Well I'm sure some might argue this with me but think about this one .....the SUN produces 400 trillion trillion..... ummm yeah alot of watts so does that mean if someone flowers outside they'll get a gram per watt... the answer is obviously no.( and no distance of the sun 93 trillion miles versus the 24 inches of a 1000 w hps is not relative in this equation.) The sun still produces more heat and luminosity than any bulb can match.
The total outcome for yields are MOSTLY based upon A.) Genetics.....B.) the care the plant receives as in its growing conditions like amount of space, nutrients, etc...
Yes we all know watts and lumens are crucial for plant growth as we all know 1 20w cfl aint gonna get you crap, but when you consider the mathematics involved when it comes to yield generation then it just doesnt add up to an exact science when you estimate a figure like 1g per watt.
In order to give the plants enough light power to throw out enough lumens for their MAXIMUM YIELD OUTPUT then you need around 150-200 perhaps more wouldn't hurt watts per plant, then let your nurturing(topping FIM LST etc...) and nature take care of the rest