this is assuming the lights are running 24 hours a day (which they practically are).

also, im not sure if the rated wattage is the highest or expected. Maybe the actual wattage usage is lower or higher.

Going by the stated wattage, you would be billed about $.66 per day. This does not necessarily include loss in a ballast or other sources of waste. I would estimate at $1.00 per day just to be on the safe side. Over a month, $30 and for a year $360.00.

DarJones

Maybe I should move all my seedlings into the house and use lights. :-( I've got 3 heaters running at least 12 hrs a day to keep my greenhouse heated (last year there were a few times I actually had 5 heaters going). Husband is starting to complain about the electric bill. haha, ain't no way I'm going to take the time to figure out how much we are spending on those heaters, I'd probably tear down the greenhouse if I actually knew what we were spending. Next year I'm putting up bubble wrap.
Pam

I'm growing for the first time this year. I started out thinking how wonderful it would be to have close to a year's supply of chili "free of charge" :) I have shifted my thinking to "these CFLs have an expected life of 10 years, and with 16 hours parts of the year, that might mean 20 years, and IF SO, ..." :)