PURPOSE: To provide a nonlinear discharge lamp made of soda glass with an extremely small deterioration rate of luminous flux due to coloring, by applying the phosphor material whose specific surface area being 2,500cm2/g to 5,000cm2/g to the inner surface of the soda glass tube.

CONSTITUTION: As the inorganic compound to be applied, oxide of alkaline earth metal such as pyrophosphate, orthophosphate, or halophosphate, or alumina, silica, titanium oxide, or the like is preferred. As for the applied amount, it is desired that the specific surface area of the phosphor material after the application will be 2,500 to 5,000cm2/g. While the specific surface area of a normal phosphor material is 2,000 to 3,000cm2/g, the phosphor material whose specific surface area is below 2,500cm2/g is less effective in preventing the deterioration of luminous flux due to coloring by mercury; in this case, the applied amount of the phosphor coating must be 7mg/cm2 or more. With the phosphor material of 2,500cm2/g or more, the coloring is effectively prevented by application of the phosphor material of 5mg/cm2 or more.