Current densities that are very high, approaching 4000 A/cm2, tend to favor black-body radiation. Spectral lines all but disappear as the continuum radiation dominates, and output center shifts toward the ultraviolet. As current densities become even higher, visually, xenon's output spectrum will begin to settle on that of a blackbody radiator with a color temperature of 9800 kelvins (a rather sky-blue shade of white). Except in cases where intense UV light is needed, such as water decontamination, blackbody radiation is usually not desired because the arc becomes opaque, and much of the radiation from within the arc can be absorbed before reaching the surface, impairing output efficiency.