Perfect Lightmapping but Black Edges

Hi Guys,

I’ve been doing tonnes of UE4 Archviz recently, and I have been doing tonnes of research on lightmaps, as poor lightmaps will result in terrible renders.

My recent renders generally look crisp, however I’m still getting a couple of issues with black shadows on the edges of polygons after rendering, despite the fact I’ve snapped the UVs to a 2nd channel, and left spacing for UV islands.

I’ll add some photos below with annotations so you can see what I mean:

As you can see, The 2nd UV Channel is snapped to the grid (64x64 grid). I used snapping to get the edges of the polygons to touch the others, so there is definately no gap.

However in game you can see after the lighting has been built, we get these black shadows. Is this down to the lightmap resolution? its currently 64x64, however most the walls are bigger than the step and are also 64x64 for the lightmap.

What I’m wondering is, is it something to do with the lightmap resolution, a render setting, or have I completely missed something?

If you have any questions I’d be happy to answer them!




By Increasing the resolution it helps to make the black lines less visible, but its still faint.

Surely there has to be a better fix?

Those black edges are related to how your uv islands are split. Problem should be removed by sewing together uv islands, otherwise darkness from gaps between islands will bleed on them creating such artifact.