UVA is a normal part of the light spectrum used by plants. It is at the far end on the deep blue spectrum and is included in most deep blue LEDs used for grow lights. There is active photosynthesis in this part of the light spectrum. Our lights include this as does every decent LED grow light – accept maybe the cheap ones from china.
UVB is deeper into the ultra violet part of the light spectrum. This is normally damaging to plants in high doses. In cannabis high levels of UVB will damage the reproductive cycle. Strains of cannabis that are native to areas close to the equator are exposed to very high levels of UVB and they have developed a natural defense to protect against UVB damage.
Whenever the plant senses high levels of UVB it will produce a protective coating around the reproductive system – in the case, it coats the trichromes. This acts as a natural pair of sunglasses for the plant. In the absence of UVB, the plant will produce less of this coating. This coating is called THC and, as a little joke of nature, this also has interesting effects on humans. This is why strains of cannabis that are native to northern and southern latitudes do not produce THC and are called hemp.
The sun naturally contains a lot of UVB – that’s why we wear sunscreen. However, LED grow lights do not include any UVB – unless you put it there. California Lightworks is currently the only LED grow light manufacturer that includes supplemental UVB (that I personally know of) – because they only focus on cannabis LED grow lights.