La reponse de James Dowling :
"The dial was patented by Rolex in 1941 and used by them on manual and automatic watches for about 7 or 8 years. It was known by Rolex as the ‘High visibility" dial, as it used quite large luminous numbers.
In the 1970s, when the vintage watch boom started, a L.A. based dial refinisher, Kirk Rich, did some dials with this design. They became popular & many vintage watch stores in California sent their dials to KR. So dealers in the rest of the US & the rest of the world began to call them the ‘California’ dial".