A light leak is any light reaching flowering plants during their scheduled night: gaps in tent zips, indicator LEDs on equipment, a hallway light under the door, a streetlamp through a window. Photoperiod cannabis measures the length of uninterrupted darkness through phytochrome, and even a brief or dim interruption can reset that clock.
In practice
Eckels and Bugbee (2024) reported that low-level night light pollution delayed flowering in cannabis. Other short-day crops respond to remarkably low levels. A practical test: sit inside the tent with lights off for five minutes until your eyes adjust. If you can see your hand, find the leak. Cover equipment LEDs with tape, seal zip ends and use a green headlamp only for brief checks.
In veg, leaks are harmless. In flower they show as delayed pistil formation, a return to vegetative growth (re-veg) or uneven ripening.
Don't confuse with
- Sunrise/sunset ramp: planned dim light; it counts as day.
- Night break: a deliberate interruption used to hold plants in veg on short days.
Myth check
"Light leaks cause hermaphrodites" needs care. GenetixBay's house position: herms are mainly a sign of genetics from poor breeding, not normal cannabis. Stress such as light interruption can reveal a susceptible line; it does not make a stable one herm. Fix the leak, but cull plants that throw intersex flowers and don't breed from them. See hermaphrodites.
