Windows now blacked out.
Unfortunately there is light flooding in from the ceiling area!
Turns out this and the adjoining room was once a single room. A dividing wall was built to create two rooms. The ceiling has profiled shaping to give it more strength, but the wall was built to meet the ceiling and not fill in the gaps.
Difficult to photograph, but after around 5 minutes when my eyes adjusted to the light levels I could see everything in the room. That’s no good. The idea now is to temporarily block the gaps next week when the Genie will be used to install my banner paintings.