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.
The amplifier shown in figure 2 is based on the MAX9715 integrated circuit from Maxim...
This stage for JFETs was found in a 1965 US publication, but is valid for modern components. |...
This circuit was found in a Japanese publication from 1971. The circuit uses components from the...