It doesn't really effect it too bad... I'd say Ive only seen bills $15 bucks a month more. But I also have to run the heat less..A simple space heater runs 1500watts, and I'm only running 800w total for both lights..and not 24hrs a day. I can leave the door open and heat filters out of the room. The house is all 13w (60w equivelent) spiral lights in every room to offset the cost a bit. I figure my tomato habit is worth the extra cost overall
but it is a consideration...I could have used an LED system they sell at grow shops...but a quality one is a lot of money, and I like the natural looking light they produce.
Jon