Originally Posted by Hoppy
I stumbled onto this a few days ago: http://www.apogeeinstruments.com/apo...l-information/
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.
yup, you have to ask apogee to calibrate your sensor for indoor or outdoor light. There's a 10% difference.