There is a fairly long thread on here about gm/watt, verses gm/sq meter, verses other ways to measure efficiency.
We pretty much decided that there is no single “perfect” way to measure efficiency.
The problem with gm/watt, and gm/sq meter is that neither one takes time into consideration.
For example, say you have two growers that are using the same exact lights, and the same exact tent, and the same exact plants, all from the same mother, and both grow the same way with the same nutes, same temps, etc etc etc.
BUT… one of them veges his plants for 2 months and the other one veges for 3 months.
If they both get the same number of grams at harvest, they would both have the same gm/watt and the same gm/sq meter, but the one with the shorter grow time would have saved money with the shorter time.
Or one guy grows 3 plant in a 100 sq ft room with three lights, and the other one grows the same plants in a 7 sq ft tent with one light. The guy with the bigger room may get more yield because he has space to spread out the plants in a bigger SCROG which gave him more yield per plant.
Which is more “efficient”, and what is the best way to judge that?
We did agree that no single point of comparison was really much use when comparing two different grows. Just doing a single point of comparison will always result in inaccurate comparisons. In the end, we couldnt agree on what would be a perfect method - none of them really work for all situations. We did agree that time and size of the grow were important though. We also talked about total cost, but then do you include initial investment, or just daily costs, or costs over the main grow or total costs, or?
On the other hand, if you are just interested in how well your personal grow is doing, and you are always using the same basic setup as far as lights, space etc, then you can pick any single point you want to see if your grows are doing better or worse from one grow to the next.
.
The problem with doing that is you will never buy an LED light, or a new TV or a new phone, or etc etc. 
Tech is always going to be changing, and improving and getting cheaper and better. Moore’s Law is a real thing.
I think another advantage to LED’s is that you have the option of keeping the drivers in the tent if you need more heat, or you can locate them outside the tent if you have too much heat.