Abstract
The spatial distribution of luminous layers first observed by Holst and Oosterhuis (1921) in low pressure neon in plane-parallel gaps with prebreakdown currents has been calculated by a Monte Carlo simulation technique for He, Ne, Ar, Kr and Xe. Some examples of the calculated density distribution of excited atoms as a function of distance from the cathode are presented, and the conditions necessary for observing the luminous layers are given.