Only one person commenting has got the joke….and my DH, he thought it was funny, but then I married him for his warped sense of humour.
From Red Dwarf – Series VI
Rimmer: Step up to Red Alert!Kryten: Sir, are you absolutely sure? It does mean changing the bulb.
Maybe you have to hear it in context!
Quote from http://en.wikiquote.org/wiki/Red_Dwarf