it all depends on elements your havent mentioned...
soil? hydro?
how many plants under the 1200W?
the most ive seen was 60g from a single 18" LR2 grow in soil/perlite in a 20 gallon trashcan with 15 plants under 1000W
learn the growing process first...grow from clones to learn the basics...ive known newbs to the game to fuck up major grows with seeds from lack of experience and knowledge
good luck
