I set up a scene where there is a cuboid like indoor room with 6 walls (no windows). Inside the room, there is one sphere, with translucent materials:
The lighting mode is set to Surface ForwardShading. On top of the sphere in the room, there is one rect light facing downwards to the sphere.
When I set the translucent type to be “raster”:,
the result looks normal:
However, when I set it to ray tracing, the sphere is completely black.
After a lot of investigation, I found that the reflection/refraction color is solely related to the sky light outside of the indoor room, even though no sky light can enter the closed indoor room. If I setup a sky light outside of the indoor room, which includes sky light, directional light and sky atomsphere, the sphere is no longer black anymore.
The refraction is similar to what it looks like when room is hidden. These results make me think that the ray tracing translucent is working as if the walls do not exist.
This is what it looks like without the surrounding walls:
My rendering is Lumen with ray tracing on.
Does anyone have any ideas of why this is happening and how to fix it? Why doesn’t the translucent material capture the surrounding walls?