First off, if you want to run a carbon filter, you will want a stronger exhaust for that.

You can run an air-cooled light in 2 basic configurations:
-Open to the inside of the box, with the light in line with the general room exhaust
-On its own duct run with its own intake, completely isolated from the air in the box (necessary for CO2 injected rooms).
If you aren't doing sealed room, and still want to isolate your light ducting, you will need a second exhaust to refresh the air in the box. That is the exhaust to which you will add your carbon scrubber.
If you want to run only one exhaust, with the light and fan in line, you go: Open end, Light, duct, Blower, Scrubber, Out. With limited space, I'd put the blower and the filter both outside the box. Inline fanst work best when they are PULLING air.