what size tank...I mean if its like a 30g
1000w of PC..or 150w of MH or 4x39 Individual reflected T5HO...Watts dont mean crap it all depends on the kinda watts of light they are.
There are too many variables to put a number on minimum wattage.
Let's just say that any amount of light less than what it would receive in its natural habitat decreases the odds of survival. The further away from natural habitat the less the chance of survival.
Watts doesn't mean squat, it is the quality of light. As someone else has said 200 watts of PC light and 200 watts of MH lighting are totally different.
200 watts of PC light?