I had some problems getting my light cooled too. I had too mush air moving around the cabinet.
Heres what I did.
I unplugged all my fans except the exhaust from the light. Make sure that you have as few bends as possible in the ducting, also make sure its as short as it can be. I repositioned my fan to the end of the exhaust so it pulls the air out from the light. Besides the llight exhaust fan I use a passive intake (a hole) and have 1 fan that exhausts the cabinet. It worked like a charm, my temps dropped instantly.
If there is a ton of air movement in the cabinet your exhaust fan is fighting against it. Give it a shot, it worked for me.