Contrary to what the other replies tell you an HPS would be much better than fluros due to lumen output alone. I've benn growing for just over ten years and have never had a problem using an HPS bulb during vegitative growth. The plants do stretch a little but with fluros you will get much much more stretching and very airy buds. So basically in my opinion use the HPS light you have and you can use the fluros as supplemental lighting for the bottom of the plants. A better suggestion would be to use an Eye Hortilux Bulb or a MH Conversion Bulb but by no means is an HPS light inferior for vegitative growth however fluros are. Fluros have very low lumen ratings and are out of the optimum CRI range(Color Rendering Index) for cannabis growth not to mention produce small yields. The HPS bulb you own is anywhere between 50,000 to 55,000 lumens and the CRI rating is between 2.0 and 2.4. If you do follow my advice but want to purchase a hortilux bulb or a MH conversion bulb I would tell you to check out www.mdhydro.com for the lowest prices I've ever seen. I order from these guys all the time and are excellent to deal with. I myself use a 400 watt Eye Hortilux Super HPS bulb which provides 30% more light in the blue and green spectrum which are needed for healthy cannabis growth while still providing the nessacary red spectrum which is nessacary for flowering. Hope this was of help.