ppfd formula

i am just getting into diy cob lights, however i am having trouble figuring out ppfd per sqft. is there any formula that could help me figure this out?

Take your lumen output per square meter and convert to average ppfd( ~.0145 for our 3500k Crees)

4000 lumens/sq ft * 10.7 (sq ft per sq meter) * .0145 = average ppfd of 620/sq ft


Or I guess you could combine the 2 factors and use .155 per square foot.

4000 lumens * .155 = 620


Par watts is the other conversion method. Lumen output is just usually quicker to find.

if you know your efficiency its PAR W/SF * 45

aka 800 par W over 40 SF = 800/40 * 45 = 900 ppfd

BOBBY_G said:

if you know your efficiency its PAR W/SF * 45

aka 800 par W over 40 SF = 800/40 * 45 = 900 ppfd

Click to expand...

thank you.