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Impact of visible light on cannabis
By Rene February 25th, 2024
Impact of visible light on cannabis

There are visible light and invisible light in the Sunlight and the visible light has the greatest impact on plants.In the led grow lights,the most common visible lights are blue light, green light, yellow light and red light . In this article, we will give you a detailed introduction to the effects of blue light, green light, yellow light and red light on cannabis growth. 

Likewise, if you’d like to learn about the full spectrum LED grow light effects on cannabis growth, click here to find out.

1、Blue light

The wavelength of blue light is 455~492nm and the energy is high. Blue light plays a very important role in plant growth. 

Promote cannabis photosynthesis

The figure above depicts the absorption spectra of chlorophyll and carotenoids, where chlorophyll comprises chlorophyll a and chlorophyll b. Chlorophyll a, chlorophyll b, and carotenoids predominantly absorb blue light. This implies that blue light exerts a strong impact on plant photosynthesis.


Regulate the opening and closing of pores in cannabis

In 2017, the research group led by Ken Ichiro Shimazaki at Kyushu University in Japan unveiled that plants regulate the opening and closing of pores by integrating signals from blue light and CO2. The results were published in Nature Communications.

Pores are tiny openings that facilitate the intake and release of carbon dioxide, water vapor, oxygen, and other gases. These pores influence the processes of transpiration, photosynthesis, and respiration. For instance, when CO2 levels are low, pores open to maximize photosynthesis.


Assisting cannabis in producing more cannabinoids

 The potential mechanism of the effect of blue wavelength on cannabinoids also needs further study. Some growers claim that during the flowering stage, exposing cannabis to blue light can increase cannabinoid production. The reason for this phenomenon remains unclear. Some believe that blue light primarily affects the nutritional stage of cannabis, leading to rapid growth of stems and leaves. When cannabis is exposed to blue light, it may 'think' that it has reverted to the nutritional growth period, promoting additional growth and resulting in increased production of cannabinoids and terpenes.


Promote shorter stems, more compact, thicker, and darker leaves in cannabis

Insufficient sunlight can lead to the elongation of cannabis stems in an attempt to capture more sunlight, known as shade avoidance syndrome. This phenomenon also occurs when the proportion of blue light in the environment is relatively low. However, tall and overgrown plants pose risks, as they are more prone to falling. Therefore, increasing blue light can prevent the onset of the plant's shade avoidance reaction, ensuring that the stem remains short and promoting leaves that are more compact, thicker, darker, and resistant to lodging.


2、Green light

The wavelength of green light ranges from 492 to 577 nm. Although some people claim that green light has no impact on plants, this statement is incorrect. When green light illuminates the leaf surface, the majority of it is absorbed, a small portion is reflected, and a small fraction penetrates the leaf.

Absorption of Green Light:

From the figure, it is evident that although the absorption rates of carotenoids, chlorophyll b, and chlorophyll a for green light are relatively low, they still absorb some green light for photosynthesis.

Furthermore, what may not be widely known is that, in addition to the carotenoids, chlorophyll b, and chlorophyll-a depicted in the figure, there are other pigments in plants. These pigments also absorb green light and contribute to photosynthesis, such as phytochrome and cryptochrome.


Reflection of Green Light:

Undoubtedly, leaves appear green because plants reflect green light. What may not be commonly known is that plants not only reflect green light but also reflect light across the entire spectrum. Most plants exhibit a green coloration because their leaves reflect more green light than red or blue light. Additionally, the majority of the reflected green light is absorbed and utilized by other leaves, with only a small portion being reflected to maintain the green coloration of the leaves.


Penetration of Green Light through Leaves:

What might not be widely known is that, in addition to being absorbed and reflected by the leaves, green light can also penetrate the leaves. In fact, green light can penetrate the leaves more deeply than blue or red light.


Enhancing the Photosynthetic Rate of Cannabis:

Green light does not act in isolation on cannabis. Typically, a combination of green light, red light, and blue light can enhance photosynthesis in cannabis.

Numerous chlorophylls are present not only on the leaf surface but also at the bottom of the leaf. The green light penetrating the leaf can effectively stimulate the chloroplasts at the leaf's base, aiding them in utilizing both green and blue light for photosynthesis. This helps enhance the efficiency of photosynthesis.


3、Yellow light

The wavelength of yellow light ranges from 622 to 780 nm. While it is true that yellow light has a relatively minor impact on plants compared to other wavelengths, it still exerts some influence on plant processes.

Promote the photosynthesis of cannabis

According to the images above, chlorophyll and carotenoids exhibit lower absorption of yellow light compared to green light. Existing studies suggest that appropriate supplementation of yellow light can significantly enhance plant growth, such as increasing the average length of leaves. Furthermore, it has the potential to alleviate the effects of weak light stress caused by low light intensity, influencing both growth and flowering.

Some cannabis growers assert that incorporating yellow light into plant lighting can foster plant growth and development. However, it is not advisable for the intensity of yellow light to be excessively strong. Overexposure of cannabis to too much yellow light can substantially reduce photosynthetic intensity, thereby inhibiting the growth and development of cannabis.


4、Red light

The wavelength of red light spans from 622 to 770 nm, and it possesses the lowest energy within the visible light spectrum. Despite its lower energy compared to blue light, red light, much like blue light, plays a crucial role in promoting plant growth.

Promote cannabis photosynthesis:

 As illustrated in the figure, red light demonstrates efficient absorption by chlorophyll a and chlorophyll b, playing a pivotal role in the photosynthesis of plants. Specifically, red light stands out as the most effective spectrum, following closely behind blue light, in promoting photosynthesis. When absorbed by plants, red light facilitates the synthesis of their organic matter, contributing significantly to their overall growth and development.


Elongation of Cannabis Stems and Leaves:

During the vegetative stage, if cannabis is exposed solely to red light, the plant may undergo a shade avoidance reaction, leading to elongation of its stems and leaves.


Increasein Cannabinoid Production:

Cannabinoid production can be enhanced by expanding the flower area and increasing the number of flowers. Cannabis flowers develop trichomes, which are responsible for producing cannabinoids such as THC and CBD terpenes.


Based on past experiences, exposing cannabis to a combination of far-red and red light has been observed to extend the width of flowers. Additionally, subjecting cannabis to higher intensity red light has shown to increase the number of flowers.

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