The photo FET is not a common component today. In this 1964 Electronic Design application we have a light switch circuit.
Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors....
This switched filter was found in the 1969 documentation. The FET should be current-matched and eventually...
The frequency of the blinking of this circuit is given by the capacitor that can have its value...