Custom-made plasterboard ceiling with hidden lighting.
The model is designed for anti-aliasing.
For inserting built-in light sources, I recommend using CoronaSlicerMtl to avoid cutting geometry.

Made in Corona 9.
The model uses CoronaLegacyMtl materials, which may not display correctly in very old versions of the engine.
For Corona render, it is recommended to install version no lower than 1.5, since the glossiness of materials is configured taking PBR into account.