UV light great for sterilizing surfaces, however not great for shining on skin or eyes
https://en.wikipedia.org/wiki/Pyrimidine_dimer
http://iverson.cm.utexas.edu/courses/310N/MOTD%20Fl05/ThymineDimers.html
Just think sunburn from hell
For UV, the shorter the wave length, the less depth of penetration. The newer UV light source of 222 nanometer wavelength does not get past the dead cell layer of human skin, nor through the tear layer of water coating the cornea of the eye.
An extreme example of frequency dependent property would be Extreme Ultraviolet Light (EUL) used for lithography of semiconductor chips (etching with light.) In air the free path for absorption is about a tenth of a millimeter (forty-thousandths of an inch.) By necessity, the processing is conducted in a vacuum chamber. Only front surface mirrors are suitable as the focusing optics. Wavelengths shorter than about ten nanometers reverse the trend and become more penetrating, the so called Soft X-Ray.
The other end of the UV spectrum, UVA, is the more penetrating frequency of light within ocean water (if free of microscopic life.) If bacteria and/or plankton are present, then blue light wins. We can’t perceive UV light and only see the color shift to blue with depth—some ocean life is sensitive though.