A lightworker is a nuclear-scientist, who while working with nucleons and fission, got hit by a spare nuetron, which struck his cerebellum, and caused it to mutate, whence he began to see sound, matter, and all energy as light.

His type is therefore known as a light-worker.

But seriously, I think Light worker, refers to the new-age dimensional spiritual ascension types, who believe that we humans are entering a higher dimension, and will be interacting with spiritual light-beings.

Or some such chit as that.
Either way its all swammp gas.