Tomatoes have different requirements for photosynthetic photon flux density (PPFD, unit: μmol/m²/s) at different growth stages. A reasonable PPFD range can significantly affect its growth rate, flowering and fruiting rate, and fruit quality. The following is a detailed analysis and light management suggestions:
I. PPFD requirements for tomatoes at different growth stages
1. Seedling stage (germination to 4-5 true leaves)
PPFD requirement: 100-200 μmol/m²/s
Lighting duration: 14-16 hours/day
Function: Promote root development and prevent excessive growth (thin stems).
Notes:
The proportion of blue light can be slightly higher (30%-40%) to enhance the robustness of stems and leaves.
PPFD <100 μmol/m²/s can easily lead to weak seedlings.
2. Vegetative growth period (from planting to before flowering)
PPFD requirement: 300-500 μmol/m²/s
Lighting duration: 14-16 hours/day
Function: accelerate leaf expansion and accumulate photosynthetic products.
Key points:
Red light is mainly required (60%-70%) + blue light (20%-30%) + a small amount of far-red light (5%).
PPFD < 250 μmol/m²/s will delay flowering.
3. Flowering and fruiting period (flowering to fruit maturity)
PPFD requirement: 500-800 μmol/m²/s
Lighting duration: 12-14 hours/day (too long may inhibit fruit setting)
Function: improve fruit setting rate and promote sugar accumulation.
Optimization suggestions:
Red light ratio increased to 70%-80% (660nm deep red light is particularly important).
PPFD＞1000 μmol/m²/s requires supplementation of CO₂ (to prevent photosynthetic saturation).
2. PPFD adjustment for different cultivation environments
1. Supplementation of insufficient natural light (greenhouse/indoor)
Rainy days: supplementation of light to more than 300 μmol/m²/s is required (to maintain basic growth).
Winter high latitude areas: it is recommended to supplement light all day, and PPFD should not be less than 400 μmol/m²/s.
2. Artificial light planting (all LED or mixed light source)
Home potted plants:
LED plant light PPFD 200-400 μmol/m²/s (hanging height 30-50cm).
Commercial planting:
Multi-layer vertical farm: PPFD 600-900 μmol/m²/s + CO₂ supplementation (800-1200ppm).
3. PPFD measurement and light intensity management
Measurement tools:
Use quantum sensors (such as Apogee MQ-500) to directly measure PPFD.
Light intensity distribution:
Ensure that the difference in PPFD between the top and lower leaves of the canopy is less than 30% (can be improved by multi-layer supplementary light or reflective film).
Photoperiod control:
Continuous light > 16 hours/day may cause photoinhibition, and the recommended dark period is ≥ 6 hours.
4. Precautions
Light quality and PPFD synergy: A reasonable spectrum needs to be matched under high PPFD (such as increasing red light to promote photosynthesis).
Temperature and CO₂ coordination:
When PPFD > 600 μmol/m²/s, the recommended temperature is 25-28℃ and the CO₂ concentration is 800-1000ppm.
Variety differences:
Large-fruit tomatoes (such as beefsteak tomatoes) require higher PPFD than cherry tomatoes (about 20% increase).
5. Example of economical supplementary lighting solution
Low-cost option:
White full-spectrum LED lamp (PPFD 200-300 μmol/m²/s, covering 0.5m²/lamp).
High-efficiency solution:
Adjustable spectrum LED light bar (PPFD 400-500 during the growth period, adjusted to 600-800 during the fruiting period).
The ideal PPFD range for tomatoes is 200-800 μmol/m²/s, which needs to be adjusted dynamically according to the growth stage. Precise control of the light environment can increase yield by more than 30% and improve the flavor of the fruit!
