yah, four hundred watts is four hundred watts, regardless if your running cfl or hps or led, and the energy usage to run either will cost the same as your using the same amount of watts.. the way your electric company charges you is kw/hour.. so if your using 4oo watts. that would be .4kws/ hour.. and say your electirc company charges your $.15/ hour. you therefore multiply your .4 kws x your price per unit, in this example case, $.15, you are therefore paying $.60 an hour for four hundred watts of power, wheter it be hps, cfl or a hairdryer..
hope that helps you out some..