How many plants (specifically nirvana AK48's) would grow under a 400w MH/HPS?

In a square box, with the light in the center, just wanting an idea of how many lights my friend would need

i would say 6 under 400w

Thanks alot mate My friend is looking at doing 10, so I'll adivse him on a 600w instead

You could do 2 but i would stick to just the one flower at 2ft tall if you have the height and you will get same amount of one than you will 2,has long has the nutes and room are all keyed perfect.tyke

i run 12-12 from seed and ive only got 7 under a 600 and its pushing it........

Depends on how you train and veg. I've done 12 in a 4x4 under 1000 and 6 in the same setup. With two weeks of veg both times the 6 are looking much nicer.
Under a 400 I would do maybe 3 plants with 2 weeks of veg, or 6 plants with no veg. Cramming plants doesn't increase your yeild unless you're doing some sort
of SOG.