After some trial, the flipped normal method doesn’t work either.
But I did find out that, it is actually possible to hide the emissive material from the camera and inject light into LPV.
You simply hide the emissive object inside your wall and let the emissive light bleed out from the wall.
Player won’t see the emissive object, but LPV will propagate that light info into the scene.
I’m not sure if the author uses this method for his LPV scene setup, but at least this method works for me.
As for your emissive light setup issue, did you have a directional light in your scene? (Set as movable?)
Did the directional light have the option “Dynamic Indirect Lighting” and “Cast Shadow” turned on?
If you go to Show > Visualize > Light Propagation Volume, toggle the option on, did you see the voxel representation of your LPV?
If all the above are correctly set, then you should have a working LPV already.
(Edit: There’s also this setting inside your UE4 installation folder, “Engine\Config\ConsoleVariables.ini r.LightPropagationVolume = 1” need to be added)
You mentioned you set an option in the material editor, is it “Emissive (Dynamic Area Light)”?
If that is the case, then you and I have the same setting, maybe there’s something wrong with your other settings?
I’m using UE4.16.1 by the way.