u can set it up different ways, u can suck through the filter,then have the air pass through the lampm and have a single exhaust hose exiting the room,personally if u only have one or 2 lamps,i would have the fan sucking the air through the light then on the other side have regular ducting with your filter hooked up to that and then hung from the wall.u can do it several ways,i personally think sucking is much more affective.but i run my lights on there own fan and have a seperate exhaust "wich is also an option ....any who from my understanding,u should only be pulling air through a filter .and i think can filter brand is the only company that makes a filter that is exhaust only.it makes sense to me.i have several vapor and water charcol filters at work that i fill.activated carbon needs to be seated correctly in order to have the air molecules pass around packed carbon so the odor can be caught.if u have loose seated carbon the air passes through with out catching the odor.when companies roll the aluminum cylinder ,its designed to have the carbon packed straight down and pressed,exhaust only filters are packed,then spun.with a metal pre screen"kinda like u would see if u removed the cloth pre filter.i could be wrong. shit if any one has an old filter and a saw zaw cut one down the center,it could be helpful if this ever come up again