A ballast is something the provides stability. In this case, Its' providing stability and distance regulation for my lights.. In terms of a flourescent-hps, lighting system, ballasts are used for starting and regulating fluorescent and discharge lamps. Its not jsut the hangers.. The carboard frame arond the lights are the other part to it.. the hangers provide a frame structure..

I no longer use this though, as I have leared to place the cardboard frame, wedging it nicely behind one of the fl tubes.. The bulbs rest right above the tubes, horizontally above the plants at appx 4in"