Measuring PPF? (and Apogee question)

[ba]

Hi,

I need a method to find the ppf of MH HID. I would like to find a relatively inexpensive quantum meter that takes measurements from the whole PAR range.

I read the article (1) by Dana "Li-Cor vs. Apogee" and the resulting thread (2):

1) http://www.advancedaquarist.com/2005/7/review
2) http://reefs.org/phpBB2/viewtopic.php?t ... light=ppfd

I have some questions:

Dana wrote:
Knowing that the Apogee meter underreports PPFD in most cases...

Is it known what % it under reports? Would the % of error be the same for air measurements?

Dana wrote:
It is possible for high wattage metal halide lamps to produce more radiation than the Apogee meter is capable of reporting....[snip]...There are some options...[snip]...use a small piece of non-metallic window screen. Compare readings in a lower light environment to arrive at the appropriate correction factor for use in extreme light conditions.

Could someone explain how to do this in further detial?

-----------------------------------------------------

I was going to buy the basic Apogee quantum meter (around $170.00) but it doesn't measure 650-700nm range and weights blue too heavy and only measures up to 1,999 µmol which is not high enough. Then I found the LI-COR meter, it's perfect but I think it's over $1,000 and I can not afford that.

I am ok with close accuracy, so would the Apogee be what I should use? (I'm a bit concerned about the 650-700nm range not being measured)

cheers

 

[Len]

:welcome:

I own the Apogee. It's a decent tool, but I would not call it accurate. As you know, it weighs certain spectrum differently, so the percentage of underreporting will differ depending on the spectral plot of the bulb.

I've not found a MH that maxes out my Apogee when the measurement is taken at 12". I'd imagine putting it right next to the bulb would max it out though. I'm not totally clear on what Dana Riddle is recommending, but I suspect it means you get a semi-translucent screen and take the measurement of a lower light source with and without the screen. Once you figure out the multiplication factor to apply to the measurement with the screen in place (measurement without the screen divided by the measurement with the screen), you can then use the screen on your higher output light sources (e.g. metal halides), take measurements, then use the derived multiplier to figure out the true reading.

I personally would just take the measurement further away from the bulb. It's a more pragmatic measurement anyhow, and light falls off fairly predictably over distance.

 

[Anonymous]

Dana's article came out prior to the release of the new "blue" sensor. Email Apogee direct as many people aren't even aware of the new sensor

 

[ba]

Hi,

Thanks to both of you for that info.

> Welcome to reefs.org

Thanks

> new "blue" sensor

Is this what you are referring to?


I can deal with the under-reporting of 400-500nm but the non-measurement of 650-700nm makes Apogee a non-starter for me as those 50nm are important (especially for chlorophyll A). Is there any other method to measure/estimate PPF in 650-700nm? Or is there a good place to buy a used Li-Cor?

the sensor underestimates the 400 to 500 nm wavelengths (blue light), overestimates the 550-650 wavelengths (yellow and orange light), and has little sensitivity above 650 nm (red light).

Thanks!

 

[ba]

Hi,

Has anyone tried the quantum meter from specmeter? It looks exactally like the Apogee, except the specmeter looks like it's intended for horticultural use. The Specmeter is $179.00 and the Apogee is $199.00:
http://www.specmeters.com/Light_Meters/ ... Meter.html

I couldn't find any tech info about the specmeter quantum meter so I may email them it turns out it is not the same one as the Apogee.

thanks

 

[Len]

I have the old Apogee (about 10 years old). Maybe it's time I look at either the new one or the Specmeter. FWIW, the Specmeter looks awfully like my Apogee. I wonder if it isn't simply a rebranded Apogee (or whoever actually manufacturers the Apogee unit .... China probably ).

 

[ba]

Hey Len,

I just emailed specmeters for more info as I couldn't find the specs:

My email:

Hello,

I am interested in your basic quantum meter and I have a few questions:

-Does your meter measure the whole PAR range?
-Does your meter weigh all wavelengths equally?
-Does your meter measure using the "cosine response"?
-What is the maximum µmol measured by your meter?
-Is your meter an Apogee? That is, are you distributing the Apogee meter? (I ask as your meter looks exactly like the Apogee)

Best regards,
Mr. Hammen

While the specmeter 'basic' meter may be the same one as the Apogee 'basic' I definitely don't think it offers the same spectral response as the Apogee 'blue'.

 

[Anonymous]

Apogee OEMs FWIW. Several companies are rebranding, like General Hydroponics. My bet is the Specmeter is just an Apogee OEM