The arc in a Low Pressure Sodium lamp extinguishes each half cycle as the lamp current reverses direction. This occurs at a speed imperceptible to the human eye. The re-ignition of the arc requires an adequate available sustaining voltage from the ballast. Failure of the arc to re-ignite will result in lamp outage, which can occur under any of the following conditions:
In the event of lamp outage, up to 80% of Low Pressure Sodium lamps operated on high reactance autotransformer circuits will relight immediately; the remaining lamps will require several minutes to relight. Lower wattage lamps are more likely to relight immediately than higher wattage types. However, all LPS lamps operated on hybrid ballasts, which contain an ignitor, may be expected to relight immediately.
