I've actually just recently added 4 new options for LPVs:
: multiplies the intensity of the lights injected into the grid
: same as light intensity only for emissive materials
: multiplies the intensity of the light after each propagation step.
: multiplies the intensity of the final result. This is useful if you like the spread but the overall result is too strong or too weak.
This allows a much greater degree of control over the final result. Also, while lighting rooms entirely with emissive I noticed a big missing piece. Ambient occlusion! We have SSAO, so I tossed it on. Unfortunately SSAO only applies to the sunlight, so I added support for it in the LPV shader:
All these changes have been pushed. I'm pretty much out of new things to add at this point. The only thing left to do is tweak the algorithms to see if we can reduce light bleed and improve propagation. It's my first time doing anything with spherical harmonics so I'm sure it could be better. My goal was to make an Offline Light Propagation Volume and it's getting close to complete. There's lots more than can be done (dynamic lights, voxel cone tracing, etc) but it starts going outside the scope of an offline light propagation volume. I've got to get back to working on other things though so I'm going to try to wrap this up in the next few days.