2x4 led grow lights

2x4 = 9 ... 8/10.764 = .74 m^2 1000 * .74 = 740 umol/s That's what you want out of your light, assuming it's accurately rated, which is not always teh case, but the bigger companies are getting better at not being manipulative dicks... the no-name brands still lie through their teeth. some incorporate distance in the ppfd they give, but that's retarded. it is related, but that'snot the equation for PPFD / DLI... it's a way to manipulate the resulting value to look better than it is for reasons that don't necessarily correlate at all times... easy to corrupt the value. 750-800 is safe... you always lose a little to the walls and some misses the plants. so calculating from what the ligh produces is a slightly bloated value, but not by much... and if you do it that way each time, it'll be familiar nonetheless. you still need trial and error to find what any plant can handle, and most will not handle 1000 ppfd over 12 hours let alone 18 without tightly controlled temp/rh and CO2. otherwise, even if the plant doesn't show damage/symptoms, it's probably not using that extra light... just throwing money out the window. if the co2 isn't there in proportion, it's not growing faster with excess light. Carbon makes up the backbone of nearly every molecule and replicated organelles/dna etc necessary for cellular growth. law of conservation of mass appplies.. carbon will not manifest itself out of nothing. divide umol/s by area of coverage == PPFD this assumes some common sense about light distribution and geometry of distance from canopy and good coverage from middle to corners etc etc... raise it too high and you get a whole lot more wasted photons and a reduced PPFD even with 90% reflective walls. sometimes it's what you have to do, but context will dictate that too, with a little common sense applied.