Is that 6 feet tall, and 24 feet of square footage? If so, use a 1k light, or even better, two 600s. A 600 watt light is just great for 12 square feet. (I built myself two 12 square foot cabinets, a 600w light in each one, works just fantastically.) The two 600s will get you a significantly better yield for the extra 200 watts of electricity.