Lol., OK granted light output is light output I understand, I've accurately measured my space now and it's more Like 6ftX5.5ft so by your theory of a 600w hps covering a 3ftX3.5ft grow space during flowering, two of them old cover 6ftX7ft during flower?? I'm growing all from seed, they all have similar flowering times as one another too so I hope that will work to my advantage., also don't you think I would have trouble with heat running 4x600w hps in such a small space? It already gets too hot in there with one 600w but the inline fan helps dramatically., and as for yield I've only grown 4 plants from seed in one go before, but I've done that about five times with id say good results, usually pullin around 12Oz dry depending on which strain and how long I veg of course, haven't had a chance to try and yield 4lbs yet so who knows
I might invest in another dimmable ballast just to add another 600w lamp to the room just to top up in light, would using a bare bulb hanging vertically just from the mogul socket be good for some extra light as I don't have the room for anther reflector I don't think..?