KNOWLEDGE CENTER
Plan lighting for commercial fresh-herb production around the crop species, growth stage and growing system. Explore how DLI, PPFD, photoperiod, spectrum and light uniformity influence growth, morphology, colour and marketable quality in greenhouse and indoor production.
CROP-SPECIFIC LIGHTING
Fresh herbs are a diverse crop category rather than a single lighting group. Basil, coriander, parsley, mint and other herbs can differ in growth habit, canopy structure, development rate and response to light. Even cultivars within the same species may not produce identical results under the same conditions.
The lighting strategy should therefore begin with the crop being grown and the product being sold. A compact potted herb, a bunching crop, a cut-leaf product and a crop intended for repeated harvest may require different priorities for plant shape, leaf size, stem length, colour and production time.
Research confirms that light intensity and spectrum can influence basil biomass, morphology, volatile compounds and sensory characteristics, while responses can vary by species and cultivar.
Record the species and cultivar before establishing the lighting plan. Differences in canopy form, leaf orientation, growth rate and flowering behaviour can affect how the crop intercepts light and responds to the production environment.
Determine whether the crop will be sold as a living plant, a complete bunch or harvested leaves and shoots. The desired plant height, leaf size, colour, tenderness and shelf presentation should influence the lighting objective.
Identify whether the crop will be harvested once or cut repeatedly. A repeated-harvest system must support both the initial canopy and consistent regrowth after each cut while maintaining suitable quality for subsequent harvests.
DAILY LIGHT DELIVERY
PPFD describes the light intensity reaching the crop at a particular moment, while the photoperiod determines how many hours that light is provided. Together, they establish the daily light integral, or DLI, received by the crop.
For greenhouse herbs, sunlight contributes part of the daily total and supplemental lighting supplies the remaining requirement. Because natural light changes with weather and season, the electric-lighting schedule may need to change throughout the year rather than operate at one fixed
duration.
In indoor production, the fixtures provide most or all of the crop’s light. PPFD and photoperiod must therefore be planned together to deliver the intended DLI while preserving an appropriate dark period and avoiding unnecessary operating hours.
Increasing light can affect biomass, leaf development, morphology and crop quality, but higher PPFD is not automatically better. The appropriate balance depends on the herb, cultivar, growth stage, climate conditions and marketable characteristics being targeted.
When PPFD is expressed in µmol·m⁻²·s⁻¹ and the photoperiod in hours, the result is expressed in mol·m⁻²·d⁻¹.
Published lighting treatments provide useful reference points, but a value tested successfully on one basil cultivar should not automatically be applied to coriander, parsley, mint or another production system.
Establish initial targets from crop specific information, then validate them under the facility’s actual temperature, humidity, carbon-dioxide concentration, nutrition, planting density and harvest schedule. Evaluate marketable yield and quality—not biomass alone—before increasing light delivery.
Basil research demonstrates why this distinction matters: changing PPFD and DLI affected volatile compounds, appearance, texture and consumer preference differently, so the highest tested light level did not produce the most preferred product. Basil radiation-intensity study
SPECTRUM AND CROP QUALITY
Light spectrum influences more than photosynthesis. The spectral environment can affect plant morphology, leaf colour, development and the production of compounds associated with aroma and flavour.
These responses are not controlled by one wavelength acting independently. They result from the complete spectrum interacting with light intensity, photoperiod, crop genetics, growth stage and environmental conditions. Spectrum should therefore be selected around the desired marketable product and validated on the herb and cultivar being grown.
Spectral composition can influence stem elongation, leaf expansion and overall plant stature. This may affect whether an herb develops the compact form desired for a living-pot product or the larger canopy preferred for cut-leaf production.
Blue and shorter wavelengths can contribute to photomorphogenic and pigmentation responses, but the result depends on the species, cultivar and total lighting environment. Evaluate colour against the appearance expected by the target market.
Research with basil demonstrates that spectral treatments can change the relative abundance of volatile compounds associated with aroma. A measurable chemical change, however, does not automatically mean that consumers will prefer the resulting flavour.
A broad, visually comfortable spectrum helps workers inspect leaf colour, crop uniformity, nutrient symptoms, pests and disease. Spectral efficiency should therefore be considered together with practical visibility and crop-management requirements.
Independent research example: Controlled-environment and greenhouse studies have demonstrated that spectral composition can alter basil morphology and volatile profiles, with responses varying according to the lighting treatment and production conditions.
PHOTOPERIOD AND DAILY CONTROL
The lighting schedule determines how long the crop receives light each day. It contributes directly to DLI, but it can also provide developmental signals that influence plant form and the transition from vegetative growth to flowering.
For many fresh-herb products, premature flowering is undesirable because it can redirect growth away from marketable leaves and change stem length, texture, flavour or harvest timing. The response, however, varies among species and cultivars and is influenced by temperature, crop age and environmental stress as well as day length.
Select PPFD and photoperiod together rather than choosing the number of lighting hours independently. A longer schedule can deliver the required DLI at a lower instantaneous intensity, but it must remain appropriate for the crop and production objective.
Document when the crop’s dark period begins and ends. Avoid accidental light from service areas, neighbouring zones or poorly coordinated schedules when consistent photoperiod control is important.
Warm conditions, root-zone temperature, water stress and crop maturity can contribute to flowering or reduced vegetative quality. Lighting changes should therefore be evaluated together with the complete climate and irrigation strategy.
Where premature flowering limits production, consider cultivars selected for slower bolting or extended vegetative growth. Match the cultivar, sowing interval and intended harvest age to the facility’s seasonal conditions.
Do not assume that shortening or extending the photoperiod will prevent bolting in every herb. Coriander, basil, parsley, dill and mint differ in life cycle and flowering response, while temperature and plant stress may alter the result.
Record the cultivar, photoperiod, DLI, day and night temperatures, crop age and first signs of stem extension or flower initiation. These records help identify whether the lighting schedule is supporting the intended harvest window.
Independent crop example: Utah State University identifies cool growing conditions and cultivar selection as important considerations for extending coriander leaf production.
CANOPY-LEVEL UNIFORMITY
Average PPFD does not show whether every part of the growing area receives similar light. A production zone can achieve the intended average while still containing bright areas beneath fixtures and lower-light locations between fixtures, near boundaries or beneath structural obstructions.
Uneven light can contribute to differences in plant height, canopy density, leaf development and harvest timing. In repeated-harvest systems, it may also produce inconsistent regrowth after cutting, making crop scheduling and labour planning more difficult.
Fixture spacing, mounting height, optical distribution and overlap should be evaluated at the actual crop plane. The design should also account for benches, crop rows, walkways and greenhouse structures that influence where the light reaches.
Position the sensor at the representative crop plane and maintain the same height and orientation throughout the measurement grid.
Do not collect readings only beneath the luminaires. Include the complete cultivated area so lower-light and transitional zones contribute to the evaluation.
Compare average, minimum and maximum PPFD together with the spatial measurement map. A single value cannot show where uneven conditions occur.
Learn how to create a measurement grid and evaluate PPFD distribution in Understanding PPFD for Commercial Growing →
REPEATED HARVEST SYSTEMS
Fresh herbs may be harvested once as complete plants or managed through several cutting cycles. In a repeated harvest system, the lighting strategy must support both the original canopy and the smaller canopy that remains immediately after cutting.
Harvesting changes plant height, leaf area and the distance between the crop and fixtures. It also changes how much light the remaining foliage can intercept. The conditions used successfully before the first harvest should therefore be reviewed rather than automatically repeated throughout every regrowth cycle.
Define a consistent cutting height that leaves suitable foliage and active growing points for the crop being produced. Lighting cannot compensate for a harvest that removes the structures required for reliable regrowth.
After cutting, the canopy is lower and the fixture-to-crop distance increases. Confirm PPFD at the new representative crop plane and ensure surrounding structures or remaining plants do not create unexpected shading.
Record the days between cuts, marketable fresh weight, stem length, leaf size, colour and rejected material for each harvest. These records reveal whether regrowth remains consistent or quality declines over successive cycles.
Do not compare first- and second-harvest results without recording the conditions preceding each cut. Crop age, remaining leaf area, DLI, temperature, humidity, nutrition and the length of the regrowth period can all influence the outcome.
Where fixture output or the lighting schedule is adjusted after harvest, document when the change occurred and maintain an untreated comparison area whenever practical.
Independent research example: A controlled study of basil found that successive cuts changed productive and quality characteristics, demonstrating why each harvest should be evaluated separately.
WHOLE-ENVIRONMENT PLANNING
Lighting is one component of the production environment. As light availability changes, the crop’s photosynthetic activity, temperature and demand for water, nutrients and carbon dioxide may also change.
Increasing PPFD without confirming that the surrounding environment can support the crop may produce a smaller benefit than expected or contribute to inconsistent quality. Lighting decisions should therefore be coordinated with climate control, irrigation, nutrition and production scheduling.
Record air, canopy and root-zone temperatures during both illuminated and dark periods. Fixture operation, sunlight and climate-control settings can create temperature differences that affect crop development and quality.
Monitor humidity within the crop canopy rather than relying only on a sensor elsewhere in the facility. Adequate air movement and moisture removal become particularly important as dense herb canopies develop.
Changes in light delivery can alter crop water use and nutrient demand. Review irrigation timing, root-zone moisture, electrical conductivity and nutrient balance when adjusting PPFD or photoperiod.
Confirm that carbon dioxide remains available during the illuminated period, particularly in enclosed production areas. Any enrichment strategy should be coordinated with ventilation, worker safety and the crop’s complete environmental conditions.
A lighting adjustment should be evaluated as part of the complete production system. If temperature, carbon dioxide, root-zone conditions or moisture management limit crop performance, increasing PPFD may add energy cost without producing a proportional improvement in marketable yield.
After changing fixture output or operating hours, monitor crop response and environmental data together. Allow sufficient time to distinguish a consistent production improvement from a temporary response.
Independent research example: Controlled-environment basil research demonstrates that temperature and carbon-dioxide conditions can interact to influence growth, physiology and crop composition.
COMMERCIAL VALIDATION
Published research can help establish a starting point, but the final lighting strategy should be validated with the herb, cultivar, growing system and market requirements used in the facility.
A controlled production trial helps determine whether a proposed change improves marketable yield, quality or production consistency sufficiently to justify its operating cost. The comparison should be documented
carefully enough that differences in lighting can be separated from changes in climate, crop management or harvest timing.
Identify the decision the trial must support, such as selecting a DLI, comparing two photoperiods or evaluating a change in fixture output. Avoid changing several lighting variables simultaneously.
Maintain a suitable control or existing production treatment wherever practical. Use the same cultivar, sowing date, growing system, planting density and harvest criteria in both areas.
Record PPFD distribution, photoperiod, calculated DLI, spectrum where relevant, fixture height, dimming level and the dates of every lighting adjustment.
Monitor temperature, humidity, carbon dioxide, irrigation, nutrition and crop density. Note any event that affects only one treatment or prevents a direct comparison.
Evaluate more than total biomass. Record marketable fresh weight, production time, plant form, leaf size, colour, aroma or flavour criteria, rejected material and regrowth where applicable.
Compare the production result with connected load, operating hours and energy use. Repeat promising treatments when practical before applying them across the complete facility.
Differences observed between separate benches, rooms or production cycles may result from position, climate, cultivar, crop density or management rather than lighting alone.
Describe the comparison accurately and retain the underlying measurements. Where formal experimental replication is not practical, treat the result as facility specific operational evidence rather than a universal crop recommendation.
PROJECT INPUTS
A useful lighting proposal begins with a clear description of the crop, facility and production objective. Providing the information below helps define the cultivated area, estimate supplemental light requirements and identify the fixture layout and control strategy that should be evaluated.
List every herb species and cultivar that will use the lighting area. Indicate whether different crops will be grown together, rotated seasonally or managed in separate production zones.
Describe whether the product is sold as a living plant, bunch, cut leaf or shoot. Include the target plant size, production time and whether the crop is harvested once or through repeated cuts.
Provide the cultivated dimensions, bench or channel arrangement, row spacing, crop density, walkway locations and any structural elements that could affect fixture placement or light distribution.
Share available DLI records, greenhouse transmission information, crop-level PPFD measurements and seasonal light conditions. For an indoor facility, document the existing fixtures, output settings and operating schedule.
Confirm the available fixture-to-canopy distance, support structure, supply voltage, phase, circuit capacity and control interfaces. Identify any restrictions affecting installation or maintenance access.
Define the intended DLI, photoperiod, seasonal operating strategy and dimming requirements. Include current production challenges and the marketable improvements the project is expected to support.
When exact measurements are not yet available, provide facility drawings, crop photographs and the best current operating information. CultiLight can help identify the additional data required before a final lighting layout is developed.
LET’S PLAN YOUR HERB LIGHTING
Planning supplemental lighting for a commercial greenhouse or developing an indoor fresh-herb facility? Contact the CultiLight team to discuss your crops, production system, facility conditions and marketable-lighting objectives.
Whether you have complete crop-level measurements or are still defining the project, we can help identify the information required to evaluate the next step.
Already have your project details ready?
