The Dungeon Master's Guide description of the Shadowfell says (p. 51):
It is a place of darkness that hates the light, where the sky is a
black vault with neither sun nor stars.
I don't quite understand this. If it is a place of darkness that hates light, then everything should be pitch black. If everything is pitch black, then only creatures with darkvision can see their surroundings.
But I also read a lot of evocative descriptions of things that you can see in the Shadowfell "far away" (jagged mountains, castles, wretched villages, etc.), which makes no sense, because your vision would be limited to 120 feet.
So, how does illumination work in the Shadowfell? Are creatures without darkvision blinded on this plane (unless they have light sources)?
How did earlier editions handle this plane?
Best Answer
It's up to the DM
There is currently no official 5th-edition sourcebook detailing the mechanics of the Shadowfell. Until such a companion is released, there is no correct answer outside of "It's up to the DM".
The closest official answer comes from page 50 of the 4th-edition Manual of the Planes, where it states approximately that all light sources are reduced to 50% functionality: