A discharge lamp ballast is designed to limit or interrupt its AC output
power to the discharge lamp upon occurrence of an abnormal discharge
outside of an arc tube. A detector is included to examine a lamp voltage
once in each of the positive and negative half-cycles or in each one
complete cycle of the AC output power, and identifies the abnormal
discharge when there is a particular change in the monitored lamp
voltage. The particular change may be defined by a single logic or by
combination of several logics each designed to represent specific
characteristic for the abnormal discharges of several types.