The sensor used in this circuit is uncommon today, however equivalent types can be tried. The comparator also supports modern equivalents. The circuit is from 80's documentation.
Found in Popular Electronics from the 90's, this circuit uses 555 integrated and common...
This circuit activates an incandescent lamp when the light stops falling on the sensor. The...
In the figure we have the configuration of a variable voltage regulator with two transistors and a...