In my veg/mother cab I use 3 2 1/2 in pvc piping for intake. I use an elbo on each pipe to help creat a small light trap, I also cover each end of the piping up with black cloth from old black socks with rubberbands and duck tape. This prevents any light geting in and dust and bugs as well. Oh yah , I also use black piping because it smuthers the reflection of light better than white piping.
Adieu