this isn't from experience, but from research, so take it with a grain of salt, but:

1. flouro is generally best for youngins, whether they be clone or seed. you can get the light very close, and a big ole MH is mostly wasted

2. when it comes to lumen/watt (efficiency) a T5HO bulb gets 92 lumen/watt. this is very high. MH i believe generally get more like 80 lumen/watt. couple this with the fact that you can get flouro's MUCH closer to the plant and my conclusion is: why would anyone use MH ever again? 4ft T5HO's put out more light/watt and they run a lot cooler. as far as i understand the situation, i see no reason that MH's should still be used. maybe i'm missing something

3. HPS can get upwards or 150 lumen/watt. 250's get about 115, 400's and 600's generally get about 130+. so i can understand using those. and i guess if you have just one growroom and want to use a conversion bulb, then maybe you'd use MH for veg


but as far as i can see, the most efficient growing is gonna be: T5HO for veg, and HPS for flower; you could even use T5HO for flower as well, with 3000k tubes. considering how close you can get them, i really can't say if that might even be more efficient as well

rock on