Fluorescent bulbs have an advantage in that they are more energy-efficient than conventional bulbs. This particular model has a so-called G13 socket, so make doubly sure that it will fit.
Conrad Electronic
OSRAM Fluorescent tube EEC: G (A - G) G13 18 W Cool white Tube shape (Ø x L) 25.5 mm x 604 mm 1 pc(s)