# Comparison of quantum PAR sensors



## naoki (Apr 11, 2019)

I happen to find this document by Apogee comparing many different quantum sensors (probably they covered all available ones):

https://www.apogeeinstruments.com/content/Comparison-of-Eight-Quantum-Sensor-Models.pdf

Some results are quite interesting (e.g. how Hydrofarm lied about the spectral response).

Also, here is another comparison of Apogee, Li-Cor, and Seneye (which might be ok for reef aquarium, but not for plants):


BRS also have 7 day rental for Apogee (MQ-510 and MQ-210). These have the calibration factors for underwater application, so to use them for plants, you need to divide the PPFD values of MQ-510 and MQ-210 by 1.32 and 1.08, respectively (info about Immersion Effect Correction Factors).


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## TyroneGenade (Apr 11, 2019)

Fascinating study. Horrifying revelations about the li for and apogee. All that research funding possibly wasted... Sadly, I don't expect a rush of extractions and corrigenda. 

thanks for posting.


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## terryros (Apr 11, 2019)

Naoki, it is very tempting to rent the MQ-510 to make my measurements more accurate. Obviously, my current Apogee meter is undermeasuring PPDF because of the decreased sensitivity at both ends of the PAR spectrum. Since the MQ-510 seems to be specifically for underwater use, I think you are saying we could still use the meter/sensor and reverse the correction factor for underwater by dividing the value by 1.32?


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## naoki (Apr 12, 2019)

Terry, is your grow light deep-red (> 660m) dominated? If not, the error with Apogee 100 series is pretty small (about 10% or less) as shown in here).

Yes, MQ-510 can be used. They have MQ-500 and MQ-510. They differ in the multiplier. So if you dived the value by 1.32, MQ-510 gives the same number as MQ-500. I would think they should have made a switch to change the multiplier. WIth SQ-520 (USB connection to computer), which I have, the software can change the multiplier for under water and above water.


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## terryros (Apr 12, 2019)

My LEDs are ALT “true white” and “natural white”. Maybe it is reasonable to just conclude that the values I get from the 100 series are just low by 10-20%, depending on which end of the PAR spectrum they might favor? But, it is tempting to spend $50 for a week to verify. If I do it, I will post.


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## coronacars (Apr 14, 2019)

I have both the Apogee MQ-500 and the Lighting Passport. I prefer the Lighting Passport it costs a lot more, but also gives me ton of additional features. I'm selling my Apogee MQ-500 if anyone is interested.


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## terryros (Apr 21, 2019)

I did rent the Apogee MQ510 for one week from Bulk Reef Supply for $50, which was easy. I am glad that I did! It turns out that the drop off in spectrum sensitivity at both ends of the PAR spectrum was important for my ALT LED bulbs. In particular, the ALT bulbs have a strong peak in the blue part of the spectrum that was being partly missed by my series 100 meter. The MQ510 reading needs to be divided by 1.32, which is the correction applied by the meter for underwater readings. When this was done, with four different versions of ALT LED bulbs, my series 100 readings needed to be multiplied by 1.5 to equal the full spectrum reading from the MQ510. I have been delivering substantially higher photon flux to my orchids than I thought. The full spectrum readings are more in keeping with other published literature for Cattleyas and Phalaenopsis. I would suggest LED orchid growers consider renting this meter for a week to check setups if spending $500 for the meter is unreasonable.


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## naoki (Apr 22, 2019)

Wow, that is a big difference from the expectation (from Apogee website). Is your Apogee 100 series electric calibrated or sun-calibrated?

For people who are interested in buying Apogee 500 series, BRS and other reef aquarium suppliers have black Friday sales. I could get SQ-520 (USB) for $310 last year. But as terry mentioned, you can rent it and make a calibration factor for a cheap light meter (fc or lux meter is enough for this purpose) for the particular light source.


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## terryros (Apr 23, 2019)

I did not sun-calibrate the 100 series (although I have seen the variables needed for the calculation). It is just out of the box in “ELEC” mode. When you see the spectrum of the ALT LED bulbs with a very strong blue peak, it is easy to see why the fall-off in sensitivity at each end of the PAR spectrum causes the 100 series to undermeasure the photons.

I might try and do the sun calibration later this spring when the sun is up high where I live. That would help clarify whether my meter is perhaps inaccurately calibrated. For now, with my bulbs, I just use the 1.5 correction factor to get my peak photon density.


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## naoki (Apr 24, 2019)

Terry, I just wanted to see which column of the Apogee correction table applies to yours (i.e. SQ-110 vs SQ-120 columns), and I didn't mean that you need to do sun calibration. It is interesting that if you look at the Royal Blue LED (around 450nm), the correction factor is supposed to be only 1.12. The blue peak of all phosphore based white LEDs are at this range (except a few exotic LEDs). So I expected the blue peaks shouldn't influence the reading of Apogee 100 series. This is consistent with BRS video because the LEDs for reef aquariums which they used are very heavy in blue. On the other hand, Deep Red (660nm) requires a big correction factor (e.g. Illumitex RB LED). So I'm rather surprised to see your results. Did you see how different the values are with other light (sun light, white CFL etc)?


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## terryros (Apr 24, 2019)

No, and I think that is why I need to do the sun correction procedure. I should have taken both meters outside just for the fun of it, but the weather wasn’t great so I didn’t do it. I think I have the location and altitude data to do the sun correction measurement, but will wait until the sun is more over head. Your logic is arguing for an issue with my MQ-100 meter. If the sun correction procedure shows the meter is reading correctly, then my 1.5 difference can only be related to spectrum from the ALT bulbs that the MQ-100 isn’t measuring. I am eager to find out which!


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## ElleBlyth (Jan 14, 2021)

Hi....PPFD is the only thing that is important, however to make it mean something you need a similar area... The explanation being is that PPF is generally the center estimated... In any case, when your light is the size of a space it is kinda trivial. PPDF discloses to you how much light is arriving in the zone.


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