Hey,
How could i solve this? I dont know what I should search in the forum for…
- build your light
- increase the lightmap resolution of your meshes
- create a 2nd uv channel with a proper lightmap for your mesh
- add a lightmass importance volume to your level
Okay. This is a Landscape in the image. I have a DirectionalLightStationary and a Lightmass Importance Volume. But i still got this black lines… 
Just rebuild the lights ^^
Hi ,
As suggested you’ll want to rebuild the lights. You’re seeing the seams of the components that make up your landscape there.
A tip for the next step because you’ll probably run into this issue as well. When you start adding objects to your level you’ll run into shadow problems on the landscape.
Ie. If you place a tree it will look blocky and not necessarily show the detail you would like. You would want to adjust the lightmap resolution for the landscape. The default is 32 so you’ll want to lower this incrementally to get the shadow detail that fits your needs. 
Feel free to ask questions when you’re having issues. We’ll all gladly help!
Hey .
I rebuilded my lights and did all the suggested steps. Now it saids I have still to rebuild 64 lights. I only got one light … Furthermore one square of my landscape is lighter then the others …
Looking at your image above again, it looks like your lightmass volume is only in the center of your landscape. You will want to expand that to be a bit bigger as well.
Can you post an image of the rebuild 64 lights message you’re getting. It does say often “lights need to be rebuilt for (X number) of objects.”
In that case the lighting would just need to finish building for the entirety of the scene.
Can you also post a full screen shot of the editor. This will allow me to see the scene outliner as well and what’s in your scene so far for better feedback!
Thank you!