Seven. One to install the new bulb and six to figure out what to do with the old one for the next 10,000 years.
or
The ceremony was rubbish - but the reception was brilliant.
or
Pointless
or
Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or