We found this circuit in the 1964 RCA transistors manual. The sensor may be a common LDR and the transistor BC558. The relay has an operating voltage according to the power supply.
This circuit was found in a Radio Electronics magazine from November 1992. The components are from...
This circuit was found in a 1969 Mullard publication. The transistor may be the modern equivalent...
This simple expandable circuit was obtained from a Popular Electronics from the 80's. The supply...