By the present, uniform electric field region of the sphere gap is utilized for the high tension proofreading. Generally, the discharge voltage is difficult to get stabilized discharge voltage, when spherical electrode is used. Especially, beginning of use is discharged low-voltage, when there was long-time unused hour of spherical electrode, since there is a position which is easy to discharge the electron. Such discharge is known as an irregular discharge phenomenon. Therefore, pre-discharge, etc. is done near in the use.

In this report, the relationship between applied voltage downtime and ULD was investigated as a factor of irregular discharge phenomenon from the viewpoint of ultraviolet radiation linear discharge (ULD).