LUM # will say you, what are the equivalents of the luminance of # cd/m2 (candela per square meter) LUM m # will compute the luminance of a star of # magnitudes defocused to one "square minute"; LUM S # will do that for the defocusation of one "square second", LUM D # for that of one "square degree" LUM m<diam> # and similarly for S and D will do that for a star defocused to a circle of <diam> minutes diameter. 1999 (C) Jan Hollan, N.Copernicus Observatory and Planetarium in Brno, subject to the GNU General Public License, http://www.gnu.org/copyleft; source code available at http://astro.sci.muni.cz/pub/hollan/programmes) source code available at http://astro.sci.muni.cz/pub/hollan/programmes)
For more info on the queer units in astronomy, see in Czech mainly this paper, in English just a short explanation here (in both cases, the html versions may be not really OK).
For more info on units etc. in general, see The National Institute of Standards and Technology Reference on Constants, Units, and Uncertainty: http://physics.nist.gov/cuu/index.html.