# PAR and PAR meter query



## Soilwork (10 Nov 2017)

Hi all.

Does anyone have PAR readings for the chihiros A series 60cm?

If not does anyone loan out their PAR meter across the U.K.

I’m not paying £400 for the Apogee as tempting as it may be. 

I’m really curious what these lights are really putting out. 

Cheers 

CJ


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## Zeus. (10 Nov 2017)

*ADA | WASMAS | ZETLIGHT | TWINSTAR | CHIHIROS | LED PAR DATA [The power of light]
*
Been looking into getting an apogee MQ210 myself had a quote from cambells of £382 plus £16 deliverly plus VAT , which works out at £477.60 Not cheap and cant  get an import either


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## Edvet (10 Nov 2017)

Didn't Seneye have an more affordable alternative?


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## Soilwork (10 Nov 2017)

Zeus. said:


> *ADA | WASMAS | ZETLIGHT | TWINSTAR | CHIHIROS | LED PAR DATA [The power of light]
> *
> Been looking into getting an apogee MQ210 myself had a quote from cambells of £382 plus £16 deliverly plus VAT , which works out at £477.60 Not cheap and cant  get an import either



Thanks for this. I may have to reign the light in a touch.  I’m running 2 x A series 60cm at about 18inch on level 5.  

I got quoted the same price forgot to factor in VAT which makes for an even uglier price.


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## Zeus. (10 Nov 2017)

Edvet said:


> Didn't Seneye have an more affordable alternative?



Read a review somewhere where the MQ210 came top and I think it did say the only one worth really getting 



Soilwork said:


> I got quoted the same price forgot to factor in VAT which makes for an even uglier price.



YES and I can see one on Amazon here from the US $349 thats £265 on todays rate, but wont ship to UK  same with Bulk reef supply here $375 wont ship to UK


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## Edvet (10 Nov 2017)

Not for underwater but good for testing
https://www.specmeters.eu/quantum-meter.html


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## Zeus. (10 Nov 2017)

Well would like to know the PAR reading under 50cm of water and glass to, Plus in various parts of the tank like under the trident, take the hit and miss out of turning light intensity up and down. Also over the week and the glass covers get deposits on them and the water colours up what impact is it having on the PAR.

Under water PAR meter would just help make it easier IMO


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## ceg4048 (11 Nov 2017)

Hi Zeus,
               Using PAR data in air still provides good data. Reflections from stones, substrate, neighboring plants and even from the underside of the water's surface do have an effect but some are additive while others subtractive.
I would not really worry too much. The numbers won't be too far off and will be valuable.

The PAR meter Edvert points to will work fine if you lower the water level and survey across the tank's dimensions. It's just not as convenient as a submersible probe, but it's also not as expensive.

Still, €200 is a lot to pay for what is essentially a garage door opener. 

Cheers,


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## Zeus. (11 Nov 2017)

Hi Clive

Yes the one Edvert points out would be useful, however the apogee MQ210 has two advantages, one you pointed out as its more convenient being submersible OFC. The other is I would be able to link the PAR sensor direct via USB cable to my siemens Programmable Logic Controller (PLC) which would read the analog voltage produced by the sensor, which is the given PAR at the sensors position, which by a little software programing I could have it automatically adjusting My Kessil A160s intensity and/or spectrem output direct. Well OTT OFC, but would be nice also.

But yes its the cost that puts me off ATM esp at UK prices. Its the price that puts many of us off, but whilst sales of PAR meters is low prices remain high


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## Cactusface (23 Nov 2017)

Hi,
    Is not a PAR meter just a fancy light meter? Perhaps not, perhaps it light quality and not quanty! Making a waterproof meter would be failry simple (or you could measure the 3 primary colours). You could then at least make comparative readings from the bottom of the tank/s. Sorry my photo days still work in foot-candels, etc. Must give it some thought and warm the soldering iron up.  Let's have your thoughts too!! could it be done, would it be useful?


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## ian_m (23 Nov 2017)

Cactusface said:


> Is not a PAR meter just a fancy light meter? Perhaps not, perhaps it light quality and not quanty!


Yes but no. The PAR sensor has a particular spectral response that matches the spectrum better used by plants. A typical light sensor might respond to UV or Infrared where as a plant doesn't make use of these wavelengths.

Below graph of Apogee Instruments PAR meter spectral response. No response in UV or Infrared regions.


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## Cactusface (23 Nov 2017)

HI,
    UV and IR can be filtered out, or find a sensor that don't react to them....  Vishay are OK! https://www.vishay.com/photo-detectors/ambient-light-sensor/   I still think there's something worth trying??  Even if you only got relative reading from different tank vertical sizes. Some lights emit very little UV or IR, take a look at Vishay's range of LEDS (or any you can get data on).


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## ceg4048 (23 Nov 2017)

Cactusface said:


> HI,
> UV and IR can be filtered out, or find a sensor that don't react to them....  Vishay are OK! https://www.vishay.com/photo-detectors/ambient-light-sensor/   I still think there's something worth trying??  Even if you only got relative reading from different tank vertical sizes. Some lights emit very little UV or IR, take a look at Vishay's range of LEDS (or any you can get data on).


Unfortunately it is not a matter of simply filtering out IR and UV. The response characteristics of the chlorophyll has specific characteristics at each wavelength from 400-700 nanometers wavelength.
Any light meter can be used, as long as you have a correction factor at each wavelength to match the response characteristics of the pigment cells in the plant.

It's this correction factor, or, calibration curve that makes the difference. The meter must take into account what the plants reaction to the excitation is, based on the particular wavelength, so that, for example, at wavelengths between about 500-575 nm, the response is substantially less than at, say, 450nm.

PAR meters have a calibration curve to take this response into account so that as it sees different colors (or combination of colors) the PAR reading will change.




 

Cheers,


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## ian_m (24 Nov 2017)

ceg4048 said:


> PAR meters have a calibration curve to take this response into account so that as it sees different colors (or combination of colors) the PAR reading will change.


PAR meter construction consists of some special filter optics that includes the spectral compensation for the plants spectral absorption, as well as spectral compensation for spectral response of the light sensor. Also includes "cosine" correction for incoming light angles.

From the Apogee Instruments site....
"The waterproof sensor incorporates a blue-enhanced silicon photodiode and custom optical filters with a rugged, anodized aluminum body with acrylic diffuser"

I you dig around on the internet people have tried to make their own PAR sensors, but when checked against a real "big boy" PAR sensor were hopelessly inaccurate to the point of being absolutely no uses other than indicating that there is light present. .


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## ceg4048 (24 Nov 2017)

Hi Ian,
           There really is nothing all that special about the optics in terms of plant response. The lens or lenses have some filtration, but the specialization is more about geometry than anything else, so that for example the light from various angles will hit the sensor properly. That's why there is a "dome" shape to the sensor housing. It's more or less like a contact lens. All that other technobabble is for marketing purposes. Apogee has to compete with high end, high cost PAR meters.

The reason cowboys have not been able to come up with useful home made meters is that they lack the mathematics to develop a proper calibration curve for the sensor they are using.

I was mentioning to someone on a previous thread that even the light meter in a DSLR camera can be used - - but you need to calculate a calibration curve for the meter's response. There is an journal article written by NEC where they developed the calibration curve for a Nikon D300 as a low cost alternative to high end PAR meter for researchers who do not have the budget to purchase the meter. They compared the readings with a high end meter and were within 8% of the expensive meter readings. The Apogee meter is also within 8% of high end meters.

PAR meters, in general, should reproduce an output that is a fair representative of something in plants called the "Quantum Yield".
This Quantum Yield is the ratio of the amount of CO2 that is fixed during photosynthesis to the amount of photons absorbed by the photosystems.
So just look at the graph above. At a wavelength of about 450, for example, since the response has a high peak, fewer photons of that wavelength are required to fix the same amount of Carbon compared to light at the 500-575 wavelength. The Quantum Yield at 450 therefore is higher than it is at 550.

PAR means Photosynthetically Active Radiation. So the meter must take into account how active that particular incident wavelength of radiation is in order to display a correct reading.

Different sensors, whether in a camera or other type of light meter, have a different response than a plant. So one has to calculate a transfer function for that particular sensor in order to calibrate it to a plants response. That means you need to know what the sensors native curve looks like and then you have to determine the transfer function to bring the native curve in line with the curve representing the Quantum Yield.

So if you are good at Calculus and Differential Equations, and if you have a copy of the native response curve for your chosen sensor then you are well on your way to calibrating your home made PAR meter.

This is why Apogee and others can charge that kind of money. It's much less about special optics that it is about the fact that there are only a few eggheads that can figure out the math...

Cheers,


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## tmiravent (24 Nov 2017)

ceg4048 said:


> Hi Ian,
> I was mentioning to someone on a previous thread that even the light meter in a DSLR camera can be used - - but you need to calculate a calibration curve for the meter's response. There is an journal article written by NEC where they developed the calibration curve for a Nikon D3000 as a low cost alternative to high end PAR meter for researchers who do not have the budget to purchase the meter. They compared the readings with a high end meter and were within 8% of the expensive meter readings. The Apogee meter is also within 8% of high end meters.
> Cheers,



HI,
In theory works, if you guess how much you put in each RGB channel. Camera light meters are accurate for this kind of reading.
i also thought that you could use a (rgb light sensor) dslr camera to measure PAR, but...

- Cameras read reflected light, PAR meters take direct readings. Make accurate reading from reflected light is more difficult and less accurate.
- If you want incident light, putting camera inside the tank can be tricky to make some readings. You could have a grey card reference to take more precise readings, maybe...

- Ceg could you give the link to that article? i'm interest in it.
- Any idea about using a RGB sensor, and how much weight for each channel? Maybe R 20% G 10% B 70%? 

- I've made some readings with and apogee along with a normal (cheap) Lux Light Meter. 
  For LED's the conversion factor is quite stable. For RGB light's can have some variation, but once you get the factor for a specific light you have the KEY.
  I think you read the measures that me and Nuno Matos made with a few LED's, not a professional test but enough to give a comparative idea.
  There are a few guides in apogee about using their PAR sensors, even table conversions for some type of led's.

cheers


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## ceg4048 (25 Nov 2017)

tmiravent said:


> - Cameras read reflected light, PAR meters take direct readings. Make accurate reading from reflected light is more difficult and less accurate.
> - If you want incident light, putting camera inside the tank can be tricky to make some readings. You could have a grey card reference to take more precise readings, maybe...
> 
> - Ceg could you give the link to that article? i'm interest in it.
> - Any idea about using a RGB sensor, and how much weight for each channel? Maybe R 20% G 10% B 70%?


Hi tmiravent,
                  I'll have to search for the link on one of my other computers. It doesn't really matter whether you are measuring reflected versus incident. Again, you have to calculate the transfer function to make the correction.

If Apogee have measured some LEDs then that would be great. The user can then make some adjustments as long as the LED brand and model is the same.

Cheers,


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## ceg4048 (26 Nov 2017)

OK, here's the link, but you have to join (free) and purchase the article.

http://www.actahort.org/books/1170/1170_125.htm

Again, it doesn't help if you don't have the camera's sensor response curve.

Cheers,


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## tmiravent (27 Nov 2017)

ceg4048 said:


> OK, here's the link, but you have to join (free) and purchase the article.
> http://www.actahort.org/books/1170/1170_125.htm
> Again, it doesn't help if you don't have the camera's sensor response curve.
> Cheers,


Many thanks Clive!
I'll see if i can get the sensor profile for my camera.
I'll see if i can get something with this.
cheers
Tiago


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## ceg4048 (27 Nov 2017)

Hi Tiago,
              You're very welcome! I hope you have friends in the Mathematics Department at Universidade de _Lisboa_. You'll need to buy them a few drinks and maybe even dinner so they will agree to help you with the maths. 

Cheers,


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## ElleBlyth (14 Jan 2021)

Hello....Your light setup looks nearly identical to my 45p setup.  I took the measurements using the following:
Legs at maximum extension are = 22.5cm to the rim of the tank
Par meter = 1cm below the water line
Total distance = 23.5cm

At the highest setting (7), Par reading were : 190 middle / 132 back / 136 front / 109 left / 117 right
At setting 6, Par readings were: 170 middle / 119 back / 109 front / 92 left / 96 right

The substrate reading were done in the middle of the tank where I had the most room to work with: setting 7 = 100, setting 6 = 85.

I’m not surprised your stems are growing quickly, mine are as well.  It appears that setting 4/5 does a good job of growing plants not algae.   At setting 6 for 2 days, various types of algae showed up…


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