The way I've always understood it: it's g/w of just the light(s) wattage used, not grams per total power used (kwh). The only real difference then is the amount of veg time. Co2, fans, ac, bla bla bla.... none of that is in the g/w calculation and doesn't matter until the conversation changes to; "holy fuck! how did you grow that much, that fast". If extended veg times are used; then that should be mentioned up front. This I believe started as g/watt, not
g/kwh convo..... my .02
That being said, the best I've managed is around 2 g/w...