12 Hour Light Trigger

The 12-hour light trigger refers to photoperiod-dependent cannabis plants that initiate flowering when exposed to 12 hours or fewer of continuous light per 24-hour cycle. This trait is foundational to traditional photoperiod breeding and cultivation, distinguishing these plants from autoflowering varieties that flower independent of light duration. Most indica and sativa landraces, as well as modern photoperiod hybrids, carry this light-sensitivity trait. Breeders working with photoperiod genetics rely on this characteristic to maintain distinct vegetative and flowering phases, enabling extended selection periods and controlled cross-breeding. Understanding light-trigger thresholds is essential for indoor cultivation scheduling and outdoor harvest timing prediction.

Photoperiod sensitivity allows breeders to control flowering timing precisely, facilitating backcrossing, hybrid stabilization, and multi-generation selection within single calendar years under controlled lighting. This trait has been preserved across most commercial and heirloom cultivars, making it central to conventional breeding programs.