This light bulb has an F energy rating. On this light bulb you'll find a G5 socket.
From Amazon
Osram 999047285046 14 Watt Lumilux T5 High Efficiency Fluorescent Lamps
LED Bulbs
Osram T5 Fluorescent Tube 14W 550mm 21 Inch Cool White - 591384
Big on Electricals
Osram T5 Fluorescent Tube 14W 550mm 21 Inch Cool White - 591384