Light seams at edges of objects

I’m having a tough time figuring out what is causing the visible light seams where my objects meet. In the picture you can see three room models next two two hallway segments. The lighting is drastically different where all of these objects meet. It is particularly noticeable on the floor.

The floor obviously has the same material, the faces are flat shaded, the objects line up perfectly. It happens even if I turn off all of the point lights in the scene, in fact it gets way worse and becomes horribly apparent even up into the walls. Which is horrible, because I need the lights to turn off in game. It happens whether or not the floor is set to static. It gets worse if I turn off the reflection and light probes. It happens if I subdivide the floor to ridiculous levels, or set the maximum point light count to equally ridiculous levels. I’ve tried playing with just about every option in the mesh import settings and lighting panel. Nothing fixes it. I never had a problem assembling meshes in the 4.x series, but I’m clearly missing something in 5.1. Also, if it is a clue, when I move to the other side of the seam in the hall and turn around, the problem is the same. That is to say it’s always the mesh further from my character that is brighter. Although it isn’t as noticeable on the floor if I stand in a room and look into the hallway. I have no idea what to make of that though, since the lighting setup is the same everywhere.

I really have no clue how to fix this, and it is making my scene look ugly. I’m sure it would be fixed if I made all of the objects one mesh, but that is completely unacceptable for the massive level I am building. As it is I’m trying to maximize the level for optimal occlusion culling. Is there anything I can do to fix this?

It turned out to be a reflection probe problem after all. When I disabled HDR on the cubemaps for the reflection probes, the problem went away. If I disable the probes it goes away as well, so I’m not sure why it didn’t do that before. I had to disable all of the reflection probes though, even ones that weren’t connected to the offending geometry.

Of course, going from HDR probes to LDR probes completely changed the look and feel of my scene, so that’s a bit of a pain. And now I appear to be having a similar problem elsewhere that I think is related to GI, so I’ll ask over in that forum. For all the powerful new lighting features of Unity 5, they sure are a pain to work with.

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Sigh. Turning of HDR on the probes breaks PBR. My metals all turn out black. If I turn HDR on the probes, they look like metal again, but there are ugly seams all over the place. And this seems to be completely separate from the ugly lighting the indirect GI is giving that I mentioned in another thread. I’m beginning to think I can’t use Unity for this project.