...

Actinics would for example get very low PAR-values with the Apogee meter.


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## addo (Apr 20, 2007)

I have to shake this thread to life, i want to know how it ends LOL


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