hey guys,
For some reason i become this error message after building light… can someone tell me please what this is about?
You need to put a Lightmass Importance Volume into your scene that encapsulates the area you want to build the lights for.
Thanx!
Where is this Lightmass Importnace ? Is it a option or what excatly? Where i can find it ? UE4 never asked before for something like this…
Just go to volumes and then drag it into your level + scale it up or down 
Thanx, i found it… can you maybe tell me what the use of this Lightmass Importance is? I guess it has something to do with the lightmass 
but what excatly, in my last scenes UE4 never asked for a Lightmass Importance…
"Lightmass Importance Volumes are used to focus Lightmass calculations. Lightmass is the precalculated lighting and global illumination system used in Unreal Engine 4. In order to minimize - and thereby optimize - the amount of processing needed to generate precalculated lights in a level, Lightmass Importance Volumes are use to enclose the areas of the level geometry. Lightmass will only calculate within that area, skipping anything outside of it.
For more information on Lightmass and Lightmass Importance Volumes, please see the Lightmass documentation."
https://docs.unrealengine/latest/INT/Engine/Actors/Volumes/index.html#lightmassimportancevolume
Basically it limits the area lightmass calculates so that you dont spend hours trying to build lights for infinity. It is needed only when you build lights for static lighting.
Ok got it, thanx! But i’m still curious why UE4 didn’t asked for a lightmass importance in my few last scenes…
I think because now you have used a big landscape → just in a big level with many meshes you need a lightmass importance volume .