Q: How many Heisenbergs does it take to change a light bulb?
A: If you want to know how many, you can observe them as they come in the door. But if not observed, they come in waves.

Q: How many heterosexual males does it take to screw in a light bulb in San Francisco?
A: Both of them.

Q: How many Microsoft employees does it take to change a lightbulb?
A: One–but Bill Gates must inspect every single bulb and socket before the operation is started.

Q: How many vegans does it take to change a lightbulb ?
A: Two, one to change it and one to phone round and cancel the party they were going to have to celebrate the old one burning brightly for 50 years.

Q: How many NBC news producers does it take to screw in a light bulb?
A: Three, one to drill a hole in the light bulb so it blows up when he turns it on, one to film it, and one to insist on the truth of the report despite the manipulation.

Q: How many Tuba players does it take to screw in a light bulb?

A: Two to drink the keg of beer, and one to hold the bulb while the room spins!

Q: How many Chinamen does it take to change a lightbulb?
A: Thousands, because Confucious say many hands make light work.

Q: How many software engineers does it take to change a lightbulb?
A: None: Well document it in the manual.

Q: How many sales directors does it take to screw in a lightbulb?
A: (pause) I get it! This is one of those lightbulb jokes, right?

Two. One to change the bulb, and one to change it back again.