To improve the luminous flux maintenance factor by providing a front surface protective layer made of inorganic powder, using a material as inorganic powder, having the filling ratio of a compact compressed by pressure of a specified value beyond a specified % and for improving the life of luminous flux, and restraining deterioration of luminous flux.

A fluorescent coating 3 is formed on the inner front surface of a translucent airtight container 1, and a front surface protective layer 9 is formed on the inner front surface on a discharge space 2 side of the fluorescent coating 3. The discharge space 2 is an airtight space in which discharge plasma 11 is to be formed in the translucent airtight container 1, the fluorescent coating 3 is formed of fluorescent grains 7. The front surface protective layer 9 is formed of inorganic powder, and as inorganic powder, a material having a high transmission factor of ultraviolet ray is selected among metallic oxides such as silica, alumina, or the like having a relative low cost. The front surface protective layer 9 is formed by using inorganic powder in which the filling ratio of a compact formed at pressure of 3000 kgf/cm2 is not less than 46.1%; and not more than 52% as a material.