Ludvig Valentin Lorenz (/ ˈ l ɒr ən t s / ; 18 January 1829 – 9 June 1891) was a Danish physicist and mathematician. He developed mathematical formulae to describe phenomena such as the relation between the refraction of light and the density of a pure transparent substance, and the relation between a metal's electrical and thermal conductivity and temperature (Wiedemann–Franz–Lorenz law).