alesh
Well-Known Member
The conversion factor is quite easy to determine if you know SPD of a light source.Return does drop off drastically above 1000 PPFD, and water usage goes way up. But yeah, g/kWh does make more sense. Unfortunately, PAR meters are rather pricey so everybody can't just go get one. We need a cheap Chinese PAR meter for $20, like a little pen type thing that only reads PAR. Whoever invents one makes millions from the Cannabis industry. How hard could it be? I've seen iPhone apps that turn the phone into a lux meter, though probably a crappy one. Actually, if you have a lux meter you could convert to PAR with fair accuracy by using the conversion factor for cool white fluorescent, 74 or warm white, 76. Probably close enough.
PPFD [µmol/s/m^2] = illuminance [lux] / (LER [lm/W] / QER [µmol/J])
with LER/QER being the conversion factor
Ie 3000K/80CRI CXB spectrum:
PPFD = illuminance / (325 / 4.87) = illuminance / 66.735
edit: illuminance is what you measure with a luxmeter