Impact of Under-Canopy Lighting

The Role of Leaf Structure in Light Absorption:

For over half a billion years, plants have evolved to optimize light absorption through photosynthesis. This natural process enables them to convert sunlight into energy efficiently. Through phototropic responses—where leaves position themselves towards light sources—and the evolution of leaf architecture, plants maximize their ability to capture and utilize light.

At the heart of this process are chloroplasts, the specialized organelles responsible for photosynthesis. These structures are primarily located within the palisade layer of leaves, where they absorb sunlight and use it to convert carbon dioxide and water into sugars, carbohydrates, and oxygen. This energy is then used by the plant through respiration.

As shown in the diagram, chloroplasts are concentrated near the upper epidermal layer, allowing them to absorb up to 85% of incoming light. Some light is reflected, while approximately 5% is transmitted through the leaf. This efficient arrangement ensures that plants make the most of available light by orienting their leaves accordingly.

Light Absorption from Below the Canopy

While the upper leaf surfaces are highly efficient at capturing light, the underside can also absorb light, albeit at a lower efficiency—around 25% compared to the upper surface's 85%. Traditionally, growers have focused on top-down lighting, overlooking the potential of under-canopy illumination.

As shown in the diagram, the underside of the leaf is capable of absorbing light, though much less efficiently than the upper surface. This has long been overlooked by growers who primarily use top lighting.

As plants mature, lower leaves receive less light due to shading from upper foliage. This reduction in light exposure can limit photosynthesis in these lower regions, potentially affecting overall plant health, reducing yields, and impacting the quality of lower flower sets.

The Advantages of Under-Canopy Lighting

Under-canopy lighting addresses this issue by introducing light from beneath the plant, illuminating shaded leaves and stimulating photosynthetic activity in areas that would otherwise receive minimal light.

This technique offers multiple benefits:

Enhanced Lower Flower Development: Light penetration to lower parts of the plant supports the growth of flowers that would otherwise remain underdeveloped, leading to increased yields and improved harvest quality.

Improved Light Distribution: By supplementing top lighting, under-canopy lighting ensures a more balanced light distribution across the entire plant.

Increased Photosynthetic Efficiency: Lower leaves become more active in photosynthesis, contributing additional energy for overall plant growth and productivity.

Reduced Shading Effects: By mitigating the impact of a dense upper canopy, under-canopy lighting ensures that lower regions of the plant receive sufficient light for optimal development.

Regulated Root Zone Temperature: The presence of under-canopy lighting generates heat, which can raise lower plant temperatures and promote faster growth.

The Role of Inter-Canopy Lighting in Plant CultivationInter-canopy lighting takes a different approach by placing light sources within the plant canopy rather than solely above or below it. This technique enhances light penetration and distribution, particularly in bushy or vertically growing plants.

As shown in the diagram, inter-canopy lighting ensures that light reaches the middle and lower sections of the plant, reducing shading effects and allowing for a more uniform distribution of light.

Studies on LED inter-lighting have demonstrated its effectiveness in improving photosynthetic photon flux density (PPFD) at various canopy levels, ensuring a more uniform exposure across different layers of the plant.

Key Benefits of Inter-Canopy Lighting

Optimized Light Distribution: Even illumination throughout the plant ensures uniform growth and better overall health.

Higher Yields: By directing light into the middle and lower sections of the plant, inter-canopy lighting promotes the development of buds and fruits in areas that might otherwise be underdeveloped.

Reduced Vertical Stretching: Ensuring that all plant sections receive adequate light minimizes excessive stretching towards the primary light source, resulting in a more compact and manageable canopy.

Enhanced Quality: Improved light penetration results in higher-quality produce, particularly for buds and flowers lower on the plant.

Conclusion

Both under-canopy and inter-canopy lighting present valuable strategies for modern plant cultivation. By understanding how plants interact with light at different angles, growers can harness these techniques to improve yield, optimize growth, and enhance crop quality.

While implementing these methods requires additional energy investment and careful setup, the long-term benefits—such as higher efficiency, increased productivity, and superior crop quality—often outweigh the challenges. As agricultural and horticultural practices continue to evolve, these lighting techniques will likely become even more integral to successful plant cultivation.