In my previous studio I had a remote to control the different kinds of light (lava lamps, small spotlights aimed towards the walls, regular bright lamps in the roof) and I did just like you during vocal sessions, lowering the lights in the control room so that it was very dark. I had an uplight in the recording room with a dimmer so that the vocalist could get the mood light desired.
What I also did was to always position the singer facing to the left, turned 90 degrees from the window. This way he/she can't see me when performing but I could still make sure distance and all of that was in check.
And between the takes I could have immediate eye contact while coaching. I consider this to be one of the most important things when producing.
I've never had a problem with this, and shy vocalists just had me slide over to the corner of the control room where se could barely see eachother. That is, he/she couldn't see me at all. But I could.