I found this photo on my research...
You probably already know this stuff Rahz but it helps me understand now how lumens possibly could not be simply converted to par.
Lumens is measuring certain wave lengths and misses out several wave lengths that are included in par
Plants do see a little beyond 400-700 but that chart seems exaggerated. Look up the Mcree Curve to see what I consider a proper representation of photosynthetic response. Even in that case, important people decided anything under 400 and over 700 wasn't worth worrying about. And when it comes to maximizing the response, blue in the 5-20% area along with the bulk in the 580-680 nm range seems best in theory. Basically, assuming the Mcree Curve is correct that doesn't mean the best spectral distribution scheme will be the same as the Mcree Curve. Stealing away from the lower responses to add to the higher responses should provide better photosynthetic efficiency in theory. As it turns out 3000K 90CRI is pretty close to perfect (although it's the source of much debate). The only thing else to consider is the efficiency of 3000K 90CRI compared to a slightly less desirable spectrum like 3500K 80CRI for instance. Slightly more par from 3500K/80CRI, but slightly less par efficiency. Despite the testing that's been done over the last few years, nobody can objectively say which spectrum is best. That's how little difference it makes apparently. 3000K 70CRI has a notable increase in PAR over 3000K 90CRI, however it's never out yielded high CRI. It's a better veg spectrum and seeing a side by side, you would expect the low CRI plant to win because it looks much fuller and grows a little bigger, but once the flowering period is over the high CRI always wins by a hair. It would take a lot of that to suggest objectively the 90CRI produces more yield, and it might be by about a percent or so.
So, lumens can be converted to par with the right information. Between your LUX meter and your PAR meter you will find an exact conversion factor for your 3000K 85CRI lamp, assuming both meters are calibrated.
I bought a MQ-520 because I was running a company and it was an investment in the integrity of the operation. In your situation, building a light that massive could also warrant a nice PAR meter but still optional IMO. We've squabbled here occasionally over whether the LED manufacturer datasheets are accurate, and for the most part they're pretty close, readings being taken in a specialized chamber with thermal junctions at precise temperatures -vs our ability to successfully get a good estimate with meters in an open space and somewhat unknown temperatures. Now a couple members here have similar equipment to the ones LED manufacturers use. 1212s and the CLU lineup is legit. You're getting 2400 par watts from your light, and you will be able to achieve average of 60g/sqft over the 120 sq/ft of space once you get things dialed in if you know what you're doing. I did it with 850 PPFD. Your average PPFD will be 1000 minus reflective loss. If you try to restrict the light pattern and grow space to 80 sq/ft your average PPFD will be 1500 minus reflective loss. That would be a mistake IMO.
There are times when it's desirable. Dude only has a 2x4 tent to work with, want's 1300-1500 PPFD and maximum yield for his small space. In your case you will get much better results with 1000 PPFD in 120 sq/ft as opposed to 1500 PPFD in 80 sq/ft... CO2 or no CO2.
You might consider that with reflective losses you should have planned on 1600 PPFD to get an actual 1500 PPFD average in your 80 sq/ft, but it's really splitting hairs, and for myself (and probably most) we measure efficiency by watts and estimated par watts. So the numbers I've been throwing at you are no joke. At 1000 PPFD there's no reason why you can't achieve 1.5 GPW, 3.5 GPPW or more in hydro.
The best reflectors for a 6x10 area will be similar to the second diagram I posted. It allows for an extra 4 inches at the lamp plane on each side before beginning the angle. This results in 4 inches of flat after the angle before reaching your expected canopy level. If you want to be exact about it, get the foam/reflective material closer to the outer cob and with a 90 degree angle, the angle will end that much closer to the canopy layer. But I figure 4 inches would be a good margin for error to give the plants some extra room in case they grow a little more than you are expecting. How you build it exactly will be up to you, but you may find it desirable to make modifications after the first couple grows regardless of how well you plan for a system you've never ran before.
Regarding that, your plants will attempt to take up the whole 6 feet of space. You may find that the lower area gets colonized before the top or vice versa, and/or you may find that things are too thick in the middle, so that will probably be the biggest modification you will need to make, possible adjusting where the pots are in the future, how many rows, distance between rows, how big you let the plants get, etc.
