Part of my job by the POCO is sorting out streetlight circuits, and to sort out faults after road works being done and cables damaged.
In New Zealand we use 4 systems.
These are unmetered supplies.
Lightcell controls single or double streetlight at T intersections in rural areas.
Pilot system. Lightcell at substation controls ON / OFF cycle of streetlights which are controlled via contactors, which control a string of say 20 streetlights, the end of circuit drives the next contactor coil for the next string, and so on.
Reliable yes.
Disadvantage, if one contactor fails or fuse blows, large area is in the dark.
This system has a master relay in the substation which can dump the streetlight load in an emergency, if a feeder is lost and loadshedding has to be applied.
Ripple system A Zellweger or Cyclo ripple relay controls a string of streetlights and is controlled via ripple injection of 1050 Hz, superimposed on the 230 Volts mains. A lightcell is often in series with the relay which does the ON / OFF cycles. The ripple relay is used in case of emergency load shedding.
Timeclocks Are used as a temporary solution when an underground controlcable is faulty and scheduled for repair. These are astronomical timeclocks and adjust themselves as days get longer or shorter.
Thermal runaway If a lightcell gets faulty the light usually stays on. A small internal heater (power resistor) in series with the LDR or selenium cell controls the bimettallic strip. The default when power is applied is lamp ON.
When R heats up switch turns off, during day hours.
The on / off cycling is most likely a high pressure sodium lamp on its last legs. It takes usually a few minutes for the lamp to attain full brightness. The internal pressure in the lamp builds up. lamps goes out, needs to cool down before it can restrike and the cycle repeats it self over and over again.
SON lamps usually go for about 15,000 hours which is about 3½ years taking into account ±4350 hours night time.