Hi, I am bit confused about the intake ventilation for my grow tent. I know about the fan+filter to draw air out, but in regard of air intake and circulation, is an internal regular fan enough? Or should I also set up a fan like the one used for the filter, but that only pulls air in? As it happens I have another spare such fan. Because I checked online but they talk about *leaving one of the precut holes in the tent open for air intake, but I can’t do that when lights are off.
Thank you
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If you have a in-line fan it will pull air in through the bottom vents that’s all you should need. I also have a fan in all 4 corners in a 4x8 tent. Oscillation fans.
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In your tent leave all vents closed apart from one on the bottom preferably on the opposite side of your fan.
When you zip up the tent it should look like its sucking inwards, if not, turn your exhaust fan up some.
When the tent is sucking inwards its drawing fresh air in from the one open vent at bottom, then that fresh air rises (and circulates via fans inside tent) through your tent until its up and out the exhaust.
If you’re just on a small grow then bringing fresh air into the room as often as possible will suffice instead of needing a lung room, but if you can set that up that would be a good addition.
No need for 2 intake+exhaust fans going, almost made that mistake myself
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I have my exhaust up top with the fan and filter outside the tent. Instead of just leaving one of the bottom flaps open, I put a piece of ducting in it to keep the light from getting in but still allowing the fresh air. I run my exhaust fan at a level where it creates a slight negative pressure.
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I use a 4" intake fan blowing up under the scrog for airflow under and 2 occolators fans (one on the top of canopy and one above lights heatsink and a 6" with carbon filter exhausting out the tent).
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Thank you, i was not aware of the bottom vent use, I saw it was there but didn’t know why, make sense now.
.Yes, the sides of the tent get sucked inward. At first I tuned down the exhaust because I didn’t yet open the bottom vent and it looked it pulled too much inward. It’s now OK,
Thanks for the rest of the tips as well,
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Do you think the bottom vent let’s too much light in?
In my grow space it’s possible for light to get in, but everyone’s space is different. I just don’t want to chance it 
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I googled “occolators” 
I was embrassed to ask 
now I got it:
Oscillators!!, 
thank you
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You can always cut the bottom out of a cardboard box and place it in front of your open vent to create a tunnel to help cut down on light leaking in.
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Hi, yes, but fortunately my bottom vent is almost in the dark even during the day but thank you
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I don’t understand the desire to prevent plants from absorbing even a few photons during night phase. In nature, they’re illuminated at night by stars and, especially, the moon. It might even be beneficial to simulate the lunar illumination cycle. Don’t know whether anyone’s tested that idea.
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That’s true. I am not sure why, but I do remember reading about how they have to stay in “total darkness”. I think a feeble light, like you said, of the moon, it’s ok, but I understand if people do not want to risk it 
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Makes it easier to diag a problem which could be related to light during the dark, or some other cause, if you can immediately rule out light leaks or lights during the dark, & just move on to considering other causes.
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How can light exposure that’s roughly the same or less than plants get at night in nature cause a problem? Has anyone demonstrated that minor light leaks have undesirable effects? Speaking as a noob, I’m having trouble understanding this, but realize there’s plenty for me to learn, yet.
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I can attempt an explanation aside the “it makes it easier to identify a problem because the lights issue is ruled out”
As you said, the plant is not going to completly die if exposed to some feeble light, but the idea is to grow the best plants we can. Most of us, buy few precious expensive seeds(may not be too expensive you say, but at the end we dont buy 100 seeds, in nature there are hundreds of thousands of seeds, most of them will die, some will live, but we cant afford that) and we invest money, time and resources.
All that considered, it makes sense that no one wants to take uneccessary risks and plus we want to maximise their potential with the right light, nutrients, climate so one, from a plant, can get, idk, 5 ounces, instead than 3, and everything we do or dont counts toward achieving that.
So, some light during the dark hours may not hurt them, but it wont certainly helped them, and i think that it’s all there is to it… Hope i was of some help.
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I understand the desire to get the best possible results from seeds that cost $15 - $20 each. I belong to that club, too, and would be a member even if the seeds were free.
I’m not certain that providing the night-time light levels plants are exposed to in nature doesn’t help them. Utter darkness is not natural and may therefore interfere with their growth.
I’m happy to be proven wrong, but in the absence of evidence, it seems to me that insisting on unnatural lighting conditions at night is poorly reasoned superstitious behavior that may be counterproductive.
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I found lot of stuff online, to much to put links, also i am in the UK, some links ask you to change country to view them.
Anyhow it’s interesting and covers lots of your questions about the moonlight, why total darkness and if is true.
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The way dr bruce bugbee describes it. Ambient light is ok as long as its not enough to read a newspaper at normal distance. There is not as much light with a full moon as you think. Does not need complete darkness but why not eliminate the risk.
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I don’t know why, after all these years, I still don’t think to do an internet search sometimes. Thanks for the nudge!
The source @Poseidon1 mentioned is by far the best on this topic that I’ve found:
How Dark is Dark Enough? Darkness level requirements for plants with Dr. Bruce Bugbee
The first thing I learned is that all the research (which isn’t much) that’s been done deals exclusively with flowering. If night-time light levels are excessive, flower size decreases. (There may be other effects, and perhaps effects at other stages, but they haven’t been tested.)
There’s a threshold, though, below which night-time light has no effect. Moonlight is well below that threshold. Typical PPFD meters lack the sensitivity to measure these levels, but there’s an easy way to gauge whether they’re above or below threshold. It involves sticking your head in the tent with a large-print book to see whether there’s enough light to read it, after you dark-adapt. Simple and clever.
Because it’s easy to determine whether there’s a problem and, if not, time spent plugging leaks is wasted.
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