Lighting bleeds through mesh help

Hello, i want to achieve natural effect from underground ceiling with emissive but mesh receives light through itself. Below is spotlight to illuminate bottom better than emissive could but emissive goal is to illuminate vent walls with natural brightness.

Seems that best solution still is to build object thick as tank to avoid leaks, very weak leaking still remains but better than thin mesh. Is there any solution yet for thin meshes than do not require massive build times?