Vent question

Just set up my tent. Im confused on the vents on the bottom of my tent. If the vents need to be open for the intake of fresh air, then how do the plants get complete darkness in 18/6 cycle? There is going to be some light coming through the vents when its Dark time. Can someone help me with this? Thanks

If you have a fan on that vent, you can add some ducting to it and make a few bends and voila no more light problems.

What he said
And/Or
Black panty hose/dust cap(what ever you are comfortable saying) over the end.
Put a filter on the intake side.
25 ft of Angle and U's

Such an easy fix! Ducting would definatly fix it. Thanx!