Okay so,
The Vive cosmos works a lot on light & it's cameras.
In regards to the controllers, It can see the light loops on the controls. It knows which control is left & which is right and does what is needed with the loops for hand tracking via it's cameras and other sensors.
In regards to the room & lighting your environment it relies on the cameras (6 of them) to track your room.
The way the room is mapped via gradient map (Lots of little photos it takes and turns into data) it creates a depth table for tracking.
If you have black furniture, mirrors, dark windows etc. it will also affect your tracking. Basically anything light absorbing or lacking.
You can re-map your room in the evening to help as well or get some lamps, If you have other room doorways you can see that are dark try turning those room lights on as well.
Another way is double click the (Vive) button on the right controller when it's dark to enable camera view. And look around, Look what is obnoxiously dark and try to fix that.
Cheers