...In game mechanics, I mean. Photosynthesis isn't in the game code.
I know, that's why I said I see what you mean, yeah I agree it should be a permanent thing. Although perhaps with the Elder Scroll(s) you would have the power to either block it out or allow it to shine, allowing you to control day/night.
I can't see many players being happy with CONSTANT night. Might get a bit boring after a while.