Make this room fairly dark, and use a hologram planet/ring as mentioned to light it. Also, could you make the "middle" platform raised up instead of lowered down, then have the "central" platform level with "outer ring"? You could (possibly) then fill the gaps between the supports from the "middle" to "central" platforms with a dark tinted unbreakable glass. Then people on the "outer ring" can see who/what's on the central platform without being able to shoot them without going up to the "middle" ring (visa versa for people on the "central ring" looking out to the "outer ring").
Used your previous terminology so you know what I mean.
Bookmarks