Is there anyway I can build a light trapper to stop light leaking in from my veg room into my flower room through the passive vents?
You can hang curtains/blankets/tarps around the flower area. duct tape them to create a seal. it will help keep light out. Also the cheapest way is to go to fred meyer. The section with utility stuff. a large roll of black 4millimiter thick mylar costs 20$ and tax. will definitely keep the light out.
They are two separate rooms that are sealed with the exception of two vents in each room. I want to open up the vent in between my veg and my flower room to help cool down my veg room a little bit. The problem is, too much light comes in from the veg room when flower lights are off.
Two pvc pipe elbows or a simple cardboard box construction that forces the air to go through at least two 90 degree angles. Paint the insides flat black.