I see Heath pulled 2.5 so yeah I should have said 2.6+
And that's just dry weight.
42.5" to the outer edge seems for 600w a tad too far. Not sure, it actually is... they will indeed lean in but not like 20" or so because they obviously won't grow entirely horizontally.
Are you going to use 2x600w? Ideally you roll out the octagon into a horizontal plane to calculate the surface area. Based on that you can perhaps guesstimate (based on typical HPS use) or calculate the desired total pff to get high yield and not too much fluff.
Just thinking out loud here... 96" dia is roughly 300" circumference, that's 25'. If the "canopy" vertically, of all rows combined, is 5 feet, you have 125sqft to cover. IF it were horizontal that would justify at least 4k of HPS... Obviously not a good comparison, that's kind of the point. What normally would be the top of the canopy is going to be closer than 96" of course. Start for example at the inner side of the pipes, subtract 14" for plant, and the diameter of the canopy is already roughly 40" less. Let's say roughly 56" left, which makes the circumference roughly 16' instead of 25', so 5x 16 = 80sqft surface area. That would in a horizontal setup justify 3kW and without hoods and very little loss from light not reaching the plants 2K could suffice (that's not a suggestion...).
Even if that plant would lean 14" it would leave roughly 28" between plant and bulb. Which is already too much in a horizontal setup, while you can (because no hood concentrating the beam to one end) and should get closer. Adding only 2" to those plants already reduces the surface area of the inner canopy with nearly 10sqft. If the rows of plants will in total be 4feet tall instead of 5 the required total amount of light drops with 20% too.
16sqft is suitable for a great 600watter (stretching it already) horizontally. Let's say in a vertical setup you could be able to stretch that to 20sqft. If you have 2x600watt you could cover perhaps 40sqft, which rolled up in a cylinder of 4 feet tall would leave 10ft circumference is 38 inch diameter (of inner canopy), based on that, adding 14" for both plant and pipe on both sides and the diameter should be roughly 66" instead of 96". That 38" minus bulb self leaves about 18" between plant and bulb. Normal for 600w would be 24", but again that's with a hood concentrating the light to one side, you should get closer, so that 18" could work very well. You have 15" more than that which would make (2x) 1K watter more suitable.
Normally you start with a grow surface and match the light to it, or get a light and match the surface to that. The distance is than the output, while in your case the distance and hence the surface too (although flexible by adding/reducing rows) are inputs, so ideally match the light to that. The distance is not so irrelevant as long as it's not too close and as long as there's enough light for the surface. Especially in an enclosed vert setup, and as long as the total amount of light on the eventual canopy surface suffices. No place else to go for the light then hit the plants. The higher the distance is, the larger the surface area it shines light on. Too far would mean spreading the light out too much, over "too much plant".
Turned out a bit longer than planned, I hope my stoner math examples makes sense.
