Hi,
In my experience an Revit File for Electrical fittings will use a ‘Space’ which is sync’d to the Architect’s ‘Room’… The ‘Spaces’ are then used for calculations and are added to ceiling voids, that kind of thing. Then your graph only has to find elements from spaces in the host model, which is a lot easier.
That said, if you are sure you want to get from a linked room, you could look at this link…
It physically clashes rooms in the host model against rooms in the linked model. This might be useful to you, or you might adapt it to clash lights instead of rooms.
Hope that’s helpful,
Mark