Lux Mundi font here refers to the font used in the cover artwork of Lux Mundi, which is the ninth studio album by Samael, an industrial black metal band formed in 1987 in Switzerland.
The album title on the cover is set in Brandon Grotesque Black, a TDC2 2011 winner typeface from Hannes von Döhren while the font used for the band title seems to be a modified Trebuchet, designed by Vincent Connare in 1996. Both are available as commercial typefaces and you can details about them here and here respectively.
Download Lux Mundi Font
We are currently unable to find a free alternative or a font similar to the commercial font identified above, and you will need to follow the relevant links above and purchase the font.