UV-A is the long wave UV light—most commonly seen in a black-light. Its primary effect on plant growth comes at a hormonal level. This wavelength will eliminate or limit certain hormones within the plant, effecting the plant’s growth. Over millions of years, plants have created a synergistic relationship with their hormones and UV light. UV-A wavelengths can effect the structural growth in plants due to the hormones it helps to regulate.
UV-B light is the medium UV wavelength. This wavelength will effect trichome production in medical marijuana the most. A medical marijuana plant will create trichomes to protect itself from the would-be harmful rays of UV-B.
Trichomes are mostly made up of water, which acts as an absorber of the UV-B radiation. It also contains the majority of cannabinoids, found in a medical marijuana plant, including THC, CBN and CBD. In other words, the more trichomes a plant produces, the more cannabinoids (medicine) in the plant.
Many gardeners add UV-B specific bulbs to their indoor gardens to maximize trichome production. You can purchase UV-B bulbs at any pet shop where they are used for keeping reptiles. Another way to ensure your indoor garden has enough UV-B is to use metal halide bulbs in your blooming room because they naturally have a higher UV light output than high pressure sodium bulbs.
UV-C is the short wave UV wavelength. This frequency can cause adverse effects on plant growth. Receiving an abundance of UV-C light will cause severe radiation poisoning resulting in deformed growth, color loss or even death.
As biological creatures are concerned, UV light can be good or bad. I believe moderation is key when supplementing UV light in your indoor garden. If you want to add UV-B specific bulbs, I recommend supplying around 1/10th of the wattage in your garden. For example, if you have a 1000 watt flowering room, add 100 watts of UV-B. Another rule of thumb is to run 1/3rd of your blooming watts in metal halide. For example, in a 3000 watt bloom room, have 1000 watts metal halide and the remaining 2000 watts high pressure sodium. By adding additional UV-B light,t you should see an increase in essential oil production and, in turn, an increase in potency of your medical marijuana.
Take an ultra-close look at some Trichomes packed with THC.