Protected Cultivation
Photoperiod Integrity, Blackout & Light Leaks
Photoperiod-sensitive flowering depends on the timing and duration of light and darkness. Protected structures can introduce unintended night lighting from fixtures, work lights, nearby buildings, incomplete blackout, or control failures.
Key concepts
- Photoperiod is a timing signal separate from total DLI
- Night interruption can alter photoperiod responses in sensitive plants
- Blackout systems must control light while still accounting for heat, humidity, and airflow
- Timers, sensors, curtains, and human activity can all create schedule failures
What to measure or observe
- Audit the structure during the intended dark period
- Check curtain edges, doors, vents, indicator lights, and neighboring light sources
- Record actual fixture and blackout schedules rather than assumed schedules
- Inspect temperature and RH changes after blackout closure
Common mistakes
- Assuming a closed curtain means complete darkness
- Ignoring work lights and equipment indicators
- Closing blackout without planning for heat and humidity buildup
- Changing photoperiod and light quantity at the same time without documenting both
Visuals this lesson still needs
- Light-leak audit map
- Photoperiod versus DLI comparison
- Blackout curtain airflow tradeoff
- Night-interruption timeline