High pressure sodium lamps inherently exhibit an end of life condition by "cycling". The classical description of cycling of a high pressure sodium lamp is that the lamp voltage rises to a point at which the ballast can no longer maintain the arc. The lamp then extinguishes and the restarting process begins. In the restart process, the starter or ignitor imposes the same high-voltage, high-frequency pulses which are used for ignition of a cold lamp. However, when the lamp is in a hot, deionized state, the re-strike time can be up to several minutes in length as compared with a substantially instant cold start condition. This restart procedure will continue as the failing lamp warms up and cycles again. The process of cycling repeats, becoming more frequent until the lamp fails completely. When that happens, the starter continues its high-voltage pulsing which stresses the dielectric system of the lighting fixture.
If cycling were unique to the end-of-life condition of a high pressure sodium lamp, the process of protecting the electrical integrity of the fixture would be relatively simple. Unfortunately, a condition very similar to end-of-life cycling can occur with new or, at least, quite usable, functional high pressure sodium lamps. New lamps often cycle due to an initial, but self-correcting, problem with the amalgam inside of the arc tube. Functioning lamps will also cycle in response to a drop in supply voltage, as will all high intensity discharge lamps. To totally disable the starter in these two situations would be wasteful because of lost operating time as well as the possibility of a good lamp being mistaken for a bad one.