What's wrong with my lightmap?

Hey guys,

Here’s a simple mesh - a wall with straight siding. My UV is unwrapped with no overlapping polys. I set the resolution to 512. Why the big lumpy black marks? Also, why the shadow variation from piece to piece?


Hi Ian,

It would be helpful if you posted a screenshot of your UV for your Lightmap as well. It’s not always easy to diagnose or offer suggestions just based on the final result.

From the looks, this does look like it would be the result of overlapping UVs though. Do you get an overlapping UV warning when you build lighting?

Thank you!


Here’s the UV.


No overlaps.

EDIT: it says “UV Channels: 2”, but I only created/imported one - is that an issue?

The 2nd uv channel is here for the lightmap. The unreal engine generates one when you import a mesh, but sometimes it’s not good enough -> then you have to create one in your 3d program: :slight_smile:

The problem with the lines could also be a normal map problem (when you have assigned one to your mesh) -> make sure that you set the mode from the normal map to “normal” (in the texture editor) + flip the green channel

+as Tim mentioned, do you get any warnings after you have built the light?

I was under the impression that if your main UV channel had no overlapping segments, it would also be used as the lightmap.

I don’t have any normal maps on the mesh - I’m actually avoiding them since my main focus is VR.

I had no warnings regarding this particular mesh.

By default, if you only have a single UV channel it will generate lightmap UV’s in a second channel. It’s in the window when you import the mesh.

Okay, thanks - that’s good to know!

I double checked the second UV, it looks good. No overlaps.

So, I’m still confused…why the ugly shadows?