Find out how much you are charged per kilowatt hour - bill or google it. So if you had 100 watts and it was .12 dollars a kilowatt hour it would be .00012 dollars per watt per hour 100 Watts * .00012 cents = .012 dollars an hour, so 1.2 pennies an hour. 18/6 grow cycle = 21.6 cents everyday. 30 days = $6.48 I'm a little baked, but basically you want even notice it, someone wanna check my math?

Your math is good. I've always tried to answer this question the other direction -- calculate total kilowatt hours used per month and then multiply by the rate, I like doing it this way. Some power companies charge different rates at different times of the day, but you can see that using your average rate gets you close enough to understand the impact on your bill.

HTML: So if you had 100 watts and it was .12 dollars a kilowatt hour it would be .00012 dollars per watt per hour 100 Watts * .00012 cents = .012 dollars an hour, so 1.2 pennies an hour. 18/6 grow cycle = 21.6 cents everyday. 30 days = $6.48 I'm a little baked, but basically you want even notice it, someone wanna check my math? \t\t Intense research

Dude, 100 watts is nothing...a standard incandecent light bulb uses 100 watts. Your bill will not really be affected by that.