Nest your light families.
I've done this with theatrical light fixtures I've created. Since I want to throw different colors of lights when I render a stage scene (Revit nerrrd).
1. Make a light fixture family and create a light source.
2. Modify the light source and save out different versions.
3. Make a new light fixture family and load your saved out light fixture families into this new host.
4. Create a new parameter:
Whether or not you want it to be an instance parameter is up to you. You can make it a type parameter if you want it to do something specific.
This might be handy if you have say, a recessed parabolic or troffer, with different lamping. The different lamping can change both the IES values and the model properties. Or you might have strip lighting, where you want to have multiple heads in a single family. This will solve this too.
ALTHOUGH I DO AGREE. It would be nice to have multiple light sources in a family!!!!
---Adam
Good call! Although it can get confusing if you have a bajillion lights in a project.
Naming conventions and standards becomes extremely important at this point.