With all the rave about the best under canopy lights 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?
It's no secret that lighting is the engine of indoor bud cultivation. More ambitious growers have pumped upwards of 1000 watts over a 4x4 canopy and upwards of 1400 watts over a 5x5 area like with the popular 1400 Watts GML. This definitely works provided you realize the impact the added light is going to have on feeding and climate control inputs and of course the added electricity costs of boosted lighting, boosted AC and dehumidifier.
I think that there's a logical approach to this and it's what I tell my customers; "get as much light (photons) to as much of your plant as you can - efficiently". We'll call this the "Split Approach". But does this approach outperform a single, ultra-powerful top light? Is it worth the extra investment, complexity, and energy use?
In this guide, we’ll deal 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.
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.
Light absorbed in the fan leaves aid in photsynthesis and the mechanism for providing sugars and metabolites to the plant but they distribute energy steadily like protein to the human body.
On the other hand light absorbed directly at the bud and sugar leaves provides "fast" sugar similar to sugar in the human body. Added benefits of ight absorbed directly by the buds is local metabolism boost, resin production and maturation.
When light hits the top of the leaf, about 90% of photosynthetic active radiation (PAR) is absorbed.
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.
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.
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.
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.
If you've grown cannabis indoors, you've almost certainly encountered popcorn buds — those small, airy, underdeveloped nuggets that form on the lower and middle sections of the plant. They get their name from their size and loose structure, roughly resembling a piece of popped popcorn.
Popcorn buds are essentially the plant's response to inadequate light. When lower bud sites don't receive enough photons to support full development, the plant deprioritises them and redirects energy toward the upper canopy where light is abundant. The result is dense, potent top colas and disappointing, larfy buds lower down.
They are not a sign that something has gone catastrophically wrong — they are a natural consequence of growing tall plants under a single light source. In outdoor growing, the sun moves across the sky and provides light from multiple angles. Indoors, light comes from a fixed point above, meaning lower bud sites are always going to be at a disadvantage without intervention.
Popcorn buds are significantly lower in THC and terpene content than top colas. They are harder to trim, less visually appealing, and command lower prices in commercial operations. In a typical indoor grow without supplemental lighting, popcorn buds can account for 30–40% of total harvest weight — yield that is technically there but worth considerably less than premium flower.
By delivering targeted light directly to lower and mid-canopy bud sites, under canopy and inter canopy lighting gives those bud sites the photons they need to develop fully. Research from the University of Guelph found that supplemental sub-canopy lighting brought lower bud cannabinoid and terpene content in line with top colas — effectively eliminating the quality gap between top and bottom of the plant. Combined with lollipopping and defoliation to remove the most unproductive growth, supplemental lighting is the most effective tool for eliminating popcorn buds from your harvest.
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):
Under canopy lighting adds about 39% of the energy use of above-canopy lighting, but specifically targets zones where that energy produces more bud yield gain per watt.
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
Let’s get practical.
Suppose you’re choosing between these two approaches for a standard 4’x4’ grow table (or similar area):
In both cases, the total wattage per area is similar.
All research and commercial experience says:
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.
Best results always come from using canopy management, good top lighting, and supplemental under-/inter-canopy lighting together.
| Option | Top Wattage | Under/Inter | Total Wattage | kWh (56d) | Energy Cost | Yield (est.) | Premium Bud % |
|---|---|---|---|---|---|---|---|
| 1000W Top Only | 1000W | 0 | 1000W | 672 | $100.80 | Baseline | 40–50% |
| Split (Top+UC) | 640W | 250W | 890W | 598 | $89.70 | +20–30% | 60–80% |
Energy cost at $0.15/kWh. Bud Yield and premium bud% based on cited studies and commercial reports.
Run all lights 12 hours/day for the entire flowering stage.
Good airflow to minimize mold risk.
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 bud 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.
The era of “top light only” is fading in high-end bud cultivation. Peer-reviewed research and top commercial growers agree:
Splitting your total wattage between a strong top fixture and targeted under-canopy (and/or inter-canopy) bars gives you superior yield, quality, and profitability, without significantly increasing your energy bill.
By combining canopy management techniques like lollipopping and defoliation with supplemental lighting, growers eliminate popcorn buds, increase flower density, and improve cannabinoid uniformity throughout the entire plant.
With strategic investment in LED supplemental lighting and proper canopy management, you can turn your lower buds into top-shelf flower, increase total bud yield by up to 30%, and command higher prices for a more uniform, potent crop.
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