Spotches + LightmapResolution + UVUnwrap + BuildTime questions

Im learning UE4 and Im working on my first Archviz Interior scene.
I’m struggling with some things.

What is the recommended lightmap resolution? My walls have those strange spotches on the walls.
There is a point light in my room (in the Lamp model). It looks like the spotches are coming from that light.
What is causing this? The lightmap resolution of the wall is 1024 from the couch is 128. The Build time on this scene took
the whole night (set to Production with a custom Lightmass.ini). Im thinking of replacing my new lightmass.ini file with the original one to see
if that helps.

The second question is which of the UV layouts is the best for lightmaps? The example is a teapot unwrapped in 3dsmax.
First with the default flatten method and the second with “Polygon angle set to 0”.

What is a normal final quality buildtime for an interior scene?

I’ve got a HP Z620 workstation (dual xeon e5).

Hope you guys can help me out.


First of all, customizing the lightmass.ini is not really necessary anymore, unless you really want to finetune things.
The recommended lightmap resolution depends on the size of your object of course, but you can check the lightmap density to visualise the size of the pixels from your lightmap. Then you can use that to decide what size of lightmap you want.

Dont let the colors throw you off too much. Red isn’t necessarily bad, it just means that the object has a high resolution lightmap. Just use the size of the pixels to judge what lightmap size you want to use.

Generally speaking though, 512-1024 for a wall like yours should be fine. Unless it receives a lot of shadow detail, in which case you might want to go all the way up to 2048.

The strange splotches on your wall might be caused by compressed lightmaps. You can turn this option off in World Settings. (This will however up the size of your project quite a bit)

Thank you very much for this comprehensive explanation. I was indeed looking at the red colors in the lightmap density and changed everything until it wasn’t red anymore. But as I see in your example the squares need to be a lot smaller then I have
at this moment. The square size on your wall (in red) is that the size I should take as example?

And how about the UV layout in my 2 examples? Which one is right?

Most of the issues arise from lack of indirect lighting and bad UV unwrapping. Increase Indirect Light Bounces and Indirect Light Quality under World Settings.

With regard to unwrapping, manual unwrapping gives the best result. But you want to trade between performance and time/effort needed for unwrapping, you can use default flatten but need to increase Lightmap resolution to avoid any artifacts.

Time is entirely dependent on your scene. If you see some of the works here in forum, it may take from minutes to even 10-12 hours.

There are lot of posts in the forum dealing with these issues.

For example, this post!

and this

(Note this talks about ini changes, though it is not required now, the thread gives you detailed information on lighting)

thank you MSL. Very informative video.