[Arran]

Mershon had most of the patents (not all) but Amrad was the licensed manufacturer. That division was sold to Magnavox in Ft. Wayne.  Presumably Magnavox licensed Sprague.

I'm not aware that Fessenden had anything to do with electric lamps after leaving Edison's employ in the 1880s.

 It was in a biography I read years ago called "Radio's First Voice, The Reginald Fessenden Story" or something similar to that. No doubt that it has some errors in it such as the Christmas Eve broadcast story, but Westinghouse did have a habit of hiring former Edison employees. It also said that he had some involvement with the hydroelectric development at Niagara Falls in various ways, but given the pioneering nature of that they probably hired scores of engineers and scientists.
Regards
arran