The effect of ultraviolet (UV) light on cannabis growth is an interesting yet controversial topic when evaluating grow light spectrums. While there are known positive effects of UV, some of the claims regarding the benefits of UV are not necessarily proven in research or data.
Very Likely: UV Can Increase The Production of Terpenes in Cannabis Plants
Like with human skin (i.e. sunburns), cannabis plants are damaged by exposure to UV light. However, if the plants only receive a small, tolerable amount of UV light it can trigger defense mechanisms that may be appealing to growers. One example of this is increased terpene production which can alter the color and aroma of the flowers.
Additionally, UV has been seen to draw resin to the exterior of the flower giving them a frostier appearance. It is believed the plant uses the resin-like we use sunscreen to protect its cells from the damage of UV light. Both of these defense mechanisms have the convenient side-effect of making the flower buds seem more desirable and have a better curb appeal in dispensaries, however, this is not to get confused with the cannabis being “stronger” or more potent.
Claimed: UV Increases Yield and Cannabinoid Content
Many people have claimed that UV light causes greater yields and produces more potent cannabis plants. However, these claims are mostly anecdotal, as research conducted so far has shown very little effect on the production of cannabinoids like THC and CBD. It also has not shown any impact on increasing overall yields, and when too much UV is in use, it conclusively has a negative impact on yields due to the damage that UV light causes to plant cells. This, coupled with the added costs and much shorter life span of UV LEDs compared to standard white and red diodes, does not make adding UV directly to an LED grow light a compelling option when evaluating lighting options.
This does not mean UV serves zero benefits but is rather a topic still being further researched regarding its proven effects. If a grower does want to have UV in their spectrum, the best implementation would be a standard full-spectrum grow light combined with separate dedicated UV light bars. Shop VOLT® FL-1 or VL-1 grow lights and pair them with UV light bars that can be easily replaced when they deteriorate.
Proven: Far Red Light Increases Cannabis Yield
On the other end of the spectrum, research has shown a direct positive effect of far-red light on cannabis plant growth. Far-red light is currently not included in the PAR range (light that can be used by plants for photosynthesis) which includes light with wavelengths between 400 to 700 nanometers. Testing has shown that far-red light is being used by the plant and does in fact contribute to photosynthesis. It is also better at penetrating deeper into canopies since it is harder for plants to absorb. It has been seen to have positive effects on plant morphology, specifically increasing the size of leaves.
Some researchers theorize this is because in nature when a smaller plant is underneath a larger plant or tree, they are hit with a higher ratio of far-red light, as other more easily absorbed spectrums are taken by the larger plant above it. This results in the plant increasing its leaf size so it is better able to capture what light does reach it. Therefore, including far-red light in the light spectrum would increase cannabis growth and yields.