Hello, I'll try and answer in general terms.
First, you need to insert the light fixtures into the model properly. They can be either hosted on a ceiling or a work plane. Open a ceiling plan and make sure the view range extends high enough that the lights will be visible. Then insert the light fixtures to the ceiling (if you have one in the model) or to a work plane set to the ceiling height.
You can choose to display the light fixtures in your floor plan (for a combination plan) by extending the view range of the floor plan up high enough to see the lights.
Brian Muir, P.Eng, Muir Engineering