Using a front projector you need to completel yeliminate all possible light sources except the projector of course. Ideally, you should not be able to see your hand in front of your face when the lights and the projector are off.
To have or not have any ambient light is a matter of personal preference and what you are looking for in your HT. If you are trying to create a “Movie Theater” like experience then some ambient light is necessary. However, if you are looking for the best possible picture quality and immersion (suspension of disbelief) then total blackout is the way to go. My preference is total blackout, but it’s not for everyone.
