KNOWLEDGE CENTER
Plan lighting for commercial tomato production around crop stage, available daylight and canopy structure. Explore how DLI, PPFD, top lighting, inter-canopy lighting and operating schedules fit into a greenhouse lighting strategy—from young plants to established fruiting crops.
LIGHTING FOR TOMATO PRODUCTION
Commercial tomato lighting should be planned around the crop’s stage of development, canopy structure and production schedule. Young transplants and established fruiting plants differ in size, spacing and how their leaves intercept light, so the same lighting arrangement may not serve both equally well.
In high-wire tomato production, the crop forms a tall, layered canopy. Upper leaves intercept light from above, while leaves farther down can experience substantial shading. A PPFD reading above the crop is therefore useful, but does not fully describe the light environment within it.
Start with the tomato variety, planting density, row arrangement, training system and available seasonal daylight. Use these details to establish appropriate light targets and evaluate fixture positioning and operating schedules. The objective is to support the crop “throughout its development, not simply…” to achieve a high reading above the plants.
Technical reference for the canopy explanation: Research on light distribution within tomato crops.
CROP-STAGE PLANNING
Lighting priorities change as tomato plants establish roots, develop their canopy and carry fruit. These stages overlap: an established high-wire tomato crop can produce new leaves, flowers and developing fruit at the same time. The lighting strategy should therefore support the whole crop rather than treat each stage as an isolated phase.
This overlap is described in UF/IFAS greenhouse tomato guidance.
During propagation, the priority is to produce sturdy, well-rooted transplants with healthy leaf development. Provide evenly distributed light across the growing trays and monitor the daily light integral at seedling height. Adjust lighting alongside temperature and plant spacing to support consistent development without excessive stretching.
The emphasis on transplant quality and daily light is supported by Purdue’s vegetable-transplant guidance.
After transplanting, reassess light delivery in the production area. Plant spacing, fixture-to-canopy distance and available daylight may differ substantially from the propagation environment. Check PPFD at the new canopy height and review the lighting schedule as roots establish and the leaf canopy expands.
As flowering and fruit set develop, lighting must support continued plant growth alongside the developing reproductive load. Review light availability together with temperature, humidity and pollination conditions. Increasing light alone cannot correct poor pollination or an unsuitable greenhouse climate.
Temperature and pollination are important influences on fruit set, as explained in UF/IFAS production guidance.
During sustained production, consider light delivery alongside the number and size of developing fruits, retained leaf area and seasonal daylight. Review how light reaches productive leaves throughout the canopy. Adjustments should support both fruit development and the continued growth needed for later harvests.
The connection between canopy lighting, photosynthesis and fruit development is explored in this tomato inter-lighting study.
DAILY LIGHT TARGETS
Daily light integral (DLI) describes the total photosynthetically active light received over a day. PPFD describes the light arriving at a particular moment.
For greenhouse tomatoes, establish the total daily light target first, then account for the daylight reaching the crop. Supplemental lighting supplies the remaining requirement within an appropriate operating schedule. A total DLI target therefore includes both daylight and electric light—it is not the amount the fixtures must provide alone.
Published guidance provides this general DLI range for tomato transplant production. Use it as a starting point, then adjust for seedling development, cultivar, temperature and observed plant response. Measure light at the height of the young crop.
This range is specifically listed for tomato transplants in Purdue’s published guidance.
Published guidance provides this broad DLI reference range for tomato production. It is not a universal optimum or an upper limit. Confirm the project target with the grower or crop advisor, considering crop condition, production goals and the greenhouse environment.
Virginia Cooperative Extension lists this range while emphasizing that targets require adjustment for specific conditions. DLI guidance.
Suppose the selected total DLI target is 24 mol·m⁻²·d⁻¹ and daylight supplies 12 mol·m⁻²·d⁻¹ at the crop’s reference measurement plane.
The supplemental requirement is:
24 − 12 = 12 mol·m⁻²·d⁻¹
If the fixtures deliver this additional light over 16 operating hours at constant output, the required supplemental PPFD is:
12 ÷ (16 × 0.0036) ≈ 208 µmol·m⁻²·s⁻¹
The fixtures supply the light deficit, while daylight supplies the rest. These figures are illustrative—not a prescribed tomato target or lighting schedule. Select operating hours around the crop’s photoperiod and dark-period requirements.
The example uses the standard conversion between PPFD, operating hours and DLI described by Virginia Cooperative Extension.
LIGHT THROUGHOUT THE CANOPY
Top lighting and inter-canopy lighting deliver light from different positions. The appropriate choice depends on the tomato canopy, available daylight and where additional light is needed—not simply which arrangement produces the highest individual PPFD reading.
Top-lighting fixtures sit above the crop and direct light downward across the growing area. Their spacing, mounting height and optical distribution determine how evenly supplemental light reaches the upper canopy.
As the tomato canopy becomes denser, upper leaves intercept more of this light, leaving less available farther down. A uniform above-canopy PPFD map therefore does not necessarily mean uniform light delivery throughout the plant.
Inter-canopy lighting, also called interlighting, places fixtures within the crop at selected heights to illuminate leaves that receive less light from above.
Its purpose is to reach retained, productive foliage—not simply the lowest part of the plant. Positioning should account for row spacing, leaf distribution, pruning, crop lowering and access for harvesting and maintenance. Follow the fixture manufacturer’s clearance and installation requirements.
Tomato research demonstrates improved light delivery to shaded leaves, while also showing that crop responses vary with growing conditions. Interlighting study.
Combining top lighting with inter-canopy lighting can provide coverage from above while improving light availability deeper within the crop. However, a combined system is not automatically necessary or more economical.
Evaluate the complete light distribution, crop response, installation requirements and operating costs before selecting the balance between the two. There is no single top-lighting-to-interlighting ratio suitable for every tomato greenhouse.
An upward-facing sensor above the canopy does not fully describe light delivered sideways within the crop. Assess inter-canopy lighting at documented positions, heights and sensor orientations.
Do not simply add a sideways inter-canopy PPFD reading to an upward-facing above-canopy reading and report the result as total canopy PPFD or DLI. Measurements must refer to a consistent location and sensor plane before their contributions can be combined.
Research comparing these layouts uses different sensor orientations and examines light distribution throughout the canopy, rather than relying on one above-crop value. Tomato-canopy measurement and modelling study.
PHOTOPERIOD AND DAILY CONTROL
A tomato lighting schedule must consider both daily light quantity and the timing of light exposure. Delivering the same DLI over different photoperiods does not necessarily produce the same crop response.
Set the period during which supplemental lighting is permitted, accounting for natural daylight and all installed lighting systems. Coordinate top lighting and inter canopy lighting so that one system does not unintentionally extend the crop’s light exposure beyond the planned schedule.
Use crop-level light measurements and accumulated DLI to guide dimming or switching. Fixtures may operate before sunrise, during low-light daytime conditions or after sunset within the selected window. A 16-hour lighting window does not mean the fixtures must operate at full output for all 16 hours.
Select the photoperiod with the grower or crop advisor, considering cultivar, crop stage and greenhouse conditions. Static, continuous lighting can cause leaf injury and reduced productivity in tomatoes. Specialist strategies that vary light intensity and spectrum have shown promising results, but they should not be treated as permission to leave ordinary grow lights on continuously.
Research comparing equal-DLI treatments found different outcomes under conventional, static continuous and dynamically controlled lighting. Tomato photoperiod study.
An illustrative schedule could permit supplemental lighting from 04:00 to 20:00—a 16-hour window—with a planned dark period from 20:00 to 04:00.
Within that window, fixtures may dim or switch off when daylight is sufficient. Calculate their DLI contribution from actual output and operating time, not simply the length of the permitted window.
The eight-hour interval is only a dark period if daylight and other lighting do not illuminate the crop during it. Adapt these example times to the season, location and crop-management plan.
LIGHTING AND CROP ENVIRONMENT
Lighting is one part of the tomato crop’s growing environment. Increasing PPFD cannot fully compensate for unsuitable temperatures, limited carbon dioxide or inadequate water availability. Review these conditions together whenever lighting intensity, operating hours or fixture technology changes.
Review both air and leaf temperature alongside humidity and airflow. Changing from HPS to LED lighting can alter the thermal conditions around the crop, even when PPFD remains similar.
Do not assume that the previous greenhouse temperature settings will produce the same leaf temperature after a lighting upgrade. Check the crop’s actual conditions before adjusting heating, ventilation or humidity control.
Tomato research has measured different leaf temperatures and transpiration rates under LED and HPS lighting. Lighting and leaf-temperature study.
Carbon dioxide supplies the carbon used in photosynthesis. If CO₂ becomes depleted around the crop, the benefit of additional light can be limited.
Monitor CO₂ during illuminated periods. Where enrichment is installed, coordinate its operation with light availability, crop conditions and ventilation. Use appropriately designed equipment, monitoring and worker-safety controls rather than treating enrichment as a simple lighting accessory.
CO₂ management depends on light intensity, temperature, ventilation and crop stage. Ontario greenhouse CO₂ guidance.
Changes to light intensity, operating hours and canopy conditions can change crop water use. Reassess irrigation against observed demand rather than adjusting it directly in proportion to fixture wattage.
For substrate-grown tomatoes, review root-zone moisture, drainage and electrical conductivity (EC) trends. These observations help guide irrigation timing and nutrient-solution management as the crop and its lighting conditions change.
Monitoring crop demand, drainage and EC is emphasized in UF/IFAS guidance for substrate-grown tomatoes.
Agree lighting, climate and irrigation adjustments with the grower or crop advisor. Record the settings and crop response before and after changes so that future decisions are based on observed performance rather than assumptions.
PROJECT PLANNING
A useful tomato lighting plan begins with accurate crop, facility and operating information. The following details help define the evaluated growing area, required light delivery, suitable fixture arrangement and controls needed for the project.
Identify the tomato type or cultivar, crop stage, planting schedule and expected production cycle. Include any established crop-quality, production or seasonal lighting goals that the lighting plan should support.
Provide greenhouse drawings or dimensions, including the cultivated area, bay and gutter spacing, crop rows, walkways and excluded spaces. Clearly identify whether the project covers the complete greenhouse or only a defined production zone.
Record row orientation and spacing, plant or stem density, representative canopy height and the crop’s training and lowering system. For inter-canopy lighting, include the retained leaf zone and available space between rows.
Share available daylight or DLI records, greenhouse transmission information and the use of shade or energy curtains. If lighting already exists, provide fixture models, output, mounting positions, operating schedules and control capabilities.
Identify the intended total DLI, supplemental PPFD, uniformity objective and lighting window where these have already been established. Indicate whether the project is considering top lighting, inter-canopy lighting or a combined arrangement.
Provide available supply voltage, electrical capacity, mounting locations and known structural obstructions. Include existing climate-control interfaces, dimming requirements, installation timing and any operational limitations that could affect the lighting system.
LET’S PLAN YOUR TOMATO LIGHTING
Planning a new commercial tomato greenhouse or upgrading an existing lighting system? Contact the CultiLight team to discuss your crop, facility conditions and lighting objectives.
Whether you have complete greenhouse drawings and crop data or are still defining the project, we can help identify the information needed to evaluate the appropriate next step.
Already have your project details ready?