Block Light NOT Air... ???

I'm sure this has been gone over but really not sure how to form a search query for it so...

How do i insulate my intake holes on a grow box to allow good air circulation but cutting out any light from getting out...

Was thinking about making the carbon scrubber on the inside of the box and that should block any light from the exhaust hole...

Was thinking of just covering the intake holes with the same carbon filter (cloth type) but i have not used it before and do not know how well it would block light...

Is there something better i can use as i would rather save the scrubber fabric for exhaust only it serves no purpose on intake so a cheaper or better solution would be good here...

Put some crazy ass tubing on the front so light can't get through it.

Thats not a bad idea i was thinking about using rocks... Seeing as how we use them to protect the roots from light but they allow air to pass through...

you make a light trap with black pipe, you can put 2 90 degree turns in the pipe or even 1 does the trick very well.....

I decided to go with 90 deg pipes with a bit of carbon filter, or any type of air filter that can be cut to size but carbon filter are black and better for light blocking, attached between the pipe and the box wall...

Seems to work very well... =]