How to reduce the builing lighting time?

Title pretty much says it all, how can I reduce the building time? Is it possible to tell the editor to build the light only in a certain area? I thought lightmass importance volume would do that …but no.

Lightmass importance volume controls how it focuses the quality, so it will increase speed by using it, but the stuff outside of it is still going to build as well. There’s quality settings under the Lightmass section of the World Properties, and then of course you can set the build quality setting.


Would this be hard to implement? The possibility to select with a volume a certain area and build light only there?