How LED Grow Light Spectrum, PPFD, DLI and Fixture Dimensions Affect Indoor Farming

Choosing an LED grow light involves more than comparing wattage or visible brightness. An effective horticultural lighting system must deliver the appropriate spectrum, intensity and daily light exposure while fitting the physical dimensions of the grow space.

For commercial greenhouses, vertical farms, propagation facilities and university research programs, fixture size can be just as important as photon output. The light must fit above the canopy, provide consistent coverage and integrate with the facility’s mounting, electrical and environmental requirements.

This guide explains how light spectrum, photosynthetic photon flux density (PPFD), daily light integral (DLI), canopy uniformity and fixture dimensions work together. It also compares three LED grow-light formats available from SJS Products.

If your project requires a specific fixture size, spectrum or output, you can request a custom grow-light design based on your crop, facility and lighting goals.

Why Grow-Light Spectrum Matters

Plants respond to light differently than people do. Human vision is most sensitive to certain visible wavelengths, but plants use light through photosynthetic pigments and photoreceptors that influence photosynthesis, leaf development, stem elongation, flowering and other growth responses.

Light spectrum is measured in nanometers, abbreviated as nm. Horticultural LED systems may combine multiple wavelength regions to support different crops, growth stages and production objectives.

However, spectrum should never be evaluated by itself. Plant response also depends on:

• Crop species and cultivar
• Growth stage
• Light intensity
• Photoperiod
• Canopy density
• Temperature and humidity
• Carbon dioxide availability
• Water and nutrient availability
• The ratio between different wavelengths

There is no single spectrum that is ideal for every crop or facility. A lighting plan should be developed around the crop, grow-space dimensions and complete cultivation environment.

Understanding the Main Horticultural Light Regions

Blue light: approximately 400–500 nm

Blue wavelengths can influence leaf development, stomatal response and plant morphology. Blue light is frequently included in seedling and vegetative lighting strategies because it can support compact growth in many crops.

The appropriate amount depends on the plant and production objective. Excessive blue light may limit leaf expansion or biomass development in some crops, particularly when other wavelength regions are restricted.

Green light: approximately 500–600 nm

Green light is sometimes considered less useful because chlorophyll absorbs certain green wavelengths less strongly than red or blue light. However, green photons can penetrate deeper into leaves and dense plant canopies.

This deeper penetration may support photosynthesis in lower leaves that receive less direct red and blue light. Green light also improves visibility for workers inspecting plants for stress, pests, diseases and nutrient deficiencies.

Red light: approximately 600–700 nm

Red wavelengths are efficiently used in photosynthesis and are a major component of many commercial horticultural lighting systems. Red light can support biomass production and can influence plant development during vegetative and reproductive stages.

Although red light provides photosynthetically useful energy, plants generally benefit from an appropriately balanced spectrum. Red-only systems can produce undesirable morphological responses in certain crops.

Far-red light: approximately 700–750 nm

Far-red wavelengths can influence stem elongation, leaf expansion, shade responses and flowering behavior. The ratio between red and far-red light helps plants respond to surrounding vegetation and perceived canopy competition.

Far-red can be useful in carefully designed lighting programs, but its effects depend on the crop, cultivar, intensity and timing. Excessive far-red exposure may cause unwanted stretching in some plants.

Ultraviolet light: below 400 nm

Controlled ultraviolet exposure may influence pigmentation, plant-defense responses and the production of certain secondary metabolites. However, UV must be applied carefully because excessive exposure can damage plant tissue and create safety concerns for workers.

UV-equipped systems should include suitable controls, operating procedures and protective measures.

These are generalized responses. Actual plant performance depends on the species, cultivar, growth stage, intensity, photoperiod and environmental conditions.

PAR, PPF, PPFD and DLI Explained

Grow-light performance cannot be evaluated accurately through wattage or visual brightness alone. Several horticultural measurements provide more useful information about the amount of light produced and delivered to the canopy.

What is PAR?

Photosynthetically Active Radiation, or PAR, traditionally refers to the 400–700 nm wavelength range commonly associated with photosynthesis.

PAR describes a region of light rather than a measurable amount of light. A fixture should not be described only as having “high PAR” without identifying the actual output or canopy measurement.

What is PPF?

Photosynthetic Photon Flux, or PPF, measures the total number of photons within the PAR range emitted by a fixture every second.

PPF is measured in micromoles per second:

µmol/s

PPF indicates how much photosynthetically active light a fixture produces. It does not show where that light lands or how evenly it reaches the crop.

What is PPFD?

Photosynthetic Photon Flux Density, or PPFD, measures how many PAR photons reach one square meter of surface area every second.

PPFD is measured in:

µmol/m²/s

PPFD helps growers evaluate the instantaneous light intensity reaching the canopy. Measurements should be taken at several points across the grow space rather than only at the brightest location.

A high center reading can be misleading if the edges receive substantially less light. Average PPFD, minimum PPFD and overall uniformity are usually more useful than a single maximum reading.

What is DLI?

Daily Light Integral, or DLI, measures the total number of PAR photons received by one square meter over an entire photoperiod.

DLI is measured in:

mol/m²/day

PPFD describes the intensity at a particular moment, while DLI describes the total light accumulated throughout the day.

A simplified DLI calculation is:

DLI = PPFD × hours of light × 3,600 ÷ 1,000,000

For example, an average PPFD of 400 µmol/m²/s delivered for 16 hours produces:

400 × 16 × 3,600 ÷ 1,000,000 = 23.04 mol/m²/day

This calculation does not mean that 23.04 mol/m²/day is appropriate for every crop. The target DLI should be selected according to crop requirements, growth stage and environmental conditions.

Why Higher Light Intensity Is Not Always Better

Increasing PPFD can increase photosynthesis up to a point, but plants cannot use unlimited light. The useful intensity depends on whether the crop has sufficient water, nutrients, carbon dioxide and environmental control to use the additional energy.

Excessive light intensity can:

• Increase plant stress
• Raise leaf and canopy temperatures
• Increase irrigation demand
• Create bleaching or light-damage risks
• Increase electrical and cooling costs
• Produce uneven growth when distribution is poor

Insufficient intensity can also limit crop development. The objective is not to install the highest-powered fixture available. It is to deliver an appropriate PPFD and DLI with consistent distribution across the intended growing area.

Why Fixture Dimensions Matter

Fixture dimensions are an important engineering consideration in vertical farms, propagation racks, research chambers, laboratories and facilities with restricted mounting clearance.

The physical size and shape of a grow light can affect:

• Rack and bench compatibility
• Distance between the fixture and canopy
• Available plant-growth height
• Air circulation and heat management
• Installation and maintenance access
• Light distribution across the canopy
• The number of fixtures required
• Electrical and cable routing
• Mounting-point locations

A high-output light is not automatically suitable for every facility. The fixture must physically fit the growing environment while delivering the required spectrum, intensity and uniformity at the intended mounting height.

SJS Products LED Grow-Light Form Factors

SJS Products offers linear, modular and hanging fixture options that can be evaluated according to the crop, canopy dimensions and available installation space.

Titans AGHK-1640 Linear LED Horticultural Lights

The Titans AGHK-1640 Series LED Horticultural Light is a compact linear system available in five listed lengths and power levels.

All five models have the same listed 59 × 46 mm cross-section. This makes it possible to select different lengths and power levels without substantially changing the fixture profile.

The series has a listed input range of 85–265V AC, a power factor above 0.9 and a 120-degree beam angle. IP44 and IP65 versions are available, depending on the selected configuration.

Its narrow linear form factor may be suitable for:

• Propagation shelves
• Seedling trays
• Narrow vertical-farming racks
• Research benches
• Teaching laboratories
• Growth chambers
• Supplemental greenhouse lighting
• Multi-level cultivation systems

The AGHK-1640 fixtures can be connected using daisy-chain cables, helping simplify wiring across long benches or multiple rack levels.

Available spectrum selections include:

• 6400K cool white
• 6400K and 2700K mixed white
• 6400K, 2700K and 660 nm red
• 2700K warm white
• 8:1 red-to-blue ratio
• Sunlight-style spectrum extending from UV to far-red

Titans Modular H60, H120 and G240 Grow Lights

The Titans Modular LED Grow Light is available in three listed power classes.

The modular series is designed for projects that may require greater output or configuration flexibility than a compact linear bar. Potential applications include commercial greenhouses, hydroponic facilities, vertical farms, flowering rooms, breeding programs and research environments.

Published technical features include:

• 90–305V AC input
• 0.95 power factor
• Operating-temperature range of −40°C to 50°C
• IP65/IP68 protection
• Osram or Bridgelux LEDs
• Meanwell drivers
• Customizable spectrum configurations
• Hoist, ceiling and boom-mounting options
• CE, RoHS and cETLus certifications
• Five-year listed warranty

Custom spectrum options can include UVB and 440, 465, 535, 625, 660, 735 and 760 nm wavelengths, depending on the selected configuration and project requirements.

Technical planning note: The physical length, width and height of the H60, H120 and G240 configurations are not currently published on the product page. Request a dimensional drawing for the selected model before finalizing rack clearances, mounting locations or electrical routing.

GG 120W Hanging Light Bar

The GG 120W Hanging Light Bar provides a suspended fixture format for controlled-environment agriculture.

The fixture includes hanging carabiners, while additional mounting hardware is sold separately. The product page identifies Osram and Meanwell components and describes them as ETL-certified components.

The hanging format may be considered for:

• Indoor grow rooms
• Greenhouse production areas
• Open cultivation benches
• Propagation zones
• Facilities requiring suspended overhead lighting

Installation planning should account for the 5.5-inch fixture height, suspension hardware and required distance from the canopy. The 12.2-pound fixture weight should also be considered when specifying rails, ceiling supports or other mounting structures.

LED Grow-Light Format Comparison

These fixtures should not be compared by wattage alone. The final selection should account for canopy dimensions, mounting height, target PPFD, spectrum, uniformity, environmental exposure and available electrical infrastructure.

Why Canopy Uniformity Matters

A fixture’s maximum PPFD does not provide a complete picture of its performance. A light may produce a very high reading directly below its center while delivering substantially less intensity around the edges.

Plants in the center may receive excessive light while plants at the perimeter receive too little. This can create differences in growth rate, crop quality and harvest timing.

A complete lighting layout should consider:

• Average PPFD
• Minimum and maximum PPFD
• Edge-to-edge distribution
• Mounting height
• Fixture spacing
• Beam angle
• Reflective surfaces
• Canopy height and density
• Changes in plant height over the production cycle

A useful PPFD map should identify the measurement area, grid spacing, fixture mounting height and operating power. Without this context, PPFD values can be difficult to interpret.

Lighting Strategies for Different Applications

Seedlings and propagation

Young plants generally require less intensity than mature crops. Uniform tray-level coverage is particularly important because uneven lighting can create inconsistent rooting and plant development.

A propagation system may prioritize:

• Moderate intensity
• Consistent tray-level coverage
• An appropriate blue-light component
• Low heat near young plants
• Dimming and scheduling controls
• A compact fixture profile

The narrow profile and multiple length options of the AGHK-1640 Series may be useful for propagation shelves and multi-level racks.

Leafy greens, herbs and microgreens

Leafy crops are frequently grown in vertical racks where fixture dimensions, heat output and canopy uniformity are important. The objective may be to achieve compact growth, consistent leaf quality and predictable production cycles while controlling energy use.

Lettuce, basil, spinach, herbs and microgreens should not automatically receive the same spectrum, PPFD or DLI. Requirements can vary by species, cultivar, growth stage and production target.

Fruiting crops

Tomatoes, peppers, strawberries and other fruiting crops may require higher daily light totals than many leafy greens, especially during flowering and fruit development.

A lighting design for fruiting crops may need to account for:

• Changing canopy height
• Light penetration into dense foliage
• Supplemental greenhouse lighting
• Seasonal sunlight variation
• Flowering and fruit-development goals
• Heat and humidity management
• Energy use over longer photoperiods

Cannabis cultivation

Cannabis cultivation requires careful management of spectrum, PPFD, photoperiod, canopy uniformity and environmental conditions. Lighting requirements may change between propagation, vegetative growth and flowering.

A properly planned system can help cultivators establish appropriate intensity for each growth stage, improve uniformity, manage photoperiods and integrate lighting with facility controls.

Spectrum is only one part of the production system. Genetics, nutrition, irrigation, temperature, humidity, airflow and post-harvest handling can also influence plant development and final crop quality.

SJS Products’ horticultural fixtures are intended for lawful cultivation and research applications. Customers are responsible for complying with applicable federal, state and local requirements.

Universities and agricultural research

Universities, laboratories and agricultural education programs often require more control and repeatability than standard commercial fixtures provide.

Researchers may need to reproduce lighting conditions across multiple treatments, maintain consistent intensity between experimental groups or isolate responses to specific wavelengths. Custom fixtures may also need to fit existing growth chambers, teaching benches, greenhouse bays or laboratory shelving.

Custom LED systems can help research teams:

• Adjust or specify individual wavelength channels
• Reproduce defined photoperiods
• Simulate seasonal lighting conditions
• Maintain consistent intensity between test areas
• Compare plant responses under different spectra
• Create independently controlled treatment zones
• Record and repeat lighting protocols
• Integrate lighting with sensors and environmental controls

The 12-, 18-, 24-, 36- and 48-inch nominal AGHK-1640 formats may be useful when fixtures must fit narrow shelves, laboratory benches or growth chambers. Research requiring higher output or additional spectral flexibility may benefit from the modular H60, H120 or G240 configurations.

SJS Products also provides custom LED grow lights for colleges and universities, including adjustable spectrum options, modular configurations, technical documentation and support for institutional purchasing or grant requirements.

Measuring Grow-Light Efficiency

Visible brightness and lumens per watt are not the best measurements for evaluating horticultural lighting. Lumens are weighted according to human visual sensitivity rather than plant photosynthesis.

More relevant grow-light measurements include:

• PPF: Total photosynthetic photon output in µmol/s
• PPFD: Photon intensity reaching the canopy in µmol/m²/s
• Photon efficacy: Photosynthetic photon output per unit of electrical energy in µmol/J
• DLI: Total daily light delivered in mol/m²/day
• Canopy uniformity: Consistency of distribution across the growing area
• Electrical input power: Energy consumed by the fixture
• Thermal performance: Heat generation and management

An efficient fixture is not necessarily the one with the highest output. It must deliver the required photons to the correct area without wasting substantial light outside the canopy or creating unnecessary electrical and cooling loads.

Standard vs. Custom LED Grow Lights

Standard grow lights may be suitable when a facility has common rack dimensions, broadly compatible crops and straightforward control requirements.

However, an off-the-shelf fixture may not fit every growing environment. A custom grow-light design may be beneficial when a project requires:

• A specific fixture length, width or height
• Unusual mounting clearances
• Narrow racks or research benches
• Independently adjustable spectral channels
• Crop-specific intensity and distribution
• Specialized connectors or power requirements
• Dimming, scheduling or wireless controls
• Integration with sensors or building systems
• Scalable or modular construction
• Repeatable configurations for research trials

Custom engineering should solve a defined production or research problem rather than add unnecessary complexity. The process should begin with the crop, canopy and facility instead of a predetermined fixture.

Custom Grow-Light Engineering from SJS Products

SJS Products develops custom LED lighting solutions for commercial cultivation, controlled-environment agriculture, research and education.

Through its manufacturing relationship with Titans, SJS can evaluate the physical, electrical and spectral requirements of a project before recommending a fixture configuration. Learn more about the partnership and made-to-order process on the Custom LED Grow Lights Manufactured by Titans page.

Depending on the application, custom engineering may account for:

• Crop species and cultivar
• Growth stage
• Required wavelength distribution
• Target PPFD and DLI
• Canopy dimensions
• Rack, shelf or bench dimensions
• Mounting height
• Available vertical clearance
• Fixture dimensions and weight
• Beam angle and fixture spacing
• Electrical voltage and circuit capacity
• Power-cable and connector requirements
• Humidity and water exposure
• Thermal-management requirements
• Dimming and control options
• Sensor or building-system integration
• Future expansion plans

SJS offers multiple fixture formats rather than requiring every project to use one standard design. These include compact 12–48W linear bars, modular 60–240W systems and a 120W hanging fixture.

The appropriate format depends on the geometry of the grow space. A narrow linear fixture may suit a propagation shelf, while a higher-powered modular or hanging system may be more appropriate for a greenhouse or open cultivation bench.

Questions to Ask Before Selecting a Grow Light

1. What crop are you growing?

Identify the crop, cultivar and production objective. A propagation facility has different requirements from a flowering room, fruiting greenhouse or research chamber.

2. What growth stage will the system support?

Determine whether the lighting will be used for propagation, vegetative development, flowering, fruiting or an entire production cycle.

3. What are the grow-space dimensions?

Record the length, width and height of the room, rack, shelf, bench, chamber or greenhouse section.

4. What fixture dimensions will fit?

Measure the maximum allowable fixture length, width and housing height. Include space for mounting hardware, cables, ventilation and safe separation from the canopy.

5. What is the available mounting height?

The distance between the fixture and canopy affects intensity, distribution, fixture spacing and available plant-growth height.

6. What is the mounting structure’s load capacity?

Consider the combined weight of the fixture, cable and mounting hardware. For example, the GG 120W Hanging Light Bar has a listed fixture weight of 12.2 pounds before separately sold mounting hardware is added.

7. What PPFD and DLI are required?

Lighting targets should be based on crop requirements and environmental conditions, not simply the highest possible output.

8. How uniform must the lighting be?

Uniformity can be especially important for propagation, commercial crop consistency and controlled research experiments.

9. Will the fixture operate in a humid or wet environment?

Confirm the required ingress-protection rating. The AGHK-1640 Series lists IP44/IP65 options, the Titans Modular Series lists IP65/IP68 protection and the GG Hanging Light Bar lists IP65/IP66 wet-rated components.

10. What electrical infrastructure is available?

Confirm the operating voltage, circuit capacity, connector requirements and limitations on total electrical load.

11. How will heat be managed?

Consider fixture temperature, total heat added to the room, ventilation and the potential effect on HVAC requirements.

12. Are controls required?

Determine whether the project needs manual dimming, scheduling, independently controlled spectral channels, wireless control or sensor integration.

13. Are dimensional drawings available?

Request a current technical drawing before finalizing rack fabrication, mounting-hole locations or electrical routing. This is particularly important for customized fixtures and products whose dimensions are not published online.

14. Will the facility expand?

A modular lighting plan may simplify future expansion and help maintain consistent conditions between production areas.

Frequently Asked Questions

What is the best light spectrum for indoor plants?

There is no single best spectrum for every plant. The appropriate spectrum depends on the crop, cultivar, growth stage, intensity, photoperiod and growing environment. Spectrum should be selected as part of a complete cultivation strategy.

What is the difference between PPF and PPFD?

PPF measures the total amount of photosynthetically active light emitted by a fixture every second. PPFD measures how much of that light reaches one square meter of the plant canopy every second.

Is a higher PPFD always better?

No. Excessive intensity can increase energy use, irrigation demand and plant stress, particularly when temperature, nutrients and carbon dioxide are not managed appropriately. The objective is to deliver a suitable PPFD and DLI for the crop.

Why are fixture dimensions important?

Fixture dimensions determine whether a light will fit above a rack, bench or chamber while maintaining the required distance from the canopy. Fixture size can also affect airflow, maintenance access, mounting design and light distribution.

Why is canopy uniformity important?

Uniform lighting helps plants receive consistent photon exposure across the growing area. Poor uniformity can produce differences in growth rate, crop quality and harvest timing.

Can one grow light support every growth stage?

Some broad-spectrum fixtures can support multiple stages. However, required intensity, photoperiod and spectrum balance may change as plants develop. Dimming and customizable spectrum options can provide additional flexibility.

When is a custom grow light necessary?

A custom system may be useful when standard fixtures cannot provide the required dimensions, spectrum, footprint, mounting configuration, intensity, environmental protection or control integration.

Which fixture is suitable for narrow shelves?

A linear fixture such as the AGHK-1640 Series may be considered for narrow shelves, propagation racks and research benches. The correct model and spacing should be selected according to shelf dimensions, mounting height and target PPFD.

Which fixture is suitable for larger growing areas?

The Titans Modular H60, H120 and G240 systems or the GG 120W Hanging Light Bar may be considered for higher-output or suspended applications. Final selection should be based on a site-specific lighting layout rather than wattage alone.

Request a Grow Light Designed for Your Crop and Facility

Fixture dimensions, mounting height, canopy size, spectrum and light intensity should be evaluated together. SJS Products offers compact linear bars, modular systems and hanging fixtures for commercial farms, greenhouses, vertical racks, propagation facilities and academic research.

To begin, provide your grow-space dimensions, crop information, research subjects and lighting goals through the Custom Grow Light Request form. The SJS Products team will review your requirements and respond within one to two business days.

You can also contact SJS Products at 1-602-502-8887 or info@sjsproducts.net.

Plant responses to spectrum and intensity vary by species, cultivar, growth stage and environment. This article is intended as a general educational resource and does not replace crop-specific testing, facility engineering or professional lighting design.