.... don't quote me on this, but I'm pretty sure I read that the illuminated panels on the Death Star sets were sheet metal.
They seem pretty thin as they buckled quite badly as Hal points out, and they shake quite a bit during the pyro effects.
That's a very cool discovery Treadwell! I'd put good money on the answer being that Dick George had a hand in making those ceiling features for 'Deadlier Than The Male' and simply adapted and reused the same tooling on Star Wars. Too much of a coincidence otherwise imo.
There are SW set photos that show some of these illuminated 'lozenges' covered over to black them out in order to vary their pattern, which is a genius yet simple way to create a bit more variety. I've been working on Death Star wall panels in miniature on and off for some time, so I love this stuff!