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DIY PAR meter, Yeah you heard me

299K views 740 replies 110 participants last post by  henrybri 
#1 · (Edited)
*Edit 5-10-13
NOTICE - Firmware has been updated for outdoor lighting.

Final product list:

Photodiode: VTB8441BH
price: $4.660
http://www.alliedelec.com/search/productdetail.aspx?SKU=70219652

Cosine diffuser: 1/8" thickness, 2447 white plexiglass
price: varies, get the sample or buy a big sheet of it.
http://www.eplastics.com/Plastic/Plexiglass_Acrylic_Sheet_Black_and_White
http://www.usplastic.com/catalog/item.aspx?itemid=23681

Basic 16x2 Character LCD - Black on Green 5V
price: $14 but you can get it cheaper on e b a y
http://www.sparkfun.com/products/255

Arduino Uno
price: $30
http://www.sparkfun.com/products/10356
http://www.sparkfun.com/products/11021 (newer model)


Diagram
 
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#29 ·
I plotted your data for the 3 bulb unit on log log paper and got:

The line is the slope if the data follows the inverse square rule. You can see how much scatter there is, and that the close to the bulb readings diverge from the other data. This isn't much different from the data I got from other sources. And, it is why the charts I made are only good for approximating the PAR - you have to measure in your tank with your lights to get really accurate measurements.

If I were to add your data to my charts I would read off data points from that line, not your actual data. That reduces the scatter a great deal, and makes it possible to do this.
 
#30 ·
This is the best I can do, with my sensor
(multiply 8 to the single bulb data)



But as we know I went outside into the sun I'd get 8000 PAR :)

I'm curious to see if the mamamatsu photo diode would give me a better output. I think the Infra Red is affecting the readings.
 
#33 ·
well i thought this would help alot of ppl out and so i thought i would do a lil research to help further this along and if it can be built cheaper than buying one thats great cause we all know how expensive the world of fish keeping is wether it be freshwater or saltwater
 
#34 ·
Hey, guys, I think I found a better photodiode.
http://www.alliedelec.com/search/productdetail.aspx?SKU=9800079#tab=Specs
Cost: $3.19

It's basically, the photodiode I have but it has a IR filter in it and the resulting spectrals are:


But the problem is minimum order is 25... that's like $70+.....
hmmmm. Maybe I can look for a IR filter instead or just call up hamamatsu.
 
#38 ·
All photodiode will output a small voltage when excited by light but the voltage alone is not not good enough in terms of resolution.
So what you do is apply 5Volts through it and gather the output signal from the diode (0V-5V).
Here's a typical setup (photoresistor/photodiode)



the $3 photodiode data you provided does looks better and somewhat matches the $17 photodiode. good find.

I am very interested to find out how everything turns out. I have been reading this thread every day since it started. With Hoppy providing useful input, I have a strong feeling it will turn out good.
Yeah, I think it'll turn out well. I'll go ahead and get the hamamatsu diodes. I think I'll get 5 diodes for that $17. I can sell off the rest to you guys.
 
#36 ·
the $3 photodiode data you provided does looks better and somewhat matches the $17 photodiode. good find.

I am very interested to find out how everything turns out. I have been reading this thread every day since it started. With Hoppy providing useful input, I have a strong feeling it will turn out good.
 
#41 ·
I called up Hamamatsu, wow what a hassle. I think they'll do a background check hah...

And I had to order at least $50 worth. I think I might wind up with 15 diodes so I'll have plenty to share.
hmm......... first they did a 'background check' on you and then asked you to make a minimum of $50 purchase? That is outrageous!
 
#45 ·
Hah, I have no idea what kind of weapons you can make but I know photodiodes are used regularly to detect lasers.. I have heard news stories of people buying cheap components from the States and shipping them to NATO embargoed countries which is a big no-no.

In my research, I found out that a green LED, can read PAR visible light pretty darn well. The spectrum matches up but the resolution is so low I'd need an expensive millivolt meter.


Well, the conclusion on this so far is that the current photodiode is not reliable because it reads Infra Red as well. Different bulbs will have different IR output and will skew the readings. Since a photodiode is the key foundation for this, I'll wait for the correct diode to arrive and restart the calibrations.

I can worry about the cosine corrections and such later. I wouldn't even know where to get a cosine correction filter :)... But from looking at the charts & graphs, I can leave it out and call it 'goodnuff'.
 
#54 ·
I was looking around the web for a company that sells cosine correction filters. I finally found one but prices are a bit steep.

T UV-Vis Internal Diffuser
$67
Used in addition to the W for improved cosine response, especially with thin film filters. For spectral ranges 250- 700nm.
TD Low Cost UV-Visible Diffuser
$67
Domed teflon diffuser for use with IL detectors for spectral ranges 250- 700nm.
W Quartz Wide Eye Diffuser
$144
Internal hemisphere of solid quartz for use with IL detectors for cosine response
A312 Opal Diffuser
$144
Opal Diffuser, Mounted in A310 Ring
A313 Flat Quartz Diffuser
$167
Flat Quartz Diffuser, Mounted in A311 Ring
A cheaper router would be go onto ebay and buy a cheap light meter and harvest the diffuser.


Or maybe look around hobby and art store for anything spherical and can act as a diffuser.
 
#56 ·
Well, it's harder to find opal acrylic than I thought. There are suppliers in China but I'm not going that route.

I used a regular piece of white plastic instead...



And the result is quite funny.


A linear line, no inverse law what soever :) . Very strange.... I'll have to remove the piece of plastic.

I did learn one thing though. My initial reading from the very beginning might have been affected by the tank and water... I remember reading where hoppy said the water and sides of the tank might act to reflect and magnify the light. I'll have to remove my light and test it outside the tank.
 
#57 ·
Latest readings


Good nuff.... Now to go measure stuff. I have a feeling my 75G tank has too much light and that's the source of my minor algae issues.

Oh, I'll build a JAVA app that'll output the 'PAR' too. It's cross platform for anybody that wants it.
 
#107 ·
Looking at this graph, a little adjustment to your formula and you'll be virtually spot on!

Try:
average = (average/counter * 3) - 100;

I came up with this guesstimating values from the graph above, and it could use a little tweaking.
Can you tell me the new values using this formula and how they compare to Hoppy's data?
 
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