How dark is dark?

I am a newbie just building a grow room and have some questions. When the plants go into the night cycle, how dark does it actually have to be for them? Im concerned that if I put and intake fan in the wall, light will come through. however I would think natural dark isnt like so dark you cant see your hand in front of your face, so any feedback would be great. Thanks

put fan outside run duting into room put bend in ducting

Thanks for the info. Very helpful.

They sell things like this at home depot which should prevent the light leaks from ducting.




I would look in the isle where they sell the sheet metal and air conditioning materials.

yes dark is so dark you cant see your hand in front of your face.

yip make a light trap,black ducting,black pvc pipe and bends

yeah, when you turn the lights off in your grow, you should not see light coming from anything. I even tape over the glowing panels on the AC unit, camera lights, and lights on the computers.