Here is a thread that gives you a glimpse as to what is actually possible in terms of growing in small containers. http://forum.grasscity.com/micro-grows/1255215-infamous-solo-cup-challenge.html?hl=solo
[quote name="SupaaBaked" post="19376410" timestamp="1390261667"]I would want a 400w at least. 600 or 1000 is better though, i'm using a 600w right now.[/quote]My space is 3'x27"x5' what size would you recommend? I would be concerned about heat though I am doing cfls right nowWhy so serious????? He puts the bong to my mouth!! WHY SO SERIOUS???? LETS PUT A SMILE ON THAT FACE!!! *bongin* (cough cough)
A 400w is fine for that size. They cover a 3'x3' square. As long as you got an air cooled hood or cool tube temps won't be an issue. Air cooled hoods put out a beigger light footprint than cooltubes but in a space like that i doubt you would notice a difference.
As a general rule, you can tweak your growing approach to be able to get roughly the same yield per square foot no matter how many plants (within reason) you are talking about.
This^ Ultimately lighting is going to limit your yield no matter what. It comes down to plant count vs veg time. More plants in smaller pots and a quicker grow, or fewer plants in larger pots with a longer grow. Total time spent often gets left out of the yield equation on forums for some reason. It sounds great to get 4 ounces each off of 4 plants. But if you have to veg another 4 weeks and get the same yield you would have gotten if you pulled 2oz each off of 8 plants and half the veg time it isnt that great. Same yield per grow but lets say you have an eight week flower cycle. 4 weeks veg + 8 weeks flower would mean about 3 months total and you could have four cycles per year. 8 weeks veg + 8 weeks would be about 4 months total and three cycles per year. If your pulling one lb per cycle, thats an extra lb per year, roughly 25% more productive than running larger plants. Not exact numbers but you get the idea. I prefer to veg three to four weeks in 5g pots and set my plant count to what ever it takes to fill in my grow area if not running a perpetual grow.
^ The trade-off is: Longer veg time means fewer, larger plants (each with more root volume) to get the same yield out of the same square footage, which is better if you grow from seed. Good if you want to grow a variety of strains and/or don't have the space or inclination to mess with cloning. Shorter veg time means more, smaller plants (each with less root volume) to get the same yield out of the same square footage, which is better if you are time-crunched and/or have a mother/clone operation (usually too expensive to buy seeds for this approach). Generally more efficient time-wise and cost-wise, but also better matched to a larger operation.