Using an incandescent bulb is highly inefficient as a light source. A fluorescent light is more efficient, but not as good as a high pressure sodium (HPS) lamp. Your marijuana garden could feasibly be lit by a 100-watt HPS lamp, which will produce considerably more light than what you’ve got now. You can find these lights at indoor garden shops. If you wanted, you could even use two smaller watt HPS lamps. You can find these in hardware stores marketed as outdoor security lights. You might also think of using two 105-watt compact fluorescent lamps. These lights can be screwed into conventional incandescent sockets, and the warm-white spectrum bulbs will adequately get your garden through the vegetative and flowering stages.