Intra-canopy lighting (ICL) for cannabis cultivation involves placing light sources within the plant canopy, rather than just above it. This technique can improve light penetration, enhance photosynthesis, and optimize plant growth. Here are the pros and cons: Here is a breakdown of the differences between inter-canopy, under-canopy, and intra-canopy lighting in cannabis cultivation:
- Intra-Canopy Lighting (ICL)
- Definition: Lights placed within the canopy, usually at mid-level, to improve light penetration to lower bud sites and leaves.
- Purpose: Targets shaded inner growth, ensuring better photosynthesis efficiency and yield.
- Placement: LED bars or strips positioned horizontally or at an angle between plant rows or branches.
- Best for: Dense canopies, SCROG, high-yield setups needing uniform light distribution.
- Inter-Canopy Lighting
- Definition: Lights placed between plants, rather than within individual plant structures.
- Purpose: Enhances light exposure to the lower and middle parts of multiple plants in high-density grows.
- Placement: Vertical LED bars or side lighting positioned between rows or columns of plants in a grow space.
- Best for: Vertical farming, commercial multi-tier growth, and Sea of Green (SOG) setups.
- Under-Canopy Lighting
- Definition: Lights placed beneath the canopy, pointing upwards.
- Purpose: Targets the underside of leaves and lower branches, helping with uniformity and stimulating lower bud growth.
- Placement: LED strips or panels installed underneath plant canopies, often reflecting light upwards.
- Best for: Bushy plants, reducing popcorn buds, and experimental lighting setups.
Key Differences:
Pros of Intra-canopy Lighting:
- Improved Light Penetration – Helps distribute light more evenly, reaching lower buds and leaves that might otherwise be shaded by the upper canopy.
- Increased Yield – More light exposure throughout the plant can lead to denser, more uniform bud development.
- Enhanced Photosynthesis Efficiency – Directly supplying light to shaded areas ensures that more leaves contribute to energy production.
- Better Canopy Management – Reduces stretching as lower branches get sufficient light, promoting a more compact, manageable canopy.
- Potential Energy Efficiency – Can reduce reliance on high-intensity overhead lighting, leading to optimized power usage.
- Improved Bud Quality – More uniform lighting can lead to more consistent cannabinoid and terpene production across the plant.
- Reduced Heat Stress – LED-based ICL systems produce less heat compared to traditional overhead HID lights, reducing stress on upper canopy leaves.
Cons of Intra-canopy Lighting:
- Increased Setup Complexity – Requires careful placement of lights and possibly additional wiring, which can be more time-consuming.
- Higher Initial Costs – Additional lighting fixtures and infrastructure may increase upfront investment.
- Potential Heat Management Issues – Even with LED lights, improper placement can lead to heat accumulation within the canopy.
- Maintenance Challenges – More lights within the canopy mean more potential failure points and more complex maintenance.
- Risk of Overexposure or Burn – If lights are too close, plants can experience light stress, leading to bleaching or other damage.
- Electrical Safety Concerns – More wiring and lights in humid grow environments increase the risk of electrical issues.
- Not Always Necessary – Increasing overhead lighting is more effective based upon how plants absorb light. In existing HPS facilities, it may be far more effective to replace your overhead lighting with high intensity LED fixtures that increase your PPFD at the top of your canopy while lowering your power costs.
How Do Plants Absorb Light?
Cannabis leaves absorb light much more efficiently from the top (adaxial) surface than from the bottom (abaxial) surface. It is not equal, and here is why:
- Leaf Structure & Light Absorption
- Top of the Leaf (Adaxial Surface)
- Contains more chlorophyll and denser chloroplasts, which are responsible for photosynthesis.
- Optimized to capture direct overhead light.
- Stomata (pores for gas exchange) are usually fewer on the top surface, minimizing unnecessary light diffusion.
- It has a waxy cuticle that helps prevent water loss but still allows efficient light absorption.
- Bottom of the Leaf (Abaxial Surface)
- It has fewer chloroplasts, making it less effective at capturing light.
- Typically contains more stomata, which are better for gas exchange rather than light absorption.
- It can absorb some light, especially if it is reflected from grow room surfaces, but much less efficiently than the top.
- Practical Implications for Grow Lighting
- Overhead lighting (HID, LED, CMH) is the most effective since it mimics natural sunlight and targets the most light-absorbing part of the leaf.
- Side and intra-canopy lighting helps light reach shaded leaves, optimizing overall plant efficiency.
- Under-canopy lighting (pointing upward) is far less effective but can still be beneficial in specific setups by reducing shading effects.
- Can Under-Canopy Light Be Useful?
Yes, but its efficiency is lower compared to top-down or side lighting. It may help reduce popcorn buds and encourage growth in lower branches, but it should not replace overhead lighting. For new construction, best practice would be to use the highest intensity overhead lighting you can afford.
Sources:
The information about leaf structure and light absorption comes from a combination of botanical research, plant physiology studies, and cannabis-specific cultivation research. Here are some key sources and principles:
- Plant Physiology & Leaf Structure
- Taiz & Zeiger – “Plant Physiology and Development” (6th Edition, 2014)
- Explains how chloroplast distribution is denser on the upper (adaxial) surface, optimizing light absorption.
- Discusses leaf anatomy, including the role of palisade mesophyll cells (top) vs. spongy mesophyll (bottom).
- Raven, Evert, & Eichhorn – “Biology of Plants” (8th Edition, 2012)
- Details how leaves are adapted to absorb sunlight from the top where most chlorophyll is concentrated.
- Stomatal distribution and gas exchange mechanisms.
- Cannabis-Specific Research & Horticulture
- Chandra et al. (2008) – “Light Effects on Cannabis sativa Morphology and Cannabinoid Production”
- Found that light penetration affects cannabinoid yield, with top-exposed leaves playing a dominant role.
- Cannabis leaves, like most C3 plants, absorb light mainly from the adaxial surface due to chloroplast density.
- Bugbee, B. (2020) – Utah State University, LED Research for Cannabis Growth
- Studies on how different light angles affect photosynthesis efficiency in controlled environments.
- Highlights that top-down and intra-canopy lighting are far more effective than under-canopy light due to natural leaf adaptations.
