Do You Need UV Light for Growing Cannabis

As we all know, photosynthesis is critical for plants growing. Plants absorb and convert light energy to chemical energy for their growth. But the climate change and the shortage of land resource urge the development of indoor growing, such as vertical farming and greenhouse. To support indoor growing, artificial grow lights are added. Most of them concentrate on the photons from 400 nm to 700 nm, which is the efficient range of photosynthesis.

Legal cannabis growing is allowed in certain countries due to high medicinal and industrial value. Various of artificial grow lights are typically designed for growing cannabis with the spectrum around 450 nm to 660 nm, the wavelengths that efficiently absorbed by cannabis. Higher cannabinoids makes higher value for cannabis. However, it is claimed that most potent cannabis are growing in high altitude mountain peaks and near the equator in nature. Both of the places are of highest intensity of ultraviolet rays. Then researches were operated to find out whether UV lights have positive effects on growing cannabis. If UV lights are beneficial for growing cannabis, adding artificial grow lights in UV wavelength may add value.

The researches have found that UV light increase the levels of cannabinoids and benefit for growing of cannabis. However, do you really need UV light for growing cannabis? In other words, would artificial UV light are cost-effective for growing cannabis? This post would analyze whether you need UV light for growing cannabis.

What is UV Light

Firstly, let’s take a look at what is UV light.

UV is the acronym of Ultraviolet Radiation, a form of solar radiation with wavelength ranges from 100 nm to 400 nm. The wavelength of UV light is longer than X-rays but shorter than visible light. UV light is mainly composed of UV-A (315 - 400 nm), UV-B (280 - 315 nm) and UV-C (100 - 280 nm). UVA has the longest wavelength but the least energy and it is transmitted by atmosphere. UVA also known as ‘black light’ that may darken the human skin.

UVB has the medium wavelength but it is powerful. Atmosphere absorbs about 95 percent of UVB, resulting the risk of skin cancer. Since UVB is energetic, it has antimicrobial effect on growing plants.

UVC has the shortest wavelength and it is almost absorbed by atmosphere. UVC also has germicidal effect. The peak UV absorption of deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and nucleoprotein in bacteria is between 254 nm to 257 nm. The UV absorption causes DNA strand breaks, leading to cross-linking of nucleic acids and proteins, killing the biological activity of nucleic acids, and causing the death of bacteria.

UV light is often ignored as the lack of energy of photons. But UV light can cause chemical reactions for both humans and plants. Short time exposure to UV light helps better absorption of Vitamin D while long time exposure raise the risk of skin damage. Proper UV lighting enrich nutrient content and help plants grow better.

How UV light effect cannabis

Since UV light is consist of UV-A, UV-B and UV-C, each fragment of wavelengths may have different effects on cannabis. Therefore, the effects of UV light on cannabis should be analyzed separably. Generally speaking, appropriate UV spectrum alleviate negative impacts and maintain the healthy growing environment for cannabis by antimicrobial activity, like reducing mildew, pests and fungi. Moreover, appropriate UV light boost the production of cannabinoids, like THC or CBD.

• UV-A

UVA (315 - 400 nm) is the long-wave but soft UV light as a part of natural sunlight. It can boost cannabis yield by boosting photosynthesis without damaging the DNA of cannabis. Cannabis is being able to grow in a faster and robuster form with low levels of UVA radiation. Studies have shown that the photosynthesis of can be increased up to 12% under the exposure to low levels of UVA light. In addition, UVA light can improve the production of cannabinoid, terpenes, flavonoids, antioxidants, and vitamins. Low levels of UVA also trigger the defense mechanism to suppress the microbial development like the powdery mildew and produce higher cannabinoids throughout the flowering stage. Tough UVA has positive effect on cannabis, it may also do harm to cannabis. But it will still trigger the photomorphogenesis while causing damage to cannabis. The multiple advantages and limited damage to cannabis make UVA light ideal for indoor cultivation.

• UV-B

UVB (280 - 315 nm) will alter and damage the DNA of cannabis in long time exposure, casing the problem with photosynthesis, respiration and growth. But UVB also have its own benefits. Studies show high levels of UVB can increase the Δ9-tetrahydrocannabinol (Δ9THC) levels, which is the main medicinal ingredient of cannabis. The Δ9THC levels are increased by up to 32% in flower tissues and 48% in leaf tissues. UVB encourages cannabis to produce natural sunscreen to protect themselves from damaging. As a result, trichomes and terpenes are affected. Furthermore, UVB can protect cannabis from fungal infections and pets. Tough studies show UVB is beneficial for increasing THC, there is no development of other cannabinoids in both flower and leaf tissues.

Cannabis UV Lighting Solution

From former analysis of the UV lighting effects on cannabis, we can conclude that certain spectrum of UV light is beneficial for growing cannabis. UV can boost the production of resin, increasing cannabinoids and reducing the possibility of disease and pests. But you do not need all the UV light for growing cannabis. For indoor cannabis growing, UVA and UVB are both beneficial.

Studies show that UVB is capable of producing higher THC. However, separately used of UVB is not recommended. The reasons are as followed:

• UVB will alter and damage the DNA of cannabis in long time exposure, casing the problem with photosynthesis, respiration and growth.
• UVB is not cost-effective. UVB light sources are more expensive than UVA, making it may not affordable for growers. Moreover, Study have found that combination of UVA and UVB do not have remarkable improvement on the content in dry inflorescence compared with the use of UVA.
• For indoor growing, prolonged exposure to UVB will raise the risk of skin cancer for growers. Therefore, the use of UVB light should be restricted.

To sum up, UVA light is more suitable for using as the supplement lighting for growing cannabis. UVA light source is more affordable than UVB. Furthermore, UVA and shorter wavelength radiation (400 - 500 nm) can provoke photoreactivation, repairing the mediate cell damage caused by UVB and regulating chemical composition.

Atop is pleased to provide LED UV-A lighting solution for you. Contact us to find more information.