PAR & DLI Requirements for Carrots at Different Growth Stages

Carrots (Carrot, Daucus carota) are a root-vegetable crop whose yield, root size, and quality are influenced by light levels as well as soil/temperature conditions. While many sources focus on root zone and spacing, optimizing lighting in controlled environments (greenhouse/indoor) can also drive performance. Below are guideline targets for PAR (Photosynthetically Active Radiation) and DLI (Daily Light Integral) at each major growth stage.

---

1. Germination / Early Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	~100–200	Gentle to moderate light to initiate shoot emergence and root primord

---

2. Vegetative Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	200–400	Supports leaf expansion, photosynthetic efficiency, and energy storage for root thickening.
DLI (mol·m⁻²·day⁻¹)	12–18	Promotes strong canopy development and consistent root initiation.

Tips:

• Maintain moderate light levels to avoid excessive leaf growth that diverts resources from the root.
• Blue light (≈450 nm) helps maintain compact foliage and increases chlorophyll activity.
• Ensure at least 12–14 hours of photoperiod for steady vegetative progress.

---

3. Root Enlargement Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	350–600	Drives carbohydrate accumulation and sugar conversion in the storage root.
DLI (mol·m⁻²·day⁻¹)	18–24	Higher daily light promotes faster root swelling and deeper orange pigmentation.

Tips:

• Maintain stable DLI to ensure uniform root diameter.
• Red light (≈660 nm) promotes biomass allocation to roots and increases β-carotene synthesis.
• Avoid sudden DLI drops — they can lead to uneven coloring or cracked roots.

---

4. Maturation / Pre-Harvest Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	250–400	Supports final sugar accumulation without excessive foliage stress.
DLI (mol·m⁻²·day⁻¹)	12–18	Balanced light sustains root quality and storage capacity.

Tips:

• Gradual reduction in light intensity before harvest helps balance moisture and sweetness.
• Maintain good air circulation to prevent leaf scorch under high PAR.

---

Key Insights

• Carrots prefer consistent PAR and DLI, rather than abrupt peaks.
• Excessive shading (DLI < 10) leads to small, pale roots.
• Overexposure (DLI > 30) can toughen root texture and reduce color quality.
• Monitoring DLI throughout the season ensures optimal photosynthetic energy for sugar storage.

With the AquaHorti AH-PARDLI PAR/DLI Logger, growers can:
Log PAR and DLI for up to 180 days.
Identify morning–afternoon PAR imbalance.
Export data in CSV format to optimize lighting schedules.