How to cull the backside of a mesh but keep the lights inside? First off: the &quot;backface culling&quot; option for materials doesn't seem to do anything.
Second: I got the effect I wanted (almost) by using the Geometry node to mix a Transparent shader with a Principled BSDF using Backfacing as the Factor:

I need to keep the lights inside the rooms &quot;trapped&quot;. The light should not be escaping like it is. How can I fix this?
In your picture, lights look like point. try with out lights and change the color of cubes:
picture 1

secondly, add black ground with a material with many roughness: picture 2

And play with cube's nodes
according to me it's the only solution.