How to design a Circuit that can turn a LED ON depending on the input voltage
The classic LM3914 contains multiple comparator stages that are used to drive LEDs in either a bar or a dot configuration. Using a 4:1 voltage divider will let you sense voltages of up to 44V given a supply voltage of at least 12V.

Designing a Li-Ion Battery Gauge with the LM3914 - EEVblog #204