i just picture it like if you had one of those light strips of light bulbs above your sink in the bathroom with 6, 100watt light bulss in it. thats all it takes when you run a 600watt hps, so its just like leavin the bathroom lights on for 12 hours a day
you can also replace all your bulbs in the house to cfl to save electricity.
I put motion senser light switched from lowes in many rooms in my house cux the whife and kids never turned off the lights,
so now when they walk in the bathroom the lights come on automatically and turn off after they leave.
lots of little tricks you can to save more electricity, and then you can get the 600 watter instead,