150 watts is a little more than you need. For cloning, less is more. If you use too much light, the cuttings will want to grow foliage, rather than directing that energy towards rooting. No, it won't prevent them from rooting, but it'll slow them down, to some degree. I use a 20 watt fluoro bar light, spectrum unknown, placed about 12" above the cuttings, and it works great. The main purpose of lighting, while cloning, is to keep the cuttings in veg, by maintaining the correct photoperiod(18/6, 20/4, 24/0, etc....). With a 150 HPS/MH, it should be placed at least 18" above the cuttings, more is even better. 2', is what I'd be shooting for, maybe even a little more.