PAR & DLI Requirements for Specialty Crops at Different Growth Stages

Specialty crops—such as herbs, leafy greens, berries, microgreens, and ornamentals—often have unique light requirements compared to conventional vegetables. Managing PAR (Photosynthetically Active Radiation) and DLI (Daily Light Integral) precisely is essential to optimize their flavor, color, nutrient density, and market value.

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1. Germination / Early Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	80–200	Light intensity should be low and uniform to avoid drying out seedlings.
DLI (mol·m⁻²·day⁻¹)	5–10	Gentle daily light helps root and cotyledon development.

Tips:

• Use diffuse or indirect lighting to maintain even moisture.
• Most microgreens and herbs germinate better with cool white light.
• Excessive PAR can inhibit germination or cause leaf curl.

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2. Vegetative / Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	250–500	Moderate light promotes leaf expansion and stem thickening.
DLI (mol·m⁻²·day⁻¹)	12–20	Encourages carbohydrate production and stronger biomass.

Tips:

• Specialty crops like basil, mint, or microgreens thrive around 300–400 µmol·m⁻²·s⁻¹.
• Include enough blue light to maintain compact, flavorful leaves.
• Uniform canopy lighting prevents uneven coloration.

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3. Flowering / Fruiting Stage (for applicable crops)

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	500–800	Higher PAR levels stimulate flowering and fruit pigmentation.
DLI (mol·m⁻²·day⁻¹)	20–35	Required for full yield potential in crops like strawberries or peppers.

Tips:

• Red and far-red light enhance flowering and color development.
• Monitor leaf temperature to prevent photoinhibition under strong light.
• Gradually increase DLI rather than sudden exposure to full intensity.

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Quick Reference Table

Growth Stage	PAR Target	DLI Target	Example Crops
Seedling	80–200 µmol·m⁻²·s⁻¹	5–10 mol·m⁻²·day⁻¹	Lettuce, herbs, microgreens
Vegetative	250–500 µmol·m⁻²·s⁻¹	12–20 mol·m⁻²·day⁻¹	Basil, kale, parsley, mint
Flowering / Fruiting	500–800 µmol·m⁻²·s⁻¹	20–35 mol·m⁻²·day⁻¹	Strawberries, peppers, tomatoes

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Why Specialty Crops Require Precision Lighting

Unlike large-scale field crops, specialty plants are often grown indoors or in greenhouses where light control = profit control. Small variations in PAR or DLI can change:

• Leaf color and aroma compounds
• Nutrient concentration and sugar levels
• Flowering timing and uniformity

By using a PAR/DLI logger like AquaHorti AH-PARDLI, growers can:
Track hourly light curves automatically.
View daily and seasonal DLI totals via Bluetooth.
Export CSV logs to fine-tune light recipes for each crop type.