Contrary to the rule book, ultraviolet light does not penetrate water well. The absorption spectrum of water has a minimum at 400 to 500 nm (green to blue-violet) and rises sharply in the near UV. Ultravision should give no benefit to underwater vision.
Also contrary to the rule book, the amount of UV light from the stars reaching the ground is of lower intensity than stellar visible light, which is so very dim as to be largely negligible when there are other sources of light present. Ultravision gives no benefit outdoors at night.
There are two main "bands" of UV which can penetrate the atmosphere - UV-A (400 to 320 nm) and UV-B (320 to 290 nm). Some UV-A (between 400 to about 350 nm) is transmitted by ordinary glass, and UV-A is produced by the sun, stars, fluorescent lights, and some specialty lights made for medical, horticultural, or herpetocultural purposes. UV-B is produced by the sun and stars, as well as a few specialty lights (although generally in low intensities). UV-B does not penetrate glass. Flame, ordinary incandescent lights and most other common artificial light sources produce no UV.
If you can see into the ultraviolet but cannot distinguish UV as a separate color, there is no cost. You may be able to pick out some details others could see, but other details will be obscured (you could not pick out blue from UV, for example).
If you can see UV as one or more colors separate from the normal visible part of the spectrum, this is best represented by a level or two of acute vision to represent your ability to pick out details that others might miss. If part of this is due to UV-B vision, you can purchase those levels of Acute Vision with an accessibility limitation Not Indoors -20%.
Back to Modified GURPS Advantages and Disadvantages