This is based on MH's coloured light and multithreading version of aguirre's Light.exe utility.
I've included the original readmes.

Two new command switches are added:

-fakeGISun2
 Makes sunlight2 cast additive light in a full sphere (as opposed to a dome).

-fakeGIMode
 Makes sunlight2 not require skybrushes (ie: the light comes from the void)
 NOTE: REQUIRES -fakeGISun2

Everything else is exactly like the original.