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MQ 520 is not a PAR meter. Right?


Trailermann
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With great excitement, I take home the Club's Apogee light meter, USB version, plug it in and see nothing but strange low numbers followed by umol/m-2s-1.  I guess it pays to read the small print.  Model SQ 520 gives PPFD values, and the SQ 510 reads in PAR numbers (if I understand this right).

Now that I can get these PPFD measurements, I need to know what to do with them.  All my sources of lighting information refer to PAR measurements in the approximate range of 150-400.  I can't find any guidance of desirable light levels using PPFD numbers.  A query on this forum gives a thousand responses to "PAR" and only nine for "PPFD".  Reef Central and Reef2Reef have been no help.

I realize that there is no magic all purpose light level for SPS, LPS, and Softies, but can someone give me a PPFD range that I can start with in setting up my lL Hydra?

 

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Hey Trailermann,

just saw this and now I see what you were trying to get at with your PM.   I would need to look at this a bit more - just took a quick peak at the wiki on this subject- but seems like this is an interesting question regarding definitions and methodologies as to PAR readings (energy vs photons per area per second). As I read it, PPFD (photosynthetic photon flux density) is considered a more accurate reading of PAR by plant biologists (and by analogy coral keepers) due to the quatntum nature of photosynthesis. So, there are PAR measurements made either by energy per area or by photons per area (PPFD) over time,  Both of these are considered measurements of photosyntheticaly active radiation (PAR) by virtue of the wavelengths being measured but the latter more biologically relevant due to the nature of of the measurement and it's more direct translation to the process of photosynthesis.  In short, PPFD is PAR measured by a particular, more biologically translatable method  

Does this make sense? Someone else can step in and rescue me here if I totally miss interpreted.

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Technically there is no such thing as a PAR meter.

PAR refers to the portions of the electromagnetic spectrum of light that plants and algae use for photosynthesis. These meters have filters over the sensor that let the wavelengths of light that plants and algae use for photosynthesis pass through and be read by the sensor.

PPFD is referring to the number of photons hitting a square meter per second.

These meters are measuring PPFD but have a PAR filter in front of the sensor that is rejecting portions of the electromagnetic spectrum that plants and algae do not use for photosynthesis.

A more accurate name for the meter would be:

PAR filtered PPFD meter

Edited by xmas_one
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Thanks for adding on xmas. All that is helpful clarification. I think the thing that adds confusion, and what Trailermann was picking up on, is that the common mechanism of measuring/reporting "PAR" values has evolved somewhat from a purely energy based reading to the more specific photon based measurement (PPFD) so you can find references to PAR that contain different units of measurement. As pointed out here - the SQ520 we have is using the PPFD approach based on its sensor.

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33 minutes ago, Emerald525 said:

So what I want to know is how do you convert that into numbers that mean anything to me. I'm used to thinking about the bottom of my tank maybe being in the 200 range and higher up around 800 to 1000.

That is consistent with what I was getting (well 600 top 200 bottom).  

Edited by albertareef
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@Bicyclebill, we talked about numbers like 500 sounding crazycakes high, so maybe you understand this conversation better than I do and have something to add that might help @Trailermann? I think he just wants to know what kind of numbers he should be aiming for when programming his LEDs, but I use T5 and just accept whatever that gives me, so I have no idea how to help.

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Someone tell me if this is wrong.  First, we should ignore all the scientific goobligook.  Since the "literature" in the aquarium hobby world only talks about "PAR" values (100-400 range, or so), those numbers become our targets.  Now I am learning that the numbers derived from the PPFD measurement are interchangeable for us hobbyists.  Right?  The PPFD numbers supposedly are more accurate, but really who cares.

By the way, Apogee's usb device is giving me readings around 40 at the sandbed and 170 at the top of reef.  Everyone says that the AI Hydra is so powerful that I should only set it about 50% for my 30 gallon nano.  I plan to check with the tech people at Apogee and Aqua Illumination come Monday to figure out what I am missing.

Today has been a real workout, but I am making progress and climbing the learning ladder to boot.

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On April 8, 2017 at 7:46 PM, Trailermann said:

Someone tell me if this is wrong.  First, we should ignore all the scientific goobligook.  Since the "literature" in the aquarium hobby world only talks about "PAR" values (100-400 range, or so), those numbers become our targets.  Now I am learning that the numbers derived from the PPFD measurement are interchangeable for us hobbyists.  Right?  The PPFD numbers supposedly are more accurate, but really who cares.

By the way, Apogee's usb device is giving me readings around 40 at the sandbed and 170 at the top of reef.  Everyone says that the AI Hydra is so powerful that I should only set it about 50% for my 30 gallon nano.  I plan to check with the tech people at Apogee and Aqua Illumination come Monday to figure out what I am missing.

Today has been a real workout, but I am making progress and climbing the learning ladder to boot.

I will be curious as to what they say.  Those numbers do seem low given your setup.  I would be suspicious of the meter except that it gave me numbers that made perfect sense and fit well within my expected range - granted, I don't have anything to compare them to other than experience.  If I get a chance, I will try and compare directly to the other meter so that we can have some independent confirmation.  Cherany - maybe you would want to do this experiment with me some time you have both the meters in your possession?  Don't want to slow anyone down but might be a helpful bit of information for people.  Alternatively, you could try them both on your tank if they ever cross paths again...

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