You need to have the fan pushing air over the light and not pulling it.
I have my fan in the attic pushing air from my attic down into my room and then back out.
During the summer though I use a 18" ducting and split it off to 2, 8" ducts and run those through 2 lights apiece.
I also run an 8" into the room.
This all ties into my CH/AC and works beautifully.
Although your A/C might not be putting out alot of CFM, it is very cold air.
I have my fan in the attic pushing air from my attic down into my room and then back out.
During the summer though I use a 18" ducting and split it off to 2, 8" ducts and run those through 2 lights apiece.
I also run an 8" into the room.
This all ties into my CH/AC and works beautifully.
Although your A/C might not be putting out alot of CFM, it is very cold air.