well found this page. for me to run a 400w light 18 hours a day for veg it will cost me $50.00 bucks more a month. same light now on for 12 off 12 on / $20 to$25 bucks a month not to bad . thats in a room by 6H x 4L X 3W
http://www.northernlightswindsor.ca/faq.html#q9