The Planted Tank Forum - View Single Post - Convert Lux meter to PAR meter?
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post #160 of (permalink) Old 12-13-2012, 08:12 PM Thread Starter
Planted Tank Guru
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 21,015
Originally Posted by mistergreen View Post
Did you find a big different with and without the minus green filter?
No, that filter is just there to theoretically broaden the spectral response. What I did find, was that using many filters stacked up to get the broad response I wanted, jacked up the IR respons excessively, so hot light sources gave 10X response by the meter compared to cool light sources. So, I went for the minimum of filtering. The 1/8" aperture alone didn't drop the meter reading enough, and 3/32" dropped it too much, so the aperture size to correct that would have required buying a set of drills in very small increments of size around 1/8th inch. So, I looked for a filter to fine tune it, one which would do a minimum of IR emphasis, and not drop the response in the blue area. This one fit that criteria.

Before I can do actual calibrating of the sensor I have to glue it all together and paint it black, making it a permanent assembly, so I was very reluctant to do that kind of testing. I just used black electrical tape to hold it together and block light leakage as I experimented, with just a 10000K PC bulb. Even with this I used up 3 of the photodiodes in unsuccessful assemblies. But, I plan to try to saw them apart to salvage the diodes. This has been a very interesting project, but also extremely frustrating.

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