The light at the floor aims at a difficult insulation opportunity, behind finished knee walls.
Let's see what is behind this crude door.
A conscientious installer of cellulose insulation made a best effort to weatherize the ceiling of the home Living Room. Coverage is a spotty twenty percent, with none in the lee of obstructions.
I will fix this, from a new, better access. Attic Access is what I do, and that involves willingness to cut and crawl through plaster walls.
With a hole in the knee wall, the problem is manageable.
I have improved ceiling insulation to R40, over 80 sq ft, and the accessible areas of the cut knee wall to R15. After rebates, despite access cost, the job cost will be repaid by energy savings, in less than ten years. For the homeowner, it is one more thing to feel good about.
The real-plaster patch need not demand support by a professional plasterer. Block opening edges and reset lath. Repair pre-existing cracks with flexible grout as a nice plus of the weatherization. Prime edges, brushing on Plaster-Weld. Screw-attach expanded-metal lath. The patch area is easily filled in one application of Structolite plaster, struck level with a 4-foot feather-edge if it fits. Here, there was compromise, using other tools to level the patch.
Final finish is with broad application of mud. This will need texture and primer.