Is it possible to put an sf1000d and an sf1000 together in a 60x60x180?

If you want to obviously can and then control from the dimable 1... just make sure the balance of temp and humidity it correct. Never in my life have I used an equation to work out lightage, they love light it's just if you have prepared them to handle that and your grow area can handle it.. Good luck

give them 1-3 days much less ! light and they get taller :) ; they are so small becauße they are happy whre they are and have no need to stretch anywhere for light. We want to grow buds or plants? they could also get taller with bigger pot and some days of low light.

they list a 2.5umol/j effiacy, which i don't entirely beleive, but probably not more than 10-20% off, either. 500 umol/s PAR total production rate for 2 of those lights. For 12 hour operation you need roughly 80umol/s per sq ft... 4sq ft x 80 = 320umol/s for 18h operation (autoflowers) - only 214 umol/s -- again, a ballpark value that requires minimal fine-tuning. So, you could very likely benefit from using both for photoperiods (Run at ~65% to start), but probably won't notice a huge difference in "Autoflower" plants -- what you saw was likely more about genetic diversity than the power of your light. What you would benefit from is more uniform spread of light using 2 SF1000D. So, it's still and option and won't really cost too much more in watts, either. A good starting point would be ~44% power -- 2/3rds of what is required for 12 hour operation - the 65% value above for each light. These suggestions won't be far off, but every garden has slightly different variables - primarily temp, rh% and co2 - that will impact how much you can give per day. Use new growth to fine-tune power of lights. Not too tight; not too stretchy... and you'll find that happy zone quickly. If i was right about SF over-calculating efficacy, may need 10-20% more power... not +10% but 45% * 110% = about 50% for both lights. Regardless, you are using the plant growth to dictate the exact power you want, so you'll find the 'right' spot through some trial and error.