agree, I usually get like 150-200g of dried/cured smoke of 480W of LEDs (true watt) but it more like 120g of top quality smoke and some lower bud`s (I use to make oil of)
so its more like 1/2 or even 1/4 gram per watt, depending on how you see it (wet normal weight 4x depending on how tight the nug`s are)
now I don't say it is`t possible, a single plant with a long Veg time in a scrog and a 600W HPS might grow close to the 1g per watt, if every thing is optimal and the genetics is top line and a top yielder, maybe some +14 week`s sativa, but IME most normal indica hybrid`s with a Veg time on 5-8 week`s yield 2-3 oz on averages in 8 week`s time, remember its not just gram per Watt. its also how long time it take, at least if you do find power use ages important, what is important for me is that I can grow enough smoke for myself, of good quality, with out using to much power