first reaction: plants will be bigger in flower than veg so use the bigger light for flower. also i think the more powerful the light is the more tight and compact the buds will be, due to the increased penatration of the light. plus the more expensive light to run will be on less saving some cash on the ol' lecky bill.



...i reckon. i hear MH is best for veg and HPS is best for flower. i used HPS throughout my grow with no adverse affect on the plant so i'd say that it would be ideal but not required to use mh first then hps. if you're going to all the trouble of having 2 grow rooms (presumably to have a constant supply) then you might as well change the lighting type...