Even light bulbs have an energy rating, and this one is B-rated. On this light bulb you'll find a G24d-2 socket.
From Amazon
Osram Energy Saving Light Bulb, 2-pin Socket to Operate ECC G24d-2, 18 W
LED Bulbs
Osram 18W Dulux CFL D 2 PIN Cool White - OS012056
Big on Electricals
Osram 18W Dulux CFL D 2 PIN Cool White - OS012056