Which rear brake light bulb to get???

[skyline-sl]

My rear light is out...

Not the one where you brake, but just when you have the regular lights on

Can anyone tell me which to buy!

Much appriciated!

Car is 04' Audi A4 B6 1.8TQ

* Halfords is close by so a link would be sick!

 

[bubstar]

Stop and tail bulb.

12volt 5/21watt 380 type