Hi tynyplantas,in my opinion, 2x COB 4 with total of 360 watt dimmable have realy one of the best PPFD flow and optimal distribution for your space. in your case is an ideal condition as positioning COB4, because the system is designed to radiate uniformly spaces 2x2 (60x60cm), max 2.5x2.5. with over 1000 PPFD.
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