Ergonomicists 
~ Forty-five. One to decide which way the bulb ought to turn, one to calculate the force required, one to design a tool with which to turn the bulb, one to design a comfortable - but functional - hand grip, one to design warning labels for the bulb, the switch ... and ... 

Film directors 
~ Just one, but he wants to do it thirty-two times and when he's done, everyone says that his last light bulb was much better. 

Firefighters 
~ Four; Three to cut a hole in the roof, one to change the bulb 

Fitters 
~ None; just assume it's changed. 
~ None; that's the electrician's job. 
~ One to take out the old bulb, and put it back 

Flies 
~ Two. but I do not know how you get them in there. 

Folk singers (of the Traditional English Variety) 
~ Five; one to change the bulb, one to complain that it's electric, one to stick his finger in his ear, two to write a dirge in honour of the old bulb. 

Freemasons 
~ Wouldn't you like to know? 

Gas fitters 
~ Three; one to turn up the day before, when you're out; one to change the switch; one to realise that light bulbs don't run on gas. 

Gods 
~ Two. One to hold the bulb and the other to rotate the planet. 

Gorillas 
~ Only one, but it takes a heck of a lot of light bulbs! 

HiFi anoraks (CD) 
~ One, but the old bulb keeps getting stustustustustustustustustustuck 

HiFi anoraks (LP) 
~ One, but the old bulb keeps getting stuck ... getting stuck ... getting stuck ... 

Hippies (Authentic 60s) 
~ Oh wow, is it, like, dark, man? 

Hippies (New Age) 
~ None; if the light bulb is out, that's the way Nature intended it! 

Historians 
~ Ten; one to do it and nine to document it. 

Honour Guards 
~ Twenty-two; one to screw in the new bulb, 21 to shoot it. 

Investment brokers 
~ Two. One to take out the bulb and drop it, and the other to try and sell it before it crashes. 

Isaac Asimovs 
~ Two, but it's actually the same science fiction writer. Isaac1 went back in time and met Isaac2 in the doorway; Isaac1 then sat on Isaac2's shoulders so that they were able to reach the bulb. Then the temporal instability created by this paradox caught up, and the entire room, light bulb and all, was blown out of existence. Both Isaacs continue to exist in a parallel universe, however. 

Jay Lenos 
~ Three; one to screw in the new bulb, one to ask the old one how it feels to be replaced, and one to take questions from the audience. 

Jugglers 
~ One, but it takes at least three light bulbs. 

Lawyers 
~ It only takes one to change your bulb ... to his. 
~ How many can you afford? 

Leninists 
~ Leninists don't change light bulbs, they change the entire system. 

Liberals 
~ Two; one to do it and the other to keep the first one's knee from jerking. 

Libertarians 
~ None, because somebody might come into the room who likes to sit in the dark. 

Librans 
~ Er, two. Or maybe one. No - on second thoughts, make that two. Is that okay with you? 

Librarians 
~ I don't know, but I can look it up for you. 

Lumberjacks 
~ One, but he uses a chainsaw.