Which is where you got to searching on “defoliation” which was a (far) red herring…
Dead horse: any decent grow book goes into how flowering is induced, and should give enough of a handle on this particular subject. There are a couple in the books section of the Data Dump! (Scientific Papers) which was linked above.
The parallel with your photography experience is absolutely valid, and I’m suspicious it is as using such “safelights” and finding they didn’t work is what first lead folks down the phytochrome trail. It’s been more than 20 years since I worked closely with folks doing basic phytochrome work. I don’t recall ever hearing that explanation, but it rings true enough that I’m gonna have to go digging now…
Edit: Looks like 1930s-50s and unlikely to divulge itself trivially. Found this which might be useful for other folks finding themselves here and curious: Photoperiodism - Wikipedia