lightmass limitations?

hi, are there any quality limit for lightbaking? i mean there is a limit for maximum squaremeters we can make or something or its just takes longer? for example if my 10m x 10m house takes 1 hour to bake, than 50m x 50m will just take longer time to lightbake with same quality? i want to make a very huge spaceship crash zone scene, half-interior half exterior ( say 200m x 200m ) and want to bake all its lighting to better visuals. thank you.

There are limits, one of them being the lightmap texture limit.
Normally thats 4096/4096, though with some .INI file tweaks you can increase that a bit.
Which means, that if you have a 10m by 10m house, the detail of the shadows need to be baked on a decent sized lightmap texture.

If that house has loads of walls, decoration, trim, floors, ceilings, roof tiles, pipes, wires, etc, etc…
Even a 4096 by 4096 lightmap texture might not suffice because all the uv’s of the house flattened out are so big, the shadow detail baked into the lightmap texture only takes up a few pixels per uv-island.

This is why we break things apart, make seperate walls, floors, ceilings, pipes, etc, etc… so we can assign seperate lightmap textures to each of these objects.
Now, you dont want to have the highest resolution lightmap for everything, but thats a whole other story.

This doesnt mean a 50mx50m house just takes longer, if its one model, the shadow quality will be lower as the lightmap texture has less pixels per surface to render shadows on.
Again, break apart the building, make them seperate objects, and you will have multiple lightmap textures.

As for your giant spaceship crashzone with half interior and half exterior, if that was one object… the shadow quality would be so poor, you’d probably let go some tears of agony.
So think of the spaceship as lego, besides some hero props, see what you can re-use over and over.
Pipe-meshes, monitor meshes, floor meshes, walls, props, lights, lamps, rocks, etc, etc.
This way each of those objects have their own lightmap.

Keep in mind though, that lightmaps cost memory.
A 4096/4096 lightmap texture can be up to 50 or more megabytes, so imagine having 100 objects with a lightmap that size. thats 5000 mb or more just for those objects.
now imagine having thousands of objects…

Sure, the engine can LOD/MIP/Load in/remove parts of the meshes and textures depending on the distance… but there are limitations on what you can do… and you can only find those limitations when you hit them, or have the experience to know what to do to try and make sure you dont hit those limitations.

thank you so much for clear and detailed long answer. i got it now.