Protected Cultivation
Supplemental Lighting & DLI in Greenhouses
Greenhouse crops receive changing amounts of natural photosynthetic light across the day and season. Supplemental lighting should be evaluated as part of total daily light integral, canopy distribution, photoperiod, energy use, and crop response rather than as a fixed fixture setting.
Key concepts
- DLI integrates photosynthetic photon flux over time
- Greenhouse glazing, structure, season, cloud cover, and shade reduce or redistribute natural light
- Supplemental lighting can fill a light deficit but also adds heat and electrical load
- A crop-level light plan should distinguish total light quantity from photoperiod signaling
What to measure or observe
- Measure or log DLI at crop height in representative zones
- Map PPFD from both sunlight and fixtures at several times or conditions
- Record fixture schedules and dimming state
- Track crop response alongside total daily light and temperature
Common mistakes
- Using one instantaneous PPFD reading as the daily light total
- Ignoring seasonal changes in natural greenhouse light
- Adding light without checking heat load and canopy uniformity
- Treating a DLI target from another crop or system as universal
Visuals this lesson still needs
- Natural plus supplemental DLI timeline
- Greenhouse PPFD distribution map
- Glazing and structure shading diagram
- Light-energy-heat interaction graphic