Low light, and what one lamp does to an hour
Turning the ceiling light off and leaving one low lamp is a small change that alters a great deal of an hour, which is why the practice is named for it.
Most rooms in this city are lit from directly overhead, brightly, by a fitting nobody chose. That light is designed for finding things and it does nothing useful for an hour spent with your eyes closed.
What changes when the overhead goes off
The edges of the room stop being sharp, which quietly tells a body it is not being examined. Skin temperature seems to rise even though nothing has been done to the heating. Voices drop without anyone deciding to lower them, which is why a guest who wanted less talking often finds he gets it simply by turning a switch. And the awkwardness of the first minute, which is mostly a matter of being visible, more or less dissolves.
Practical arrangements
One bedside lamp is enough. A towel over a shade dulls it further, though not over anything hot. Hotel rooms usually hide a dimmer on the panel by the bed, and a phone torch pointed at a ceiling is a reasonable substitute in a room with only one hard light. Leave enough to see by: a room in complete darkness makes ordinary movement clumsy and is not the point.
Saying it in advance
Add it to the quiet request in the thread rather than mentioning it at the door. She will then come in expecting a dim room, which stops the first exchange being about the lighting. Guests who want the same effect applied to sound should read the hub on a session without music, since a dim room with a playlist in it is a strange combination that nobody enjoys much.