[Anders Peter Amsnæs]

Can I create a generic ambient light in a 100% closed room?

It's an exhibition room and I have no ideas what the lighting is going to be like yet.

[shen.de]

just put an invisible "area" right under the ceiling. 100m-150m distance to the walls.
add just some IES as spotlights to highlight smaller regions or object if necessary.

that should do the trick and give u a even lit room

[choo-chee]

I'd give a test with the room walls as emitters.