I photoscanned a hallway and imported it into blender. It looks fine at first but when I try to connect the diffuse texture to the emission socket, random patches of the of the mesh do not emit, and these patches seem to correspond to the separate pieces of geometry that make up the model. Some other observations I have made are that there are three images that are imported with this model, each of them different. Each island on each of the three textures has a corresponding UV island, but since there is only one UV map many of the islands are overlapped.
Below are images of: a selected chunk of unconnected geometry matching with the no-emission area, examples of two of the textures sharing the same UV map with overlapping islands, and a screenshot of my viewport and material setup.
