The current due to cold tunneling of electrons from a metallic surface exposed high electric fields, regularly named ``dark current,'' is commonly described in modern literature using an analytical approximate solution provided by Murphy and Good [Phys. Rev. 102, 1464 (1956)]. This expression, which corrects earlier work Fowler Nordheim, Fowler-Nordheim-type equation: $I\ensuremath{\sim}{E}^{2}...