replace all of the other lights in the house with CFLs...that will go a long way towards bring the power bill down, you can calculate the exact numbers with the wattage of the CFLs, the average time they are left on, and your electric rates off your power bill. Its really a no brainer.... just a little basic arithmetic. That will tell you if you have reduced your usage enough to be able to run the HPS without running up your power bill.