Even light bulbs have an energy rating, and this one is A-rated. On this light bulb you'll find a GR8 socket.
From Amazon
Osram PL Q CFL Square, 28w 2 Pin 827 Extra GR8,Warm White
LED Bulbs
Osram 28W 2D 2 Pin Warm White - OS816913
Big on Electricals
Osram 28W 2D 2 Pin Warm White - OS816913