It frustrates the living hell out of me when I come across threads talking about gram per watt, that number is absolutely meaningless. I've convinced people on other forums to calculate their efficiency with the true measure, grams per kilowatt hour, but I don't think I'm going to get anywhere trying that here. Too many people. My voice would just get lost in the din, along with the small number of other people saying the same thing.
Finally, someone that makes some sense here. Grams per KWHr used through the entire grow is the only measurement that makes any sort of sense if you want to compare yield/efficiency.
Grams per KWhr takes all variables into account, like for instance it doesn't matter whether you're running 24/0, 20/4, 18/6, 16/8, 12/12. Nor whether you veg for 3 weeks or 3 months. Bottom line is how many KWhr's you used to get the final weight. It would (should) also account for things like fan, exhaust, air conditioning usage etc.
Problem with this measurement is that most people have no clue what their actual KWhr usage is for their grow op. Going by a hydro bill doesn't break down what is being used for the grow op only, unless you had some history and it was consistent over a period of time. Even then, bills don't start/end on your cycle start/end. Metering every device used, then logging the usage by device throughout the grow would be the only accurate way to determine your grams/KWhr. Too much work, likely why we continue to see this grams/Watt being used, even though it has no valid accuracy.
2 cents