Also small things like light through a crack in the door. OR a red LED on a power strip. Even a HPS street light two blocks away, through a window can stop it from happening.
When you put a plant on 12/12 a chemical build up happens during lights out. ANY photosynthesis will stop this from building up. Once enough of this chemical builds up in the plants tissues, flowering begins. However as I said, if ANY photosynthesis occurs during lights out,.. The process will eat up this chemical, and it will not trigger flowering.
