i like to look at the graph that shows the monthly usage for the year. i can't really go by the cost because i pay the bill sporadically and the charges for use and delevery and crap are never the same. i am sitting in a hot ass house right now because according to my graph i'm already using the same amount of electricity as last year when i ran an a/c in the house but fewer watts growing. so no a/c this year. i still have a few fixtures around the house that have regular bulbs but they don't get used that often. before i started growing i changed most of the bulbs to cfl and the graph went way down, then back up when i started the grow. i love that graph.