Looks like a lot of progress since I last checked. Cool.
But so far as I can tell, these are still using the Excelitas VTB8441BH sensor.
As I understand, a PAR meter has spectral response like an "M" - sharp cutoff of UV/IR, rejection of green in the middle, and strong sensitivity to red/blue.
But the VTB8441BH's peak sensitivity is 580nm, which is yellow; and it tapers off towards red/blue. That resembles the response of a LUX meter more than PAR.
Granted the results may "close enough", but then wouldn't a $20 commercial LUX meter, adjusted by the closest correction factor
, be only a little further off?
Back on page #9 I suggested a RGBW sensor, which is available in single quantity from Mouser and Digikey. Combined with a bit of cheap IR filter material, this would provide a better PAR reading by summing red/blue (and possibly subtracting some amount of green/white). By displaying raw RGB values, it would also allow a user to determine spectrum, and shift over time, of their lighting; a capability which would set this PAR meter apart even from commercial ones, and provide additional info to help users decide when a bulb replacement is really necessary. It even costs less than the Excelitas part. I was surprised that no one even commented on it.
And it's not the only sensor that would have been superior in the same price range, like this one from Sparkfun
. Either one would interface to the Arduino with the CAT5 cable you're already using.
Seems a darn shame to have put so much time and effort into a PAR meter, when it could have offered more accuracy and capabilities; with no increase in hardware or price.