a hps will flower better but the other mh bulb WILL work also ....depends on what you already have and what money you want to spend .....one bulb swap would be cheaper but 2 whole systems would cost more but you could have to seprit grow areas....so more bud for your time so you have to decide ,money,time,and personal motivation....growing is not a little ol hobbie its a way of life ....lol...