like the first poster said.. if you run 3 1k lamps, all you do is check your bill to see how much you are getting charged per kwh, killowatt hour.. say it is $.15 per kwh, all you have to do is mutiply the 3k watts for your lamps times the 15 cents per hour charge and you will come up with 45 cents an hour to run them.. 45 cents times 18 hours a day to veg will give you $8.10 a day to run three one k lamps at a cost of 15 cents a kwh.. you just have to find out what your company is charging you per kwh and follow what i did above and you will know exactly how much it will run you, per hour, per day, per month, or however you want to break it down..