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Running HID hard... Hadn't seen that one before. But yeah, you basically are doing just that. The more you spread out the light, the more space for plants/buds. And the higher the ppfd, the less extra yield for every increment. If space is not a limit but you got like 1500 ppf to spend, you get higher gpw from running 750ppfd than 1500. It'll be more leafy and relatively more branches under 750 than 1500.we'll see. im not as amazed with the CMH as i thought i would be but maybe im just running too hard. (4) 315s in a 5x5 is throwing down 1000-1300 ppfd at 20-24"
In fact, @Rahz is not correct with his 1 par = 4 gram "basic math". It omits an important factor, it depends on the space used. See ppfd/temp graph from uni of Utah...
That phenomena seems to play more a role now with replacing hps with cmh than led though, as led builders don't tend to go lower than hps (anymore). Replace a 600w on 3x3 with a cmh 315 and you will increase the gpw, even if you get less grams in total.