Working on a bunch of projects for a "smarter" grow.....
1st one is a DIY lux meter....build it for less than $12....[soldering required...]
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http://rollitup.org/Journal/Entry/arduino-2-1-build-a-diy-lux-meter-for-12.31448/
I will post more up about
Conversions but you can use a lux meter to convert to both Lumens per meter squared [photometric]... lu/m^2 or they can be converted to PAR readings too....
umol/s ..[radiometric].
I will get into both of those when I get some time....legit way to measure light cheaply....Google the differences between the way we perceive light [photometrically] and actual light energy including UV and IR bands [radiometric].....This is the reason that lumens can be misinterpreted in some cases....yes lumens can be converted from radiometric data, but not all lumens can be converted back to Radiometric data.....So in theory that would be two different readings.....
I am working on a battery powered version [9v] with the smaller Arduino [Nano]....so that it will be far more portable.....