so im planing to use 2 lights of theese http://www.ecat.lighting.philips.com/l/oem/hid-systems/high-pressure-sodium/master-son-t-pia-plus/928158409208_eu/ but someone told me if i let them in for 18 hours / day at end of month its around 500 euros the electricity bill wich is not really good *very bad* ........anyone have any advice ?