I'd close that vent..patch up your plaster then think of a pendant..

do you need an AC vent for your dining? blows down to where your food is ..

Select something lower, so the eyes are not drawn to the AC, or a series of single lights along the ceiling above your table, especially with a dimmer and good quality light bulbs.

I agree with Vy if you are set on a pendant then close up the vent. If that's not an option, consider another source of light, other than from above such as wall lights or a floor lamp or both. They will create a lovely ambience for dining. I notice that you have two down lights on the other side of the vent so that should give you plenty of light.

rfgt what a brilliant idea..that would work..direct the airflow to the sides and not directly down and still can have a pendant ..:) you've solved the problem :)

I've heard of elephants in the room, but that takes the cake. If it works, I'm with rfgt.

I would suggest a glass pendant so that the view through to the window isn't obstructed. Also, a pale cord and ceiling rose would result in the eye being drawn to the pendant itself and away from the ceiling and A/C.

Thank you all. I have hated these for the last 12mths and it's been a challenge to replace based on size of apartment and budget dedicated to renovation ( would rather re tile my fabulous north aspect balcony) so I had to make compromises. The new smaller units have been installed and when patched and painted I'll review the whole lighting situation. All your comments have been extremely helpful.

A crisp white square under the duct is a great idea. You could then have a simple flush mounted fitting, though a clear glass pendant would also look nice. Or maybe a square chandelier type fitting mounted on the square? One of those very simple ones with glass tears rather than crystals. It's a very interesting problem, and I think the blown glass tears are very appealing.

Its funny talking about pendants when its near an airconditioning outlet because that airflow will move the light and give a really wild effect moving in the breeze. The best effect would be as suggested wall lights Dimmable and aimed upwards to use the ceiling as a reflector and giving a lovely ambiance to the room in the corner where the Dyson is put a floor lamp something people will look at and , not even notice the duct in the roof, trick the eyes from going up, it will become invisible eventually