Circuits containing purely resistive loads such as filament lamps, strip heaters, cooking stoves, etc., operate with a power factor of unity. When the power factor is 1, all the energy supplied by the source is consumed by the load. Circuits containing inductive or capacitive elements usually have a power factor below 1. When the power factor is equal to 0, the energy flow is entirely reactive, and stored energy in the load returns to the source at the end of each cycle. Good power factor is considered to be greater than 0.85 or 85%.