Does Under Canopy Lighting Increase Yield? What a 2025 Study Found
Short answer: yes, in a controlled trial. A 2025 peer-reviewed study of medicinal cannabis found that adding light below the canopy raised dry flower yield by 24.58%, and adding light inside the canopy raised it by 29.95%, compared with top lighting alone. Both methods also made plants more uniform. The gain comes from lighting lower bud sites that top lights can't reach once the canopy closes. How much you gain depends on your cultivar, plant density and how you run the lights.
Source: Garrido J., Corral C. et al., peer-reviewed supplemental lighting study, Plants 2025, 14(10), 1469. https://pmc.ncbi.nlm.nih.gov/articles/PMC12115249/ (doi:10.3390/plants14101469)
What the study tested
The researchers grew a high-THC medical cultivar ('Moniek') indoors in Spain under licence. They used 72 genetically identical plants on a 6 m × 1 m bench at 12 plants per m², with 24 plants in each of three treatments:
TL, top lighting only: 600 W overhead LEDs, ramped to 700 µmol·m⁻²·s⁻¹ at the top of the canopy from week 3.
SCL, subcanopy lighting: top lighting plus LED bars mounted on both sides of each pot row, pointing up into the lower canopy (6 units).
ICL, under canopy lighting at two heights: top lighting plus LED units at two heights on both sides of each row, pointing in (12 units), raised as the plants grew.
The supplemental lights came on in week 4 (day 22), once the plants averaged about 80 cm tall and the lower canopy was getting a fifth of the top-level light or less. Flowering ran 10 weeks on 12/12, and the crop was harvested on day 76.
The results
Measure | Subcanopy (SCL) vs top only | Two-height under canopy (ICL) vs top only |
Dry flower (inflorescence) yield | +24.58% | +29.95% |
Extra dry flower per m² | +167.64 g/m² | +204.24 g/m² |
THC yield | +18.67% | +24.42% |
Lighting energy used | +13.13% | +23.21% |
Grams of dry flower per kWh | 1.61 (vs 1.49 top only) | 1.48 (vs 1.49 top only) |
Other findings:
More uniform product. Both treatments cut the plant-to-plant variability in dry flower yield. Variability in THC and total terpene yields fell by more than 50%.
Terpenes. Two-height under canopy light (ICL) raised total terpene concentration by 12.5%.
Efficiency. Subcanopy lighting produced the most flower per kWh, about 8.2% better than top lighting alone. Two-height under canopy lighting (ICL) produced the biggest absolute gain, at about the same g/kWh as top lighting.
What this means for your room
Under canopy light pays off most in a dense, closed canopy. The trial ran 12 plants per m² with canopies overlapping. Top light alone left lower bud sites under-lit, and that's where the extra yield came from.
Upward-facing bars on both sides of each row (the subcanopy setup) are the simplest to install and gave the best yield per kWh. That's the layout under canopy bars like the AG-140 are built for.
Timing matters. The researchers turned the supplemental light on in week 4, once the lower canopy was clearly shaded, and pointed out that the best timing depends on how your cultivar stretches after the flip.
Budget the extra power. Expect your lighting kWh to rise. In this trial the yield gain (+24.58%) was much larger than the energy increase (+13.13%).
Limits of the evidence
This was one cultivar, one crop cycle and one research room, and the supplemental fixtures were a different brand from ours. The study didn't test AG-140 bars, so treat the percentages as what's possible under good conditions, not as a guarantee. We'll publish our own customer results as we collect them.
How to set it up with AG-140 bars
Fixture: the AG-140 is a 140 W bar delivering 420 µmol/s at 3.0 µmol/J (3K Full Phase) or 455 µmol/s at 3.25 µmol/J (R80 Red). It's IP65, ETL and DLC listed, and runs on 120–277V.
How many bars: see How Many Under-Canopy Light Bars for a 4×4 or 4×8 Bed?, or start with the AG-140 Under Canopy LED Kit (2 or 4 bars, with cords and stands).
Control: one Master Controller drives up to 100 AG-140 bars directly (50 per side). The AG-140's built-in signal booster lets one group run up to 1,000 bars, so you can schedule under canopy light separately from your top lights and turn it on when the lower canopy closes.
Not sure? Ask for a free light plan and we'll lay out bars, PPFD and rebate eligibility for your room.
Browse all under canopy lights.
FAQ
Does under canopy lighting increase yield?
In a 2025 peer-reviewed cannabis trial, subcanopy lighting increased dry flower yield by 24.58% and two-height under canopy lighting by 29.95% compared with top lighting alone (Garrido et al., Plants 2025).
Is under canopy lighting energy efficient?
In the same trial, subcanopy lighting produced 1.61 g of dry flower per kWh, compared with 1.49 g/kWh for top lighting only, about 8.2% better, even though it used 13.13% more lighting energy.
When should I turn on under canopy lights in flower?
The study turned them on in week 4 after planting, once plants were about 80 cm tall and the lower canopy was clearly shaded. The best timing depends on the cultivar.
Does under canopy light improve consistency?
Yes. Both supplemental methods reduced plant-to-plant variability in dry flower yield, and cut variability in THC and terpene yields by more than 50%.
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