How do I stop light leaking out of my grow tent?

Leaks matter in the dark period of flowering. Light at night breaks the dark period photoperiod plants rely on, and it stresses them, especially if it is bright or repeated. Pinpricks around zippers, corners and the fan or cable ports are the usual culprits.

The easy fixes: tie off duct sleeves with a strap or Velcro, close the spare ports with a sleeve or tape, and put a strip of blackout tape over any damaged seam. Tent accessories like port covers help too. Do this check before the first 12/12, not after.