Energy-efficient light bulbs use, as the name suggests, less energy than certain other types of bulbs. On this light bulb you'll find a GX24q-2 socket.
From Amazon
Osram 18 Watt Compact Fluorescent Light Dulux T/E Plus Lamp
LED Bulbs
Osram 18W Dulux CFL TE 4 PIN Cool White - OS342221
Big on Electricals
Osram 18W Dulux CFL TE 4 PIN Cool White - OS342221