Living Daylights?

Hey, Bud, Got a Light?

Have you ever wanted to "beat the living daylights out of someone"? Apparently, it means to beat someone unconscious, such that his eyes - the "living daylights" - are blinded, if only temporarily. I haven't heard of 'nightlights' with respect to the eyes, perhaps because our eyes do not see anything on a moonless night.

But this is all dependent upon an ancient, outmoded theory of an inner light . . .