Ultra Violet (UV）light is broken up into three sections within the electromagnetic spectrum. UV light is on the far left section of the spectral charts.
UVA = 400-315 nm, UVB = 315-280 nm, UVC = 280-100 nm
Ultra Violet (UV) light plays a significant role in all aspects of plant growths. Plants, in their natural environments, are exposed to natural sunlight which includes UVA and UVB. Think of what happens to your skin when you are exposed to sun for long periods of time. It begins to burn and sweat. Plants are no different. UV light activates a plant’s defense mechanisms. UV causes plants to produce oils, antioxidant vitamins and flavonoids to protect themselves from the damaging effects of UV. These compounds produce the vibrant colors, smells and tastes of your plants. If your light source does not produce UV, you are affectively changing the color, smell and taste of your crop. Many of the lights used for indoor plant growth produce very small amounts of UV and some produce none at all. It is theorized that some plants such as Cannabis benefit from UVA light in the late stages of flowering.