Components:

R1 - 22K
R2 - 22K
R3 - 1K

C1 - 100 microFarad
C2 - 100 nF
C3 - 100 nF
C4 - 22 microFarad
TR1 = TR2 - BC237B or similar
IC - SN78L12
DZ1 - zener diode 12V 1/4watt
DZ1 - zener diode 3.3V 1/4watt

The power is by 2 X 9V batteries, when battery voltage is more then 16V ( 12 + 3.3 + 0.7 (base/emitter voltage)) TR1 is saturated and collector voltage is about zero, then led is off; when battery voltage is less then 16V TR1 is off and the collector voltage is near 12V and the led is on; the value of R3 can be decreased to have more brightness.