Weird lighting bug, not lightmap related


I have this weird lighting bug in my scene, they are both different blueprints, one is for straight hallway and the other is for a T-cross hallway.

The bug:

The left blueprint:

The right blueprint:

This is only a recent problem and it has not happened before that.

The lighting is build and it didn’t change anything.
The lightmaps are correct and big enough in resolution.

Moving the left hallway to another position doesn’t change anything.

That’s a lightmap smoothing issue, you can try to reduce smoothing and increase lightmass quality

just to debug, can you place the same two meshes next to eachother (same config) but not the BP versions, just regular static meshes dropped into the scene. Also same thing with the lights, place the same lights but not BP ones, regular level placement.

Do this test and see if the problem remains, at least to check it’s not a BP problem when there’s lights nested in them.

That is not the problem.

The lights aren’t nested in them, they are slightly above them.

The problem is only with that particular blueprint, the other blueprints that use the exact same assets don’t have this problem.

When I place the same blueprint again in another area it looks normal again, it is only in that chunk it seems.

Moving it 15 cm to the + y-axis fixed it for now.


Wild guess…the “T” vs the “O”. With the “O” the lighting calculation is bouncing light only off of, effectively, 8 ‘sides’. With the “T” it is bouncing off of a lot more…the connection part, and some of the walls of the other corridor sections. Maybe the Lightmapping is bouncing it around enough that it ‘brightens’ the whole thing? I mean, if you take a flat plane and put a green light on it, then build the lightmap, you get a green light with dark, almost black (if not black) outside the lights radius. If you put a wall on one side, you get distinctively lighter floor area (more light bounces). Add another wall, get more light. Maybe this is the thing going on?

Try putting a full ‘wall’ blocking off one side of the “O”, and a small, half-wall on the other side…then build. See if you see it brighten up like the “T”.

Just a thought…


Paul L. Ming

make sure mikktspace is turned on for both your models… (I’ve seen it randomly go off)