[78-L] Lighten my darkness

[John G.]

Can any kind person tell me when Brunswick stopped using the "light ray"
method of recording ?

I have some early (British) Brunswick paper sleeves : the first  reads
"Electrical light ray process records"  in bold type, and over on the right,
under two small graphs,   "Electrical light ray recording"  and  "Electrical
light ray reproduction."   However, instead of the last-named, another cover
now reads  "Electrical Panatrope reproduction".  Finally,  another, more
common,  cover simply refers to "electrical"  records with no mention of
light rays at all.
I am guessing therefore that it didn't last long.
And can someone also explain to me how  it worked ?  I understand how light 
ray
recording was done for film soundtracks; but how was it applied to produce a
master disc ?
And are the results really much better than the traditional
needle-in-a-groove  method ?

Regards

John  Goslin