electric rates vary widely between countries. give us a hint where you are, how much is your electric per kilowatt hour (what do you pay normally). are your lights on 24/7? are they timed? a standard 40w bulb incandescent, cfl, fl, hid, metalarc, whatever burns thru about $2.50 per month if left on a 18/6 schedule where I am. I live in the North east US. multiply that by your wattage, times your bulbs. it really isn't much more than if you had say, a fish tank or three. as long as there isn't a major spike in your 'lectric usage, you shouldn't raise eyebrows. just pay your bill legally. don't steal electric. you should be safe. I am in a household that has four fish tanks and a rat cage and a heated snake tank, so our electric is high anyhow! but with my bulbs going I've noticed an increase in about $6/month. I'm only running 2, 4foot flourescent fixtures on a (for the 6th day anyhow) 12/12 schedule. hope this helps a little but without your wattage rate, it's really a ballpark guess.