Introduction to Cannabis Photobiology


Light is an important factor for a successful vegetative life; when cannabis is being deprived of or is deficient in getting natural light, it is affected by seasonal affective disorders. This is where the need for artificial light comes in.

Nowadays, the production of cannabis is more commonly done indoors and is therefore incredibly reliant on having a properly controlled environment. This includes providing them with the appropriate light cycles for both the vegetative and flowering stages. To be able to place cannabis growth to a maximum, high light intensity should be used. On the other hand, when it comes to initiating budding, proper photoperiodicity control should be done.

Growing your cannabis indoors also have their upsides. When you grow indoors, there is uniformity and continuity in the lighting, which will help your cannabis plants produce a high yield of good quality buds. However, to do this successfully, you must understand cannabis photobiology. High-quality lighting can be very expensive and energy-intensive; that is why the lighting and light cycle works are extremely important.

Selecting and having the appropriate lighting systems with the right light spectra are vital for maximizing the success of cannabis growth, especially for commercial or large scale operations. A better understanding of cannabis photobiology will greatly improve every grower, novice and experienced, to improve cannabis growth and productivity while effectively reducing costs.

What is Photobiology?

All living things have always lived around sunlight, and as a technology tool, it has played a significant role in our society. Far more than the reason why light bulbs were invented in the first place. A proof that light is not just something to brighten our way and help us see. Moreover, light has played a foundational role in environmental biology and ecology through the relationship with UV and ozone. Additionally, light is fundamental to optics present in today’s grow lights used in cannabis growing.

Photobiology is generally the study of interactions between light and living organisms. This study covers a large area of research that includes investigations into the nature of how organisms see, how light can become harmful, and how light can produce energy for plants. In this article, we will dig into specifically the interaction between light and cannabis plants.

When it comes to plant biology, photobiology studies how plants were able to discriminate between types of light according to the spectrum, intensity, and duration. It has eventually helped growers understand how light is used to improve plant cultivation. Harvesting of energy by plants is truly the most important application of photobiology.

What are Photoreceptors?

Plants can recognize light through photoreceptors, and they are specialized cells that have light-sensitive proteins that get the job done. When photoreceptors come in contact with sunlight, they will then absorb units of light that are referred to as photons. The photoreceptors will receive and segregate vital information about the environment through these photons, such as the wavelength of the light. Your plants will eventually use up this information to start a biological activity such as their growth patterns. The effect of light on the form and structure of plants is referred to as photomorphogenesis.

To understand the use and function of photoreceptors, we will need to understand light and color as well. The human eye can see a particular amount, and these are the “visible light.” The visible light contains wavelengths that fall in the 400 to 700 nm range, and this falls between the infrared and ultraviolet. These UV lights are broken down into two more categories, the UV-A (315-400nm) and UB-B (280-315nm).

Plant biologists, horticulturalists, and botanists truly understand how plants utilize different color spectrum components during their growth phases. When it comes to the horticultural industry, the growers use different light spectra and intensities to effectively and healthily manipulate plant growth, morphology, and flowering. Upon the utilization of the correct lights, photosynthesis will then occur. The process of photosynthesis includes a set of reactions where the plants will acquire and store light energy in the carbon bonds of carbohydrates in the plants.

Cannabis growers know that determined light properties play a significant role in cannabis vegetative growth and flowering phase or plant reproduction. Nowadays, artificial lighting systems have been widely used and will eventually require improvements in large-scale cannabis production. Artificial lighting systems will work perfectly fine combined with a detailed understanding of cannabis photobiology.

Photoreceptors and Plant Growth

Red and Far-Red Light

Red light (~625-700nm) affects leaf and stem growth and leaf nutrients, and it is also required for chlorophyll production. In some plants, flowering is brought about by the red light being delivered during the early part of the photoperiod. However, this may not work for all cannabis strains. So it is important that you learn how the cannabis strain you are growing will react to your choice of the cannabis plant.

Blue and UV Light

Both Blue (~450-520nm) and UV (<400nm) light have functions when it comes to regulating various physiological and developmental processes. Blue light moderates chlorophyll and chloroplast development, enzyme synthesis, plant density improvements, and environmental stress responses. A study concluded that cannabis plants that are grown under blue light with a shorter photoperiod greatly improved cannabinoid content—a combination of UV-A and blue light-induced cannabigerol accumulation in cannabis buds. UV-B is typically damaging to plants, but they have their own set of benefits when used in controlled amounts, such as contributing to pest resistance, increasing flavonoid content, and improvement of photosynthetic efficiency. UV-B light also elicits THC accumulation in both the leaves and buds. There were also reports that after a daily three-hour supplemental UV-B radiation, THC concentrations significantly increased. These studies suggest that cannabinoids play a vital role in UV protection.

Green Light

Greenlight (~520-560nm) is considered unavailable for plant growth since photoreceptors have only limited absorbance for lights in this wavelength. Greenlight is reflected off the surface of the leaves. That is why leaves appear in shades of green. The green light negatively affects the THC levels in cannabis plants, so the small benefit it offers may not outweigh the damage that it might cause.

Light Stress in Plants

Chlorophyll might be responsible for direct absorption, and there are also other pigments that greatly contribute in their unique ways. The carotenoids and xanthophylls support the chlorophyll by effectively absorbing excess light that could cause photoinhibition. Photoinhibition is a phenomenon where there is a decrease in photosynthesis efficiency when plants are exposed to too much light. Excessive light exposure will then result in light stress in plants.

Light damage and light stress in plants are serious issues, especially when it comes to growing cannabis. However, plants have their mechanisms to fight off light stress and protect themselves. The presence of carotenoids and xanthophylls in plants can catch excess photons. Plants can also deliver a process of self-shading, and they do it when the chloroplasts move into a low-absorbing position. Antioxidants in plants can also catch free electrons resulting in the mitigation of the damage of plant molecules.

However, it is our responsibility to limit light stress because whenever plants need to protect themselves from intense light, they consume and eventually waste a good deal of energy. That energy could have gone towards a healthier plant and fruit production. Therefore, light stress has a great impact on the post-harvest yields. However, remember that cannabis plants are also stressed if thrown under low or insufficient light conditions. In other words, low light dramatically affects plant growth, and if low light conditions are prolonged, it may result to plant death.

LED, Metal Halide, and High-Pressure Sodium

Light cycles and light spectrum greatly influence plant growth, flowering time, plant health, cannabinoid production and quality, and secondary metabolites production. Based on a study, cannabis sativa flowers that were made to bloom under LED lights were able to produce 9.5% THC, and those flowers are grown under high-pressure sodium lights or HPS wa able to produce 15.4% THC. A separate study showed observations that combining 530nm LED lights, 440nm LED lights, and 655nm LED lights with metal halide lamps significantly increased the dry bud yield by 18% to 24%.

Several studies have found that responses light can be strain-specific, and a constructed light cycle or recipe will not result in uniform reactions in plant growth. Thus, with proper light combinations and the utilization of correct wavelengths, you will surely be able to grow healthy cannabis and harvest a good amount of yield.

An emerging and important field of study, encompasses several key areas:

Photoreceptors and Plant Growth

Photoreceptors in cannabis plants absorb photons from sunlight, triggering various biological activities such as growth patterns and photomorphogenesis. Understanding how these receptors work is crucial for optimizing plant growth and development.

Light and Cannabis Growth

Different light spectra have distinct effects on cannabis plants. For example, red light influences leaf and stem growth and is necessary for chlorophyll production, while blue and UV light regulate various physiological and developmental processes, including chlorophyll development and cannabinoid content. UV-B light, in particular, is known to increase THC accumulation in leaves and buds.

Photosynthesis in Cannabis

This is a complex set of reactions where plants convert light energy into chemical energy. It occurs within the chloroplasts of plant cells. The process is essential for plant growth, with a direct correlation between plant productivity and photosynthetic rates in a given environment.

Impact of Light on Secondary Metabolites

Light can influence the production of secondary metabolites in cannabis, such as cannabinoids and terpenes. These compounds have significant implications for the plant’s medicinal properties. For instance, cannabinoids are known for their therapeutic potential in treating various medical conditions.

Light Stress in Plants

Excessive light exposure can result in light stress, decreasing photosynthesis efficiency and causing damage to plant cells. However, cannabis plants have mechanisms to protect themselves from light stress, such as the movement of chloroplasts and the production of antioxidants.

Lighting Technologies in Cannabis Cultivation

Advances in lighting technologies, such as LED and high-pressure sodium lights, have significantly impacted cannabis cultivation. These technologies allow for better control over light spectra and intensity, enabling growers to optimize plant growth and cannabinoid production.

Cannabis Cultivation and Legal Considerations

The legal status of cannabis varies across regions, affecting the extent and nature of research and cultivation practices. In regions where cannabis cultivation is legal, there’s a greater scope for applying photobiology principles to improve crop yields and quality. However, in places where it’s illegal, such research and application are restricted.

Environmental and Economic Impact

Efficient lighting not only improves plant health and yield but also has environmental and economic implications. High-intensity lights, while beneficial for plant growth, can be energy-intensive and costly. Therefore, finding the right balance between light intensity, energy consumption, and plant health is crucial for sustainable and economically viable cultivation practices.


We hope that this introduction to cannabis photobiology has helped you understand the relationship of light, wavelengths, and photoreceptors in your plants to promote plant growth. It is extremely important to remember that all photoreceptors act synergistically to transmit relevant information to the plant regarding the ambient and environmental lighting conditions.

Because of the awesome photoreceptors, the cannabis plants are able to detect from ultraviolet to infrared. They determine their intensities and send signals about the time of exposure, and they can also be sensitive to temperature. Plants can sense and adjust to light changes such as day to night transition or changes in light cycles when it comes to indoor growing.

Ideally, you adjust the amount, spectrum, and the time of exposure of light according to the cannabis strain being grown, the growth stage that they are in, and the environment of cultivation. All of these factors are essential for the optimization of light use. Therefore, the selection of high-quality lighting systems and light spectra is extremely important for cannabis growth both indoors and outdoors.

We hope that this informative post has greatly helped you and will support your future cannabis growing plans.