Plant Physiology & Development
Phytochrome & Photoperiod Signaling
Phytochrome photoreceptors help plants interpret red and far-red light and participate in measuring light–dark transitions. In photoperiod-sensitive cannabis, flowering behavior depends on integrated signaling over repeated daily cycles rather than on one isolated light reading.
Key concepts
- Phytochrome interconverts between light-responsive states influenced strongly by red and far-red wavelengths
- Night length and interruptions can matter independently of total daily photosynthetic light
- Photoperiod signaling interacts with developmental state and genotype
- Brief unintended night lighting can be biologically meaningful depending on intensity, spectrum, duration, and timing
- Photoperiod and DLI describe different aspects of the light environment
What to measure or observe
- Document actual lights-on and lights-off times
- Audit dark periods for leaks, work lights, indicators, and neighboring light sources
- Track flowering transition across cultivars and canopy zones
- Record blackout timing and environmental effects after closure
- Distinguish photoperiod changes from changes in total light quantity
Common mistakes
- Treating DLI and photoperiod as interchangeable
- Assuming any tiny light exposure has the same biological effect
- Ignoring genotype and developmental stage
- Changing spectrum, intensity, and photoperiod simultaneously without records
- Diagnosing delayed flowering without checking the actual dark period
Visuals this lesson still needs
- Phytochrome red/far-red state diagram
- Photoperiod and night-interruption timeline
- DLI versus photoperiod comparison
- Dark-period audit map