we cant say how much light you need, because we dont know the size of your grow space ... you could have way too much light and heat there, or, not nearly enough ... in general, a 400-watt covers 4ftx4ft, etc , so assuming youre devoting a minimum of one sqare foot per plant, two 600 watters should be enough for about 18-20 plants, I would personally give them a bit more room for less plants, larger pots, for bigger buds .... hope this helps ...