electric

running a 250 watt hps within a month of running the light the electric company came,checked the meter and increased the quarterly bill by £20 so your talkin £80 a year increase for just a 250watt i presume a 400 watter will increases that a bit more ;)

Go here to calculate cost of electrity for HIDs. Oh and check your bill for the cost for 1 kilowatt hour. Should be $0.5 to $0.15

http://www.overgrow.com/tools/powercost.php