This circuit was obtained in a 1970 EEE and applies to almost any operational amplifier. The supply voltage depends on the operational amplifiers used.
This circuit for incandescent lamps was found in the January 1980 Radio Elecronics magazine. The...
When the voltage supplying the circuit falls below the zener value, the LED lights up, and if a...
Indicated for automotive use, this circuit was found in a Popular Electronics from the 90s. The...