The cost of running a light bulb varies on the bulb type. LED bulbs are cheaper to run than CFL, incandescent and halogen. On average 15W LED bulb costs around £0.002 per hour to run, a 20W CFL bulb costs round £0.003 per hour, a 70W halogen bulb costs around £0.008 per hour and a 100W incandescent bulb costs around £0.012 per hour.