None *et al.*
A hundred but they'll all be competing to be the one to change the bulb and bring light to the world.
Just one, but the light bulb really has to want to change.
One. We are efficient and don't like humour.
OC It only takes 1. But another 999 to repost this 100% original joke. I made this.
0mg !!!!
He had a very esteemed colleague.