According to Ken :
A lightbulb is a two wire device. *There is _no_ ground on a lightbulb
to connect to.

Unless its a socket for a three-way bulb.

It's not a ground, and you're rather unlikely to see a threeway
socket on a direct-connected ceiling fixture.

I've certainly not.

But yeah, threeways bulbs are three wire devices. But it won't be the case
at hand.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.