I've pushed up to a dozen plants with one 400 watt hps and harvested over a lb. It's enough light for a sq meter of 3' x 3' space.
I've also supplemented with florescent side lighting (4) 4' T5HO).
Recently I'm running (2) 400 watt MH/HPS with the side lighting. I've got 14 plants finishing up soon (in Week 11 Bloom cycle)
Eight of them are AK-47, mostly sativa dominant.

Best of luck, looking decent!