I received the photodiode yesterday. Got to play with it a little. In this picture, I'm trying to find the right resistor for this set up.
A 4.6K resistor seems to work. I'm calibrating the max output to sunlight.. 1024 (5V) is the max reading and sunlight through a window gives a reading of ~900. So I think I got it.
Mounted the photodiode on a electrical cap
Assembled the jar... This nub in the jar is a problem. It casts a shadow on the photodiode.
I moved the diode to the side and gave the plastic a little frost with fine grit sandpaper to scatter the light a little.
Next step is to calibrate these numbers to the PAR readings.