Blocking light from exhaust vent?

Okay I have a grow box going and heat is beginning to be an issue. One of my two exhaust vents are on top of the box and I can't cover it with a blanket because my temps raise to high. Is there any materials that anyone knows of that I can use to cover it and keep it dark inside for my plants night time?

I just did a little 1hr test constantly checking and the temps rose from 84 to 95. My temps are usually at 78 but I added an ice pack by the fan to help it blow cold air and the temps actually rose?? I guess I was blocking more air than I was cooling.

Any help will be appreciated.

O yes and I only have 1 intake but 2 exhausts. I'm going to add another isolating fan on the inside to try and get some more air movement but I'm mostly worried about the light that can get inside my holes.

i have 1 x 1 same big fans on my box

Drewet88 said:

O yes and I only have 1 intake but 2 exhausts. I'm going to add another isolating fan on the inside to try and get some more air movement but I'm mostly worried about the light that can get inside my holes.

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Hey Drew, welcome to the forum. Only having one intake and two exhaust is not good. You would create a negative air pressure, making the exhaust fans ineffective. If your intake is passive it needs to be twice the size of your exhaust ducting. If you can't pull 'fresh air' into the room you won't be able to exhaust the 'stale' air.
Putting ice in front of our fan...hmmm..I wonder if that high of humidity will kill your plants or just make them stop growing?
Try an experiment. Next time you are out for a drive. open your window, just a crack and see how much air comes in. Now crack open the passenger side rear window. Notice the difference?
Panda plastic, black one side, white on the other, makes a pretty good light block. You can get it from HydroShop, usually about $1.20/ per linear foot, the roll is 10' (3 meters) wide.
If you are talking about light shining thru your exhaust fans into the box, a couple of ideas, black paint on the inside of the exhaust pipe, espacially at any bend, can reduce light penetration and if that is not enough for your situation, you might investigate Dark Room air vents. They are designed to let air into a darkroom, no light is allowed in one, one guy installed his backwards to keep light from leaking out of his grow area. I think they were about $10.
Think of it this way, can you breath out twice for every breath you take? VV

The second exhaust fan only comes on when the lights are on. Its hooked up to the timer. My first exhaust ent doesn't have a fan on it its just a hole. I think I may have helped actually because my original exhaust hole was only about half the size as my intake because I started getting worried about light getting through.

O and there is no hydro shop near me.

EDIT: Just looked at the size of my fans intake is 2.5in and both exhausts are 1in. is that still a bad thing since there's more than one exhaust I can add another intake.

lots of good ones from victor, I like that dark room exaust thing,and painting the bends, that would have saved me time. I had problems like this before and sometimes just a bend in the duct at the end would cut off the light, but still let the flow of air go through. But with the bends it slows the flow. I once had a window exaust that would shine out light at the exaughst so I bent the ducting a little to cut off some light and on top of the exaust i covered it with some plastic and cut out half a circle to make it like an exaughst flap that would bearly let light out.

Nice I bent the venting like he said didn't notice that much blocked airflow and I have a almost completely dark box. It will be completely dark in about 5 minutes had to bondo up some of my drilling holes for wires.

Thanks for the advice guys I just didn't want to get any hermies but I don't know if it'll make a difference this isn't my flowering box.