Day 1

tough to say. i don't trust their spec sheet.. plus all this X ppfd @ 12" bullshit isn't how you calculate ppfd. could mean anything without a defined area of coverge - the area the light is focused on. Quantum boards are generally good at 18" or so when properly matched to a tent. In this case you may want a bit higher as it is a bit underpowered for a 32"x32" footprint. I'd wager it produces at least 300umol/s PAR. If you can get accurate info on that it'll help give a better starting point. No matter what, some trial and error is involved. Simply watch how the plants grow. the spacing of new nodes is a guide to light intensity... too tight, need less... too stretched out, need more. You need to contact manufacturer or find an accurate umol/s PAR specification for this light. It may be higher than 300, but it looks like diodes from an mediocre brand if the Q90 is 36,000 hours. These are not the top of the line samsung diodes (lm301). just swap out any math i did with "300" for the correct value. Just shoot for 35-40 DLI and it's a good starting point. DLI is what matters. umol/s PAR is a rate... like mph or km/h. The rate without time is only part of the story. With time you know how far you traveled or how many photons were given to the plant. DLI takes this a stepp further and eliminates area differences between one garden and the next. 35D LI is 35D LI whether over 12h or 18h or focused on 1m^2 or 10m^2.. So, mature marijuana plant swill most likely handled 40DLI as calculated from full production of the light. It'll technically be a bit less than that as some is absorbed by walls and some just misses the leaves. For 18hour operation in a 0.66m^2 tent and 300umol/s PAR maxes out at ~450 PPFD (simple division to calculate PPFD). The only way to go higher is to get the light closer and reduce area of garden to match. 450ppfd over 18h is 29.2 DLI. Reference a DLI table.. no math needed. This is fine for autoflowers. You might be better off with a few more hours of operation. Normally this is not something i sugget, but it is very possible that increasing DLI will overcome any slight negative to a limited or reduced dark cycle. 24/0 gets you up near 40DLI, but start well short of that first and see how it goes -- again.. watch new growth and adjust. For 12 hour operation wiht photperiods, you should not try to fill the entire tent's area. It will be too weak. It's 19.4 DLI for 12 hour operation. This is bare minimum and will likely result in fluffy, airy buds. As long as only 1 factor changes, it's 1:1 inversely proportional to changes in area or hours of operation. So, 1/2 the area would be ~38.8 DLI. This light is good for half your tent if growing photoperiods. All other factors the same, they stay pretty proportional to the dimmer optiosn... so 50% power would be half of whatever DLI you calculate etc... Now, with seedlings you can save watts by getting the light very close, since the seedlings don't take up much space and run the light at much lower wattage, but this takes a lot more trial and error to figure it out. A free app to measure light would help... If you hammer it out for normal 100% power / normal hanging distance, simply match the klux at top of canopy to the klux measuremnt at top of seedlings. Still may need slight adjustments, but nothing extreme... maybe 1/4" up or down etc.. again -- new growth node spacing is the guide to ensure it's in a good spot. If i'm right about the 300umol/s PAR estimate, i'd run these autos at 100% power from ~20" or so... i'd also go with a 20/4 schedule to start to eke out a bit more DLI... whether or not the slight negatives of no dark cycl is mitigated by 33% more DLI is a question you'll have to test out.. .24/0 might be best for this light and .66m^2. maybe 22/2 or 23/1... these put you into the upper 30s DLI. Your climate will impact how much dli you can give more than genetics... rate of photosynthesis is fairly steady from one plant to the next. A proper temp and rh will allow it to maximize rate of photosynthesis. less than ideal vpd will make it sensitive to lower levels of light than normal as well as impact transpiration, which direclty impacts water uptake rate... which would impact fertilizer concentration needs etc... this shit is all relative to each other.