Lighting difference on similar objects

I have set up a very basic scene using a couple of basic floor pieces and the default direct light. I would expect this scene to be lit properly but as you can see in the picture the separate ceiling meshes are lit very differently. I just used an empty scene deleted all meshes except the “floor mesh” and copied that a couple of times.

I tried fixing it with a “Lighmass Importance Volume” and also tried to tweak some light settings in the world settings. But all without results.

I have read that I should insert some static meshes over the seams, this would indeed get rid of the seams but if the light received on the pieces above in the picture is massive and will still look strange. I am also aware the results would look less obvious when the texture is less clean but I am planning to make some clean looking sci-fi meshes and want this to look as good as possible.

I just got UE4 so I might be doing wrong that is obvious for a experienced user. I do remember when i was fiddling with UDK a long time ago I experienced similar problems.


I think you Lighting has a low quality.

Read this

I did found the first link and using the settings from it. I just rendered the pieces with the issue with a Lightmap Resolution of 64, it took an age but this does do a better job on the light received by the meshes, however this creates seems along the edges. The stretched shadows are probably caused by the scaling i did on the floor mesh but I need to get rid of the lines in between the ceiling pieces.

I will start on some very basic meshes to do proper tests.

This looks like a common issue related to modular assets and inefficient lightmaps. Your lightmap UVs are dictated by your meshes scaling. So when you do rescale existing geometry you will often encounter bleeding shadows and/or distorted shading. If you enable lightmap visualization you will probably notice this. A further increase in lightmap resolution may remove those seems, but they will not solve the root cause of the problem. I’ve experimented with modular wall sections a lot and you may want to look into some of the following…

  • Make sure you setup your fbx system
    units correctly (meters or cm)
  • Always align vertices to the grid
  • Align lightmaps to their own grid based on the intended resolution (32 or 64 are
    most commonly used)
  • Use adequate spacing
  • Disconnect and space out faces which may cause their own shadows to
    bleed onto adjacent polygons (edge bleeding)
  • Smoothing groups may interfere with trying to reach uniform lighting
  • Accept the fact that prefabs will always be shaded more accurately than
    modular sections
  • Combining sections in advance, then exporting the whole group as a single mesh may solve related issues

My advice would be to create and export the simplest wall/ceiling mesh you can come up with in your preferred modelling software, but do so with as much precision as possible. Take your time and plan the dimensions in advance. Unwrap your lightmap manually and set it to channel 2 (1 would usually be for your textures). You will notice that once you’ve imported and setup everything correctly, those seems will be gone and you should get better looking results. But again, it is always more effective to model the ceiling in its entirity and not have any unneeded edges in the first place.