One of the biggest challenges for indoor cannabis growers is replicating the sun’s ability to penetrate the plant canopy, particularly the lower portions.
Outdoors, photons[1] from natural sunlight strike leaf surfaces at multiple angles throughout the day, ensuring light distribution throughout the plant. By contrast, traditional overhead lighting in indoor cultivation struggles to reach the lower canopy, limiting photosynthesis and yields.
To remedy this problem, canopy lighting has emerged as an effective method for ensuring all parts of the plant receive adequate light exposure. By increasing the light intensity within the canopy, growers can ensure that older but still functional leaves continue photosynthesizing, leading to higher yields and more consistent phytocannabinoid production.
In this blog post, we’ll discuss why canopy lighting is important in cannabis cultivation and best practices for implementing this technique in the grow room.
Why lighting matters
Before we discuss canopy lighting, let’s recap why light is crucial for cannabis.
Plants need light within the photosynthetically active radiation (PAR) range of 400–700 nanometers (nm) for photosynthesis. Different wavelengths and intensities affect plant morphology, yield and the production of secondary metabolites like cannabinoids, terpenes and flavonoids.
Why lighting matters
Before we discuss canopy lighting, let’s recap why light is crucial for cannabis.
Plants need light within the photosynthetically active radiation (PAR) range of 400–700 nanometers (nm) for photosynthesis. Different wavelengths and intensities affect plant morphology, yield and the production of secondary metabolites like cannabinoids, terpenes and flavonoids.
Blue light encourages compact growth and cannabinoid accumulation, while red light promotes flowering. Studies show that a 1:1 or 1:4 blue:red light ratio can optimize flowering and cannabinoid production, though responses vary by variety.[2]
Light intensity is measured by the number of photons within the PAR range that reach the plant canopy. This is called photosynthetic photon flux density (PPFD), and the amount of PPFD cannabis plants receive impacts their growth.
While artificial lighting cannot replicate the spectrum and intensity of natural sunlight, growers can use specific light intensities and wavelengths to manipulate growth and chemical production.
Light-emitting diode (LED) and high-pressure sodium (HPS) lights are the most widely used for indoor cannabis cultivation. LEDs are valued for their energy efficiency, customizable spectrum and suitability across all growth stages, while HPS lights, despite generating significant heat, are often preferred for flowering due to their intense output. Other common light sources include:
- Metal halide lights provide a strong blue light spectrum ideal for the vegetative phase.
- Ceramic metal halide lights offer a balanced full-spectrum option for the vegetative and flowering phases, but at a higher cost.
- Florescent lights are ideal for seedlings and clones, but they lack the intensity required for mature plants.
Selecting the right light source depends on energy efficiency, heat management, budget, plant growth stage and light spectrum requirements.
- Metal halide lights provide a strong blue light spectrum ideal for the vegetative phase.
- Ceramic metal halide lights offer a balanced full-spectrum option for the vegetative and flowering phases, but at a higher cost.
- Florescent lights are ideal for seedlings and clones, but they lack the intensity required for mature plants.
Selecting the right light source depends on energy efficiency, heat management, budget, plant growth stage and light spectrum requirements.
- Metal halide lights provide a strong blue light spectrum ideal for the vegetative phase.
- Ceramic metal halide lights offer a balanced full-spectrum option for the vegetative and flowering phases, but at a higher cost.
- Florescent lights are ideal for seedlings and clones, but they lack the intensity required for mature plants.
Selecting the right light source depends on energy efficiency, heat management, budget, plant growth stage and light spectrum requirements.
Importance of canopy lighting in cannabis
With traditional overhead lighting, growers can try to increase the intensity to reach the lower canopy. However, given that light is strongest at the top of the plant, increasing the intensity too much can have undesirable effects on the upper colas. At the same time, if lower branches receive inadequate light, buds in that area may be underdeveloped. A lighting setup that maximizes penetration into the lower canopy helps achieve a more uniform crop.
Research supports the benefits of canopy lighting. One study investigated the effects of under-canopy lighting by comparing plants grown with no supplemental lighting (control) to those receiving red-blue or red-blue-green (RGB) supplemental under-canopy lighting (SCL). Compared to the control, both SCL treatments significantly increased yield and THC concentrations (Figure 1) in lower-canopy bud tissue and enhanced concentrations of the terpene cis-nerolidol in the upper and lower canopy. RGB SCL also increased concentrations of the terpenes α-pinene and borneol in the lower canopy, while α-pinene, limonene, myrcene and linalool levels were higher in the upper canopy. Red-blue SCL resulted in more consistent cannabinoid and terpene concentrations throughout the upper and lower canopy.[3]
Figure 1. THC content of plants grown without canopy lighting (control), with red and blue sub-canopy lighting (red + blue) and with red-green-blue sub-canopy lighting (full spectrum). Image source: Hawley, Dave, Thomas Graham, Michael Stasiak, and Mike Dixon. 2018. “Improving Cannabis Bud Quality and Yield with Subcanopy Lighting.” HortScience 53 (11): 1593-1599. https://doi.org/10.21273/HORTSCI13173-18.
Figure 1. THC content of plants grown without canopy lighting (control), with red and blue sub-canopy lighting (red + blue) and with red-green-blue sub-canopy lighting (full spectrum). Image source: Hawley, Dave, Thomas Graham, Michael Stasiak, and Mike Dixon. 2018. “Improving Cannabis Bud Quality and Yield with Subcanopy Lighting.” HortScience 53 (11): 1593-1599. https://doi.org/10.21273/HORTSCI13173-18.
Figure 1. THC content of plants grown without canopy lighting (control), with red and blue sub-canopy lighting (red + blue) and with red-green-blue sub-canopy lighting (full spectrum). Image source: Hawley, Dave, Thomas Graham, Michael Stasiak, and Mike Dixon. 2018. “Improving Cannabis Bud Quality and Yield with Subcanopy Lighting.” HortScience 53 (11): 1593-1599. https://doi.org/10.21273/HORTSCI13173-18.
Best practices for canopy lighting
Canopy lighting is more suitable for compact plants or large operations where a long strip of plants can be illuminated.
To implement canopy lighting, start with full-spectrum LEDs, which mimic natural sunlight by delivering light waves across the PAR range. While artificial light cannot fully replicate sunlight, full-spectrum LEDs provide continuous spectral coverage to support plant growth at all stages.
Using low-radiant, dimmable LEDs allows growers to place lights closer to plants without scorching them. This reduces the amount of wasted light, or light spill, that falls outside the cropping area and lowers the power requirements to achieve the same light intensity compared to traditional high-heat light sources.
Growers should also supplement full-spectrum LEDs with red and far-red LEDs to take advantage of the Emerson Effect.[4] Providing red light (~660 nm) and far-red light (~730 nm) simultaneously increases photosynthesis rates compared to either wavelength alone.[5]
To maximize coverage while minimizing spill, canopy lights can be arranged in three ways:
- Intra-canopy: Fixtures are placed inside the canopy using wires hung from above or mounted on posts.
- Side-canopy: Fixtures are positioned at the sides of the canopy, often mounted directly onto trellises. While effective for outer foliage, this setup does not illuminate the center.
- Under-canopy: Fixtures are mounted at the bottom, directing light upward into the canopy’s center.
Use enough fixtures to ensure adequate crop coverage, increasing the luminaire density until the PAR values match the plant’s growth-stage requirements. Use an LED-specific extended PAR meter (400–750 nm) to verify the accuracy of the setup. The ideal distance between lights and plants depends on the uniform light distribution and LED spacing.[6] Consider using reflective materials to minimize light loss.
Finally, adjust the light placement according to the growth stage. Canopy lights used too early in the vegetative phase may distort plant growth, so it’s best to introduce them from the late vegetative phase through flowering.
Conclusion
While canopy lighting is no substitute for traditional overhead lighting, it can serve as a powerful supplement that effectively doubles the productive canopy footprint. By increasing light exposure to both the top and bottom layers, growers can enhance yields and cannabinoid production. One lighting company reports that adding 200–500 PPFD of under-canopy lighting has significantly improved productivity.[7]
Emerald Harvest Team
Featured Image by wirestock on Freepik
[1] Light particles
[2] Danziger, Nadav, and Nirit Bernstein. 2021. “Light matters: Effect of light spectra on cannabinoid profile and plant development of medical cannabis (Cannabis sativa L.).” Industrial Crops and Products 164. https://doi.org/10.1016/j.indcrop.2021.113351.
[3] Hawley, Dave, Thomas Graham, Michael Stasiak, and Mike Dixon. 2018. “Improving Cannabis Bud Quality and Yield with Subcanopy Lighting.” HortScience 53 (11): 1593-1599. https://doi.org/10.21273/HORTSCI13173-18.
[4] An increase in photosynthesis that occurs when plants are exposed to light of multiple wavelengths.
[5] Hildenbrand, Zacariah L., and Hannia Mendoza-Dickey. 2024. “Lighting Penetration in Indoor Cannabis Cultivation.” Cannabis Science and Technology 7 (4): 14-18. https://www.cannabissciencetech.com/view/lighting-penetration-in-indoor-cannabis-cultivation.
[6] Sheibani, Fatemeh, Mike Bourget, Robert C. Morrow, and Cary A. Mitchell. 2023. “Close-Canopy Lighting, an Effective Energy-Saving Strategy for Overhead Sole-Source LED Lighting in Indoor Farming.” Frontiers in Plant Science 14: 1215919. https://doi.org/10.3389/fpls.2023.1215919.
[7] Del Ninno, Matteo. 2023. “Lighting for Your Growing Needs.” Published February 14. https://jumplights.com/benefits-of-under-canopy-lighting.
