"The Glo-Dial Corp. was in business from the 1930s until the 1950s or later. Charles Hoffritz, who founded Glo-Dial in Los Angeles, was granted a patent for an illuminated clock dial in 1934. "
Glo Dial site link
Look up the date of the patent. that will at least give you an earliest date.

Look up the date of the patent. that will at least give you an earliest date.