I was wondering how many plants one 1000w hps light can sustain. or should I be asking how big of an area can a 1000w light be effective and how many plants can I fit into that area?? in either case whats the answer?
can cover a 5x5 space if your hood has a good footprint. It would cover a 4x4 really well. How many plants you put in a given space is dependant on how you want to grow. I grow only 4 plants in a 4x4 or 5x5. I let them veg a little longer and do scrog on them so that I get a solid canopy of buds that will produce 18-24oz in the 4x4 and 24-30oz in a 5x5. However, if you don't want to do scrog, you could grow 6-8 smaller bushes or 10-12 very small single cola plants in the 4x4, or even do micro sog with 16 plants in the 4x4 where they are each taking up 1 square foot space. I personally find that the plants that are allowed to mature more will produce more, better buds than those plants that haven't matured as much.
My humble suggestion for growing nice healthy, heavy buds (if you are growing Sativa dominant hybrids to 50/50 hybrids) is to grow no more than 4 plants in a 4x4 and no more than 5 plants in a 5x5. Allow them to grow some, then top/FIM to get them to bush out so that they fill in the space and create a solid canopy. Allow them to get 15-20" tall and flip them to flower.
The best way to determine which way to grow a given set of plants is to grow them out a couple times to different sizes to see how they grow and produce, then you will be able to tell the optimum way to grow that strain to get the maximum performance from them.
There really is no answer to your question. We can tell you how much space the light will adequately cover, but plant count is another story. I do want to say right off the bat that more plants does not mean more bud. In fact, if plants are too crowded, it can mean less bud. How many plants you put into your space is dependent on strain and your growing style. So, to give you any kind of answer, we would need to know what strain you are growing, whether it is indica or sat dominant, how long you plan to veg, how you grow, pot size, etc, etc.
I have about 50 plants under my 400/600w combo in a 5x7 room (I'm doing a stadium grow) and the ones in the corners grow as well as the ones in the middle. When I'm not doing a stadium grow/SOG I have 10 full-size plants under it and was averaging 4-5 ounces per plant.
Here's a picture of about 9 plants in my flower room.