Some sources use the distinction of "hard UV" and "soft UV" - in the case of astrophysics, the boundary may be at the Lyman limit i.e. wavelength 91.2 nm, with "hard UV" being more energetic. The same terms may also be used in other fields, such as cosmetology, optoelectronic, etc. - the numerical value of the boundary between hard/soft, even within similar scientific fields, does not necessarily coincide; for example, one applied-physics publication used a boundary of 190 nm between hard and soft UV regions.