Terpene and THC production has long been perceived to be limited to mostly genetic diversity and advancements in plant breeding. In recent years, as cannabis has become more widely available through legalization, there have been many advancements that otherwise could not have easily been made without the adaptation of more sophisticated developments in the lighting industry. Among the most widely recognized of these is the introduction and implementation of ultraviolet radiation or UV light.
Breeding techniques were once regarded as the main method for increasing THC and terpene content but are now recognized as only one of several methods for increasing potency. It is currently understood that environment, nutrition, and genetic modification are mechanisms for manipulating terpene and THC yields. Environmental factors such as temperature fluctuations can also alter the production of THC and terpenes, but one environmental factor often ignored in modern grows is plantsâ€™ exposure to UV light.
The Ins and Outs of UV Light
When plants are exposed to UV light, they create natural sunscreen compounds. This is comparable to how humans produce melanin and become tan when exposed to sunlight. This reaction to exposure to specific wavelengths of light is called photomorphogenesis. Photomorphogenic responses to UV exposure create several naturally occurring compounds as an evolutionary safeguard response. In cannabis, these compounds include THC, CBD, and terpenes.
Not all UV light is beneficial though. In fact, not all UV light emitted by the sun makes it through Earthâ€™s atmosphere. UV light is broken down into three subcategories by wavelength: UVA (320 nm to 400 nm), UVB (290 nm to 320 nm), and UVC (100 nm to 290nm). UVC light has enough energy to break DNA molecules and destroy living cells, and because of this, certain companies have implemented UVC as a sterilization tool for use in hospitals, clean rooms, and water sterilization. Thankfully, Earthâ€™s atmosphere filters out almost all of the sunâ€™s UVC light before it reaches the surface.
The sunâ€™s UVB light is mostly eliminated by Earthâ€™s atmosphere and only makes it to the surface around solar noon, while most of the UVA light is not eliminated by the atmosphere. Even at noon, less than 5% of the UV light at Earthâ€™s surface is UVB, which is good for us as UVB is energetic enough to damage DNA and cause lasting health consequences, such as skin cancer. Human skin responds to UVA, and UVB light exposure increases production of melanin, a natural sunscreen compound. A suntan is a human body trying to shield the sensitive epidermis by limiting exposure to UVB through the protective melanin layer.
UVA Boosts Cannabinoid and THC Production
Cannabis plants have their own similar system of blocking damaging UVB: increased trichome and cannabinoid production (CBD, THC, and many others) coupled with increased terpene production. These natural sunscreens are produced with exposure to both UVA and UVB light, although only UVB damages the plantsâ€™ DNA. UVA is the safest and least likely to cause adverse damage in plants while still triggering this photomorphogenic response.
Exposing plants in indoor cultivation facilities to UVA light can, therefore, increase terpenes, antioxidants, flavonoids, THC, CBD, and vitamins, without causing excessive damage to plants or inducing skin cancer in workers. This makes it the best form of UV light available for indoor cultivation, which is why it is the only form of UV in the Phyto-Genesis Spectrum by Black Dog LED.
Most artificial light sources commonly used in cannabis cultivation (HPS and LED lights) contain virtually no UV light at all, so indoor growers donâ€™t get the increased trichome, cannabinoid, and flavonoid production that UV exposure can provide. Even greenhouse growers are missing out on the increased potency UV exposure provides because plastic greenhouse coverings block the sunâ€™s natural UV light to prevent the plastic from degrading due to UV exposure.
Supplementing existing light fixtures with UV fixtures is possible, although it can be tricky to get the ratio of UV to visible light correct, and discreet UV fixtures also bring problems of uneven distribution of UV light in the growing area. For these reasons, it is ideal to get a grow light with the ideal ratio of UVA light already incorporated into each light fixture.
Now, as cannabis seems to be pushing toward legalization due to increased social acceptance, there will likely be even more innovative techniques and technologies developed to increase THC and CBD yield than ever before.
Lighting Strategies for Higher Terpene and THC Content in Cannabis