What Is Under-Canopy Lighting?
Under-canopy lighting (also called subcanopy lighting, SCL) places slim fixtures below the flowering canopy, shining upward into the bud sites and leaves that top lighting can't reach. Related terms you'll see:
| Term | Fixture location | Primary goal |
|---|---|---|
| Top lighting (TL) | Above canopy | Main photosynthetic driver |
| Under-canopy / subcanopy (SCL) | Below canopy | Recover lower bud sites |
| Inter-canopy (ICL) | Within the plant structure | Mid-canopy penetration (tall crops) |
| Intra-canopy | Multiple levels | Whole-plant uniformity (research/high-wire) |
What the 2025 Peer-Reviewed Study Found
Garrido et al., Plants (MDPI) 2025, 14(10):1469
A controlled medicinal-cannabis trial (12 plants/m², top-light PPFD ramped to 700 µmol·m⁻²·s⁻¹, supplemental lighting from day 22 of a 12/12 flower cycle for 55 days) compared top lighting alone against subcanopy (SCL) and inter-canopy (ICL) supplementation.
Source: Garrido, Corral, García-Valverde et al., "Subcanopy and Inter-Canopy Supplemental Light Enhances and Standardizes Yields in Medicinal Cannabis (Cannabis sativa L.)", Plants 2025, 14(10), 1469. DOI: 10.3390/plants14101469. Earlier support: Hawley et al. 2018 (HortScience) reported +13–17% inflorescence yield with red-blue subcanopy lighting.
The finding most processors should care about isn't the headline yield — it's standardization. The supplemental-light groups showed dramatically lower variability in THC and terpene output across batches. For licensed operations selling into compliance-tested markets, batch consistency is money.
How Much Can Your Room Realistically Gain?
Honest answer: it depends on four variables — canopy density, existing top-light quality, environmental headroom (CO₂, HVAC, irrigation) and cultivar. Field results range widely:
| Facility condition | Expected total yield gain |
|---|---|
| Dense canopy, significant lower shading (most common) | 20–30%+ |
| Average commercial flower room | 10–20% |
| Already-optimized room, open canopy | 5–10% |
| Poorly managed environment | Minimal — fix environment first |
Why It Works at the Plant Level
- Reactivation of shaded leaves: lower leaves in heavy shade photosynthesize far below capacity and senesce early; upward PAR reactivates them as carbohydrate sources for flower development.
- Energy allocation balance: more even light distribution across the vertical profile shifts biomass accumulation toward middle and lower sections.
- Grade-mix improvement: lower bud sites receiving ~200+ µmol/m²/s develop full flower structure instead of airy "popcorn" — shifting weight from trim grade to top-shelf grade.
The ROI Math (Illustrative Model)
| Assumption | Value |
|---|---|
| Flowering canopy | 500 m² · 6 cycles/year · 2 kg/m² baseline |
| Grade mix before | 80% top-shelf / 20% popcorn-trim |
| After under-canopy (+15% total, grade shift) | ~1,150 kg/cycle · 88% top-shelf |
| Revenue delta at $4/g top · $1.50/g trim | ≈ +$636,000/year |
| Fixture capital at this scale | ≈ $30,000–60,000 |
Payback in this model lands at weeks, not years. Your actual numbers depend on local flower pricing — send us your room and we'll run the model with your prices.
Spec Guide: Choosing Under-Canopy Fixtures
- Form factor: slim bars (3–7 cm profile) that fit under benches/trellis without stealing plant space or casting shadows downward.
- Beam angle: 120° standard for rows; wider (240°) for dense bench layouts. Avoid narrow beams that hot-spot one bud.
- Placement: typically 20–35 cm below the trellis net, spaced 60–90 cm along the row, sized to raise lower-site PPFD toward ~200 µmol/m²/s.
- Sizing rule of thumb: under-canopy wattage as a fraction of top-light power — commonly ~25% supplemental in dense canopies.
- Environment: IP65 minimum for humid grow rooms; passive cooling preferred at close proximity to tissue.
- Controls: 0–10V dimming so you can run lower output in early flower and ramp up as canopy density builds.
Common Mistakes We See
- Adding under-canopy wattage while the environment (CO₂, irrigation, HVAC) is already at its limit — photons without headroom.
- Mounting fixtures too close, causing leaf curl on upward-facing tissue.
- Narrow-beam fixtures that create hot spots instead of even lower-canopy coverage.
- Expecting trial-level gains in an open, low-density canopy.
FAQ
Do under-canopy lights really increase yield?
Yes — in peer-reviewed trials and commercial reports, when added to (not substituted for) adequate top lighting. Gains range from 5–10% in optimized rooms to 20–30%+ in dense canopies with heavy lower shading.
Will they burn or overheat the lower buds?
No, when mounted at proper distance (20–35 cm below trellis) with slim passively-cooled bars. Under-canopy intensities are far below top-light levels; upward light is soft and diffuse by design.
Can they replace top lights?
No. They are supplemental. The trials added SCL/ICL on top of a strong 700 µmol/m²/s top-light system — that's where the gains come from.
What spectrum works best?
Full spectrum with red/far-red components, matching the phytochrome response that drives lower-site flower development. White full-spectrum bars with added far-red are the current commercial standard.
How many watts per row?
A common commercial layout runs 100–150W fixtures at 60–90 cm spacing per row (~25% of top-light wattage in dense canopies). Higher-density double-row benches move to 200–300W fixtures.
Do they work in greenhouses?
Yes — especially in light-deprivation greenhouse flower production where lower canopies are heavily shaded by training systems. Same placement principles apply.
What's the realistic payback period?
Commercial operators commonly report 1–2 harvests, driven by the shift from popcorn/trim grade to top-shelf grade rather than total weight alone. Model it with your own flower pricing before committing.
Will this raise my HVAC load?
Modestly — under-canopy fixtures are a small fraction of total lighting wattage. Include them in your room heat-load calc; we provide BTU/h figures per fixture with quotes.