Photoperiod
The duration and timing of light and darkness in a repeating daily cycle. Photoperiod-sensitive cannabis uses night length as a flowering signal.
Photoperiod includes both the light interval and the uninterrupted dark interval within a 24-hour cycle. Plants sense these intervals through light-sensitive signaling systems that regulate development and seasonal responses.
Most photoperiod-sensitive cannabis cultivars remain vegetative under long days and initiate flowering when nights become sufficiently long and uninterrupted. The exact response and critical night length vary with genetics and conditions. Autoflowering cannabis initiates flowering primarily with age rather than a short-day signal.
Photoperiod also changes daily light integral Daily light integral (DLI) The total photosynthetically active photons reaching one square meter over a day, expressed in mol·m⁻²·d⁻¹. DLI combines light intensity with duration. because the same light intensity delivers more total photons when it runs for more hours.