This index could be really useful for numerous purposes, accounting health and energy harvesting as two of the most relevant ones. The ultraviolet index obviously varies in dependance of the month, but perhaps not in every place, and the usual range is from 0 to 11+.
So UV radiation would be dangerous in several conditions, and the risk —although certainly moderate— appears at index 3. Indexes greater than 11 are common in intense summer within some locations. We recommend searching for a source of UV index in your area for knowing more about it and observe its behavior at different times. It's another clear source of energy, like other wavelengths, however, we think that there's no solar cell that achieves to harvest these frequencies. Notices about some research, but this path seems still ready for new surprises.
At index and up 6-7 it's recommended wearing sunglasses, and skin protection like clothing or sunscreen. With 11 and more, any additional protection is welcome. In these situations, at least to know about it is wonderful to take precautions!