I'm running a room right now that is 10ft x 7.5ft. I have two 1000w's in there now and have been thinking about adding another two 1000w's? From what I gathered a 1000 will cover a 5x5 foot print so if I double up the lighting in that space some of the foot prints will be over lapping causing me to think that may be too much light?
I would just get dimmable ballasts but for a room that size 4 is your best bet you can do it with two but four dimmable is your best bet buddy
I don't think you can have too much light. I wouldn't use dimmable ballasts, but hang them high enough the plants don't burn. Just like we always do. Two 1000's won't approach the sun, but will give you a great harvest. Have fun, good luck, and enjoy the fruits of your labors.