Use energy-efficient light bulbs if you're looking to cut as much energy costs as possible. On this light bulb you'll find a G23 socket.
From Amazon
Dulux S 2 Pin 7W 840 Osram 7 Watt
LED Bulbs
Osram 7W Dulux CFL S 2 PIN Cool White - OS010571
Big on Electricals
Osram 7W Dulux CFL S 2 PIN Cool White - OS010571