Part 6/10:
Street light photocontrols need to handle larger currents and voltages, typically operating under a twist-lock design that allows easy replacement. The operation varies slightly from the simpler designs used in nightlights. The photocontrols combine larger photoresistors and a thermostatic switch with more complex circuitry.
Thermostatic Switch Mechanics
Upon examining a photocontrol unit, one discovers it relies on a thermostatic switch that uses a bimetallic disc. This disc opens when it reaches a certain temperature, effectively acting as a limit switch. The power supplied to this switch is moderated by a heater circuit that responds to light conditions via the photocell.