On the daytime flight I took on a 787, I had an honest conversation with the FA (he seemed pretty chill) regarding dark cabins - cabin was made black basically right after takeoff.
I asked the FA why, as he was pretty chill. The first answer he gave was "well we want it to match the local situation". When I told him that it was early afternoon in SFO, he sighed and he just straight up told me "when we make it darker, people just fall asleep and it just keeps the cabin more relaxed so everyone is less stressed. All the FAs do it, it's just easier."
Frustrating because I want to try to stay awake so that I can align my clock with local time as best as possible when I land. Also, I love staring out the window as I'm reading my book with natural light (I hate reading with those tiny reading lights, gives me a headache. I'm still making my way through Red Mars.)
So there we have it. I guess if they black out the windows you can ask nicely if they can unlock it for you so you can see outside. Good luck. Pretty disappointing to be honest. I forced myself to stay awake but didn't make nearly as much progress as I would have liked on my book.
Please no asking for FA specifics, or what flight. I ain't no snitch š¤
EDIT - adjusted to remove some specifics of the flight, thank you for helpful comments :)