Yesterday while I was studying this BlenderSwap subway tunnel scene: https://www.blendswap.com/blend/8421, I encountered something every strange.
In the below screenshot I have deleted every irrelevant data and leave only the special part:
As you can see in the screenshot, there is a planar mesh and a single lamp - however the lamp is magically duplicated along what seemingly to be the "path" of the mesh, if we shall call it this way.
However in the scene there is no array modifier or anything I can recognize - there does seem to be a parenting relationship between the mesh and the lamp, but exactly how is this done?
I know it's not ideal to append a file but this question is quite software/data specific, so I have appended the scene file for your reference: https://drive.google.com/open?id=1lLjSAy6WDfge0fK5dLbxBaHxe3xFGaFR
Remark: The .blend file requires Blender 2.8
