PAR & DLI Requirements for Tomato Plants at Different Growth Stages

Tomatoes are among the most widely grown crops in greenhouses, high tunnels, and hobby gardens. To get consistent fruit set and strong yields, growers must match light conditions to each growth stage. Below is a guideline for PAR (instant light intensity) and DLI (daily light integral) targets for tomatoes, and tips on how to use them.

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1. Seedling / Early Vegetative Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	150–300	Keep light gentle to avoid photoinhibition or burning sensitive young leaves
DLI (mol·m⁻²·day⁻¹)	6–12	Enough light to drive growth, but not pushing energy consumption too high

Tips:

• Use lower-intensity lighting or shade cloth if using sunlight.
• Maintain good distance between lights and seedlings to avoid hotspots.
• Monitor leaf color and internode length to adjust light conditions.

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2. Vegetative / Growth Stage (Foliage & Stem Development)

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	400–600+	To support robust foliage development and strong stems
DLI (mol·m⁻²·day⁻¹)	15–25	A solid daily light dose to support faster growth and biomass production

Tips:

• Use full-spectrum lighting (balanced blue + red + some green) for uniform leaf growth.
• Avoid shading inner leaves—optimize canopy light distribution.
• As growth accelerates, watch for signs of light saturation or heat stress.

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3. Flowering / Fruit-Set / Fruit Development Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	700–1000+	High intensity supports photosynthesis demand for fruiting
DLI (mol·m⁻²·day⁻¹)	25–35	To maximize fruit set, size, and yield

Tips:

• Peak light periods (midday) are critical—ensure plants get enough intensity at those times.
• If natural DLI is insufficient, use supplemental lighting during dawn/dusk or cloudy days.
• Monitor fruit set, sugar content, and foliage health; adjust light levels accordingly.

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Why These Ranges Aren’t Fixed

• Climate, latitude, season, greenhouse shading, or greenhouse glazing affect actual light reaching your plants.
• Some tomato varieties (determinate vs. indeterminate) may perform differently under the same light conditions.
• CO₂ levels, temperature, humidity, and nutrient availability must be balanced with light inputs.

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Using AH-PARDLI to Hit Target Light

With a PAR/DLI logger like AH-PARDLI, you can:

• Monitor hourly PAR and see if peaks hit the target range.
• Track daily DLI and compare with ideal values for each growth stage.
• Export CSV data to analyze season-over-season performance.
• Adjust light schedules or supplemental lighting based on real metrics.

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Summary

Tailoring light to tomato growth stages is key:

• Seedlings: 150–300 µmol·m⁻²·s⁻¹, DLI 6–12
• Vegetative: 400–600 µmol·m⁻²·s⁻¹, DLI 15–25
• Flowering / Fruiting: 700–1000+ µmol·m⁻²·s⁻¹, DLI 25–35

Use real measurement tools — don’t just guess. With precise light management, you can maximize yield, quality, and plant health.