Carbon Filter at intake or exhaust?

Quick question from a newb- Do you put the carbon filter at the intake end of your ventilation system, or at the exhaust? I'm growing in a small (0.8m wide, 0.8m deep, 1.3m high) grow space, and I run a 4" inline fan.

Here's how the airflow works:

open tube inside the top of the grow box pulls air in,
air is ducted to the MH/HPS aircooled light,
pulled through the light to cool it,
pulled up to the fan,
out the top of the grow box, and
through a carbon filter.

I also have a 6" circulating fan clipped to the top of my grow box, to keep my girls cool and strong.

Is this the best setup, or do I want the carbon filter inside the box filtering the intake?

I have pics:

I wouldnt worry too much about the intake. I like to focus more on the exhaust, the air will replace itself. the more air thats sucked out the more fresh air and c02 you got. ~ Im growing in a similar space and im gonna hook up two inline fans to the exhaust and have them pull through the filter on their way out. ~ as long as you have an opening on the bottom or somewhere else to draw in fresh air your good - outgoing air is what you have to worry about. Hope this helps man, good luck maintaining temps. thats always my biggest challenge