Found in a 90s American documentation, this circuit uses an integrated from the time that is difficult to obtain today. The sensor is a common photodiode.
This experimental amplifier was found in the 1960 Mullard transistor reference manual. The...
This circuit from Motorola is from 1968, appearing elsewhere on this site. The transistors admit...
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...