The micro-gap type Surge Absorber is a type of discharge tubes. The discharge in the tube changes from pre-discharge to glow discharge, then to arc discharge as illustrated in Fig.9.The illustration below also shows the V-I characteristics between voltage and current for the discharge tube.
When the tube is discharging, electric current flows and moves to glow discharge then to arc discharge as the discharge voltage decreases. On the other hand, when the discharge decreases, the voltage increases as it moves from arc discharge to glow discharge.

• Pre-glow discharge

The voltage to maintain the discharge is equivalent to the DC breakdown voltage. A faint light can be seen from at this point.

• Glow discharge

The constant voltage rate remains as the current changes. The voltage to maintain the discharge depends on the electrode material and the gas in the tube. The discharge light covers portion of the electrodes.

• Arc discharge

At the end of discharge and a large current flows through the part and it puts out a bright light. The maintaining voltage at this point (voltage between the discharge tube terminals) is in the 10's of volts range.