The hidden cost behind growing in my eyes in electricity usage. Just thought I'd demonstrate how you'd go about finding out what your rooms are costing you. For this example we'll say we've got, 250 watts of light, and a 30 watt fan in veg room running 18 hours a day. 400 watts of light, and a 30 watt fan in flower room running 12 hours a day. A kilowatt hour is a unit of power equal to 1000 watts in one hours time. A light that uses 1000 watts, will use 1kWh (kilowatt hour). A light that uses 500 watts uses .5kWh, and so on. A kilowatt hour is what your electricity company goes by when they bill you. The national average is 12 cents per kilowatt hour, so we'll use that. Dividing watts into 1000 will give us kilowatt hours. 280 divided into 1000 gives us .28kWh, each hour that light is on. .28kWh multiplied by 18 hours a day, gives us 5.04kWh each day. Repeating the two steps above for the veg room, we get 5.16kWh each day. That's 10.2kWh a day, multiplied by 12 cents gives us $1.22 each day, or $445.30 each year. Well anyway that's just one example, ya can adjust it to your setup and see what ya get.