For seated games, not needing the Guardian, I'd expect to be able to play in the dark.
However, in trying to do so, I get constant alerts that the play area was not detected and I need to run the Guardian wizard. Ironically, there is the option to skip it, but after doing so the error message just pops right back up.
I don't have the Rift S, but as I understand it, the inside out tracking on the Rift S uses the onboard cameras to track your position relative to your room and objects/furniture in it. The cameras need light to work properly. I think the alerts are saying that the cameras can't see the "play area" around you.
