First of all, useing 400 watts of fluros. would cost a hell of a lot more than useing 400 watts of hps or mh. The best way to explain it is to look at the amps require to run the fixture its self , higher the amps the high the cost. In turn if you have a 40 watt fluro fixture look at what the amps are on that fixture, you would need 10 of those fixtures to equal the same amount of watts as one 400 watt hps. If your concern is cost of electricity than you shoul look at your lights and see if they are what we call in the electrical trade a multi-tap ballast. this meaning you can run your lights at different voltages, higher the voltage lower the amps less cost to the consumer. Unless you have a friend who is an electrician that you trust to know what you are doing with these light forget it. I don't recomend trying that your self. Hope this helps you in any decitions you need to make as far as cost vs. effect, GOOD LUCK.