You will need to buy different lights. Halogens may look very bright, but the spectrum and lumen output on them isn't very good at all. You can go ahead and try to grow with them, but you will get medicore results. Especially if you are trying to flower them at 3 feet. When put to flower, most plants can grow an additional 30-50% in height. You may be possibly looking at 6 foot plants if you flower them at 3 feet! The halogens will not be able to support 2 plants of that size. You will definately need a different lighting system.