A
Penning mixture, named after
Frans Michel Penning, is a mixture of gases used in electric lighting or displaying fixtures. Although the popular phrase for the most common of these is a
neon lamp, it is more efficient to have the glass tube filled not with pure
neon, but with a Penning mixture, which is defined as a mixture of one
inert gas with a minute amount of another gas, one that has lower
ionization voltage than the main constituent (or constituents).