Under-Canopy Lighting for Cannabis: 2026 Yield & ROI

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, 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, and labor access are all planned together.

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 under-canopy lighting applications.

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.

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.

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.

Existing Lighting Quality

Facilities already running high PPFD levels with excellent uniformity generally see smaller gains than facilities with uneven light distribution.

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.

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 13–17% 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. This matters for greenhouse operators evaluating the same strategy for produce.

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 5–10%.

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.

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. Many utilities also require DLC listing for rebate eligibility.

Placement and Timing

Placement varies by crop, canopy architecture, and facility layout. CannaCribs’ buying guide suggests 8–12 inches below canopy leaves as a starting point for cannabis, though this is one practical reference, not a universal rule. Bars need to clear irrigation lines, rolling benches, trellis netting, and worker pathways.

Timing advice varies too. Some operators activate under-canopy lighting 14–21 days into flower after stretch, when the canopy has closed. Others start early at low intensity and ramp gradually as the crop develops. The safer principle: begin at reduced output, increase based on canopy closure and plant response, and avoid blasting full intensity from day one.

Power Architecture

At commercial scale, dozens or hundreds of under-canopy bars create real electrical planning challenges: wiring runs, driver heat, circuit loading, and install labor. For larger deployments, Thrive’s OptiDrive remote power system moves LED drivers out of the grow space into a centralized rack, simplifying installation, reducing in-room heat, and making maintenance easier. OptiDrive DC suits new builds and large facilities; OptiDrive DE uses low-voltage distribution over standard cabling for retrofits where electrical safety and install cost are the main concerns.

Operational Impacts

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

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.

A Grow Lights article on LinkedIn makes an important point that most guides miss: 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.

For cannabis facilities, humidity control is already a constant battle. Adding under-canopy light raises the stakes. If dehumidification capacity is already maxed out, more light below the canopy will create conditions that favor mold, mildew, and bud rot rather than bigger buds.

Labor and workflow matter too. 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.

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).

• 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.

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.

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, adding CO₂.

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.

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.

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.

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.

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.

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.