None. There's a primitive for that.
or
None. Bill Gates will just redefine Darkness® as the industry standard.
or
None, but it takes at least one to sit and pray for the old one to go back on.
or
She was wearing massive gloves.
or
Got two fives for a ten?
or
Twenty. One to hold the bulb, two to turn the ladder, and 17 to be on the guest list.
or
Because E.T. eventually went home!
or
It's fine, he woke up.
or
coz Donald ducked
or
They keep dropping their trunks.
or