Copy light location in relation to object

I am just starting out with blender and could use some help. I imported an .fbx from Revit and it works great. I have some streetlights in this project and when i change one of them in blender then all of them change.

Exactly like I want. But now I want to add a lightsource to all of the streetlights, and blender won't add them to all streetlights. I set the lightsource as a child of the streetlight. So when I duplicate the streetlight the lightsource will also copy with it's parrent. However I allready have all the streetlights placed (in original model). So this doesn't help me.

Is there some way to copy the location of the lightsource in relation to the streetlight, and then paste a new lightsource to a different streetlight using those coordinates? Or is there a different way to add the lightsources to all the streetlights?

Something along these lines may work. This version assumes that your lamp-posts are instances, and the only transforms responsible for putting them where they are, are their own, without the interference of parenting or constraints. You may need to arrange that, by, for instance, clearing their parenting, keeping their transforms.

• Make a backup of your file
• Alt D create an instance of one of your lamp-posts
• (Probably, you'll want to isolate it / hide everything else, so you can see what you're doing)
• Ctrl A, or via the Header > Object menu, > Clear all its transforms
• Position your light where you would like it, relative to the lamp-post
• M Add the light and the lamp-post to a new collection, called, say, 'Practical'
• With Shift C the 3D cursor at World 0, Shift A add a new Collection Instance to the scene, based on the new collection.
• Unhide your original lamp-posts, select them, and then your 'Practical' Collection Instance, so it is the active object.

Now we want to make a copy of the Collection Instance in the place of all the existing lamp-posts. I'm surprised there isn't an operator / add-on to do this without scripting, but unless someone finds one for us, here goes.. run this script:

import bpy

C = bpy.context
D = bpy.data

src = C.active_object
src.select_set(False)
sel = C.selected_objects

cp_col  = D.collections.new('Practicals')