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.
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
mistergreen,
what data does the ardiuno gave you as an output and how do you translate that to PAR reading? I am new to electronics but would like to learn and prehaps provide some input to help out.
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.
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.
For photodiodes??... maybe its more of a marketing strategy to look into new avenues they can market their products.......... just my 2 cents. Anyways, how is the design and calibration coming along? Any new developements?
Aha! A good photodiode and and some oxidized hydrogen, and you have the makings of a powerful thermonuclear device! (Let me double check my old college physics book to confirm that.)
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'.
I got tired of the Hamamatsu runaround and by chance I was rechecking if alliedElectronics sold anything similar to that photodiode but don't have a minimum order.
I'm starting to think that cosine correction filter is pretty important to shift that line curve into place.
Readings can shift if I tilt the sensor slightly.
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
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.
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?
That's looking good now, probably as accurate as you will need it to be. How did you get the data to fall where they do now?
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