ok so i have 3 plants, alaskan ice, white widow, and durban poison. i vegged them for 30 days under cfls and then for flowering they r under a 250 watt hps. well my friend who has grown with cfls came over and told me max i can expect it an ounce per plant. i was like no way thats so low for an hps. i have perfect heat and humidity and i have 2 fans and i use fox farm ferts and micronutes. i just feel like 28 grams per plant is way to low and if thats the case then this is almost not worth it.
A common rule of thumb is to yeild .5g per Watt of HPS .... which would be 4-5 ounces off of your 250w.
Overall ..... Wattage is what determines yield more than plant numbers. You could potentially get a pound off of 3 plants ... but it'd take a 1000w light to do it I'll give you an example ..... I have a 3000w flat garden that I have run with plant numbers ranging from 35 - 60 and have always yielded in the 3.5 - 4 lb range .... the light source is the constant and generally yields in the same range despite varying plant numbers. Wattage = yield
its about getting raped on the electric bill cause they always charge more then what it should be they like double the overages.