Do Under Canopy Grow Lights Really Boost Bud Yields?

With all the rave about the best under canopy lights in 2024/2025, some of my customers have been asking me if it’s really worth it. Can bud leaves even utilize light hitting their underside when we know that nature intended light to come from above?

Lighting is the engine of indoor bud cultivation. But in 2025, savvy growers know the real question isn’t just “how much light?”, it’s “how can I get the right light to all my buds, not just the top colas?”

As LED technology and commercial practices advance, growers are increasingly turning to multi-layered lighting strategies, combining powerful above-canopy fixtures with inter-canopy (side) and under canopy lighting. But does this approach outperform a single, ultra-powerful top light? Is it worth the extra investment, complexity, and energy use? What do real-world results and peer-reviewed research show?

In this guide, we’ll answer these questions with clear numbers, actionable recommendations, and cited studies. We’ll also show you exactly how to compare an “all-from-above” strategy with a split approach, using specific products for reference.

1. The Basics: How Buds Absorb Light

Buds, like most leafy plants, are built to capture sunlight from above. The upper surface of the leaf (the adaxial side) is thick with chloroplasts, tiny green solar panels designed to harvest every photon. The underside (the abaxial side) is adapted mainly for gas exchange. 

Absorption Rates: Top vs. Underside 

Top Lighting:

• When light hits the top of the leaf, about 90% of photosynthetic active radiation (PAR) is absorbed. 

Under-Canopy (Sub-Canopy) Lighting: 

• The leaf underside absorbs only about 50–60% of incident PAR, but this is still substantial, especially in lower, otherwise shaded areas of the plant. 

Side/Intra Canopy Lighting:

• Light hitting the edges or sides of leaves generally follows similar absorption rates as the underside, but its real advantage is targeting parts of the plant that top lighting can't reach. 

What about light passing through leaves? 

Only 5–10% of PAR passes through a healthy bud leaf, and this “transmitted” light is depleted in the key blue and red wavelengths, leaving mostly green and far-red, which aren’t as effective for photosynthesis. This means that if you're using a PAR meter for LED grow lights to measure only the upper canopy, you're missing how little usable PAR actually reaches the lower buds. Measurements above the canopy don’t reflect the dramatic attenuation below.

What does this mean for yield? 

Your upper canopy is always in a position to maximize growth, but without intervention, the mid and lower canopies will inevitably suffer from light starvation.

This is why so much of a traditional harvest is “popcorn buds”—larfy, underdeveloped, and lower in THC and terpene content. 

2. The Real-World Numbers: Energy Use, Absorbed Light, and Bud Quality 

Let’s compare the energy used by different lighting setups in a typical indoor flower cycle (8 weeks/56 days, 12 hours/day, per 4’x4’ canopy area): 

Above-Canopy Lighting Only 

• Common LED Fixture: 640W
• Absorption: 90%
• Total Energy Use:
  • 0.64 kW × 12h × 56 days = 430 kWh
  • At $0.15/kWh: $64.50 

Under Canopy Lighting (Supplemental) 

• Two 120–125W grow light bars (one each side): 240–250W total
• Absorption: 55%
• Total Energy Use:
  • 0.25 kW × 12h × 56 days = 168 kWh
  • At $0.15/kWh: $25.20 

Inter-Canopy (Side) Lighting 

• Similar to under-canopy: two 120–125W bars, similar energy use.
• Main difference: Directionality. Best for hitting shaded buds in mid and lower canopy. 

Efficiency Insight: 

Under canopy lighting adds about 39% of the energy use of above-canopy lighting, but specifically targets zones where that energy produces more yield gain per watt.  

3. Academic Research: Yield Gains with Intercanopy and Under Canopy Lighting

University of Guelph (Hawley et al., HortScience 2018): 

• Under canopy lighting increased total dry bud mass by 20–24%.
• Lower buds had much higher THC and terpene content, often matching the top colas.
• Uniformity in both yield and chemistry improved. 

MDPI Plants (2024): 

• Both under-canopy (SCL) and inter-canopy (ICL) lighting increased yield.
• SCL was more energy efficient per gram of yield.
• Lower buds’ cannabinoid and terpene content matched upper buds, improving product quality and consistency. 

Commercial Results (Fluence, GrowPros): 

• Commercial growers report 20–30% total yield increases and a much higher ratio of premium flower using under- or inner canopy lighting, especially in dense and vertical setups. 

“Supplemental under canopy lighting for the entirety of the flowering stage improved yield, cannabinoid uniformity, and lower bud development compared to top lighting alone.”
— Hawley et al., 2018 

4. Real-World Grower Dilemma: Split Lighting vs. Top-Only Lighting 

Let’s get practical.
Suppose you’re choosing between these two approaches for a standard 4’x4’ grow table (or similar area): 

All-from-Above: Single 1000W Top Light 

• Example: Secret Lighting SL-1000 LED Grow Light
• Pros: Simplicity, high top intensity, fewer fixtures/wires.
• Cons: Most extra wattage is “wasted” at the top due to light saturation, little penetration to lower buds. 

Split Lighting: 640W Top + 2 x 120W-125W Under-Canopy Bars 

• Example: HLG Tomahawk 650 (640W) + GrowPros 125W Under Canopy (x2) or 120W Grower's Choice Under Canopy Lights (x2)
• Total Wattage: 890W (very close to 1000W)
• Pros: More balanced distribution of light, more efficient absorption plant-wide, increased lower bud yield and quality.
• Cons: Slightly more complex setup (mounting bars, more cables). 

Energy Consumption (8-week flower cycle): 

• Option A: 1.0 kW × 12h × 56 days = 672 kWh
• Option B: 0.89 kW × 12h × 56 days = 598 kWh 

In both cases, the total wattage per area is similar. 

Yield and Quality: Which Is Better? 

All research and commercial experience says: 

• The split lighting approach yields more total flowers per watt, with a higher ratio of premium “A” grade buds throughout the canopy.
• Lower buds develop like top colas (denser, higher THC, more terpenes).
• The top buds are only marginally less potent, if at all, with 640W versus 1000W overhead—because leaves saturate at high light and can’t use the extra photons. 

The science is clear: Balancing wattage between top and under-canopy/inter-canopy fixtures leads to better yields than simply blasting more light from above. 

5. Other Approaches: Optics, Pruning, and Reflectors 

Superior Optics & Reflectors: 

• Technologies like Scynce’s secondary optics aim to push more light deeper into the canopy.
• These help (and are worth including), but physics still wins. Dense canopies absorb most incoming light in the upper layers, limiting deep penetration. 

Pruning & Training: 

• Defoliation, lollipopping, and trellising all help open up the canopy and improve light penetration. Lollipopping, removing the lower third of the plant's foliage and bud sites, redirects energy toward the top and middle buds, making them fuller and more potent. This technique directly reduces the formation of popcorn and larfy buds.

• Essential for air flow and bud size, but even the best-trained plants can’t fully overcome light drop-off without supplemental lower lighting. 

Combining Approaches: 

• Best results always come from using canopy management, good top lighting, and supplemental under-/inter-canopy lighting together. 

Energy cost at $0.15/kWh. Yield and premium bud% based on cited studies and commercial reports. 

7. Installation & Best Practices 

Top Lighting: 

• Use a high-quality, evenly distributed LED fixture (such as HLG Tomahawk or SecretLED SL-1000).
• Height: 18–24” above canopy during flower. 

Under Canopy Lighting: 

• Two 120–125W bars per 4’x4’, one on each side.
• Mount just above the floor or at base of stalks, angled slightly inward for even coverage.
• IP-rated for splash resistance. 

Inter-Canopy Lighting: 

• Mount at mid-canopy height along sides.
• Also effective in multi-tier vertical farms. 

Schedule: 

• Run all lights 12 hours/day for the entire flowering stage. 

Combine with: 

• Defoliation to remove light-blocking fan leaves.

• Good airflow to minimize mold risk. 

8. Frequently Asked Questions (FAQ) 

Q: Are under canopy LED lights needed during veg?
A: No; veg canopies aren’t dense enough to justify the added energy. 

Q: Is intercanopy lighting better than from below?
A: Both boost lower yields. Under-canopy is best for bottom-most buds; side lighting excels for mid-level branches. 

Q: Will extra top light (over 800–900W/4x4) make up for no under canopy grow lights?
A: No; upper leaves can only absorb so much, and extra light is mostly wasted or causes heat stress. 

Q: What’s the best spectrum for under-canopy lights?
A: Red/far-red–dominant spectra have been shown to drive flower bulking in lower buds; many grower-focused bars use a blend for optimal results. 

Q: Can you use fewer under canopy LED grow lights to save energy? 
A: Two bars per 4’x4’ is standard for uniform coverage, but smaller grows can sometimes get by with one. Avoid over-lighting to prevent leaf stress. 

9. Real-World Examples & Product References 

• HLG Tomahawk 650 LED
• GrowPros 125W Under-Canopy Bar
• Grower's Choice Full Phase Under Canopy Lights
• Grower's Choice Red Enhanced Under Canopy Light
• SecretLED SL-1000 LED 

10. Step-By-Step Guide: Building a High-Efficiency, Multi-Layered Lighting Setup 

1. Start with a quality top fixture—choose a wattage that won’t cause leaf saturation (600–700W per 4’x4’ for LEDs is ideal).
2. Add under-canopy (and/or inter-canopy) bars, two per table, IP-rated, 120–125W each.
3. Install bars at floor or mid-canopy height, depending on desired coverage.
4. Set your timers. Run all lights for 12 hours/day during flower.
5. Maintain a regular pruning and defoliation schedule to maximize light penetration and airflow.
6. Monitor and tweak: track yield, bud quality, and electricity costs to dial in your system. 

11. Conclusion: The New Gold Standard for Indoor Yields 

References 

• Hawley, D., Graham, T., Stasiak, M., & Dixon, M. (2018). Improving Bud Quality and Yield with Subcanopy Lighting. HortScience. DOI
• MDPI Plants (2024). Subcanopy and Inter-Canopy Supplemental Light Enhances Yield and Quality. Link