Currently in my 4x4 tent I have everything closed shut except the right bottom vent open for air intake. When i switch to flower can I just angle a piece of cardboard over it so it still gets some form of air intake to avoid light leak or would it need to be closed bypassing any air intake exchange to avoid risk of light exposure?
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A lot of people do exactly what you’re talking about. Anything you can MacGyver to keep light out will do the trick. Gotta have fresh air cycling in so closing off that vent is a no go.
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Which allows for air intake still? Where would you buy that local hardware? Im assuming its cut to fit and some how afixed across the intake vent?
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It’s going to stink real bad if that vent is open
Yep it lets air thru even filters dust . Aquarium stores, pet stores all over amazon probably even home depot. Just measure for the size you need and shop. Jus dont get one too 'fine" get a “course” filter.
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Why not run your 12/12 concurrent with your day time hrs and not worry about light leaks at all?
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Easier said then done via location of my grow tent. More so worried about lights in the house being my issue.
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Even if you use something else to keep light out putting one of those over your vent is a good idea. I have a pack of the cheapest, green air filters and keep one of them propped up over the air vent on my tent. Keeps dust from getting into your tent and keeps dust from building up on the vent. All autos in there so far so no need to worry about light leaks.
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I ran a dryer vent hose into the tent through an opening at the bottom of the tent . The portion outside the tent is curved a couple of times to keep light out. The hose is covered with a fine screen to keep things out. I like the idea of the black screen.
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Dr Bruce has a light leak vid. 2 umols is the brightest moon on the clearest night you can imagine. 10 umols is the threshold for light pollution to start affecting cannabis plants during their night cycle. The easiest way for anyone to understand how much light that is, if you can read print in your tent, then it is over the threshold. If you cannot read print then it is fine.
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What do you have going on there?
also does @DEEPDIVERDAVE does like that, a piece of ducting into vent for a ‘light trap’
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The portion outside the tent is curved a couple of times to keep light out. The hose is covered with a fine screen to keep things out. I like the idea of the black screen.
And that box arrived just in time.
Worked great for me, too.
Screwed lights today, forgot one tent for 3 extra hours of lowest red light.
Forgot to swap over, tough day, so far.
Post Lotto Depression, I didnt win the big one, YET. 
Sprayed black paint for less light inside tube.
“Plant NO-GROW” cloth from garden roll, works fine for air exchange and no light transfer, on tubing that extends out of tent (or wraps over tent). Static air movement not a big restriction thru tube.
Air-exchange holes in box advantage, less structural cardboard negative.
keep things out… like critters 
pets and pests
the only difference is one ‘s’ and somethimes thats the only difference
I keep the square ones closed and use the round lower intakes with a black long 6" duct with a few curves in it like an “S”… Haven’t had any issues ever.
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Running a 6 inch Ac Infinty inline with carbon filter hopefully thats not a huge issue.
You need negative air pressure to get rid of all the stink… Not sure that can be done with the square bottom vents.