Since there is no sun in your closet you will have to provide a sun loving plant like cannabis with alot of artificial light. There are three options available to the grower: flourescent lights are cheap, efficient, and don't put out much heat. Metal halide, or MH bulbs, are more expensive but put out much more light than flourescents. They also put out more heat so ventilation is needed. MH bulbs also require a separate ballst in order to work. High Pressure Sodium lamps, or HPS, put out as much light as MH lamps but with a little less heat. Ventilation and a separate ballast are also required