i have used my 1000 watt mh for flower and you lose about 1/4 of the yeild . depending on the strain. i can only say with white widow as i grew both once with 1000 watt mh and many with 1000 watt hps.some poeple use mh when they have hight restrictoins as flowering with mh keeps the plants small and the buds tight and more compact than hps but looses in weight. hps is the correct spectrum for flower and yeilds more