'How many field researchers does it take to...'
Light bulb jokes are interesting in that they aren't actually about light bulbs at all. This is good, since light bulbs in and of themselves are actually pretty humourless objects. Consisting of a glass bulb, a metal end with oversized screw threads, a tungsten filament, and a very small amount of inert gas, light bulbs do two things: produce light and heat when electricity is passed through them, and stop producing light altogether once too much electricity has passed through them.
It is this second action, or rather it is the chore of replacing the light bulb after this action has occurred that is the basis of light bulb jokes. The other interesting thing about light bulb jokes is that, despite the fact that the vast majority of them are somewhat racist, bigoted, or otherwise derogatory in nature, they are nonetheless usually considered appropriate to tell in mixed company.
The basic make up of a light bulb joke is as follows:
'How many *insert racial minority, cultural group, occupation, or shallow categorisation of choice* does it take to screw in/change1 a light bulb?
[any number, including "none"]...'
This is followed by some comment that is almost always demeaning towards whatever racial minority, cultural group, occupation, or shallow categorisation you have chosen to tell the joke about. This comment should generally have something to do with the number of people required to change the light bulb, and usually involve some bizarre method for rotating the light bulb2.
This is by no means a complete list. It does, however, give a good idea of the basic make-up of the light bulb joke.
Two, one to hold the light bulb, and one to drink until the room spins.
How many mechanics (or repairmen) does it take to screw in a light bulb?
Three, one to scratch his head, one to say it won't be ready till next Friday, and one to tally up the bill.
How many politicians does it take to change a light bulb?
None. Politicians only promise change.
Variations on a Theme
The next few play with the time honoured formula slightly.
How many surrealists does it take to change a light bulb?
How many flies does it take to screw in a light bulb?
Two, but they have to be really horny, and you've got to get them in the light bulb first.
How many Dead Heads3 does it take to change a headlight?
One, but they have to follow it around for 20 years until it burns out.