Under-Canopy Lighting for Cannabis: 2026 Yield & ROI Guide

TLDR

Under-canopy lighting is a supplemental LED strategy that places slim light bars below a dense plant canopy to deliver photosynthetically active radiation (PAR) to shaded lower leaves, buds, flowers, or fruit. Peer-reviewed cannabis research shows yield gains of 24% or more in controlled trials, though real-world results depend on canopy density, top-lighting quality, spectrum matching, airflow, humidity control, and crop management. It is not a bolt-on yield guarantee. It is a system-level upgrade that works best when lighting, climate, irrigation, pruning protocols, and labor access are all planned together.

• Lower buds are heavily shaded

• Flower quality varies throughout the canopy

• HVACD capacity has room to expand

• Additional yield directly improves revenue per square foot

• Operations can accurately measure ROI through side-by-side trials

What Is Under-Canopy Lighting?

Under-canopy lighting is supplemental horticultural lighting installed below a plant canopy and aimed upward or into the lower canopy to deliver PAR to tissue that overhead fixtures cannot reach well. In commercial facilities, that usually means slim LED bars mounted beneath the crop on benches, trellises, or support structures, running alongside (not instead of) a primary top-lighting system.

The concept is simple. Dense canopies intercept most of the light at the top. Lower leaves, bud sites, flowers, and fruit get progressively less. In cannabis, the result is “smalls,” “larf,” or “popcorn,” which are lower-value products that drag down revenue per square foot. In greenhouse tomatoes and other high-wire crops, the equivalent problem is premature leaf senescence and reduced fruit production deep in the canopy.

Under-canopy lighting addresses that by putting photons where the plant actually needs them, below the dense upper layer.

Explore Thrive’s Boost XE for a purpose-built under-canopy bar designed for commercial cannabis and greenhouse operations.

Why Growers Use It

The core motivation is economic: more marketable product from the same footprint.

Top lighting can only do so much in a dense canopy. A meta-analysis published in Frontiers in Plant Science explains the paradox well: upper canopy leaves may already be near light saturation while the whole canopy remains light-limited because the lower layers are shaded. Pushing more intensity from above just wastes energy at the top without fixing the problem below.

Under-canopy lighting breaks that trade-off by adding a second lighting plane. The goals, in order of how most operators talk about them:

1. Convert underperforming lower material into sellable product. In cannabis, this means denser, heavier lower buds instead of discardable larf. In greenhouse produce, it means more fruit per plant.

2. Improve crop uniformity from top to bottom. More uniform crops simplify trimming, grading, and packaging.

3. Increase revenue per square foot without expanding the facility. This is especially compelling for indoor cultivation operations that are already space-constrained. For a deeper look at the financial math, see this ROI guide.

Under-Canopy vs. Subcanopy vs. Inter-Canopy vs. Intra-Canopy

Most grower forums, vendor pages, and even some research papers use these terms loosely. That creates confusion. Here is how the terms actually differ:

Under-canopy lighting (also called subcanopy lighting in research contexts) places fixtures below the canopy, typically aimed upward into lower foliage and bud zones. This is the most common commercial term, especially in cannabis.

Inter-canopy lighting and intra-canopy lighting refer to fixtures placed within the canopy itself, sometimes at multiple vertical levels (basal, middle, upper). A 2025 study in MDPI Plants formally separated subcanopy lighting (SCL, positioned below) from inter-canopy lighting (ICL, positioned at basal and middle canopy levels), and found both improved yield but through somewhat different distribution patterns.

Side lighting is lateral, with fixtures placed beside the crop rather than below or within it. Practitioners on cannabis forums often compare side lighting to under-canopy placement, with most concluding that under-canopy bars offer better coverage in dense SCROG or SOG configurations.

The practical takeaway: placement matters because it changes light distribution, labor access, wiring, cleaning, and plant response. “Under-canopy” and “subcanopy” are usually interchangeable. “Inter-canopy” and “intra-canopy” imply fixtures inside the plant structure at one or more heights.

Lighting Placement Comparison

How Much Yield Increase Can Growers Realistically Expect?

One of the most common questions growers ask is not whether under-canopy lighting works, but how much yield improvement they can realistically expect.

The answer depends on four major variables:

Canopy Density

Dense canopies create more shaded bud sites and therefore have more yield potential to recover. Growers running heavy SCROG nets with fully closed canopies consistently report higher percentage gains than those with open, well-pruned plants.

Existing Lighting Quality

Facilities already running high PPFD levels with excellent uniformity generally see smaller gains than facilities with uneven light distribution. For guidance on setting top-light targets, see this cannabis PPFD guide.

Environmental Capacity

Additional photons only translate into additional biomass when irrigation, CO₂, temperature, humidity, and airflow support the increased photosynthetic demand.

Cultivar Characteristics

Some cultivars naturally produce dense lower flower sites while others concentrate production in the upper canopy. Results can vary significantly by genetics. Practitioners on Reddit report that stretchy sativa-dominant cultivars with lots of secondary branching tend to benefit more from under-canopy bars than short, compact indica-leaning genetics that already concentrate production at the top.

As a general guideline:

Does Under-Canopy Lighting Increase Yield?

Yes, it can. But the honest answer is more nuanced than most product pages admit.

What the Research Shows

The strongest recent evidence comes from a 2025 medicinal cannabis trial published in Plants. Researchers compared top lighting alone against subcanopy lighting (SCL) and inter-canopy lighting (ICL) at a density of 12 plants per square meter, with overhead PPFD ramped to 700 µmol·m⁻²·s⁻¹ and supplemental lighting activated on day 22 of a 12/12 flowering cycle for 55 days.

Results were significant:

• SCL increased dry inflorescence yield by 24.58% compared to top lighting only.

• ICL increased dry inflorescence yield by 29.95%.

• Total THC yield increased by 18.67% for SCL and 24.42% for ICL.

• Variability in total terpene content dropped by roughly 75% in supplemental-light treatments.

That uniformity finding is worth pausing on. The yield number gets the headlines, but reduced variability in chemical profiles may matter just as much for processors, brands, and compliance teams.

An earlier HortScience study by Hawley et al. (2018) had already reported a 13 to 17% increase in inflorescence yield and a 5% increase in THCA + THC concentrations with red-blue subcanopy lighting, though that was a smaller trial.

Beyond cannabis, Wageningen University & Research found that delivering 34% of daily light integral (DLI) through intra-canopy lighting and 66% from top lighting produced 14% more tomato fruit than top lighting alone, with no loss in Brix or acidity.

What Growers Actually Report

The peer-reviewed numbers are encouraging, but reports from the field tell a more complicated story. Anecdotally, operators often size under-canopy wattage as a fraction of total lighting power, with a commonly cited approach around ~25% supplemental (for example, ~360W of under-canopy lighting against ~750W of top light).

Some growers report 30% overall yield increases and far fewer “smalls,” which lines up with the research. However, other field reports suggest that in rooms where top lighting, plant structure, and airflow are already strong, gains may be closer to 5 to 10%. One project manager shared in a YouTube walkthrough that the biggest surprise was not more buds, but denser, more uniform buds on branches that previously produced nothing worth trimming.

How It Works at the Plant Level

Adding light below a dense canopy does two things: it delivers more total photons to the crop, and it distributes those photons more evenly across the vertical profile.

These are distinct effects, and conflating them leads to overclaims. The MDPI study added supplemental light on top of an already-strong overhead system. The yield gains came partly from more total light and partly from better placement. A facility that simply moves existing wattage from top to bottom without adding photons would see a different outcome.

At the leaf level, shaded lower leaves photosynthesize at lower rates and can senesce prematurely. Under-canopy lighting reactivates that photosynthetic capacity, shifting biomass accumulation toward middle and lower plant sections. The result is a more productive vertical canopy instead of a top-heavy one.

Spectrum may play a role too. The Hawley study found that red-blue subcanopy lighting produced a more consistent metabolite profile, while RGB had a stronger terpene-modifying effect. For a deeper look at how different wavelengths influence growth, see this overview of light spectra and plant growth.

Spectrum Selection: Matching Under-Canopy to Top Light

Spectrum choice for under-canopy bars is not just a marketing question. It directly affects plant morphology, cannabinoid expression, and how well supplemental light integrates with overhead fixtures.

Most top-lighting systems in commercial cannabis flower rooms run a full-spectrum white with a warm bias (heavy in the red and far-red range, typically peaking around 660 nm). Under-canopy bars come in three general categories: red-blue “blurple” combinations, full-spectrum white, and red-heavy narrow-band bars.

Each has trade-offs.

Red-blue combinations drive photosynthesis efficiently per watt and were the spectrum used in the Hawley (2018) trial that showed yield and potency gains. But they produce an unpleasant working environment and make visual plant inspection almost impossible.

Full-spectrum white under-canopy bars, like the Thrive Boost XE, create a more natural light environment that allows workers to spot pests, deficiencies, and mold with the naked eye. This matters because under-canopy zones are already harder to inspect. Thrive’s patented phosphor chemistry is designed to balance photosynthetic efficiency with a work-friendly spectrum.

Red-heavy narrow-band bars can push flower weight in the lower canopy but risk creating a spectrum mismatch with white top lights. Some practitioners on cannabis forums report that mixing red-only under-canopy bars with white top lights produces uneven flower coloring and inconsistent terpene profiles, particularly on photosensitive cultivars.

The safest approach: match the spectral character of under-canopy bars to the top light. If the overhead system is full-spectrum white, run full-spectrum white below. If the top lights are red-heavy HPS, a red-supplemented under-canopy bar may integrate more naturally. Consistency across the light environment produces consistency in the final product.

PPFD Targets for the Lower Canopy

There is no single “correct” PPFD for under-canopy lighting, but there are useful boundaries.

In the 2025 MDPI trial, supplemental bars added approximately 75 to 150 µmol·m⁻²·s⁻¹ to lower-canopy positions on top of 700 µmol·m⁻²·s⁻¹ overhead. That brought total photon delivery at lower bud sites into the 200 to 350 µmol·m⁻²·s⁻¹ range, depending on canopy density and position.

As a practical target range for cannabis flower:

• Minimum effective dose: 50 to 100 µmol·m⁻²·s⁻¹ at the lower bud site (enough to shift lower material from larf to usable flower)

• Productive range: 100 to 250 µmol·m⁻²·s⁻¹ at lower bud sites

• Diminishing returns threshold: Above 300 µmol·m⁻²·s⁻¹ at lower positions, the extra photons often generate more heat and humidity than the plant can productively use

These numbers assume the lower tissue is receiving very little light without supplementation (often below 50 µmol·m⁻²·s⁻¹ in a dense canopy). Growers should map PPFD at multiple lower-canopy measurement points rather than relying on a single reading at bar height. A quantum sensor placed at the actual bud site, not at the fixture, tells the real story.

DLI Uniformity Across Canopy Depth

DLI (daily light integral) is the total photon delivery over a full photoperiod, and it matters more than instantaneous PPFD for understanding what lower-canopy tissue actually receives over a grow cycle.

In a well-lit cannabis flower room running 12 hours at 900 µmol·m⁻²·s⁻¹ overhead, the upper canopy might receive a DLI of 38 to 40 mol·m⁻²·d⁻¹. But six inches below a fully closed canopy, that number can drop to 5 to 8 mol·m⁻²·d⁻¹. That is a 5x to 8x drop within the same plant.

Under-canopy lighting closes this gap. The goal is not to make lower-canopy DLI match upper-canopy DLI (that would require impractical wattage), but to bring it into a range where meaningful flower development occurs. Bringing lower positions from 5 to 15 or 20 mol·m⁻²·d⁻¹ is usually enough to convert throwaway larf into trimable, sellable flower.

For a deeper explanation of DLI calculations and targets by crop, see this cannabis DLI guide.

Design Considerations for Commercial Growers

Light Metrics That Matter

Watts tell you how much electricity a fixture consumes, not how much useful light it produces. The metrics that matter for evaluating under-canopy LED bars:

• PPF (Photosynthetic Photon Flux): Total PAR-range photons the fixture emits per second, measured in µmol/s.

• PPFD (Photosynthetic Photon Flux Density): How much PAR hits a given plant area, measured in µmol·m⁻²·s⁻¹. Use PPFD maps or a quantum sensor at multiple lower-canopy points rather than relying on a single center reading.

• DLI (Daily Light Integral): Total PAR delivered per square meter per day. Adding under-canopy light increases DLI, so growers need to confirm the crop, cultivar, CO₂ strategy, and irrigation can handle the extra photon load.

• PPE (Photosynthetic Photon Efficacy): How efficiently the fixture converts watts into PAR photons (µmol/J). Higher is better, but only if the distribution pattern actually serves the lower canopy.

Fixture Specifications

Under-canopy bars live in a harsh environment: close to water, humidity, soil and growing media, plant contact, and worker movement. Greenhouse Grower recommends selecting fixtures with appropriate environmental ratings, protected electrical connections, managed heat, a small form factor, and wide-angle light distribution.

Key specifications to evaluate: PPE and PPF, spectrum and red/blue/far-red balance, beam distribution angle, dimming and controls compatibility, IP or wet-location suitability, driver and power supply location, safety listing (UL, ETL, or equivalent), and DLC Hort QPL verification.

The DesignLights Consortium’s horticultural QPL is a useful third-party reference. DLC requirements include a PPE threshold above 1.9 µmol/J, driver and fan lifetime above 50,000 hours, a minimum five-year warranty, and safety certification by an OSHA NRTL or SCC-recognized body.

Stand Height and Bar Placement

Placement varies by crop, canopy architecture, and facility layout. CannaCribs’ buying guide suggests 8 to 12 inches below canopy leaves as a starting point for cannabis, though this is one practical reference, not a universal rule.

The critical variable is the distance between the bar’s emitting surface and the nearest bud site. Too close and you risk light bleaching or localized heat stress on lower tissue. Too far and the inverse square law reduces intensity to the point of insignificance.

For bench-grown cannabis in 5 to 7 gallon pots:

• Bars on the bench surface or trellis frame: Simple mounting, easy to clean, but may be too low if plants are tall. Works well for SOG setups with shorter plants.

• Bars mounted 12 to 18 inches above the bench: Reaches more of the lower canopy on tall plants, but requires stable mounting hardware that does not interfere with rolling benches.

• Adjustable-height mounts: The most flexible option, allowing bars to be raised as the canopy closes during stretch. Some practitioners on Reddit report building simple PVC or unistrut frames that let them reposition bars at weeks 2 and 4 of flower.

Bars need to clear irrigation lines, rolling benches, trellis netting, and worker pathways. If bars block access to the base of the plant, workers will damage them during daily tasks.

Bench Configuration and Fixture Layout

In facilities using rolling benches (which most commercial cannabis operations do), under-canopy bar placement requires coordination with bench mechanics. Bars mounted on stationary frames do not move when benches roll, which can misalign light delivery from cycle to cycle.

Two common configurations work:

Bars fixed to the bench itself, so they roll with the bench and always maintain position relative to the plants. This simplifies light uniformity but adds wiring complexity because power cables need slack and strain relief to accommodate bench movement.

Bars mounted on independent rails or frames between bench rows. This keeps wiring clean but means the light pattern shifts relative to plants whenever benches move. In practice, this configuration works better for stationary bench systems.

For large-scale deployments, Thrive’s OptiDrive remote power system moves LED drivers out of the grow space into a centralized rack. This simplifies the cable management problem significantly, because the in-room wiring to each bar is lighter and more flexible without onboard drivers.

Intensity Ramping Schedule During Flower

Running under-canopy bars at full intensity from day one of flower is one of the most common mistakes growers make. The lower canopy has been growing in shade. Leaves that developed under low light have different chloroplast density and photosynthetic capacity than sun-acclimated tissue. Blasting them with full output causes light stress, not more growth.

A practical ramping schedule for a typical 8 to 9 week cannabis flower cycle:

The 2025 MDPI study activated supplemental lighting on day 22 (roughly the start of week 4 of flower) and ran it through harvest. That 22-day delay is notable because it roughly corresponds to when canopy closure becomes significant at high planting densities.

Dimming capability is essential. Fixtures without dimming force an all-or-nothing approach that prevents proper acclimation. For more on avoiding this and other setup errors, see common under-canopy lighting mistakes.

Operational Impacts

Adding a lighting layer under the canopy is not just an electrical project. It changes the growing environment.

VPD Management and Microclimate Control

More photons mean more photosynthesis, which means more transpiration, which means more humidity. Multiple cultivation advisory sources note that under-canopy lighting can increase irrigation frequency, humidity generation, and dehumidification demand. The MDPI study found supplemental lighting increased energy use by 13.13% for SCL and 23.21% for ICL compared to top lighting alone.

The microclimate at the lower canopy can differ substantially from what sensors read above the crop. Temperature, relative humidity, VPD, and airflow all need measurement at the lower canopy level, not just at the top. A grow room might read 82°F and 55% RH at canopy height but 78°F and 68% RH at bench level. That lower-canopy VPD could be well outside the optimal range for flower development, promoting condensation on bud surfaces.

For cannabis in flower, the target VPD at bud level is typically 1.0 to 1.4 kPa. Under-canopy lighting increases leaf temperature slightly (through absorbed radiation) and increases local humidity substantially (through transpiration), which together can push lower-canopy VPD below 0.8 kPa without intervention. For a detailed breakdown of VPD management, see this VPD guide.

Practical steps: place temperature and humidity sensors at the lower canopy level, not just overhead. Review VPD readings at bench height separately from room-level averages.

Airflow Requirements Under the Canopy

Airflow is the most overlooked variable in under-canopy lighting deployments. Without adequate air movement below the canopy, transpired moisture pools in the dense lower growth, creating perfect conditions for botrytis (bud rot), powdery mildew, and other pathogens.

Oscillating fans at canopy height do almost nothing for the under-canopy zone. Air needs to move at the bench level, between the pots and below the lowest branches.

Effective approaches include:

• Floor-level or bench-level fans aimed horizontally through the lower canopy, providing gentle but consistent air exchange

• Under-bench ventilation channels in facilities with raised benches, allowing conditioned air to enter from below

• Avoiding dead zones where fixtures, pots, and trellis supports create pockets of stagnant air

The airflow should be enough to gently rustle the lowest leaves without creating wind stress. If lower fan leaves are perfectly still while under-canopy lights run, there is a problem.

Irrigation and Dehumidification Adjustment

Under-canopy lighting increases transpiration rates across the entire plant, not just at the lower canopy. This means existing irrigation schedules often need recalibration. Plants under supplemental lighting may consume 10 to 20% more water than identical plants without it, depending on intensity and duration.

The dehumidification load increases proportionally. Facilities already running near HVACD capacity before adding under-canopy light will hit a wall. Adding 10 to 15 kW of under-canopy lighting across a flower room can add several gallons per day of additional moisture that the dehumidification system must remove. For more on the thermal side of this equation, see HVAC requirements for LED lighting.

The sequence matters: size dehumidification capacity before installing under-canopy bars, not after. If the dehumidifier is already at 90% duty cycle, adding more transpiration without adding removal capacity is a recipe for crop loss.

Labor and Workflow

Bars mounted under benches or trellises can interfere with watering, foliar sprays, plant inspection, sanitation, and harvest. A Rollitup forum thread raised practical concerns about what physically fits under the canopy and how to protect electrical connections near irrigation. If the team cannot maintain, clean, and work around the fixtures safely, the installation will create more problems than it solves.

Pruning and Defoliation Strategy Changes

This is the topic most growers underestimate when adding under-canopy lighting.

Standard operating procedures in many commercial cannabis operations call for aggressive “lollipopping,” which removes all lower branches and bud sites during the first two weeks of flower. The logic is straightforward: those lower sites never develop into sellable flower anyway, so removing them redirects energy to the top colas.

Under-canopy lighting changes that calculus. If supplemental light can now develop those lower sites into marketable buds, removing them defeats the purpose of the lighting investment. Pruning SOPs need to be revised alongside the lighting upgrade.

The general shift:

• Before under-canopy lighting: Remove lower branches aggressively; keep only the top 12 to 18 inches of canopy

• After under-canopy lighting: Retain more lower branching; prune for airflow rather than for light access; selectively remove only the weakest or most shaded interior sites

Defoliation strategy changes too. Heavy defoliation during flower (removing fan leaves to expose lower buds to top light) becomes less necessary when light is arriving from below. Some growers on Reddit forums report that they shifted from two heavy defoliation sessions to one light cleanup, letting fan leaves remain as photosynthetic engines that benefit from under-canopy illumination.

The key principle: keep the plant material that the under-canopy light is designed to develop. Otherwise, the fixtures are lighting empty space.

SOP for Consistent Under-Canopy Results

Consistency matters more than peak performance. A room that gains 20% on one cycle and loses 5% the next is harder to manage than a room that reliably gains 12% every time. Building standard operating procedures around under-canopy lighting creates that consistency.

Pre-Cycle Checklist

• Verify all under-canopy bars are functioning, clean, and properly positioned

• Confirm dehumidification and irrigation capacity can handle the added load

• Set initial dimming level (typically 10 to 25% at the start of flower)

• Place at least one temperature/RH sensor at lower-canopy height

• Review pruning protocol: confirm crew knows which lower growth to retain

Weekly Tasks During Flower

• Week 1 to 2: Monitor canopy closure. Keep under-canopy bars at low output or off. Begin ramp only when the canopy measurably shades lower tissue.

• Week 2 to 3: Increase under-canopy intensity by 15 to 25% per week. Record lower-canopy PPFD at representative positions. Adjust irrigation schedule based on increased water uptake.

• Week 3 to 5: Run at target intensity. Monitor lower-canopy VPD daily. Adjust bench-level airflow if humidity readings rise above threshold.

• Week 5 to harvest: Maintain intensity. Increase vigilance on bud rot and mold inspections at lower sites, since these buds are now denser and hold more moisture.

Post-Harvest Data Collection

• Weigh and grade lower-canopy flower separately from upper-canopy flower

• Track the ratio of “A-grade” to “smalls” across cycles with and without under-canopy light

• Record energy consumption during the cycle for accurate ROI calculation

Small Grow Tent Implementation

Under-canopy lighting is not only for commercial facilities. Home growers and small-scale medical cultivators in grow tents can benefit too, though the approach is different.

In a 4x4 or 5x5 tent, the canopy is typically much closer to the light source and the grow area is small enough that reflective walls already bounce some light back to the lower canopy. The gains from under-canopy lighting in a tent are generally smaller than in a commercial room with dozens of plants, but they can still be meaningful for growers running dense SCROG nets where lower bud sites are heavily shaded.

Practical considerations for tent growers:

• Heat is the main constraint. Tents have limited cooling capacity. Adding a 60W to 120W bar under the canopy in a small tent raises temperatures noticeably. Monitor closely and consider reducing top-light intensity slightly to offset the heat if needed.

• Simple mounting works. Small LED bars can be zip-tied to tent poles or laid across the pot rims. No complex electrical infrastructure is needed at this scale.

• Expect modest gains. In a well-managed tent with good top lighting and reflective walls, under-canopy lighting might add 5 to 15% yield rather than the 20 to 30% seen in large commercial canopies with severe lower shading.

• Start with one bar. Test a single bar on one side of the tent for a cycle. Compare the under-canopy bud development on the lit side versus the unlit side before investing further.

Practitioners on Reddit report that in small tents, the biggest benefit is not always total yield but the quality improvement in lower buds. Flower that would have been trim-only becomes usable, which matters when every gram counts for a personal-use or small medical grow.

Under-Canopy Lighting ROI Calculator Framework

Most growers ultimately care about profit, not yield percentage.

A useful ROI calculation considers:

Additional Revenue

Additional Yield × Sale Price

Additional Costs

• Fixture purchase

• Installation

• Electrical infrastructure

• Increased energy consumption

• Additional HVACD demand

• Maintenance labor

Example

Growers should compare this revenue increase against total installed and operating costs to determine payback period. For a facility running 5,000 square feet of canopy, a 20% yield gain at $1.00/g represents $60,000 in additional revenue per cycle, which can offset fixture costs within one to three harvests depending on facility-specific variables.

When Under-Canopy Lighting Is Worth It

Under-canopy lighting is most likely to pay off when:

• The canopy is dense enough that lower leaves, buds, or fruit are genuinely light-limited.

• The crop is high-value enough that converting lower-grade material into marketable product moves the financial needle.

• Top lighting is already strong and uniform (if top lighting is weak, fix that first). For guidance on flower room top lighting, see this cannabis flower room guide.

• HVACD and dehumidification have capacity headroom.

• Irrigation, nutrition, CO₂, and airflow can be adjusted upward.

• The grow team can maintain and work around fixtures without losing labor efficiency.

• The operation can measure before-and-after results with side-by-side trials or room-to-room harvest comparisons.

The sweet spot is dense, high-value canopies in facilities that are already well run. Under-canopy lighting amplifies good cultivation. It does not fix bad cultivation.

When It May Not Be Worth It

This section rarely appears in vendor content, but it is exactly what experienced growers ask about.

Under-canopy lighting is probably a poor first investment when:

• The top-lighting system is underpowered or poorly distributed. More top light will almost always have a better return.

• The room is already limited by HVACD, dehumidification, CO₂, or irrigation capacity.

• The same wattage and capital would earn more by improving climate control or adding CO₂.

• The pruning SOP removes all lower growth, leaving nothing for under-canopy light to develop.

• The canopy is open and airy, with minimal lower shading (some indica-dominant cultivars in low-density plantings simply do not shade enough to justify supplemental lower light).

How to Evaluate Under-Canopy Fixtures

A quick checklist for commercial buyers:

1. PPF: How many plant-usable photons does the fixture actually output?

2. PPE: How efficiently does it convert watts into PAR?

3. PPFD distribution: What does the lower-canopy light map look like at the intended mounting distance and angle?

4. Dimming and controls: Can intensity ramp with canopy development and integrate with existing controls?

5. Electrical architecture: How are power, drivers, cabling, and daisy chaining handled, especially at scale?

6. Environmental rating: Is the fixture rated for humid, wet, high-contact grow room conditions?

7. Safety listing: Is it UL listed or equivalent for the intended horticultural use?

8. Third-party verification: Does DLC QPL data or independent testing match the marketing claims?

9. Serviceability: Can staff clean, move, repair, and harvest around it without damaging the fixture or the crop?

For commercial cannabis and greenhouse operations evaluating a purpose-built under-canopy bar, Thrive’s Boost XE is a 120W under-canopy fixture designed for exactly this application, backed by a five-year warranty, UL listing, and ongoing support.

Common Mistakes

Treating it as a plug-and-play yield guarantee. Under-canopy lighting is a system upgrade, not a magic trick. Every peer-reviewed study that shows yield gains also describes tightly controlled environmental conditions.

Running too much intensity too early. Ramping light gradually matters. Hitting plants with full under-canopy output before the canopy has closed wastes energy and can stress lower tissue that has adapted to shade.

Ignoring the lower-canopy microclimate. Temperature, RH, and VPD below the canopy are not the same as above it. If you add light down low, you need sensors down low.

Adding watts without dehumidification headroom. More transpiration without more moisture removal is a recipe for mold.

Continuing the same pruning strategy. If the standard operating procedure calls for heavy pruning that removes all lower bud sites, there is nothing left for under-canopy light to develop. Pruning protocols need to change alongside the lighting upgrade.

Buying on wattage or brand hype. Tested PPF, PPE, PPFD maps, and third-party data matter more than headline wattage or Instagram endorsements.

Forgetting about cleaning, water, and workers. Fixtures get dirty. Irrigation lines leak. Workers bump things. If the design does not account for daily reality, the lights become obstacles.

Mismatching spectra. Running a red-only under-canopy bar with a white full-spectrum top light can create uneven flower development and inconsistent chemical profiles. Match the spectral character of both lighting planes.

Research Summary: What Current Studies Say

Overall Research Consensus

Current evidence suggests that supplemental lower-canopy lighting consistently improves canopy uniformity and often improves yield when lower plant tissue is significantly light-limited.

The strongest evidence exists for dense cannabis canopies and greenhouse high-wire crops where light penetration is a known production bottleneck. The 2025 data also shows that chemical consistency (terpene and cannabinoid profile uniformity) improves alongside yield, which has downstream value for extraction, compliance testing, and brand consistency.

Frequently Asked Questions

What is under-canopy lighting?

Under-canopy lighting is supplemental LED lighting installed below a plant canopy and aimed upward or into the lower canopy. Its purpose is delivering PAR to shaded lower leaves, buds, flowers, or fruit that overhead top lights do not reach effectively. It is most commonly used in commercial cannabis and greenhouse produce operations alongside a primary top-lighting system.

Does under-canopy lighting increase yield?

It can, particularly in dense, high-value canopies where lower growth is light-limited. A 2025 medicinal cannabis study reported a 24.58% increase in dry inflorescence yield with subcanopy lighting under controlled conditions. However, results depend on canopy density, top-lighting quality, environmental capacity, cultivar, and crop management. Growers on forums report gains ranging from 5% in already-optimized rooms to 30% in rooms where lower material was previously wasted.

Does under-canopy lighting increase THC or potency?

This is where claims get slippery. Research shows under-canopy lighting can increase total cannabinoid yield by producing more flower, but concentration effects are mixed. The 2025 MDPI study found higher total THC yield but slightly lower THC concentration in supplemental-light treatments, likely due to biomass dilution. A separate 2025 Scientia Horticulturae study found interlighting did not significantly change lower-canopy THC values. The safest claim: more total cannabinoid output, not necessarily higher potency per gram.

What PPFD should under-canopy bars deliver?

Aim for 100 to 250 µmol·m⁻²·s⁻¹ at the actual bud site (not at the fixture surface). Below 50 µmol·m⁻²·s⁻¹ is generally too low to produce meaningful flower development. Above 300 µmol·m⁻²·s⁻¹, diminishing returns set in and the added heat and humidity may outweigh the benefit. Always measure at the plant, not at the bar.

When should growers turn on under-canopy lights?

There is no universal answer. Some operators activate them 14 to 21 days into flower after the canopy stretch has closed. Others start at low intensity early in flower and ramp gradually. The principle that most sources agree on: begin at reduced output, increase based on canopy density and plant response, and adjust timing to the specific cultivar and room conditions.

How should pruning change with under-canopy lighting?

Retain more lower branching than you would without supplemental light. If the standard SOP calls for aggressive lollipopping, revise it to keep secondary bud sites that the under-canopy bars can now develop. Prune for airflow (removing inward-facing or overlapping branches) rather than removing everything below the top cola.

Is under-canopy lighting the same as inter-canopy or intra-canopy lighting?

Not exactly. Under-canopy lighting typically places fixtures below the canopy, while inter-canopy and intra-canopy lighting positions fixtures at one or more levels within the plant canopy itself. In practice, many people use the terms interchangeably. The MDPI study that formally compared both approaches found that inter-canopy lighting produced slightly higher yield gains (29.95%) than subcanopy lighting (24.58%), likely because of more distributed light delivery.

What crops benefit from under-canopy lighting?

Commercial cannabis is the dominant use case in current industry discussions, but the concept applies to any dense or tall canopy. Greenhouse tomatoes, cucumbers, peppers, and other high-wire crops benefit from similar intra-canopy strategies. Wageningen research demonstrated 14% more tomato fruit production using an intra-canopy lighting approach with no quality loss.

Can under-canopy lighting work in a small grow tent?

Yes, though expect more modest gains (5 to 15%) than in commercial settings. Heat is the main constraint in small tents. Start with a single low-wattage bar, monitor temperatures closely, and compare bud development on the lit side versus the unlit side before scaling up.

What are the biggest risks of adding under-canopy lighting?

Increased power draw, heat generation, transpiration, humidity, dehumidification demand, and workflow interference. If the facility’s HVACD, irrigation, and labor systems cannot absorb the added load, the installation can create more problems than it solves, including mold risk, plant stress, and negative ROI.

How do you evaluate whether an under-canopy fixture is any good?

Look at independently tested PPF, PPE, and PPFD distribution rather than just wattage. Check for appropriate IP or wet-location ratings, a recognized safety listing (UL, ETL), and DLC Hort QPL verification if utility rebates matter. Evaluate dimming, controls compatibility, driver location, cabling design, and whether staff can actually work around the fixtures during daily operations.

Ready to evaluate under-canopy lighting for a commercial grow? Talk with Thrive about lighting design, power architecture, and project-specific consultation.