I am working on the map with over 3k actors on it. Without lighting built, it weighted around 80 MB.
Now that I built lighting, as you can see it’s a different story:
What steps should be taken to reduce this size (by a huge margin, preferably)?
Does your map use fully dynamic lighting or baked lighting from static/stationary lights?
Some tips for both possibilities:
Fully dynamic lighting
Disable the use of lightmaps. Use “Force No-Precomputed Lighting” in the world settings to disable generating lightmaps. (See also here)
Baked Lighting
Make sure you have activated compressed lightmaps. Check this under “World Settings → Lightmass → Lightmass Settings → Compress Lightmaps”
Look at the lightmap density of your world (See here). A more detailed lightmap (red areas) requires more than necessary space to display correctly. You can adjust the lightmap resolution of a mesh either globally in the “Static Mesh Settings” or per placed mesh under “Lighting → Overridden Light Map Res”.
Reduce the lightmap resolution on placed meshes where the player is unlikely to look (borders of the map).
Disable lightmap generation for objects by settings their mobility to “Movable”. Note that this also changes how the objects behaves in other ways than lighting.
You can see the generated light and shadow maps under “World Settings → Lightmass → Lightmaps”. Every lightmap is (by default) a 1024x1024 texture. Reduce the lightmap resolution of your meshes so you require fewer of these textures.
Also note that lightmaps are generated in a low quality and high quality version. Different platforms use different maps (more here).
It seems mipmaps are generated for lightmaps. Maybe you can tweak these settings but I haven’t tried it (more here).
