Figuring out how many plants you can grow is not done by 'plants per light' so to speak, rather, you go by how big of an area your lighting can properly cover then decide how many plants you want to put in an area that size, i.e., more plants smaller or less plants bigger. (When your lighting can handle bigger plants that is, otherwise a big plant is pointless.)
A 400 watt can cover up to a 4 x 4 area although 3 x 3 would be more in line with optimum. A 150 watt covers almost nothing properly, perhaps a 1 x 1 foot space so you can imagine how many plants fit in a 1 x 1 space: 1. The 75 watt is near useless. You would need to start flowering at a very short height to ensure your light can handle the tripling in size your plant will certainly do in bloom - if not more with that light. The small plant size combined with poor lighting equals a pathetic yield, or in other words, a lot of work for very little. Incidentally, the same holds true for the 150. It cannot properly bloom a very tall plant, even 2 feet is pushing it, although the topmost part of the plant will at least give you something to smoke. For a finished height of 2 feet you need to start bloom before the plant(s) get to about 6 inches. (I strongly suspect your plants are going to more than triple though with such weak lighting, so keep it in mind when deciding when to flower.)
To optimize your lighting you should build a box of some sort and paint the insides flat white. (I would suggest mylar or another material but I am guessing cash may be an issue.) This will at least help the light you do have from 'escaping.'
If there is any way possible, you would do much better outdoors. I certainly wouldn't want to go through all that work for the little yield you can expect, but it appears people do it ... I guess you have to go with what you have, still, not for me thanks.
.. i just bought 2 150 hps lamps..
