whenever i bake lighting with substrate the indirect lighting returns black
probably this
it makes me happy its gonna get solved but also annoyed ill have to wait until they fix it instead of there being a magical button that fixes it
you could use gpu lightmass. or use the temporary fix and copy over the .net framework folder from 5.5. there’s a thread about that in the forum.
Yes sorry about that…
@glitchered What is the temporary fix? (interested in case it help investigating the source of the bug faster).
like i mentioned… in one engine version i had to copy over the .net framework folder from the previous version. forum member suggested it. the bug was that .net or engine parts were missing some executables. swarm agent thing.
Ok that is weird but unrelated to Substrate then. Thanks.
can you link the thread
it was this problem. i’m actually not sure you have the same issue. reconsidering you bake black lightmaps? well…
it bakes lighting just fine without substrate materials enabled it just breaks when i enable substrate, rn i just disable substrate, bake, and then re enable it to get gi
altho baking lights works fine with substrate in 5.5
so i updated to 5.8 and it still hasnt been fixed? i thought it’d be resolved by now
It will probably never be fixed. The baked lighting path has become progressively more broken with every release and seemingly no effort at all has gone into improving the situation.
The way things are going I’d be willing to guess that the next time we hear about it, it will probably be an announcement that they’re deprecating it and it will be removed in UE6.
For what it is worth though, it should work in the community fork of GPULM: Epic's GPUlightmass - #917 by yujiang.wang
Hello,
Sorry this got broken… I’ll push a fix in 5.8.1.
Happy to be wrong! Thank you Sebastien!
@seb hello, please if i may ask for other fixes in this regard:
- fix the non baked GI with a stationary skylight
- fix the non occluded sky reflection with stationary skylight
- as well as stationary spotlights not casting shadows of meshes set to static.
thank you very much, you are my last hope to use baked lighting with a dynamic weather system and substrate. if you won’t fix these please at least write it here, then i can burry my dream and i have to change the whole art direction in my game.
best regards.
Ps. I would like to add, only the clearcoat roughness layer has the issues of the skylight occlusion not being visible, when you set the clearcoat coverage to 0 it works but obviously makes the whole clearcoat shader obsolete then.
Hello,
I still have those points as task to check for Substrate since you reported those in the substrate thread a while ago. It is not nice to always push like that I would say, especially on others thread: we are all busy 
but with different priorities. I had a quick look at those points today nonetheless:
(1) I do not understand that point being too large and vague.
(2) I can reproduce the second point + that is not a substrate regression (it is the same with substrate=0 or I could not see the diff myself from my test and you originally reported it in the substrate thread IIRC). This is likely because stationary was mostly thought out as a shadow caching feature in mind and never finished for DFAO which work with movable in mind.
(3) I cannot reproduce, stationary lights shadow all looks good to me.
Now for those, please use our official bug report tool THERE. If we can reproduce, we will fix. Detailed repro steps or tiny projects zip are a must to make sure we look at the exact same use cases and bugs.
Thanks!
Ok, sorry you are right and won’t happen again. Its just that the feedback from epics side is often non existent.
(1) we figured out the occlusion is working but the bounce lighting is not.
i had a issue with every downward-facing surface rendering black after a bake no bounce lighting , well i had claude fable 5 look at my issue, it took a hr of trying everything under the sun but here is what it was and the fix
"Claude Fable 5 Response
Yes, real progress — the investigation is converging on one final suspect: Substrate. Your project has r.Substrate=True in Config/DefaultEngine.ini — that’s the experimental new material system, and it changes how every material decodes baked lightmaps on screen. It’s the only remaining explanation that fits all the evidence we gathered today:
- The bake itself appears healthy: the room visibly brightened when we swapped the floor to gray (that’s real baked bounce light responding), walls receive indirect light, and both CPU and GPU bakes agree.
- Yet every downward-facing surface renders black — your ceiling planes, a fresh plane, even a proper thick box — regardless of material, mesh, or irradiance-caching settings. In this room all light comes from above, so the lightmaps’ stored dominant direction points down; a broken directional-lightmap decode under Substrate zeroes out exactly the surfaces whose normals oppose it. That also explains why the unlit green test material rendered fine (unlit skips lightmap decode entirely).
The fix : Project Settings → Rendering → Materials → uncheck Substrate (or change r.Substrate=True to False in DefaultEngine.ini), restart the editor, let shaders recompile (this can take a while — grab a coffee), then rebake. If the ceiling appears, that was it. Your materials are all standard ones, so turning Substrate off shouldn’t change how anything looks.
"
UE v5.8