Will generating lightmap UVs on models within prefabs already in a scene take affect?

Being new to Unity I didn’t know anything about lightmaps. I now have a scene that has a lot of prefabs (buildings, roads etc.) arranged how I want them. The prefabs are made up of lots of different models that together create a city. Those models all have two UV sets in their materials (UV 0 and UV1) but when I created the scene I didn’t tick the ‘generate lightmap UVs’ on the original models prior to putting the prefabs together.

I’m finding the lightmap build is taking too long (10 hrs and counting) and isn’t likely to complete. It just hangs. I suspect this is because of the lack of lightmap UVs on the original models?

My question is, if I go back to my original models and change the import settings so that lightmap UVs are generated, will that effect the prefabs that use those models and will instances of those prefabs in my scene also update too, or do I need to recreate all the prefabs and also my scene?

I’m essentially trying to troubleshoot the problem of the lightmap bake not working but am I perhaps looking at the wrong solution? If there are two UV channels for the models, do I even need to generate lightmap UVs in the import settings? The lightmapping unity manual page says “Make sure any mesh you want to be lightmapped has proper UVs for lightmapping. The easiest way is to choose the Generate Lightmap UVs option in mesh import settings.” but what does ‘proper UVs’ mean?

Any advice more experienced folk can give would be much appreciated.


Yes, applying import lightmap UV’s on the import settings will update instantiated objects in a scene.