The Planted Tank Forum - View Single Post - DIY PAR meter, Yeah you heard me
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post #512 of (permalink) Old 04-05-2013, 05:41 PM
Planted Tank Guru
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 21,015
Originally Posted by mistergreen View Post
Sorry, I'm busy with other projects and won't have time to calibrate your meter. Set the resistor to 24.7K and hope for the best.

A regular white spiral bulb.

And use the smallest guage wire you can find. I'm using an ethernet cable. There are lots of variables if you use different materials so that's why having a PAR meter to calibrate against is good.

I'm getting PMs from science people who aren't even in planted tanks wanting to measure sunlight for their tomato plants I think it works even better for sunlight since light bulbs are so varied and low in output compared to the sun.
I stumbled onto this a few days ago: The Quantum PAR meter isn't perfect either. Unless a PAR meter is made with multiple photodiodes, each measuring a portion of the spectrum, the meter will have various errors when measuring light from different sources. For the Quantum meter, it is pretty accurate with typical fluorescent aquarium lighting, but not that accurate with sunlight.

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