Blacklights are pointless for growing. There is no useable light for plants from them. In other words, you cannot grow with a black light. U can however use fluorescent lights. If you have tube black lights, you can replace them with tube fluoros. Or if you have socket black lights you can replace those with compact fluoroescents. Each plant will need at LEAST 2 fluoros to grow properly. You can grow a plant from start to finish on fluoros and get a very good yield, but if u use a different setup for flowering you can get a much heavier yield...