Determining daily light exposure is critical for plant health and productivity. This guide breaks down key principles, verified by horticultural science.
Core Metric: Daily Light Integral (DLI)
Plants require specific DLI (mol/m²/day) – total photosynthetic photons received in 24 hours. Insufficient DLI stunts growth; excessive light causes photoinhibition.
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Low-DLI plants (e.g., pothos): 6-12 mol/m²/day
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Medium-DLI plants (e.g., lettuce): 12-20 mol/m²/day
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High-DLI plants (e.g., tomatoes): 20-40 mol/m²/day
Duration Formula:Hours = DLI ÷ (PPFD × 0.0036)
Example: For lettuce (DLI=17) under 300 µmol/m²/s PPFD:17 ÷ (300 × 0.0036) ≈ 15.7 hours
Stage-Specific Recommendations
| Growth Stage | Duration | Key Notes |
|---|---|---|
| Seedlings | 16-18 hrs | Prevents legginess; blue-spectrum dominant |
| Vegetative | 14-18 hrs | Long-day plants need ≥16h for leaf growth |
| Flowering | 10-12 hrs | ≤12h for short-day plants (e.g., cannabis) |
Critical: Darkness periods must be uninterrupted. Light leaks during dark cycles disrupt flowering in photoperiod-sensitive species.
3 Essential Optimization Tools
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PAR Meters (e.g., Apogee MQ-500):
Measure actual PPFD at canopy level – LED output degrades ~10% after 50,000 hours. -
Smart Timers:
Devices like RedFarm Hydro’s WiFi Controllers enable sunrise/sunset simulations and cycle precision, reducing plant stress. -
DLI Apps (e.g., Photone):
Calculate required duration based on your light’s PPFD map.
Why Light Uniformity Matters
Poorly distributed light creates "hotspots" and shadows, causing uneven growth. For consistent results:
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Use fixtures with ±5% PPFD variance (e.g., RedFarm’s Samsung LED bars)
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Position lights 12-24" above canopy (adjust weekly)
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Add reflective sidewalls (increases usable light by 30%)
RedFarm Hydro Solutions Spotlight
For growers prioritizing precision:
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G3 Series Lights feature 0-100% dimming and tunable spectra to match DLI needs per growth stage.
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Smart-8 Controller automates photoperiods down to 1-minute increments, ensuring dark cycle integrity.
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PAR Maps for all fixtures provide verified PPFD distribution data.
*"Since switching to RedFarm’s programmable system, our cannabis DLI consistency improved by 22% – no more over/under-lit zones."* – Nevada Commercial Grower Report (2024)
Key Takeaways:
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Calculate duration using DLI and PPFD – not fixed schedules
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Invest in uniform full-spectrum LEDs (≥2.5 µmol/J efficacy)
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Automate cycles with professional controllers
Explore Science-Backed Lighting:
RedFarm Hydro’s DLI-Optimized Systems