# Par Meter Question



## Hoppy (Dec 24, 2005)

The Quantum PAR meter that we use can also be obtained as just the sensor, and any milivoltmeter used as the readout for it. That makes it quite a bit cheaper, but a lot less convenient to use. The Kipp and Zonen model you referenced is intended for use out of water, obviously, and it doesn't have quite as good a response curve as the Quantum device, based on the chart they show. It might not be possible to use the K&Z model underwater without ruining it. I couldn't find any information to judge that by. Nor did I find a price for it.


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## outcast (Jul 4, 2007)

how will just the sensor be less convienient? Quite a few people own Multimeters


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## JDowns (Mar 6, 2008)

The other problem besides submergence in water, and the responce curve, would be that it is calibrated for sunlight and not electric light.


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## Hoppy (Dec 24, 2005)

outcast said:


> how will just the sensor be less convienient? Quite a few people own Multimeters


The Quantum meter we purchased is extremely easy to use. You just turn the knob to sunlight or artificial light and start taking data. With a separate meter, you have to plug it into the meter, after you modify its electric leads, which are always "hot" if there is any light on the sensor, select the right scale on the milivoltmeter, assuming you remember which one is the right scale, then multiply the voltage by the conversion factor to get PAR. This isn't exactly a deal killer, but just noting that the Quantum meter is extremely convenient and foolproof. If the price for that sensor is down around $100 and it can be submerged in water, it would be a good deal.


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## kid creole (Dec 25, 2008)

Hoppy said:


> The Quantum meter we purchased is extremely easy to use. You just turn the knob to sunlight or artificial light and start taking data. With a separate meter, you have to plug it into the meter, after you modify its electric leads, which are always "hot" if there is any light on the sensor, select the right scale on the milivoltmeter, assuming you remember which one is the right scale, then multiply the voltage by the conversion factor to get PAR. This isn't exactly a deal killer, but just noting that the Quantum meter is extremely convenient and foolproof. If the price for that sensor is down around $100 and it can be submerged in water, it would be a good deal.


I'm calling BS on the Quantum if you have to select natural or artificial light. Why? What does the knob do?


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## outcast (Jul 4, 2007)

considering im an electrician, it doesn't sound like much of a headache. Looked into it and they sell for $139 US (+10% for outside US)

The Product i am looking for is the SQ-120 from Apogee (theres a sensor for each electric and sunlight), theres an amplified version as well

Some more facts on the sensor:

Calibrated to exactly 5.00 μmol m-2 s-1 per mV (easy conversion for using a Digital multimeter)
the cable is 3meters long (9feet), ends are your standard pigtail, just a matter of buying the ends for the cable ($2 ?).

There are correction factors you need to apply the closer your source is to sunlight, ie, flourescent = 0%, MH = 2% lower, generally not enough to make it a big deal. The meter itself allows you to choose the calibration on the dial, other than that, its a digital multimeter, nothing more.

So there we have it, Quantum Sensor that works with your digital multimeter (can pick up a cheap one for $10), have it set to millivolts. It will set you back $139 rather than $300. Sure theres room for error, but if you cant multiply by 5, then i hate to see your fish tank's Dosing regime.


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## JDowns (Mar 6, 2008)

kid creole said:


> I'm calling BS on the Quantum if you have to select natural or artificial light. Why? What does the knob do?


Well the reason most likely would be you have the option for the sensor being either calibrated for sunlight or electric light both require different radiation standards. Another benefit if I'm not mistaken is that the meter compensates for this difference. If the sensor is calibrated for electric light and is used in sunlight the reading is 8% low and 8% high if the sensor is calibrated for sunlight and used for electric light. The meter does this math for you to give you the correct reading. If you were to take readings via a multimeter you would have to multiply the mv input by 5 and then do the appropriate percentage increase/decrease.

The other benefit of the meter is its ability to store up to 99 readings.


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## outcast (Jul 4, 2007)

for most hobbyists though, they'll be using Flourescent or MH, in which case an Electric calibrated sensor would suffice, MH will be out 2% but in a tank its only a matter of a few PAR at most, whereas Flourescent will be fine. If it were to be a purchase for a club, by all means get the meter, but for those who are cash strapped and have a wife who doesn't let them go talk fishies and plants with others, the more affordable option seems to take the cake


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## JDowns (Mar 6, 2008)

outcast said:


> The meter itself allows you to choose the calibration on the dial, other than that, its a digital multimeter, nothing more.


 
Well thats not entirely accurate. 

*Each meter can store up to 99 manually recorded measurements. In automatic mode, measurements are made every 30 seconds and averages are stored every 30 minutes. Daily totals are also calculated and the past 99 days are recorded.*

That makes it a little bit more than just a cheap multimeter.

But for the general purpose in this hobby yes a multimeter with an appropriate joining method and multiplying by 5 would be more than adequate. I made two seperate soldered molex connectors, one for a multimeter and one for a labjack.


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## outcast (Jul 4, 2007)

i suppose those functions make it differ from the standard multimeter (although through work i've got access to similar meters sans par sensor). Doubt most of us would use those functions except the true die hards, seems to be useful mainly for plant placement and fixture height.


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## kid creole (Dec 25, 2008)

JDowns said:


> Well the reason most likely would be you have the option for the sensor being either calibrated for sunlight or electric light both require different radiation standards. Another benefit if I'm not mistaken is that the meter compensates for this difference. If the sensor is calibrated for electric light and is used in sunlight the reading is 8% low and 8% high if the sensor is calibrated for sunlight and used for electric light. The meter does this math for you to give you the correct reading. If you were to take readings via a multimeter you would have to multiply the mv input by 5 and then do the appropriate percentage increase/decrease.
> 
> The other benefit of the meter is its ability to store up to 99 readings.


I've made the assumption that this works like a UV sensor. You have a solar cell in combination with a high pass and low pass filter to measure the radiation in a range of wavelengths. Let's say this range is 1000 to 1500 nm. If this is the range of light available for photosynthesis, it wouldn't matter if it was all 1001 or 1499 nm, and calibration would be independent of source.


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## outcast (Jul 4, 2007)

take a peak at http://www.apogee-inst.com/quantumsensor_techinfo.htm

may have your answer


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## mistergreen (Dec 9, 2006)

OH! cool. I'll just need to buy the sensor. I have a microprocessor laying around and then have the signals go to my computer... From there, I can do the math to the input signal and BAM!

Future DIY project.


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## mistergreen (Dec 9, 2006)

outcast said:


> take a peak at http://www.apogee-inst.com/quantumsensor_techinfo.htm
> 
> may have your answer


What's the Model AL-100 ($29)? I can't find a spec for it. Wonder why it's so cheap?


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## kid creole (Dec 25, 2008)

outcast said:


> take a peak at http://www.apogee-inst.com/quantumsensor_techinfo.htm
> 
> may have your answer


That helps. Looks like it all has to do with the spectral response and correlated with guesses about the spectrum of the source. This seems appropriate to me for hobby use. I couldn't have sold NASA on this, but it looks like a good approximation. I do like the relative response greater than 1. What exactly does that mean? 

I would guess you're looking at an accuracy of something like ±20% in the real world, which is much better than guessing about wattage, reflector types, and fixture height.


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## kid creole (Dec 25, 2008)

If you want to do one of these on the cheap, all you need is any old silicon solar cell. You'd have to use something as your baseline, but there is a lot you could do with that.


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## JDowns (Mar 6, 2008)

Here was a write-up  with a comparision of the Apogee with the much more expensive Licor.

±20%?? Where do you come up with these numbers?

*Our quantum meters are accurate to within about ±5 % for common light sources. *


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## plantbrain (Dec 15, 2003)

outcast said:


> considering im an electrician, it doesn't sound like much of a headache. Looked into it and they sell for $139 US (+10% for outside US)
> 
> The Product i am looking for is the SQ-120 from Apogee (theres a sensor for each electric and sunlight), theres an amplified version as well
> 
> ...


No, it's 200$ *if you do a group buy,* now you are 60$ difference, and it's all in one, no DIY, and it looks decent.

Regards, 
Tom Barr


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## plantbrain (Dec 15, 2003)

JDowns said:


> Here was a write-up  with a comparision of the Apogee with the much more expensive Licor.
> 
> ±20%?? Where do you come up with these numbers?
> 
> *Our quantum meters are accurate to within about ±5 % for common light sources. *


 I used a LiCOR 193 spherical with a LiCOR 1400 meter and tied the Apogee meter probe to the same depth pole we use at the lab, we ran from 0- to 200cm depth with less than 1% error between them at every 10cm depth in columns with Milfoil using 400W MH's. The probes where spaced about 8cm apart. The Lab tech and a researchers all saw this when we compared them

So where is this 20% from, guessing and speculating?
Do you have access or own either of these light meters?

I do :icon_idea

For water, the LiCOR spherical probes are about as good as they are going to come for light measure in water. 

I think perhaps for deeper waters than say 200cm and perhaps for natural sunlight, there's bound to be more variation, but not for aquariums.
I've not seen any private planted tanks at 200cm depth to date.

In the above write up, the bulbs where compared and bulbs are not perfect either.
They also only had used a single 18cm depth for measurements.
I used a gradient from 0-200cm.
I also used real tanks with plants and other items, like algae on the walls etc, not a nice white bucket.

Reflectance becomes an issue and depth does as well(or was speculated to be a major issue in aquariums that where 18" or deeper).

This addressed that, also, we well know that as you increase your distance away from the MH' bulbs, the spread becomes much more even, thus getting around that major source error discussed in the article above.
Reef folks want max intensity, or at least think/assume that is the critical issue, so they want to lower those massive lights right above the coral. However, for planted folks, we do not assume or desire that much intensity, we are more interested in good even lighting, thus can place the light farther away and get more even PAR over a surface area.

This is a different question than what the Reef folks wanted to know, but likely applies well to them and could explain it's not about getting the most PAR vs even light distribution(which is the case in natural habitats more so in reefs than FW systems I'd argue).









Regards, 
Tom Barr


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## kid creole (Dec 25, 2008)

JDowns said:


> Here was a write-up  with a comparision of the Apogee with the much more expensive Licor.
> 
> ±20%?? Where do you come up with these numbers?
> 
> *Our quantum meters are accurate to within about ±5 % for common light sources. *


What's a common light source? A 5k bulb? A 10k bulb? 

Years of work on precision measurement of UV radiation for the qualification of space equipment has given me the ability to look at something like that and make up a reasonable number. With the best calibrations equipment in the world (seriously, the best) and a fat budget I had a tough time putting together an experiment that was ±5%. If I could barely do it in a lab, I doubt you can do it in your living room.

The biggest thing that I found to be a limiting factor in these experiments was that much of data is "inferred".

I will say this, things start to get really easy around 400nm, whereas I was most interested in the 180nm to 200nm.

My claims of 20% are directly to related to guessing. Here is the biggest guess, from the Appogee site: "Fortunately, common light sources are mixtures of colors and the spectral errors offset each other."


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## mistergreen (Dec 9, 2006)

kid creole said:


> If you want to do one of these on the cheap, all you need is any old silicon solar cell. You'd have to use something as your baseline, but there is a lot you could do with that.


hmmm. I doubt it's just a simple solar cell. I have a bag of solar cells and diodes. The value alone, tells me it's something else.

I'll have to look at their technical specs if there is one. Or can somebody who has one, open theirs up and take a picture?


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## plantbrain (Dec 15, 2003)

My claims are based specifically on what are used within light, photosynthesis of aquatic plants(400-700nm), and comparing LiCOR's meter and various probes to Apogee's. You'll have to pick apart the PAR sensor and meter data from LiCOR to do so and use the same criteria. I've shown they are statistically the same:icon_idea

In otherwords, I chose the LiCOR as a reference to compare the Apogee to.
LiCOR has spent decades comparing various issues with light and has a long track history in Plant Science. 

If you have something that is water proof, and easy to make, most folks could do for 200$ or less total, then by all means, but if the probe is 139$+ ship and the entire meter with a group buy is 200$, I think it will be a tough sell to the aquatic plant community.

The Apogee is very easy to use right out of the box.
Cost can be shared and the meter can be used amongst several users.

Then you are at 30-50$ for 4-7 folks.:icon_idea

Now that makes more sense economically.
It's not something you will use daily, etc, so it's a only used a few times every few months.

Regards, 
Tom Barr


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## kid creole (Dec 25, 2008)

mistergreen said:


> hmmm. I doubt it's just a simple solar cell. I have a bag of solar cells and diodes. The value alone, tells me it's something else.
> 
> I'll have to look at their technical specs if there is one. Or can somebody who has one, open theirs up and take a picture?


I don't know what's simple about a solar cell. This is a particular solar cell with a max wavelength of 700nm, but any old solar cell would be fine under tank lights because the majority of the light is in the plant growing range.


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## JDowns (Mar 6, 2008)

I have a hard time believing that Licor could get away with publishing false data on their instruments. Especially given that a simple search "LI-COR 193 NASA" will result in numerous peer reviewed studies where that instrument is used, and/or other LI-COR instruments. It doesn't take long to see that LI-COR has a very broad use across scientific fields, and a stellar reputation. Now if one takes a LI-COR and actively compares against an Apogee and is within 1%, well I'm gonna need alot more than blind data to convince me that both manufacturers are incorrect.


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## outcast (Jul 4, 2007)

just a question tom where can you get the full meter for $200, their site quotes $299 :/


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## Hoppy (Dec 24, 2005)

http://www.barrreport.com/general-p...meter-228-us-shipped-via-paypal-payments.html is the last I have seen on the subject of group buys of the Quantum meter. I'm sure there is more information on some of the reef forums.


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## kid creole (Dec 25, 2008)

JDowns said:


> I have a hard time believing that Licor could get away with publishing false data on their instruments.


There is really no such thing as false data, and I'm not accusing them of lying. I'm not disputing their usefulness. I'm just saying that the electric light switch is bull. That's their way of saying that they know it's off by at least 10% depending on the situation. I know this, because I'm familiar with their struggles. The difference is I had tougher customers. All we have to look at is their marketing materials. That's appropriate, since this site is dedicated to planted tanks and the cash outlay for one is $300. Their chart on the spectral response clearly shows the shortcomings of the meter, and it shows the need for their algorithm.

This equipment is looked upon by some as the holy grail of light measurement, and I've always doubted it. 

What you should know is that this equipment can not take a measurement from tank A and then be used to extrapolate results in tank B when there are totally different conditions within 5%. My GUESS is that you are probably talking ±20% when you go to separate tanks with different lights and different meters.


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## plantbrain (Dec 15, 2003)

kid creole said:


> This equipment is looked upon by some as the holy grail of light measurement, and I've always doubted it.
> 
> What you should know is that this equipment can not take a measurement from tank A and then be used to extrapolate results in tank B when there are totally different conditions within 5%. My GUESS is that you are probably talking ±20% when you go to separate tanks with different lights and different meters.


Then all the research done is off by 20% as well.......... since the vast majority of the biologist all use LiCOR and many use electric light, which the comparison that I made was with and under, as well as MH's, I recently used the same paired testing method to comp-are my T5's and PC light sat home, they are virtually identical in the PAR reading with the LiCOR.

I will not dispute the fact that PAR is NOT some Holy Grail. However, no one ever stated it was. Light and it's measurement is a trade off.

PAR is, by and large the best thing aquarist can use for now based on cost. 200$, shared pricing etc, the parameter itself, comparing it to a peer reviewed standard for our specific case, growing plants indoors under artificial light etc.

Plants also adapt readily to stable light(unlike sun which is a moving changing target) and this is often species specific. This can be addressed with monocultures in test, replication etc. Still, depending on the methods, we can see good variation, perhaps due to meter reading in light, but we have many other parameters that also correlate with accurate light readings in plant photosynthesis, and by running statistics, we can be confident that the light is *independent and similar between treatments.
over a confidence level*

I've done this stuff and we taught a lab on the subject for a couple of years using electron transport chain. The correlation was extremely accurate(p=0.02) using spinach and LiCOR light meters at different light intensities.

Go figure.

Biologist look at other things for comparative support, not one thing and one measurement....if at all possible, it's good science to have many supportive methods and results to compare/test. I know what plants do with light, this can be measured quantitatively and correlates really well with the light meter readings. Where's this 20% difference?
Why don't we see it with the electron transport chain also?
Why is this not seen in field and greenhouse growth test also?

Show me the results/methods that support this guess of yours in the context of plants in artificial light.:icon_excl

Regards, 
Tom Barr


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## kid creole (Dec 25, 2008)

I don't understand if you are talking about the meter's repeatability or its accuracy.

This chart tells the whole story.


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## JDowns (Mar 6, 2008)

To be thorough here. The spectral response from LI-COR. Now if the Apogee is within a 1% variance when measuring side by side, I'm still not sure where we can guess a 20% up or down, now as far as environmental and hardware variances, quite possibly. Different bulbs, age of bulbs, turbidity, height, reflectors, ballasts, etc, will all play a role. But as far as the calibrated sensor itself, I'm still not convinced. If Apogee uses a calibration standard, which I'm sure they do, then all sensors should be closely equal.


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## kid creole (Dec 25, 2008)

JDowns said:


> To be thorough here. The spectral response from LI-COR. Now if the Apogee is within a 1% variance when measuring side by side, I'm still not sure where we can guess a 20% up or down, now as far as environmental and hardware variances, quite possibly. Different bulbs, age of bulbs, turbidity, height, reflectors, ballasts, etc, will all play a role. But as far as the calibrated sensor itself, I'm still not convinced. If Apogee uses a calibration standard, which I'm sure they do, then all sensors should be closely equal.


My point specifically stated "in the real world." You hold your meter in your tank with your lights, I do mine, and then we say, "I also have X amount of light." That is the main question being asked and that measurement *does* include all the things you mention. I have seen over and over again where a new person asks what kind of light to get, and the response is that you can't tell without a PAR meter, and you can't go by W/gal. The new person is left without an answer and some of the most experienced among us have avoided giving advice to a novice. And not only did they not give advice, they told them that they needed to have access to a $300 toy to gain access to an already expensive hobby.

I hope this conversation has been intereresting for somebody, because I feel like this thread has been work for me and that sharing my expertise in this subject matter has been entirely unappreciated.


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## JDowns (Mar 6, 2008)

I completely agree. The only way to be certain of the readings from tank to tank is with par readings in hand. Only as more data comes in from those with par meters will some sort of accuracy of advice be had. The one thing that appears to hold true is that the drop off in relation to square of distance applies. Hopefully as more data comes available then maybe more accurate advice can be given from tank to tank then the wpg rule. ADA data may have to stay seperate here since that will completely throw everything out of whack given their reported low light levels when compared to other manufacturers with equal wattage.

Sorry theres been some confusion here. Its two completely different animals for the accuracy when comparing environments as to the sensors manufactured accuracy. Sorry that confusion caused you to feel unappreciated.


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