I use a SF 4000 in a 5x5. It does a fine job and is reasonably priced. You could go bigger if your budget allowed. General rule of thumb- the light should be at least 50% of budget, more if you want to spend it. I also have a SF 2000 for the 4x4 veg tent. It is an older model with only an internal dimmer, PITA but is great for seedlings, starters and veg out. I have used the 2000 for bloom but it is evident that it is under powered for that. There are many cheap, copy lights out there, be careful what you buy. These are the only lights I am familiar with so it is difficult to make a comparison, but I am satisfied with what they do.