4.25.3 - Reflection volume brightness issues

Hi there,

I am having some issues with the reflection volumes (sphere or boxes) rendering wrong brightness on half-rough surfaces. It seems the energy conservation is broken.
At first I thought it was because I was using physically based light intensities, but noticed the same behavior with low unitless intensities.

Here is the problem I see: Screenspace Reflections is turned off, there is only a sphere reflection volume captured inside the room (brightness of 1). I am adjusting the roughness of the material from 0 to 1.

You can notice how the reflection becomes brighter than the environment when the roughness is around 0.25 - 0.3. In case you would be wondering, the sky above is not brighter than the visible sunrise, so there is no real reason for it to become brighter.

As a comparison, here is the same using screenspace reflections (max roughness of 1). You can see how the energy is more accurate as I change the roughness.

Another oddity is that if I turn the reflection volume brightness to 0, it still brightens the environment a lot. I need to turn off its visibility to make it not affect the environment. Is that the expected behavior?

Brightness 1

Brightness 0 - Only a tad darker.

Visibility OFF

Finally, I noticed that overlapping reflection boxes would lead to darkening of the reflections. One volume doesn’t get priority over the other one, it just makes the overlap area darker.

I tried to reproduce these issues in the ContentExamples project but it seemed to work fine. I looked into my Project settings I tried turning on and off “Extend default luminance range in Auto Exposure settings” as this was one of the setting I had changed in my project. Otherwise everything is default. But this didn’t help.

Has anyone encountered the same problems?
There is at least this bug with reflection captures.

Thanks Kalle. It’s a bit sad to see that your fix from Dec 2019 hasn’t been merged. I don’t know if that would fix all the issues I encountered, but this just means reflection volumes aren’t really reliable :frowning:

The problem seems to come from the skylight. It is set to capture the scene with a brightness of 1, but the reflection is too bright.

I changed my HDRI skybox from movable to static so it is captured by the reflection volumes, and it fixes the brightness issue (it’s still a tiny bit brighter than SSR results but it’s acceptable).